THE 
ESSENTIALS OF PHYSIOLOGY 
INCLUDING PHARMACODYNAMICS 
BACHMANN AND BLISS The 
Essentials of Physiology 
Including the Pharmacodynamics 
of the 
Important Typical Drugs 
BY 
GEORGE BACHMANN, M.S., M.D., 
TIW 7 7 7 
PROFESSOR OF PHYSIOLOGY IN THE SCHOOL OF MEDICINE OF EMORY UNIVERSITY; 
SOMETIME DEMONSTRATOR OF PHYSIOLOGY IN THE JEFFERSON MEDICAL 
COLLEGE OF PHILADELPHIA 
AND 
A. RICHARD BLISS, JR* A.M., Phm.D., M.D., 
PROFESSOR OF PHARMACOLOGY AND DIRECTOR OF THE DEPARTMENTS OF PHARMACOLOGY 
AND PHYSIOLOGY IN THE COLLEGES OF MEDICINE AND DENTISTRY AND SCHOOL OF 
PHARMACY OF THE UNIVERSITY OF TENNESSEE 
WITH 178 ILLUSTRATIONS 
PHILADELPHIA 
P. BLAKISTON'S SON & CO 
1012 WALNUT STREET Copyright, 1924, By P. Blakiston's Son & Co. 
PRINTED IN U. S. A. 
BY THE MAPLE PRESS COMPANY, YORK, PA. PREFACE 
The response to a questionnaire sent by the authors to the teachers of 
physiology in the colleges and schools of dentistry and of pharmacy through- 
out the United States and Canada established the fact that there is a genuine 
demand for a physiological textbook specially suited to the needs of students of 
dentistry and of pharmacy. The concensus of opinion is that existing text- 
books of physiology prepared for medical students are unsatisfactory since they 
are too extensive and advanced, and that the smaller works prepared for the 
students of general science, physical education, etc. are too elementary and 
consequently unsuited to the needs of the two classes of professional students 
under consideration. 
This volume, accordingly, has been prepared in response to this very 
evident demand-a demand that has been made more urgent by the remark- 
able progress of dental medicine and surgery and of professional pharmacy; 
by the rapid rise in the standards of instruction in the colleges and schools of 
dentistry and of pharmacy during recent years; and by the further advances 
that are already scheduled for the very near future. These advances in dentis- 
try and pharmacy are in keeping with, and evidently dependent upon, the 
achievements in the field of medical education. 
The authors have aimed to present the material in a manner specially suited 
to the dental and pharmaceutical student, and although they have limited 
themselves to the discussion of those essentials demanded by the dental and 
the pharmaceutical curricula, they have endeavored not to sacrifice scientific 
accuracy and relative completeness for the sake of brevity. 
Certain portions of ANATOMY, required for the teaching of physiology, 
included in the volume will serve to refresh the memory of the dental student, 
and will also supply the pharmacy student with that modicum of anatomical 
knowledge essential to an understanding of physiology. Brief references to 
HYGIENE have been introduced at convenient and suitable places in the text. 
Following the suggestions of numerous dental and pharmaceutical teachers 
of physiology and the advice of the current edition of The Pharmaceutical 
Syllabus that instruction in PHARMACODYNAMICS 11 is best given in con- 
nection with that relating to bodily function and as a part of the physiology course, ' ' 
each chapter is accompanied by a presentation of the pharmacodynamics 
of the drugs of major importance related to the function just discussed. This 
feature of the volume does not attempt to displace the usual special instruction 
in dental materia medica, pharmacology and therapeutics of the dental curri- 
culum, or the instruction in materia medica of the pharmaceutical curriculum. 
The broad principles only of pharmacodynamics are presented with but slight 
reference to therapeutic applications. This portion of the text should conse- 
V VI 
PREFACE 
quently enhance its value as a preparation for and an adjunct to the study of 
dental materia medica, pharmacology and therapeutics; and, in the case of 
the pharmaceutical student, it will prove of valuable assistance in the study 
of materia medica, and also serve to stress the fact that "the whole spirit of 
professional pharmacy, its ultimate success and its moral and professional relation 
with medicine render the practice of counter-prescribing objectionable.y ' More- 
over, a knowledge of the broad principles which guide therapeutics (-not its 
practice-), the objects to be accomplished, and the agencies that are employed 
may prove useful in cases of emergency and poisoning where, while awaiting 
the arrival of the physician, intelligent preliminary treatment may be given by 
the properly educated pharmacist. 
In addition to meeting the requirements of the DENTAL CURRICULUM 
and those of THE PHARMACEUTICAL SYLLABUS, the authors have been 
guided as already intimated, by numerous suggestions given by many teachers 
in the dental and the pharmaceutical colleges and schools in response to the 
questionnaire referred to above. The authors are grateful for these suggestions, 
and will welcome any criticism and further suggestions concerning this text. 
The authors acknowledge with pleasure their special indebtedness to such 
standard texts as Brubaker's Textbook of Physiology, Howell's Textbook of 
Physiology, Macleod's Physiology and Biochemistry in Modern Medicine, 
the excellent Essentials of Physiology by Bainbridge and Menzies, Morris' 
Anatomy, Cunningham's Anatomy, Lewis and Stohr's Histology, Piersol's 
Normal Histology, Bastedo's Materia Medica, Pharmacology and Therapeutics, 
Sollmann's Manual of Pharmacology and Cushny's Pharmacology and Thera- 
peutics. 
Finally, the authors thank the various publishers for their courtesy in 
permitting the use of illustrations. Their source is acknowledged in the text. 
George Bachmann. 
A. Richard Bliss, Jr. CONTENTS 
CHAPTER I 
Page 
Introduction i 
Living Matter-Physiology-Unicellular Organisms-Multicellular Organs-Tissues- 
Organs-Grouping of the Organs of the Body-Pharmacodynamics. 
CHAPTER II 
The Cell 6 
Structure of Cells-The Cytoplasm-The Nucleus-Chemical Composition of the Cell-The 
Life of the Cell-Reproduction-Physiological Properties of Cells-The General Plan of the 
Vertebrate Body. 
CHAPTER III 
Pharmacodynamics of the Cell n 
Mechanism of Drug Action-Stimulation-Depression-Irritation-The Intensity of 
Drug Action-Local, Systemic, and Remote Actions-Salt-Action. 
CHAPTER IV 
Histology of the Epithelial and Connective Tissues 14 
Epithelial Tissue: Form-Functions-The Connective Tissues: White Fibrous Tissue, 
Yellow Elastic Tissue, Areolar Tissue, Adipose Tissue, Cartilaginous Tissue, Osseous 
Tissue-Composition of Bone-The Skeleton: The Axial Portion, The Skull, The Vertebral 
Column, The Ribs, The Appendicular Portion--The Joints or Articulations-Classification 
of Joints-Hygiene of the Bony Skeleton. 
CHAPTER V 
Pharmacodynamics of Epithelial Tissue 24 
The Protectives: Emollients, Demulcents, Dusting Powders or Absorbents-The Astring- 
ents-Hemostatics or Styptics-The Escharotics, Caustics or Corrosives-The Counter- 
irritants-Antiseptics and Disinfectants-Antisyphilitics or Antiluetics. 
CHAPTER VI 
Muscle Tissue 31 
Classification of Muscle Tissue-The Skeletal Muscles-Histology of the Skeletal Muscle 
Fiber-Physical Properties of Skeletal Muscle-Physiological Properties of Muscle-The 
Contraction of Muscle-Analysis of a Single Contraction-The Energy Liberated in 
Muscle-Factors Modifying the Contraction: The Strength of the Stimulus, Temperature, 
Fatigue-The Continuous Contraction: The Summation of Muscle Contraction, Tetanus- 
The Chemistry of Muscle-The Involuntary or Smooth Muscle-Histology of Smooth 
Muscle-Physical and Physiological Properties of Smooth Muscle-Cardiac Muscle. 
CHAPTER VII 
Pharmacodynamics of Muscle Tissue 43 
Skeletal, Voluntary or Striated Muscle: Veratrine, Caffeine, Alcohol, Quinine-Involuntary 
or Smooth Muscle: Digitalis, Pituitary Extract, Nitrites, Quinine, Ergotoxine andpListamine- 
Cardiac Muscle: Digitalis, Caffeine, Quinine. 
CHAPTER VIII 
Nerve Tissue 46 
General Significance-The Histology of Nerve Tissue-Varieties of Neurons-Nerve 
Centers-Nerve Endings-Structure of Nerve Trunks-Physiological Properties of Nerves 
VII VIII 
CONTENTS 
Page 
-Irritability, Nature of the Nerve Impulse, Conductivity, Fatigue in Nerve-The Nutri- 
tive or Trophic Influence of Nerve Cells-Classification of Nerve Fibers. 
CHAPTER IX 
The Nerve System 55 
The Central Nerve System-The Meninges-The Cerebro-spinal Fluid-The Peripheral 
Nerve System-The Sympathetic or Autonomic Nerve System-The Spinal Cord-The 
Gray Matter-The Nerve Cells-The White Matter-The Roots of the Spinal Nerves- 
Functions of the Spinal Cord-The Spinal Cord as an Independent, Segmented Organ- 
Reflex Action-The Reflex Arc-Reflex Irritability-Resistance at the Synapse-Inhibition 
of Reflexes-Reciprocal Innervation-Muscle Tone-The Spinal Cord as a Pathway for the 
Conduction of Nerve Impulses-Classification of the Spinal Tracts-Function of the Fiber 
Tracts-Associative or Intersegmental Conduction-Ascending or Sensor Conduction- 
Descending or Motor Conduction. 
CHAPTER X 
The Brain or Encephalon 72 
The Parts of the Brain-The Medulla Oblongata-Functions of the Medulla Oblongata- 
Special Nerve Centers-The Cerebellum-Function of the Cerebellum-The Cerebrum- 
Fissures-Convolutions-Structure of the Cerebrum-Functions of the Cerebrum-Locali- 
zation of Functions in the Cerebrum-The Motor Areas-The Sensor Areas-The Asso- 
ciation Areas-The Cranial Nerves. 
CHAPTER XI 
Pharmacodynamics op the Central Nerve System 92 
Drugs Which Stimulate Portions of the Central Nerve System: Caffeine, Strychnine-Drugs 
Which Depress Portions of the Central Nerve System: The Narcotics-The General Anesthe- 
tics: Ether, Chloroform, Nitrous Oxide-Intoxicants: Ethyl Alcohol, Methyl Alcohol-The 
Hypnotics or Somnifacients: Hypnotics Which No Dot Abolish Pain: Bromides, Chloral 
Hydrate-Hypnotics Which Abolish Pain: Morphine, Codeine, Scopolamine-Analgesics 
or Anodynes: Morphine and its Derivatives, Acetanilid, Antipyrine, Acetphenetidin, 
Quinine, Salicylic Acid and its Salts, Acetylsalicylic Acid, Counterirritation-Local Analges- 
ics or Anodynes-Antihysterics: Valerian, Asafetida, Musk, Sumbul. 
CHAPTER XII 
The Autonomic or Sympathetic Nerve System 105 
Arrangement of the Autonomic Nerve System-The Sympathetic Ganglia-Functions of 
the Autonomic Nerve System-Hygiene of the Nerve System. 
CHAPTER XIII 
Pharmacodynamics of the Autonomic Nerve System 109 
The Common Reaction to Nicotine-Pharmacodynamics of the Parasympathetic Division: 
Atropine, Pilocarpine, Physostigmine-Pharmacodynamics of the Sympathetic Division: 
Epinephrine, Ergotoxine, Cocaine-Local Anesthetics: Cold, Ethyl Chloride, Cocaine and 
its Derivatives. 
CHAPTER XIV 
The Blood 116 
General Functions-The Physical Composition of Blood-The Properties of the Blood-The 
Histology and Functions of the Blood Corpuscles-The Red Corpuscles or Erythrocytes- 
The Life History of the Red Corpuscles-Function of the Red Corpuscles-Hemoglobin- 
The White Corpuscles or Leukocytes-Varieties of White Corpuscles-The Life History 
of the White Corpuscles-Functions of the White Corpuscles-The Blood Platelets--The 
Blood Plasma-Chemical Composition of Blood Plasma-Coagulation of the Blood-The 
Cause of Coagulation-The Total Quantity of Blood-Anemia. CONTENTS 
Page 
CHAPTER XV 
Pharmacodynamics of the Blood 125 
Physiological Saline Solutions-Transfusion-Hematinics: Iron, Manganese, Arsenic- 
Systemic Alkalinizers or Antacids: Sodium Bicarbonate, Acetates, Citrates, Tartrates- 
Serums and Vaccines-Antitoxins-Hemostatics or Styptics. 
CHAPTER XVI 
The Circulation of the Blood 129 
The Circulatory Apparatus-The Heart-The Cardiac Muscle and its Arrangement-The 
Cardiac Cycle-The Course of the Blood through the Heart-The Frequency of the Heart 
Beat-The Work Done by the Heart-The Properties of the Heart Muscle-The Nerve 
Regulation of the Heart Beat-The Origin and Distribution of the Cardiac Fibers of the 
Vagus Nerve-The Origin and Distribution of the Cardiac Sympathetic Nerve-The 
Function of the Cardiac Fibers of the Vagus-The Function of the Cardiac Sympathetic 
Nerve. 
CHAPTER XVII 
The Circulation of the Blood (Continued). The Vascular Apparatus 142 
The Structure of the Blood Vessels: Arteries, Capillaries, Veins-The Functions of the 
Blood Vessels-The Causes of the High Arterial Pressure-The Velocity of the Blood-The 
Nerve Regulation of the Blood Vessels-The Vasoconstrictor Nerves-The Vaso-motor 
Center-The Vaso-dilatator Nerves-Vaso-motor Nerves to the Capillaries and Veins- 
Some facts relative to the Hygiene of the Circulation. 
. CHAPTER XVIII 
The Lymph 151 
The Lymphatic System-Lymph-nodes or Glands-The Composition of Lymph-For- 
mation of Lymph-The Flow of Lymph. 
CHAPTER XIX 
Pharmacodynamics of the Circulation 155 
Circulatory Stimulants: Digitalis, Strophan thin, Ouabain, Epinephrine, Pituitary Extract, 
Ammonia, Caffeine-Cardiac Depressants: Aconite, Veratrum-Drugs Which Affect the 
Calibre of Vessels: Centrally Acting Vasoconstrictor Drugs: Strychnine, Caffeine, Atropine, 
Alcohol-Centrally Acting Vasodilatator Drugs: Narcotics-Peripherally Acting Vaso- 
constrictor Drugs: Epinephrine, Cocaine, Ergotoxine, Digitalis-Peripherally Acting 
Vasodilatator Drugs: The Nitrite Group, Nitroglycerin, Erythrol Tetranitrate, Digitalis, 
Caffeine and its Allies, Chloral Hydrate, Potassium Iodide. 
CHAPTER XX 
Respiration 161 
Definition-The Respiratory Apparatus: The Air Passages, The Lungs, The Thorax-The 
Movements of Respiration-Inspiration-Expiration-Changes of Pressure Attending 
Respiration-The Quantity of Air Breathed-The Frequency of Respiration-Respiratory 
Sounds. 
CHAPTER XXI 
The Chemistry of Respiration 170 
Changes in the Composition of the Air-The Total Respiratory Exchange-The Respir- 
atory Quotient-The Composition of the Alveolar Air-Ventilation of the Alveoli-Changes 
in the Composition of the Blood. 
CHAPTER XXII 
The Nerve Control of Respiration 174 
The Respiratory Center-The Relation of the Vagus Nerves to the Respiratory Center- 
Influence of Other Afferent Nerves-Influence of Higher Centers-The Chemical Control 
of Respiration-Carbon Dioxide-Oxygen-Ventilation-Artificial Respiration. 
IX X 
CONTENTS 
Page 
CHAPTER XXIII 
■ 
Pharmacodynamics of Respiration 180 
Oxygen Inhalations-Carbon Dioxide-Respiratory Stimulants: Alcohol, Ether, Atropine, 
Caffeine, Strychnine, Ammonia-Respiratory Sedatives or Depressants: Morphine and its 
Derivatives, Chloral Hydrate, Bromides-Expectorants-Sedative Expectorants: Nauseant 
Expectorants: Apomorphine, Ipecac, Antimony and Potassium Tartrate: Demulcent 
Expectorants: Acacia, Licorice, Glycerin: Saline Expectorants: Ammonium Chloride, 
Ammonium Carbonate, Potassium Iodide-Stimulating Expectorants: Terpene Hydrate, 
Creosote, Cubeb, Balsam of Peru, Balsam of Tolu, Santal, Guaiacol, Tar, Benzoates, 
Squill, Senega-Anodyne Expectorants: Morphine and its Derivatives, Chloroform- 
Counterirritants-Antiasthmatics: Atropine, Epinephrine, the Nitrite Group, Iodides. 
CHAPTER XXIV 
Foods 184 
Functions and definition of Food-Hunger and Thirst-Classification of Food Principles- 
Inorganic, Organic: Carbohydrates, Proteins, Fats, Vegetable Acids, Vitamins, Accessory 
Articles of Diet-Composition of Foods. 
CHAPTER XXV 
Digestion 188 
Definition-The Digestive Apparatus-Ferments or Enzymes-Stages of Digestion- 
Mouth Digestion: Mastication-The Teeth-The Structure of the Teeth-The Movements 
of Mastication-The Nerve Mechanism of Mastication-Insalivation: Structure of the 
Salivary Glands-The Nerve Mechanism of Salivary Secretion-The Composition of the 
Saliva-The Functions of Saliva-Deglutition: The Mouth-The Pharynx-The Esophagus 
-The Act of Deglutition-The Nerve Mechanism of Deglutition-Gastric Digestion: The 
Stomach-The Structure of the Stomach-The Gastric Juice-The Secretion of Gastric 
Juice-The Functions of the Gastric Juice-The Movements of the Stomach-Duration of 
Gastric Digestion-Absorption in the Stomach-The Nerve Mechanism of the Stomach- 
Vomiting. 
Intestinal Digestion: Chyme-The Small Intestine-Structure of the Small Intestine-The 
Pancreas-Structure of the Pancreas-The Pancreatic Juice-The Secretion of Pancreatic 
Juice-The Functions of the Pancreatic Juice-The Liver: The Structure of the Liver-Gen- 
eral Functions of the Liver-The Bile-The Secretion of Bile-Functions of the Bile-The 
Intestinal Juice-The Functions of the Intestinal Juice-The Movements of the Small 
Intestine-Nerve Mechanism-The Large Intestine: Functions of the Large Intestine- 
The Movements of the Large Intestine-Hygiene of Digestion. 
CHAPTER XXVI 
Pharmacodynamics of Digestion 223 
Sialogogues: Acids, Bitters, Aromatic and Irritating Substances, Pilocarpine, Mercury 
Salts-Antisialogogues: Atropine and its Allies-Excretion of Drugs in the Saliva: Iodides, 
Bromides, Mercury Salts, Hexamethylamine, Quinine, Strychnine-Stomachics: Bitters- 
Gentian, Calumba, Taraxacum, Quassia, Strychnine, Quinine, Bitter Orange Peel, Anthemis, 
Matricaria, Calamus, Compound Tincture of Gentian, Compound Tincture of Cinchona, 
Cinchona, Cimicifuga, Condurango, Serpentaria-Aromatics: Mustard, Pepper, Pepper- 
mint-Carminatives: Anise, Ginger, Peppermint, Capsicum, Aromatic Spirit of Ammonia, 
Compound Spirit of Ether. 
Digestive Ferments or Enzymes: Pepsin, Pancreatin, Diastase-Predigested Foods-Anta- 
cids: Sodium Bicarbonate, Prepared Chalk, Lime Water, Milk of Magnesia-Emetics- 
Central Emetics: Apomorphine, Ipecac-Local or Reflex Emetics-Copper Sulphate, Zinc 
Sulphate, Mustard, Ipecac, Alum-Antemetics: Sodium Bicarbonate, Milk of Magnesia, 
Bismuth Salts, Cerium Oxalate, Atropine, Cocaine, Phenol, Ice, Chloral Hydrate, Codeine, 
Bromides, Morphine, Counterirritants. 
Cathartics: Laxatives-Fruits, Cereals, Vegetables, Salads, Olive Oil, Cottonseed Oil, 
Liquid Petrolatum, Sulphur, Agar-Agar, Soap, Glycerin and Cocoa-Butter Suppositories, 
Exercise, Massage, Enemas-Purgatives-Simple Purgatives: Aloes, Cascara, Rhubarb, Page 
Senna, Castor Oil, Phenolphthalein, Calomel-Saline Purgatives-Magnesium Sulphate, 
Magnesium Citrate, Milk of Magnesia, Sodium Phosphate, Sodium Sulphate, Potassium 
Bitartrate, Compound Effervescing Powder-Drastics-Jalap, Colocynth, Podophyllum, 
Croton Oil, Elaterium, Scammony, Gamboge, Compound Cathartic Pills-Hydragogues- 
Cholagogues-Bile Salts, Oxgall-Cathartics Acting by Special Affinity-Physostigmine, 
Pituitary Extract-Localization of Action-Rapidity of Action-Antidiarrheics-Bismuth 
Salts, Cerium Oxalate, Prepared Chalk, Lead Acetate, Vegetable Astringents, Opium, 
Camphor. 
Anthelmintics-Pin- or Thread-worms-Calomel, Castor Oil, Solutions of Tannic Acid, 
Alum, Quinine Bisulphate, Soapsuds and Oil of Turpentine, Phenol, Lime Water, Infusion 
of Quassia-Common Round-worms-Oil of Chenopodium, Santonin, Spigelia-Hook- 
worms-Oil of Chenopodium, Thymol-Tape-worms-Oleoresin of Aspidium, Filicic Acid, 
Pelletierine Tannate, Granatum, Cusso, Kamala. 
CHAPTER XXVII 
Absorption 232 
Structure of a Villus-The Portal Vein-The Absorption of the Products of Digestion- 
The Absorption of Water and Inorganic Salts-Absorption of Sugar-Absorption of the 
End-products of Protein Digestion-Absorption of Fat-Chyle. 
CHAPTER XXVIII 
Metabolism 237 
Definition-Metabolism of Carbohydrates: Glycogenesis-Glycogenolysis-The Control 
of Glycogenolysis-The Utilization of Dextrose in the Tissues (Glycolysis)-The Influence 
of the Pancreas on Glycolysis-Assimilation Limit of Carbohydrates-Metabolism of Fat: 
Disposition of Fat-The Origin of Body Fat-The Utilization of Fat by the Tissues-Meta- 
bolism of Protein: The Utilization of Aminoacids by the Tissues-The Metabolism of the 
Nucleo-proteins-Energy Requirements and Diet: The Food Principles as the Source of 
Energy-Basal Metabolism-Energy or Heat-Value of the Various Food Principles- 
Construction of a Diet-Carbon Equilibrium-Nitrogen Equilibrium-Relative Value of 
the Food Principles-Specific Dynamic Action-Inorganic Salts-Vitamins. 
CHAPTER XXIX 
The Temperature of the Body and its Regulation 247 
Physiological Variations of Temperature-Heat Production-Heat Loss-Regulation of 
the Body Temperature-Fever. 
CHAPTER XXX 
Pharmacodynamics of Metabolism 249 
Influence of Physical Stimuli-Temperature, Light, X-Rays, Radium Emanations, Elec- 
tricity-Influence of Chemical Stimuli-Water, Distilled Water, The Absorption and 
Excretion of Water-Glands of Internal Secretion-Iodine and Iodides-Quinine-Anti- 
pyretics-Coal-tar or Analgesic Antipyretics: Acetanilid, Acetphenetidin, Antipyrine- 
Anti-Malarial Antipyretics: Cinchona and its Alkaloids and Derivatives-Anti-rheumatic 
Antipyretics: Salicylic Acid and its Salts and Derivatives. 
CHAPTER XXXI 
Excretion 253 
Definition-Excretory Organs-The Urinary Apparatus-The Kidneys-Composition of 
the Urine-The Formation of Urine-The Influence of Blood Pressure on the Amount of 
Urine Formed-The Influence of the Nerve System on Urine Formation-Micturition- 
The Bladder-The Mechanism of Urination-Remarks on the Hygiene of the Urinary 
Apparatus. 
The Skin-Structure of the Skin-Appendages of the Skin-The Sweat Glands-The 
Perspiration-The Sweat Nerves-The Sebaceous Glands-The Mammary Glands-The 
Hairs-The Nails. 
CONTENTS 
XI XII 
CONTENTS 
Page 
. CHAPTER XXXII 
Pharmacodynamics of Excretion 265 
Diuretics-Diuretics Which Act by Changes in the General Circulation: Digitalis, Stro- 
phanthus, Squill-Diuretics which Act by Stimulation of the Kidney Cells-Non-irritant 
Stimulant Diuretics: Caffeine, Theophylline, Theobromine-Irritant Stimulant Diuretics: 
Oils of Turpentine, Juniper, Sandalwood, Balsam of Copaiba, Cubeb, Buchu, Scoparius, 
Asparagus, Triticum, Calomel, Alcohol, Hexamethylenamine, the Nitrates-Diuretics 
which Act by Salt Action: Water, Inorganic Salts: Sodium Bicarbonate, Sodium and Potas- 
sium Iodides and Nitrates: Organic Salts: Sodium and Potassium Citrates and Acetates. 
Diaphoretics-Methods for Raising and Maintaining the Rise of Body Heat: Exercise, Pre- 
venting Heat Loss, Artificial Heat, Water-Drugs: Pilocarpine, Camphor, Ammonium 
Acetate, Mustard, Alcohol, Salicylates, Coal-tar Antipyretics. 
Anhydro tics: Alcohol, Spirit of Camphor, Alum, Aluminium Chloride, Boric Acid, Salicylic 
Acid, Atropine, Agarcin or Agaric Acid. 
CHAPTER XXXIII 
The Internal Secretions 269 
Definition--The Thyroid-The Effect of Absence, or Disease of the Thyroid-The Effects 
of Hyperactivity of the Thyroid-The Hormone of the Thyroid-The Parathyroids-The 
Effects of Removal of the Parathyroids-The Cause of the Symptoms of Tetany-The 
Adrenal Glands-The Effects of Removal of the Adrenals-The Effects of Disease of the 
Adrenals in Man-The Significance of the Cortex-The Internal Secretion of the Medulla- 
Influence of the Nerve System on the Secretion of Epinephrine. 
Pituitary Body-Function of the Anterior Lobe-Hypopituitarism, Hyperpituitarism. 
Functions of the Posterior Lobe (Inclusive of Pars Intermedia)-The Thymus-The Pan- 
creas-The Testicles and Ovaries-Effects of Removal of the Gonads-The Corpus Luteum. 
CHAPTER XXXIV 
Pharmacodynamics of Internal Secretions 281 
Thyroid Gland-Obesity-Goiter-Adrenal Glands-Pituitary Body-Ovarian Extracts- 
Corpus Luteum. 
CHAPTER XXXV 
The Sense Organs-The Cutaneous Sensations; The Sense of Taste; The Sense of 
Smell 282 
General Characteristics of Sensations-Classification of Sense Organs-Cutaneous Sen- 
sations: The Peripheral or End-organs in the Skin-Significance of the Various End-organs 
-The Sense of Taste: The Tongue--The End-Organ of Gustation or Taste-bud-Kinds of 
Taste Sensations-The Conditions Necessary for the Stimulation of the Nerves of Taste- 
The Sense of Smell: The Nasal Fossae-The End-Organ of Smell-Kinds of Olfactory Sen- 
sations-The Stimulation of the Olfactory End-organ. 
CHAPTER XXXVI 
The Sense Organs (Continued)-The Sense of Sight 289 
The Eye-ball-Formation of an Image on the Retina-Action of the Refracting Media- 
The Reduced or Schematic Eye-Accommodation-Mechanism of Accommodation- 
Range of Accommodation-The Force of Accommodation-Functions of the Iris-Nerve 
Regulation of the Pupil-Refraction in Abnormal Eyes: Hypermetropia-Myopia-Astig- 
matism-Functions of the Retina-Functional Significance of the Rods and Cones- 
Accessory Structures of the Eye-The Eye-lids-The Lachrymal Apparatus-Hygiene of the 
Eyes. 
CHAPTER XXXVII 
Pharmacodynamics of the Eye 300 
Mydriatics: Atropine-Homatropine-Cocaine-Epinephrine-Myo tics: Physostigmine 
or Eserine, Pilocarpine. XIII 
CONTENTS 
Page 
CHAPTER XXXVIII 
The Sense Organs (Continued)-The Sense of Hearing 303 
The Ear: The External Ear-The Middle Ear-The Auditory Ossicles-The Tensor tympani 
and the Stapedius Muscles-The Eustachian Tube-The Internal Ear-The Osseous Laby- 
rinth-The Membranous Labyrinth-The End-organs of the Utricle, Saccule and Semi- 
circular Canals-The Organ of Corti-The Physiology of the Auditory Apparatus- 
Characteristics of Sound-The Function of the External Ear-The Function of the Middle 
Ear-The Function of the Cochlea-Theories of the Action of the Organ of Corti-The 
Labyrinth Sensations-The Static Sense-The Dynamic Sense. 
CHAPTER XXXIX 
Voice and Speech 312 
The Larynx: The Laryngeal Cartilages-The Vocal Bands-The Intrinsic Muscles of the 
Larynx-The Nerves of the Larynx-The Mechanism of Voice Production-The Mechanism 
of Articulate Speech. 
CHAPTER XL 
Hygiene of the Reproductive Organs. / 316 
Continence-Control of the Sex Impulse-Venereal Diseases-Gonorrhea-Syphilis- 
Chancroid-Other 'Sex' Complaints-Quacks-Sex in Life. 
Index 323 THE 
ESSENTIALS OF PHYSIOLOGY 
CHAPTER I 
INTRODUCTION 
Matter occurs in two forms, namely: living and non-living. While many 
of the phenemona exhibited by living matter are duplicated in non-living 
matter, certain fundamental characteristics distinguish the former from the 
latter. Living organisms have the property of reacting to changes in their 
surrounding medium with the apparent purpose of preserving their existence; 
they are able to grow within certain 
limits by the introduction into their 
own structures of non-living material 
which becomes transformed into liv- 
ing material endowed with all the qual- 
ities peculiar to life. Furthermore, 
they are capable at a certain period in 
their development of reproducing them- 
selves so that the species to which they 
belong are perpetuated. The study of 
these vital phenomena constitutes the 
subject matter of physiology. 
Since both plants and animals are 
endowed with life, physiology embraces 
a consideration of vital phenomena as 
exhibited in these two divisions of 
animate matter and may, therefore, be subdivided into plant physiology and 
animal physiology. As the reactions of living matter are determined by changes 
occurring in the surrounding medium, Physiology includes a consideration of 
the character of these changes. Many of the phenomena exhibited by plants 
are likewise exhibited by animals showing that life is essentially identical in 
all living things. Nevertheless, animals-particularly the higher forms- 
present such striking differences from even the most highly developed plants 
that there is no difficulty in identifying them. 
The physiological phenomena exhibited by the higher animals are exceed- 
ingly complex. It is therefore necessary for a clear understanding of physio- 
logical processes to study the vital phenomena exhibited by low forms of animal 
life. The simplest form in which animal life occurs, is exhibited in unicellular 
Fig. i.-Amoeba proteus. A, the animal in 
its natural condition; B, an animal that has swal- 
lowed a long filamentous plant; C, the animal in 
the state of division; cv, contractile vacuole; ec, 
ectosarc; en, endosarc; ex, remains of undigested 
food; p, protoplasm. (Menge, after Conn.) 2 
INTRODUCTION 
organisms, such as the Amoeba (Fig. i). This minute organism is found in 
stagnant water. When examined under the microscope it is seen to consist 
of a mass of semi-liquid material usually called protoplasm: inasmuch as this 
material is living, it is better termed bioplasm. Granules of different sizes are 
distributed in the bioplasm; a clear space, which from time to time undergoes 
changes in size, and disappears, is found within the body of the animal and is 
called the contractile vacuole. Other vacuoles are seen that do not contract 
but are filled with food material. These are called food vacuoles. At about 
the center there is a spherical structure, that appears highly granular, called 
the nucleus. The Amoeba is capable of changing its form by causing its bio- 
Fig. 2.-Gonium pectorale. a.c., amylaceous corpuscle; n., nucleus; b.g., basal granules from which 
arise the flagellae. The individuals of the colony are held in a gelatinous mass. (Rhodes.) 
plasm to extend in various directions; it is also capable of moving from place to 
place by thrusting out a process from its own body into the surrounding medium 
and causing its bioplasm to flow into this projection. In other words, it 
exhibits not only motion but locomotion. The projection of bioplasm that 
enables the amoeba to move about is called a pseudopodium from its resemblance 
to a foot. When the Amoeba comes in contact with food material it throws 
out pseudopodia that ultimately enclose the food. This food material is then 
gradually digested and assimilated. The indigestible portions of the food, 
together with the waste products of the animal's body, are discharged into 
the surrounding medium. When touched by a solid object the amoeba with- 
draws from it; this property of responding to the application of an external 
force is called irritability. Under favorable circumstances the amoeba repro- 
duces itself by simple division; a constriction appears in the middle and gradually 
deepens until the individual is divided into two. ESSENTIALS OF PHYSIOLOGY 
3 
More complex forms of animal life are exhibited when many cells are grouped 
together. The apparent purpose of such grouping is to render the organism 
more efficient in its struggle for the maintenance of its existence. In certain 
of these organisms the cells form a colony of individuals. Each cell in the 
Fig. 3.-Volvox. Colony showing, p, parthenogonidia; o, oogonidia; sp, spermatogonidia in various 
stages of formation. {Kelli colt, after Klein and Schenck.) 
colony is virtually independent of all other cells and carries out all the functions 
characteristic of free cells (Fig. 2). In other colonial forms some of the cells 
of the colony become differentiated for some special function (Fig. 3). Many 
biologists believe that the more complex multicellular organisms have originated 
Fig. 4.-Opalina ranarum. A single individual with numerous vesicular nuclei. {After Doflein.) 
from such colonial types. There are others, however, who believe that multi- 
cellular organisms have originated from multinucleated types such as Opalina, 
in which all nuclei are alike (Fig. 4), or paramecium and most infusoria, in 
which the nuclei are differentiated. 4 
INTRODUCTION 
In multicellular organisms, especially in the higher forms of life, a differentia- 
tion of the cells of the individual occurs together with a division of labor, 
certain groups of cells being set apart to perform more or less definite functions. 
The cells are no longer independent and the whole mass of cells constitutes the 
individual^ Groups of cells having the same structure and functions are 
called tissues, such as connective, epithelial, muscle, and nerve tissue. These 
tissues are found combined in various ways to form more or less well defined 
structures called organs. Examples of organs are the heart, stomach, lungs, 
brain, eye, muscles, skin, glands, blood vessels, etc. Each of these organs has 
a definite work to perform in carrying out the functions of the whole body. 
The physiology of the higher animals must therefore be chiefly concerned 
with an investigation of the functions of the various tissues and organs, as well 
as with the significance that the functions of the individual organs have to the 
entire body. It is obvious that a knowledge of the location, form, and relation 
of the various organs to one another is necessary to an understanding of their 
functions. The science dealing with this subject is called anatomy. It is also 
necessary to know the appearance of the various cells of which the tissues are 
composed and the manner in which these cells are grouped in the various organs. 
The Science investigating the minute structure of the body is called histology. 
Aside from the obvious fact that animals are subject to the same physical 
laws that affect inanimate matter, the phenomena exhibited by the various 
organs and cells take place in accordance with certain definite physical laws. 
For this reason a knowledge of physics is essential in the study of physiology. 
In common with all other matter the animal body is composed of definite chemi- 
cal substances. The food that is introduced into the body has to undergo chemi- 
cal changes before it can be utilized by the tissue cells and definite chemical 
reactions are constantly going on in the tissues. Hence it is that a knowledge 
of chemistry is also essential to an understanding of physiology. 
Grouping of the Organs of the Body.-The bodies of the higher animals are 
composed of a number of organs that can be grouped according to similarities 
of structure or by virtue of their natural association in the performance of some 
definite function. Any such grouping is called a system by anatomists and an 
apparatus by physiologists. Thus, the heart and blood vessels constitute a 
system or apparatus whose object is the distribution of blood and called the 
circulatory system. The alimentary canal, with the glands associated with it, 
constitute the digestive system whose function is the preparation of food for 
absorption. The respiratory passage-ways together with the lungs, the dia- 
phragm, the thoracic muscles, etc., constitue the respiratory system, whose 
object is the exchange of certain gases between the animal and the surrounding 
medium. The various glands may be grouped into a secretory system whose 
function is the production of some specific material essential in the nutrition 
of the body. The kidneys, ureter, and bladder constitute the urinary system, 
whose function is the elimination of certain waste products. The functions 
of these different systems are called the nutritive functions; their object is the 
maintenance of the body in a state of health. The nerves and muscles to which ESSENTIALS OF PHYSIOLOGY 
5 
they are related constitute the neuro-muscular system which enables the 
individual to produce those movements necessary in his struggle for life. 
For this reason the nerve and muscle tissues are often called the master tissues 
of the body. The eye, ear, nose, throat, and skin, together with certain related 
structures, respectively constitute the visual, the auditory, the olfactory, the 
gustatory, and the tactile systems, which when appropriately stimulated give 
rise ultimately to various sensations that may result in volitional movements. 
The skin and its appendages-hair, nails-have the additional function of pro- 
tecting the surface of the body and constitute the integumentary system. 
The brain together with the sense organs constitute an apparatus for the 
elaboration of mental processes. The larynx, the mouth, and related structures 
form the articulating apparatus that serves to produce articulate speech. 
All of these functions, namely: motion, sensation, language, and mental pheno- 
mena are termed functions of relation as through them the individual acquires 
a knowledge of the external world. This knowledge is necessary for an intelli- 
gent adaptation of the individual to his surroundings. The behavior of the organ- 
ism, in its adaptation to its environment is, in fact, the result of response to various 
stimuli, either external or internal. The testes in the male and the ovaries in 
the female, together with their respectively related structures, constitute the 
reproductive system peculiar to the two sexes. They serve to perpetuate the 
species to which the animal belongs by the production of new beings. 
The functions of the human body are very complex; only a few of these 
functions are amenable to direct observation. It is therefore necessary in 
order to obtain knowledge of the function of those organs that are inaccessible, 
to study the functions of the corresponding organs in lower animals. The knowl- 
edge thus obtained can then be attributed, within limits, to the organs of man. 
The disturbances of function occurring in disease may also be studied, and when 
followed by a thorough postmortem examination, can be utilized in checking the 
results of experimentation on the lower animals. A combination of these 
methods-namely, experimentation on lower animals, direct observation on 
man, a study of the disturbances of the functions in disease and postmortem 
examinations-constitute the basis on which our present knowledge of physiol- 
ogy has been built. 
Pharmacodynamics.-Another branch of biological science that is closely 
related to and dependent upon physiology is pharmacodynamics (or pharmacology 
in its restricted sense). Pharmacodynamics is the study of the changes pro- 
duced in living structures by substances other than foodstuffs. These sub- 
stances are known as drugs or poisons according to whether they are useful or 
harmful in a given case. All scientific knowledge concerning drugs constitutes 
the science of Pharmacology. The study of the detection and effects of poisons, 
and the diagnosis and the treatment of poisoning is termed toxicology. In 
contradistinction to physiology which is concerned with the study of the func- 
tions of the normal body, pharmacodynamics is the study of the body rendered 
abnormal by the action of drugs on its various tissues and organs. CHAPTER II 
THE CELL 
In the foregoing chapter it was stated that the organs and tissues of the body 
are made up of structural elements called cells. The cell may therefore be 
regarded as the primary anatomical and physiological unit of living organisms. 
Structure of Cells.-A typical cell consists of a gelatinous substance called 
protoplasm, bioplasm, or cytoplasm in which is located a small spherical or 
ovoid body called the nucleus. Inside the nucleus there is often seen a very 
small body called the nucleolus (see 
Fig. 5). Cells vary greatly in shape 
and size as well as in the details of their 
intimate structure. The shape of cells 
is apparently determined by their posi- 
tions in reference to other cells and the 
necessities of their functions. When 
free the cell is more or less spherical 
in form, but through mutual pressure 
may become polygonal; cells may also 
be cylindrical, fusiform, stellate, etc. 
The size of cells ranges from 7.7 
(M200 of an inch), to 135 M (>^Oo of 
an inch). 
The Cytoplasm.-The cytoplasm 
consists of a semifluid, jelly-like mater- 
ial varying in the details of its appear- 
ance in cells of different tissues. In young cells it appears practically clear and 
homogeneous. Mature cells contain granular material which has been shown to 
consist of protein, fat, glycogen, ferments, pigments, etc. The cytoplasm con- 
sists of a fine network called the spongioplasm holding in its meshes a clear 
and more fluid portion called the hyaloplasm. Young cells appear clear because 
of the greater abundance of hyaloplasm. A typical cell is surrounded by a 
membrane enclosing the cell substance; this membrane is produced by a surface 
condensation of the cell protoplasm. 
The Nucleus.-The nucleus is usually situated near the center of the cell. 
Its contents are held by a membrane. It consists of a network of fibrils holding 
in its interstices the nuclear matrix. The network of fibrils consists of a gran- 
ular material called chromatin. One side of the nucleus called the pole is free 
from this network. This pole may be occupied either within or just without the 
Fig. 5.-Diagram of a typical cell. 1, cell 
membrane; 2, metaplasm granules; 3, karyosome 
or net-knob; 4, hyaloplasm; 5, spongioplasm; 6, 
linin network; 7, nucleoplasm; 8, attraction-sphere; 
9, centrosome; 10, plastids; 11, chromatin network; 
12, nuclear membrane; 13, nucleolus; 14, vacuole. 
(Bailey.) 
1 The unit of measurement of microscopic structures is a micron, equivalent to one thousandth 
of a millimeter, and written 
6 ESSENTIALS OF PHYSIOLOGY 
7 
nucleus by a small body called the centrosome or pole corpuscle. One or more 
small bodies may also be seen within the nucleus; they are termed nucleoli. 
Chemical Composition of the Cell.-The methods employed in chemical 
investigation are such that a complete analysis of chemical structure cannot be 
accomplished without destroying the life of the cell. The results of such 
analyses are not, therefore, necessarily an index of the true chemical nature of 
living matter. The substances indentified, consist of: 
(a) Water, not less than 75 per cent. 
(b) Carbohydrates, such as glycogen and dextrose. 
(c) Proteins, particularly Nucleo-protein. 
(J) Fat Globules. 
(e) Lipoids, as lecithin (a phosphorized fat) and cholesterol (a monatomic 
alcohol). 
(/) Inorganic salts, especially Potassium, Sodium, and Calcium Chlorides 
and Phosphates. 
In addition to these substances various ferments, pigments, etc. have been 
detected. 
The Life of the Cell.-During its span of life the cell exhibits the three 
following phenomena-viz., growth, metabolism, and reproduction. 
Growth is an increase in size attended with some increase in complexity. 
The newly reproduced cell is much smaller than the parent cell but owing to its 
ability to assimilate material found in its surrounding medium, it gradually 
increases in volume until it has reached the size of the mature cell. The inti- 
mate structure of the cell at the same time gradually increases in complexity. 
Metabolism may be defined as the sum of the chemical processes upon which 
the function, growth and repair of the cell depend. The physiological activities 
of the cells are attended by the liberation of energy. This energy is derived 
from chemical changes taking place within the cell or in the medium in contact 
with it. This liberation of energy takes place by a series of chemical changes 
whereby disintegration of the molecules of the food material brought to the cell, 
and probably of a portion of the living material itself, occurs. This disinteg- 
rating process is called catabolism or dissimilation. If the cell is to continue 
liberating energy while performing its function it is necessary that it should not 
only obtain the necessary food material but also repair or build up its living 
matter. This process takes place through a series of chemical changes of an 
integrative nature, called anabolism or assimilation. Metabolism therefore 
includes two opposite processes one of which is destructive, the other con- 
structive, in character. 
The liberation of the energy locked in the food molecules is accomplished 
essentially by oxidation. The energy thus liberated manifests itself in three 
forms-viz., motion, electricity, and heat. As a consequence of the liberation 
of heat all living matter exhibits a certain temperature which varies in differ- 
ent species of animals. These oxidative processes result in the production of 
material that is of no further use to the cell. This material constitutes the 
waste products of cell activity, among which are: carbon dioxide, urea, uric acid, 8 
THE CELL 
etc. The waste products are discharged by the cells into their surrounding 
medium. A removal of the waste products and a renewal of food material are 
essential conditions in the maintenance of the life of the cell. 
Chromosomes. Centrosomes. 
Central spindle. 
Polar radiation. Nuclear spindle. 
Fig. 6.-Karyokinesis. a, scheme of the close coil and the Division of the Centrosomes; b 
scheme of the loose coils and Separation of the Centrosomes; c, scheme of the Mother Star, or Equa- 
torial Plate; d, scheme of Metakinesis, showing the Nuclear Spindle; e, scheme of the Daughter Stars;. 
f, scheme of the Division of the Protoplasm forming Daughter Cells. (Stbhr's Histology.) 
Under normal conditions the metabolism of the cellsis such that the processes 
of assimilation and dissimilation balance each other. When this condition 
obtains, the body is said to be in a state of nutritive equilibrium. 
Reproduction.-A cell reproduces itself by dividing into two so-called 
daughter cells, the division of the nucleus preceding that of the cell body. 
Division of the nucleus may be: ESSENTIALS OF PHYSIOLOGY 
9 
(d) Simple, direct or amitotic.-This form of reproduction occurs in the 
amoeba. 
(b) Indirect, karyokinetic or mitotic, which is the usual mode of reproduction 
of the cells of the higher organisms (Fig. 6). In division by karyokinesis pro- 
gressive changes occur in the nucleus which result in the division of the centro- 
some, the chromatin, and the rest of the nuclear matter into two equal portions 
that constitute the new nuclei; the protoplasm then divides, so that two new 
cells are formed.1 
The Physiological Properties of Cells.-Certain more or less character- 
istic properties are exhibited by living cells; these are: irritability, conductivity, 
and motility. 
By irritability is meant the ability of reacting in a definite manner to the 
action of external forces or stimuli. The reaction varies with the nature of the 
cell and is proportional, within limits, to the strength of the stimulus. If the cell 
be a muscle cell, the reaction will be a contraction; if a nerve cell, the reaction 
will be the discharge of a nerve impulse; if a gland cell, a discharge of secretion. 
Stimuli are classified in accordance with their nature as follows: 
(a) Mechanical; as pinching, pressure, etc. 
(b) Chemical; solutions of mineral or organic acids, salts, carbon dioxide, 
etc. 
(c) Thermal; changes in temperature. 
(J) Photic; light. 
(e) Electrical; the constant and the induced currents. In addition to 
these forms of stimulation there exists another form, peculiar to the animal body 
viz., the nerve impulse. Since stimuli bring forth the characteristic activity of 
the cell and this activity is dependent upon a transformation of energy, a 
stimulus may be defined as any agency capable of causing this transformation. 
Conductivity is the property possessed by living matter of propagating 
through itself a state of activity arising at any one point. This property is 
best exemplified in nerve cells and their processes, although it is well developed 
in muscle cells also. 
Motility is the property possessed by certain cells of executing various 
changes of shape resulting in definite movements. Examples of motility are: 
the ameboid movement of white blood cells, the contraction of muscle cells, 
the waving of cilia, etc. 
THE GENERAL PLAN OF THE VERTEBRATE BODY 
Vertebrates are distinguished by the presence of a bony segmented axis 
extending longitudinally and known as the vertebral column or backbone. 
The vertebrates include fishes, amphibia, reptiles, birds, and mammals. 
The body of every vertebrate may be divided into: 
(a) An axial portion, including the head, neck and trunk, and 
(b) An appendicular portion, including the anterior and posterior limbs or 
extremities. 
1 The details of karyokinesis do not fall within the scope of this book. Those interested will 
find the necessary information in works on histology. 10 
THE CELL 
The axial portion is divided by a bony partition, consisting of the verte- 
brae, into a dorsal and a ventral cavity. 
The dorsal cavity extends through the trunk, the 
neck, and head (Fig. 7). Its walls in the trunk and neck 
are formed by the vertebrae, while in the head they are 
formed by the bones of the skull. As this cavity con- 
tains the brain and the spinal cord, it is called the neu- 
ral cavity. Openings in the sides of this cavity allow 
nerves to pass out to connect the brain and spinal cord 
with the rest of the body. 
The ventral cavity lies in front of the vertebral col- 
umn and is confined to the trunk. The walls of this cav- 
ity are composed of muscles and skin, supplemented in 
most animals by ribs in its upper part. A musculo- 
membranous tube or canal runs the entire length of the 
ventral cavity; it is known as the alimentary or food 
canal. Beginning at the mouth, on the ventral side of 
the head, it ends in the posterior extremity of the trunk 
at the anus. The mammals, in which class man is includ- 
ed, are characterized, in part, by a transverse partition 
that divides the ventral cavity into two parts. This 
dividing partition is called the diaphragm or midriff. 
The cavity situated above or anterior to the diaphragm 
is called the chest or thoracic cavity. The cavity below 
or posterior to the diaphragm is the abdominal cavity. 
The chest or thorax contains the lungs, heart, and its 
large blood vessels, and most of the gullet or esophagus. 
The abdomen contains the stomach and intestine, the 
liver, pancreas, spleen, the kidneys, bladder, and the 
internal organs of reproduction. 
The Surfaces of the Body.-The body may be 
conceived of as a tubular structure. It has therefore 
two surfaces; viz., an external or outside surface, and an 
internal or inside surface. The external surface is cov- 
ered by the skin, which is a protective and sensitive 
organ. The skin is modified in special places in the form 
of nails, hair, etc. The internal surface-the surface 
of the alimentary canal and other canals opening to 
the outside-is covered by mucous membranes. Any- 
thing in the interior of this canal cannot therefore be 
said strictly to be "inside" the body. Material has not 
entered the body until it has been absorbed into the blood and distributed by 
this fluid to the tissues. 
The appendicular portion consists of two pairs of symmetrical limbs 
springing from the sides of the trunk. The limbs are similar in structure but 
are modified in various animals to adapt them for prehension or locomotion. 
Fig. 7.-Diagrammatic 
longitudinal section of the 
body, a, the neural tube, 
with its upper enlargement 
in the skull cavity at a'; N, 
the spinal cord; N', the brain; 
e, e, vertebrae forming the 
solid partition between the 
dorsal and ventral cavities; b, 
the pleural, and c, the abdo- 
minal division of the ventral 
cavity, separated from one 
another by the diaphragm, 
d; i, the nasal, and o, the 
mouth chamber, opening be- 
hind into the pharynx, from 
which one tube leads to the 
lungs, I, and another to the 
stomach, f; h, the heart; k, 
the kidney; s, the sympath- 
etic nervous chain. From 
the stomach, f, the intestinal 
tube leads through the ab- 
dominal cavity to the pos- 
terior opening of the alimen- 
tary canal. (Martin-Fitz.) CHAPTER HI 
PHARMACODYNAMICS OF THE CELL 
Drugs may affect cells by: (i) Entering into Chemical Combinations with 
the Constituents of the Cytoplasm of the Cells -Some of the effects of oxalates are 
due to the fact that they form insoluble salts with the calcium of the cells. 
Strong solutions of Potassium and Sodium Hydroxides owe their caustic effects 
to the fact that they form soaps with the fats, and alkali albuminates with 
some of the proteins of the cells, and, being very hygroscopic, abstract water 
from them. 
(2) By Virtue of Their Physical Properties.-Unless a drug is soluble in the 
body fluids it cannot be absorbed and circulate in the blood, neither can it 
readily enter the cell unless it is soluble in the cell contents. Some drug effects 
probably arise from the fact that certain drugs alter the surface tension of 
cells in relation to their surrounding fluids. Other drugs possibly produce 
effects through changes in the electrical states of cells. 
Although it is believed that in most cases drugs act on cells only when they 
have penetrated into the cell contents, certain powerful drugs act by altering the 
cell surface without penetrating into the interior. 
When a drug affects a cell the specialized function or activity of the cell may 
be increased or decreased but the form or kind of activity remains unchanged. 
Thus, in therapeutic dosage Chloral Hydrate lessens, and Strychnine augments 
reflex movements, but nevertheless the movements are reflex in nature and do 
not assume the nature of voluntary movements. 
Drugs which augment the activity of any organ are said to stimulate it, 
while those which decrease the activity are said to depress it. When stimulation 
is excessive or prolonged, the cytoplasm usually becomes markedly depressed, 
and ultimately loses entirely its specialized function or activity, i. e., it is 
paralyzed. An excessive dose of a stimulating poisonous drug results, therefore, 
in depression and finally in paralysis. Functionally, the cell is dead but if the 
failure to functionate does not result in the death of the organism, the cell may 
finally recover and ultimately resume its normal function. 
Another effect induced in cells by certain drugs is termed irritation. 
Although this term has been at times employed as a synonym for stimulation, 
the two conditions are not identical. As stated above, stimulation indicates an 
augmentation in the specialized function or activity of a cell, as illustrated by 
Strychnine which increases the reflex irritability of certain cells in the spinal 
cord. The term irritation is used, however, to designate changes in the condi- 
tions common to all forms of living matter, i. e., it indicates changes in the 
nutrition and growth of the cell, rather than any effects on its specialized func- 
tions. While stimulation is met with in highly specialized cells, like those of the 
11 PHARMACODYNAMICS OF THE CELL 
12 
nerve system and heart, irritation may be induced in all kinds of cells. The 
irritating action of the caustic alkalies has been explained by the chemical 
changes they produce in the proteins and fats of the cells, and the abstraction 
of water from them. 
While it is true, as pointed out above, that a cell may, under certain con- 
ditions, recover from the depression and paralysis resulting from excessive 
stimulation, undue irritation ultimately results in the actual death and disin- 
tegration of the cells. If a cold-blooded animal is poisoned with Strychnine 
certain cells of the spinal cord are first stimulated and later paralyzed, but 
after a few days the cells of the spinal cord regain their normal function as the 
poison is eliminated. If, however, an excessive quantity of a concentrated 
solution of a very irritating drug is injected under the skin, the cells which come 
in contact with the poison undergo degeneration and die, and an abscess forms. 
These cells cannot recover; they are either absorbed or removed by opening the 
abscess, and their places are filled in by the overgrowth of the adjacent tissues. 
The intensity of the action of a drug on a cell depends on the concentration 
of the drug in the cell. The concentration of a drug within the cell is in turn 
dependent upon: (i) The concentration in which it is found in the fluid surround- 
ing the cell, for the penetration of a drug into a cell is probably accomplished by 
simple diffusion which follows the usual physical laws. In other cases the drug 
is deposited in the cell in some chemical or physical combination, and diffusion 
continues until all the drug has penetrated into the cell, and the surrounding 
fluids are practically free from it. In still other cases there seems to be no 
greater concentration of the drug in the cell than in the surrounding fluid. 
(2) The Dose of the Drug Given.-This, however, is modified by the rate at 
which the drug is absorbed and excreted or destroyed. In ether anesthesia the 
object is to bring about a sufficient degree of concentration in certain cells of the 
brain without seriously involving the heart and the respiration, and without doing 
permanent damage to the cells of the central nerve system. This is accom- 
plished by gradually administering the drug in small divided doses, thereby avoid- 
ing a fatal concentration, for, while the drug is being absorbed throughout the 
period of anesthesia, its excretion is taking place at an approximately equal 
rapid rate. 
Many drugs have a special affinity for certain cells. Some attack the cells 
of the central nerve system, others the heart, and still others the endings of 
various nerves. Where a cell exhibits apparent immunity to the action of a 
drug, it is probably due to the fact that the drug has failed to penetrate into the 
cell constituents, or to the power of the cell to oxidize or destroy it. There is 
no poison which acts equally on all kinds of cells. However, those which have 
a wide field of operation are termed cytoplasmic poisons. 
Local, Systemic, and Remote Actions.-The effects produced by a drug at 
the site of application, before it enters into the circulation, are called the direct 
local action of the drug; while the effects produced because of its special affinity 
for the cells of certain organs or tissues to which it is carried by the blood stream, 
are termed the systemic or general action. Some drugs have only a direct local PHARMACODYNAMICS 
13 
action because they are not absorbed; or are absorbed in an inactive form; or 
are excreted as rapidly as they pass into the blood, so that there is not enough 
of the drug in the circulation at any given time to produce systemic effects. 
Certain very active drugs have little or no direct local action, but they have a 
decided special affinity for the cells of some organ or tissue to which they are 
carried by the blood. 
Direct or primary effects can only be produced in the cells with which drugs 
come into immediate contact. However, changes in the activity of the cells of 
one part of an organism often result, through the intermediation of impulses 
transmitted by nerves or through changes induced in the circulation and nutri- 
tion, in effects on structures to which the drug is inaccessible or for which it has 
no special affinity. Such effects are termed indirect, secondary or remote. 
Thus, a poison which weakens the heart may also produce disturbances in the 
respiration, owing to a deficiency of the circulation in the brain, which contains 
a center that controls respiration. 
Remote local effects are produced by certain drugs as they are being excreted. 
For example Hexamethylenamine ("Urotropin") may exert an antiseptic action 
while it is being eliminated in the urine. 
Salt-action.-The term salt-action is applied to certain reactions which 
result from the physical effects of solutions, and which are analogous to changes 
in dead tissues and are explained in the same manner. Any substance, like 
salts, sugars, urea, etc., capable of circulating in sufficient concentration in the 
body, can produce salt action. This depends upon the relative ease with which 
the solution of the substance diffuses into those cells with which it comes in 
•contact. Depending on the concentration, serious disturbances in the func- 
tions and composition of cells may result from salt-action. 
The reactions of the red blood cells afford an example of salt-action. 
When red blood cells are placed in distilled water, the water passes into them 
until they swell and finally burst. If a salt solution which has the same con- 
centration as that of the blood is used (isotonic), the water does not penetrate 
the cells and no rupturing takes place. If a salt solution having a decidedly 
lower concentration than that of the blood (hypotonic) is used, water penetrates 
the cells (as was also the case with distilled water) which swell and finally burst 
(hemolysis or taking). When a salt solution which has a decidedly greater con- 
centration than that of the blood (hypertonic) is employed, fluid is withdrawn 
from the cells which shrink (crenation) and finally collapse. CHAPTER IV 
HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES 
The statement has been made in the introductory chapter that a microscopic 
study of the organs of the body shows them to be made up of individual cells. 
These can be classified into special groups in accordance with their similarity 
of structure and function, each group being called a tissue. The tissues of 
the body have been named: epithelial, connective, muscle, and nerve tissues. 
Fig. 8.-Surface view of squamous cells of frog's 
skin. (Radasch.) 
Fig. 9.-Simple columnar epithelium from a. 
human intestinal villus. A, surface view; B, 
vertical section. The prominent cell outlines in 
A are due to terminal bars, shown in section in 
B, Cut., cuticular border. (From Lewis and 
Stohr's Histology.) 
Fig. io.-Pseudo-stratified ciliated epithelium from the human respiratory tract. B is a diagram of 
the condition shown in A. X 720. (From Lewis and Stohr's Histology.) 
Epithelial Tissue.-This tissue is found on the surfaces of the body both 
external and internal; it constitutes the essential part of all glands, whether 
secretory or excretory, so that all nutritive or waste material must pass through 
epithelial cells before it can be introduced into or eliminated from the blood. 
It consists of one or more layers of cells resting on a basement membrane, under 
14 ESSENTIALS OF PHYSIOLOGY 
15 
which are found the blood vessels, supplying the necessary material to the cells, 
nerves, and lymphatics. 
Form.-Epithelial cells vary in form in different locations. They may be 
flattened and thin, in which case they constitute pavement or squamous epithelium; 
they may be cubical or columnar and may be provided at their free extremity 
with hairlike processes called cilia. They may occur in more than one layer 
of cells in which case they constitute stratified epithe- 
lium, as on the surface of the skin, or transitional 
epithelium, as in the lining of the bladder (see Figs. 8, 9, 
10 and 11). 
Functions.-(a) On the surface of the skin epithe- 
lium acts as a protective covering. 
(IP) The epithelium lining the internal surface of the 
body is a part of the mucous membrane forming the 
wall of this surface. In the case of the alimentary canal, 
more especially of the small intestine, the epithelium is the agent through 
which the absorption of the products of digestion takes place. 
(c) The glands, whether secretory or excretory, consist essentially of 
epithelial cells. The secretory glands are actively engaged in the production 
of material utilized in the nutritive processes of the body. The excretory 
Fig. ii .-Transitional 
cells. (Radasch.) 
Fig. 12.-Intermuscular connective tissue bundles of man. a, fat drop; b, fat cells; c, bundles of 
white fibers; d, nucleus of a cell; e, elastic fibers. (Lewis and Stohr.) 
glands have for their function the removal of the waste products of tissue 
metabolism. 
The Connective Tissues.-These tissues considered collectively form a 
framework pervading the body, serving to bind its individual parts and support- 
ing the various organs. Several varieties of connective tissues are recognized, 
viz., white fibrous, yellow elastic, areolar, adipose, cartilaginous and osseous. 16 
HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES 
White Fibrous Tissue.-This form of connective tissue consists of bundles 
of delicate, transparent, wavy fibers that neither branch nor unite with each 
other; the fibers are held together by a small amount of ground substance 
(Fig. 12). This tissue because of its toughness, inextensibility, and pliability 
is well adapted for locations where such properties are valuable; viz., in the 
membranes covering special organs such as the heart, 
nerve system, bones, etc.; in the ligaments about the 
joints, tendons of muscles, etc. When fibrous tissue 
is boiled for a sufficiently long time, it yields gelatin. 
Yellow Elastic Tissue.-This consists of coarser 
fibers pursuing a straight course, branching and 
uniting freely with neighboring fibers (Fig. 13). It 
is often associated with the white fibrous variety, 
although it may predominate almost exclusively as 
in the ligamentum nuchae and middle coat of the 
larger blood vessels. This tissue confers to the 
structures in which it is found the important pro- 
perties of extensibility and elasticity. It will under- 
go a stretching of as much as 60 per cent of its natural 
length before breaking. 
Areolar Tissue.-This consists of interlacing 
bundles of fine, colorless, transparent, wavy fibers 
held together by a ground substance. Yellow elastic fibers may be seen inter- 
lacing in all directions. Stellate or connective tissue cells are distributed in 
the meshes of the areolar tissue together with other cellular elements (Fig. 
14). It is found very generally throughout the body, serving to bind together 
muscle and gland tissue, holding nerve fibers together to form nerves, connec- 
Fig. 13.-A, elastic fibers of 
the subcutaneous areolar tissue of 
a rabbit. (After Schafer.) B, 
Cells in relation with elastic fibers, 
after treatment with acetic acid. 
Subcutaneous tissue of a pig em- 
bryo. (After Mall.) 
Fig. 14.-Subcutaneous tissue from a cat. The fiber a has been treated with dilute acetic acid; 
the other fibers have been teased apart and examined, unstained, in water, a, c, white fibers; b, 
fat cell; d, connective tissue cell; e, elastic fibers. (From Lewis and Stohr's Histology.) 
ting the skin to underlying structures, forming sheaths for the support of blood 
vessels, etc. 
Adipose Tissue.-This is a modification of areolar tissue, in the meshes of 
which it occurs as small and irregular masses or lobules. It consists of round, or 
polyhedral cells appearing as globules of fat surrounded by a thin membrane. ESSENTIALS OF PHYSIOLOGY 
17 
This membrane thickens at the point at which the nucleus is found (Fig. 15). 
The fat is Equid during life. Adipose tissue is Hkewise widely distributed 
throughout the body, but is especially abundant under the skin, in the bones, 
around the kidneys, and in the omentum. It gives smoothness and roundness 
to the form and prevents a too rapid loss 
of heat from the body; it Hkewise serves 
as a store of nutritive material in case of 
special need. 
Cartilaginous Tissue.-Cartilaginous 
tissue is composed essentially of connec- 
tive tissue cells surrounded by solid ground 
substance. Three different varieties are 
recognized in accordance with the nature of 
the ground substance. 
(a) Hyaline Cartilage.-In this variety 
the cells are few and the ground substance 
abundant (Fig. 16A). This cartilage is 
found covering the ends of the long bones, 
between the sternum and the ribs, as well 
as in the nose and larynx. 
(6) White Fibro-cartilage.-This var- 
iety of cartilage is characterized by bun- 
dles or layers of white fibers disseminated through the ground substances (Fig. 
16B). It is found between the bodies of the vertebrae and in certain joints. 
(c) Yellow Fibro-cartilage.-In this form of cartilage, yellow elastic 
fibers ramify in the ground substance (Fig. 16C). It occurs in locations where 
Fig. 15.-Normal adipose tissue from 
an adult. X 400. Connective tissue is seen 
at the left of the figure and (as at c. t.) be- 
tween the fat cells; n, nucleus of a fat cell. 
{From Lewis and Stohr's Histology.) 
Fig. 16.-The three types of cartilage: A, hyaline; B, elastic; C, fibrous, a, b, outer and inner 
layers of perichondrium; c, young cartilage cells; d, older cartilage cells; e,f, capsule; g, lacuna. 
{After Radasch.) 
a certain degree of elasticity is necessary, as in the epiglottis, the external ear, 
Eustachian tube, etc. 
Osseous Tissue.-This is a connective tissue in which the ground substance 
is permeated with insoluble lime salts. These salts can be dissolved out by 18 
HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES 
immersing bone in a dilute solution of hydrochloric acid. The material left 
behind is soft and bends readily; it yields gelatin on boiling. 
Composition of Bone 
Organic matter (collagen, fat, etc.) 31.04 
Inorganic matter: 
Calcium phosphate. 58.23 
Calcium carbonate 7.32 
Calcium fluoride 1.41 
Magnesium phosphate 1.32 
Sodium chloride 0.69 
68.97 
(Cunningham) 
Microscopic examination of a decalcified bone shows that canals run through it, 
mostly in a longitudinal direction, although they branch and communicate with 
each other frequently. They are called 
Haversian Canals and contain blood ves- 
sels and lymphatics. Each Haversian 
canal is surrounded by a number of con- 
centric layers or laminae consisting of 
white fibers. At the line of junction of 
two laminae, small cavities occur, called 
lacunae, from which exceedingly small 
canals-canaliculi-radiate in every dir- 
ection. These communicate with each 
other freely. The entire system of Haver- 
sian canals, lacunae, and canaliculi is filled 
in life with circulating lymph carrying the 
material necessary for the nutrition of the 
bone. In each lacuna there is found a 
branched cell called the bone corpuscle 
(Fig. 17). 
Every bone is covered on the sur- 
face by a fibrous membrane called the 
periosteum except at various locations 
where cartilage forms the covering. The 
inner surface of this membrane contains numerous capillary blood vessels and 
special cells-the osteoblasts. It is from this layer that bone is formed; hence 
it is called the osteogenetic layer. 
When a long bone is sawed through longitudinally it is seen to be made 
up of two kinds of structure. One of these is compact, the other cancellated 
or spongy. The shaft of the bone is hollow and filled with marrow. The 
marrow consists of connective tissue supporting blood vessels and osteoblasts. 
The connective tissue corpuscles are filled with fat, except in the cancellated 
portion near the ends of the bone in which the marrow appears red. The red 
blood cells are believed to originate in the red marrow of bone. 
Fig. 17.-Cross section of compact bone, 
from the shaft of the humerus, showing three 
Haversian systems and part of a fourth. 
(Sharpey.) ESSENTIALS OF PHYSIOLOGY 
19 
THE SKELETON 
The connective tissues constitute a framework giving support and attach- 
ment to the more delicate structures of the body. This framework may be 
divided into two parts: (1) a fibrous skeleton, pervading and covering the various 
Cranium. 
7 Cervical Vertebrae. 
Clavicle. 
Scapula. 
Humerus. 
Ilium. 
Ulna. 
Radius. 
Pelvis. 
Bones of the Carpus. 
Bones of the Meta- 
carpus. 
Phalanges of Fingers. 
Femur. 
Patella 
Tibia. 
Fibula. 
Bones of the Tarsus. 
Bones of the Metatarsus 
Phalanges of the Toes. 
Fig. 18.-The skeleton. {After Holden.) 
organs, serving to bind the muscle, nerve and epithelial tissues; (2) a solid, bony 
skeleton, serving for the protection of viscera and the attachment of muscles. 
The term "skeleton" is commonly confined to this bony framework, and in- 
cludes the bones together with the cartilages and ligaments that bind them 
together. The skeleton is divisible into (a) an axial and (6) an appendicular 
portion (see Fig. 18). 20 
HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES 
The axial portion includes the bones of the skull, the vertebral column, the 
ribs, and breast-bone or sternum. The number of separate and distinct bones 
seen in this part of the skeleton in the adult is shown in the table below: 
Skull.: 
Single Bones 
6 
Pairs 
8 
Total 
22 
Vertebral column 
26 
26 
Cervical vertebrae, 7 
Thoracic vertebrae, 12 
Lumbar vertebrae, 5 
Sacral vertebrae, 5 (fused into one bone) 
Coccygeal vertebrae, 4 or 5 (fused into one bone) 
Ribs 
12 
24 
Sternum 
1 
I 
Hyoid bone 
1 
I 
Ossicles of the ear 
3 
6 
Total 
80 
Fig. 19.-A side view of the skull. 0, occipital bone; T, temporal; Pr, parietal; F, frontal; S, 
sphenoid; Z, malar; Mx, maxilla; N, nasal; E, ethmoid; L, lacrymal; Md, inferior maxilla. (Martin- 
Fitz.) 
The skull includes the bones of the cranium and those of the face. The 
cranial cavity contains the brain. The skull is poised on top of the vertebral 
column (Fig. 19). ESSENTIALS OF PHYSIOLOGY 
21 
The vertebral column, also called the spinal column or 
backbone, consists of individual ringlike bones, called the ver- 
tebrae. These bones are stacked one upon the other and 
held together by bands of connective tissue, termed liga- 
ments. A disk of fibro-cartilage is found between the bodies 
of the vertebrae and serves to absorb shocks. When the ver- 
tebral column is looked at from the side, it is seen to curve in 
different directions. In the cervical and upper thoracic por- 
tions the vertebral column has a forward or ventral convex- 
ity; in the thoracic portion it is concave; in the lumbar 
portion it is slightly convex; while in the sacral-coccygeal 
portion it is again concave (Fig. 20). These curvatures ena- 
ble man to maintain the erect posture. The vertebral column 
gives attachment to the ribs. 
The ribs consist of a bony and a cartilaginous portion. 
The bony portion is joined to the vertebral column by joints 
or articulations. The cartilaginous portion is joined to the 
breastbone or sternum. The ribs, sternum, and thoracic por- 
tion of the vertebral column constitute the framework of the 
general cavity called the thorax or chest. 
The appendicular portion of the skeleton includes the 
bones of the upper and lower limbs together with the bones 
to which the limbs are attached and which constitute the 
shoulder or scapular girdle and the pelvic girdle respectively. 
The bones of this portion of the skeleton are tabulated below: 
Fig. 20.-The verte- 
bral column, seen from 
the side. (Hough and 
Sedgwick.) 
Upper limbs: 
Single Bones Pairs 
Total 
Scalpuar girdle 
. . 2 
4 
Upper arm 
. . I 
2 
Lower arm 
. . . . . 2 
4 
Wrist 
8 
x6 
Fingers 
Lower limbs: 
14 
28 
Pelvic girdle 
. . . i 
2 
Thigh 
. . i 
2 
Knee cap or patella 
. . i 
2 
Leg 
. . 2 
4 
Ankle and heel 
7 
14 
Instep 
5 
10 
Toes 
14 
28 
Total 
126 
The entire skeleton contains therefore two hundred and six bones. 
The bones of the appendicular portion act as levers that enable the indi- 
vidual to perform a great variety of movements of greater or less extent. These 
movements fall into two groups: (i) Movements of one part of the body in 
reference to other more or less fixed parts; such as movements of the lower in 
reference to the upper arm; or the lower in reference to the upper jaw. (2) 22 
HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES 
Movements of the entire body in reference to the environment as in the act of 
locomotion. 
A comparison of the upper and lower limbs shows that their bones are 
strikingly similar in form and in arrangement. The lower limbs of man have 
become especially modified to support the weight of the body and to enable its 
transportation in space; while the upper limbs, through the intervention of long 
and very mobile fingers and greater freedom of motion at the shoulder girdle, 
have become especially adapted to act as prehensile organs. 
The Joints or Articulations.-The bones are united to each other so as to 
permit of more or less motion at their points of contact. Such a union is called 
a joint or articulation. 
The following structures enter into the construction of joints: 
(a) Bones, the joint surfaces of which are especially adapted in form and 
size to enable definite movements to take place. 
Fig. 21.-Diagram of a diathrosis. (From "Morris' Human Anatomy.'') 
(b) Hyaline cartilage, covering the articulating end of the bone. In 
certain joints there are disks of white fibro-cartilage between the articulating 
surfaces of the bones. 
(c) A synovial membrane, enclosing the cavity of the joint, is attached to 
the edge of the hyaline cartilage. This membrane is lined with endothelial cells 
secreting a water clear, viscid fluid, called the synovial fluid, serving to diminish 
friction. 
(if) Ligaments, that bind the bones to each other. They are composed of 
tough, but pliable, white fibrous tissue, and fulfill the function of keeping the 
bones in their proper relations while allowing freedom of motion (see Fig. 21). 
Classification of Joints.-Joints are classified as immovable and movable. 
The immovable joints are called synarthroses. Examples of such joints are the 
sutures joining the bones of the cranium. The movable joints are further classi- 
fied in accordance with the degree and kind of movement possible. These fall 
into two classes: (1) The diarthroses and (2) amphiarthroses. 
The diarthroses include the hinge joints, such as the elbow, knee and ankle 
joints; and the pivot joints, such as the joint between the first and second cervi- 
cal vertebrae permitting rotation of the head, and the joint between the radius 
and the ulna permitting movements of pronation and supination of the hand; 
and finally the ball and socket joints, such as the hip joint and the shoulder 
joint. ESSENTIALS OF PHYSIOLOGY 
23 
The amphiarthroses include those joints through which only slight move- 
ments can take place. This is the case with the joints between the vertebrae, 
between the pubic bones, and between the sacrum and ilium. 
Hygiene of the Bony Skeleton.-The number of bones in the skeleton of 
man varies according to age, as a process of fusion takes place during growth, 
making the number in the adult less than that in the child; moreover, the com- 
position of bones changes also with age. In the child the organic matter of 
bones is found in greater relative proportion, therefore a child's bones are more 
pliable, tougher, and less easily fractured. Because of this greater flexibility 
of bones in the young it is important that infants should not be made to sit 
up or walk too soon. Older children should be made to sit and walk correctly 
so as to avoid the production of lateral curvature of the vertebral column 
Correct footwear is also important in preventing distortion and displacement 
of the bones of the foot with resulting deformities, and abnormal and painful 
gait. Since calcium compounds constitute the chief inorganic substances 
of bone, the growing child must be supplied with food containing these compounds 
in sufficient quantities. Among such articles of diet may be mentioned milk 
and milk products, and green vegetables such as spinach, lettuce, etc. 
As the individual grows older there occurs a gradual decrease in the per- 
centage of organic matter of the bones. These, therefore, become more 
brittle and are more susceptible to fracture. In advanced age a slight fall 
may cause a fracture of the thigh bone which is difficult and often impossible 
to heal. CHAPTER V 
PHARMACODYNAMICS OF EPITHELIAL TISSUE 
The most important drugs which affect the skin and mucous membranes 
are substances whose actions are chiefly direct local effects. They include the 
following groups: 
I. The protectives which embrace (a) the emollients, (6) the demulcents, 
and (c) the dusting powders. 
(a) Emollients.-These are unctuous substances, such as Petrolatum, 
Lard, Cold Cream, Glycerin (50 per cent or less), Cocoa Butter, and bland, fixed 
oils like Olive and Cottonseed Oils, which are applied to the skin to protect it 
from and to lessen irritation. Most of them are colloidal or fatty and, there- 
fore, being practically unabsorbable and indifferent, produce their effects 
by adhering to the skin. They thus afford a mechanical, local protection 
against irritating agents, wind, cold weather, sunburn, etc., and also protect 
the skin against the penetration of such fat-soluble irritants as Phenol, "mus- 
tard gas," etc. They render the skin softer and more pliable, and prevent 
drying of the epithelium. In medicine the emollients are useful in such 
conditions as chapped skin, burns, chafing, and various skin diseases. 
(b) Demulcents.-The demulcents are gummy, oily, and colloidal sub- 
stances, such as Acacia, Licorice, Slippery Elm, Irish Moss, Starch, white of egg, 
milk, Glycerin (50 per cent or less), and bland fixed oils, which are applied to 
mucous membrances to protect against and to allay irritation. They, like 
the emollients, are adhesive, and protect mechanically and locally, as well as 
soothe irritated or inflamed mucous surfaces. The demulcents are used in 
the form of troches and gargles for treating conditions like sore throat, 
gastric and intestinal irritation, and poisoning by irritant drugs; and in the form 
of suppositories and enemata for rectal administration. 
These drugs serve frequently to modify the taste of substances. Sugar 
dissolved in Mucilage of Acacia tastes less sweet, and acids less sour than in 
water. Even cold is felt less when a demulcent is present in the food swallowed. 
Thus, ice-cream and ice-cold milk do not feel as cold in the mouth as ice, 
because the demulcents present form a mechanically protective layer on the 
surface which prevents the sweet, sour, or cold substances from reaching the 
nerve endings which appreciate these effects as freely as they would in simple 
aqueous solution. 
(c) Dusting Powders or Absorbents.-These are extremely fine, non- 
irritating, insoluble powders, such as Starch, Talc, Zinc Stearate, Lycopodium, 
Chalk, Bismuth Subnitrate, Kaolin, Charcoal, etc., which are dusted on the 
skin, mucous membranes and wounds to form a protective layer; to prevent 
irritation by friction and irritating agents; and to dry by absorbing secretions. 
24 PHARMACODYNAMICS 
25 
II. The Astringents.-Astringents are substances which shrink, blanch, 
wrinkle, and harden tissue, diminish secretion and exudates, and coagulate 
blood. They have a characteristic "astringent taste;" i. e., produce a feeling 
of constriction ("puckering"), dryness and roughness in the mouth. These 
effects are due to the fact that they form rather insoluble, colloidal compounds 
with the protein constituents of the epithelial cells and the secretions. The 
more insoluble and viscid the coagulated compounds are, the more markedly 
will they shrink, wrinkle and harden the surfaces on and in which they are 
formed. They thus also'inhibit or prevent their own penetration into deeper 
layers of cells; their effects are therefore strictly direct, local actions. The 
hardened tissues are also less permeable, and as a result less lymph and secre- 
tion are formed. 
Hemostatics or Styptics.-The astringents also coagulate the blood and this, 
together with the narrowing of the vessels resulting from the shrinking of the 
circular muscle fibers due to the coagulation of their proteins, arrests small 
hemorrhages. When astringents are used to stop bleeding, they are termed 
hemostatics or styptics. Since astringents precipitate the proteins of the 
cytoplasm of bacteria, as well as that of tissue cells, they are somewhat antiseptic. 
In the stomach and intestines the coagulated proteins form a protecting 
layer which lessens irritability and thus retards intestinal movements. As a 
result of the foregoing, inflammation is lessened, and, since there is more 
time for the absorption of the liquid portion of the intestinal contents, the stools 
are harder and firmer, constipation often resulting. 
The intensity of action depends both on the dosage and the concentration. 
Large doses and too concentrated solutions produce irritation and finally corro- 
sion, which are manifested by pain, nausea, vomiting, and diarrhea. 
The astringents are usually divided into two classes: 
(a) The metallic astringents like Ferric Chloride, Alum, Zinc Sulphate, 
Copper Sulphate, and Silver Nitrate. Since the acids of these metallic salts are 
set free when they combine with proteins, the metallic astringents, if not 
sufficiently diluted, possess a marked irritating action in addition to their 
astringent effect. They are, therefore, more irritating and corrosive, when used 
in large dosage and in concentrated solutions, than the vegetable members of 
the group. 
(b) The vegetable astringents, like Gambir, Catechu, Nutgall, Kino, Witch- 
hazel Bark, etc., all contain tannic acid or "tannin," which acts like the metallic 
astringents but is less irritating. 
The astringents are used externally in the form of dusting powders, solu- 
tions, lotions, or ointments to harden the skin, to lessen excessive secretion, and to 
check small hemorrhages. In the form of mouth washes, gargles, troches, 
enemata, and suppositories they are used internally for swollen gums, small 
accessible hemorrhages, and catarrhal inflammations of mucous membranes, like 
sore throat, diarrhea, etc. For medication of the intestines the galenical prepa- 
rations of the vegetable astringents are preferred because the colloidal vegetable 
matter present in them retards chemical changes and absorption of the Tannic 26 
PHARMACODYNAMICS OF EPITHELIAL TISSUE 
Acid, thus enhancing their direct local actions. Since Tannic Acid 
is changed in the intestines to Sodium Tannate and then to Sodium Gallate, 
there is no astringent or hemostatic action after absorption as these salts are 
not astringent. Myrrh and Hydrastis are astringent because of the resins they 
contain. Alcohol and strong Glycerin (above 50 per cent) are locally astringent 
because they abstract water from the tissues. Epinephrine and Cocaine produce 
astringent actions by constricting the arterioles of mucous membranes through 
their action on certain nerve endings (or on their myoneural junctions) of 
these vessels. 
III. The Escharotics, Caustics, or Corrosives.-Escharotics are substances 
which cause the death of tissue by actually consuming it, as is the case with con- 
centrated Sulphuric Acid; by precipitating excessively the proteins of the cytoplasm, 
as by Silver Nitrate and Phenol; or by producing inflammations which result in 
sloughing, as by Arsenic Trioxide. They include the following subgroups of 
powerful chemical compounds: 
(a) Caustic alkalies, such as Sodium and Potassium Hydroxides and 
Carbonates, and Calcium Oxide. These compounds abstract water from the 
tissues, saponify the fats present, and dissolve proteins, forming a viscid, soluble 
mass (alkaline albuminates) through which the caustic alkalies penetrate farther 
into the tissues and make extensive and slowly healing ulcers. 
(6) Caustic acids, like concentrated Sulphuric, Nitric, Hydrochloric, 
Trichloracetic, and Glacial Acetic acids. Such concentrated acids also abstract 
water from the tissues, neutralize their alkalinity, and precipitate some of the 
tissue proteins as acid albuminates. These are not as readily dissolved as the 
alkaline albuminates. Hence, the caustic acids do not penetrate as deeply or as 
extensively into the tissues as the caustic alkalies. Sulphuric Acid chars tissue, 
Nitric Acid turns it yellow, Hydrochloric, Trichloracetic and Glacial Acetic 
acids blister and stain mucous membranes white. Although diluted acids are 
not corrosive, they are nevertheless irritating, unless diluted well below 1 per 
cent. 
(c) Metallic Salts.-This subgroup includes such compounds as Silver 
Nitrate, Burnt (exsiccated) Alum, Zinc Chloride, Copper Sulphate, Arsenic 
Trioxide, and Mercuric Chloride. Although not so active as the preceding sub- 
groups, these compounds precipitate the proteins of tissues, forming metallic 
albuminates; and thus, if concentrated, destroy all cytoplasm with which they 
come into contact. 
Caustic Poisoning.-1The degree and extent of corrosion by caustic poisons 
depend largely on the concentration. Treatment of poisoning should consist of 
(1) dilution of the poison with water or milk; (2) administration of demulcents 
like milk, white of eggs, bland fixed oils, lard, and butter; and (3) proper chemical 
antidotes. 
Direct chemical antidotes for caustic alkalies should include dilute organic 
acids, like Acetic (vinegar) and Citric (lemon juice) acids, which neutralize 
them; and fats and oils which, in addition to acting as demulcents, form soaps 
with the alkalies. Chemical antidotes for poisoning by caustic acids include 
weak, mild alkalies, like Lime Water, Milk of Magnesia, Chalk, and Soap. PHARMACODYNAMICS 
27 
Tannic Acid and albumin are general chemical antidotes for metallic poisons with 
which they form rather insoluble metallic tannates and albuminates. 
The escharotics are used externally to remove growths, such as warts, moles, 
etc., and to cauterize tissues, following dog- and snake-bite. 
IV. The Counterirritants.-Counterirritants are remedies which through 
irritation of the skin relieve or check pain and congestion of internal organs. 
The use of such remedies is one of great antiquity. According to the intensity 
or degree of irritation produced, the counterirritants are classed as follows: 
(a) Rubefacients.-This class includes Mustard, Alcohol, Camphor, Menthol, 
Chloroform, Capsicum, and volatile oils (like Turpentine and Wintergreen), 
and heat (hot water-bag and poultices). These agents dilate the superficial 
vessels, and the skin becomes red, congested, and warm, and may itch, smart, 
or even pain. However, unless allowed to remain too long the skin returns to 
normal more or less rapidly. 
(d) Vesicants.-If counterirritation is prolonged or the agents used are 
more energetic, the rubefacient stage is exceeded and little vesicles are formed 
over the affected area. These vesicles are produced by the collection of lymph 
in tissue spaces between the two upper layers of the skin. The vesicants include 
Cantharides, Iodine, and Mustard. 
(c) Epispastics.-When vesicles coalesce, blisters are formed. Agents 
which cause blistering are called epispastics. They represent a more intense 
degree of counterirritation than the preceding groups. Cantharides, Mustard, 
Ammonia Water, and Iodine blister if allowed to act long enough. Since blister- 
ing is painful, requires treatment itself, and prevents further applications to the 
area affected, it is rarely resorted to in modern therapy. 
(J) Pustulants.-Certain drugs, such as Croton Oil, Tartar Emetic, and 
Mercuric Chloride, attack the openings of the glands in the epithelium and pro- 
duce pustules. They are rarely used today. 
If counterirritation exceeds the epispastic or blistering stage, death 
of the tissues results, i. e., eschar or corrosion. 
The manner of action of the counterirritants in relieving deep seated pain 
and congestion is doubtless largely due to a nervous relation between certain 
areas of the skin and body wall and the viscera. This relationship is discussed 
in the chapter dealing with the nerve system. 
The counterirritants are used to relieve pain, as in pleurisy, neuralgia, 
and colic, to reduce inflammation and congestion, as in pneumonia, to reduce 
swelling, as in bruises and sprains, to overcome tympanites, to stop nose-bleed 
(ice or cold article to the back of neck), and to overcome collapse (mustard 
bath). 
V. Antiseptics and Disinfectants.-Although the phenomena of fermenta- 
tion, decay and putrefaction were known for many centuries, there was no 
satisfactory scientific explanation of them until Pasteur discovered the existence 
of microorganisms. It was then demonstrated that fermentation, decay 
and putrefaction were caused by the activity of certain of these microscopic 
forms of life. Proof was also soon presented that many diseases were caused 28 
PHARMACODYNAMICS OF EPITHELIAL TISSUE 
by certain microorganisms. Most of the microorganisms belong to the class 
of bacteria, which are one-celled, microscopic plants. The bacteria which are 
more or less spherical are termed cocci; those which are rod-shaped are termed 
bacilli; while those which are spiral-shaped are termed spirilla. Other related 
microscopic plants which cause certain fermentations, for example, alcoholic 
fermentation, are the class of yeasts. Certain diseases are caused by one-celled 
microscopic animals known as protozoa. From such studies the branch of 
science called bacteriology was developed. 
Pathogenic Microorganisms.-Some microorganisms are essential to other 
forms of life. The bacteria that cause decay and putrefaction are the means 
through which dead matter is covered into compounds which can be again 
utilized for food. All plants, and therefore animal life, are directly dependent 
upon the activity of these organisms. 
There are other microorganisms, however, that are decidedly injurious, 
particularly those known as pathogenic microorganisms, i. e., disease-producing. 
Most infectious and contagious diseases, for example pneumonia, typhoid, 
and tuberculosis, are caused by certain specific bacteria; while others, such as 
syphilis and malaria, are caused by specific protozoa. 
The control of such microorganisms is one of the most important problems 
that medical science has to solve. Common modes of spreading microorganisms, 
and therefore certain diseases, are: polluted water and milk (typhoid), insects 
(plague and malaria), and air contaminated by coughing and sneezing, and 
with dried sputum (influenza, pneumonia and tuberculosis). 
Asepsis.-This term means the exclusion of bacteria. It may be accom- 
plished by thorough cleansing, or by heat or chemicals. A substance or a 
surface which is free from living bacteria is said to be aseptic or sterile. 
Bacteria, because of a highly impenetrable cell wall and by the formation 
of resistant spores, are frequently able to survive conditions and treatment 
that would destroy other cells. Although adverse conditions and treatment 
prevent their growth and multiplication, they may pass into a dormant state, 
preserve their vitality, and under favorable conditions recover their vitality 
and again grow and multiply. Substances which inhibit or check the growth 
and multiplication of microorganisms are called antiseptics; while those which 
kill them are called disinfectants or germicides. 
Boiling for from five to thirty minutes kills most of the pathogenic micro- 
organisms but not their spores. However, boiling certain foods, particularly 
milk, may be undesirable because it changes somewhat the taste and pos- 
sibly affects the food value. For such foods a temperature below the boiling 
point (i6o°F. for 30 minutes) may be used as this will destroy the majority, 
though not all, of the bacteria present. Such a process is called "Pasteuriza- 
tion." Surgical instruments are frequently boiled in a solution of Sodium 
Bicarbonate, which not only sterilizes them but also prevents rusting. 
Most antiseptic and disinfectant agents, when present in sufficient quantity, 
inhibit the activity of or destroy ferments or enzymes (see page 188) and are 
then called antizymotics. PHARMACODYNAMICS 
29 
Although modern medicine aims rather to prevent the infection of tissues 
by careful asepsis, conditions frequently arise in which the use of antiseptics 
and disinfectants becomes necessary. Even aseptic surgery depends partly 
on certain disinfectants to cleanse and sterilize the skin as well as the instru- 
ments. On the surface of wounds, the skin and mucous membranes certain 
antiseptics and disinfectants may be used to combat the microorganisms. 
Since these agents ordinarily affect equally the cytoplasm of the tissue cells 
and that of the microorganisms, they must be used in a rather diluted form to 
prevent injury to the tissues. Inasmuch as actual destruction of pathogenic 
microorganisms in a wounded surface, for example, necessitates destruction 
of the neighboring cells, disinfection can only be carried out in such parts where 
the superficial cells are not of vital importance and may be replaced by the 
growth of new cells. Consequently, it is impossible to disinfect as a whole 
all the tissues of the body because the quantity of the disinfectant needed in 
the circulating blood, to accomplish the destruction of all microorganisms 
present, would prove equally disastrous to the tissues and organs. 
Disinfection of the Skin.-Energetic and thorough mechanical cleansing by 
means of Tincture of Green Soap and a brush is undoubtedly of very great 
importance in the disinfection of the skin. This may then be followed by chemi- 
cal disinfection with Bichloride of Mercury solution (i-iooo), 3 per cent Phenol 
solution, 50 per cent solution of Alcohol or a solution of Formaldehyde. The skin 
of the field of operation may be painted with 3.5 per cent Tincture of Iodine. 
Disinfection of Mucous Membranes.-To prevent serious injury to the 
more delicate mucous membranes and also to avoid poisoning from their 
absorption, chemical disinfectants must be used in so much weaker concentra- 
tions than in the case of the skin, that in most cases they can only act as rather 
weak antiseptics. However, Hydrogen Dioxide and Potassium Permanganate, 
which are changed to non-toxic compounds by contact with the tissues, and 
some organic silver compounds, such as " Argyrol," may be used in fair concentra- 
tion. These substances are, therefore, more effective antiseptics for mucous 
membranes. Solutions of Boric Acid and Aluminium Acetate, and weak 
solutions of Bichloride of Mercury, Phenol, Cresol, and volatile oils, are used 
also, but in the concentration employed are rather weak antiseptics. 
Urinary Antiseptics.-Sodium Salicylate and Benzoate, Phenyl Salicylate, 
Cubeb, Copaiba, Sandalwood, and Methylene Blue, are used as urinary antiseptics, 
but are not very powerful. Hexamethylenamine and the organic silver compounds, 
such as "Argyrol, " are more effective. Hexamethylenamine owes its anti- 
septic properties to the fact that, in acid medium, it decomposes and yields 
formaldehyde. The urine must therefore be acid in reaction when this drug is 
used as a urinary antiseptic. 
Intestinal Antiseptics.-Phenyl Salicylate, Thymol, Camphor, Calomel, 
Resorcinol, Guaiacol, and Betanaphthol have been used as intestinal antiseptics, 
but are rather uncertain and unsatisfactory. 
Skin Parasiticides.-Certain skin diseases are caused by organisms larger 
than the bacteria and protozoa. Agents used to kill such skin parasites are 30 
PHARMACODYNAMICS OF EPITHELIAL TISSUE 
called skin parasiticides, and include Sulphur Ointment (for scabies), lotions or 
washes of Sodium Thiosulphate and Sulphite, Mercurial Ointment and Ammoni- 
ated Mercury Ointment (ring-worm, etc.,) and Tincture of Larkspur (lice). 
Antisyphilitics or Antiluetics.-The parasiticidal substances of major 
importance in the treatment of syphilis are certain compounds of Mercury 
and of Arsenic. Experimentation has proved that these substances are 
capable of eradicating this disease by direct action on the causative agent-the 
Treponema pallida. 
Mercury.-Mercurial Ointment, Diluted Mercurial Ointment, Ointment of 
Ammoniated Mercury, Black Wash (Calomel and Lime Water), and Yellow 
Wash (Bichloride of Mercury and Lime Water) are the mercurial preparations 
most commonly employed as local applications to venereal sores. 
For systemic action mercury and its compounds may be given by mouth, by 
inunction, or by intramuscular, intravenous or intraspinal injection. 
The compounds frequently given by mouth are Mercurous and Mercuric 
Iodides, Bichloride of Mercury, and, for children, Mercury with Chalk ("Gray 
Powder"). Bichloride of Mercury is often compounded with Potassium Iodide 
("Mixed Treatment"). 
For inunction the Mercurial Ointment is usually employed. The method, 
however, is unsatisfactory in that it is dirty, tends to irritate the skin, and, since 
the skin is rather a poor absorbing medium, the dosage is uncertain. 
For intramuscular injection the insoluble Mercury Salicylate suspended in 
Liquid Petrolatum, Olive Oil, etc., and the soluble Mercuric Chloride, Iodide and 
Benzoate are used. 
For intravenous injection mercurialized human or horse serum (%o to ^5 
grain of Bichloride of Mercury to about one ounce of serum) are used. 
In cerebrospinal syphilis the intraspinal injection of mercurialized serum is 
frequently employed. 
Arsenic.-Certain organic arsenical compounds that are more or less 
successful in the treatment of syphilis, have the advantage of acting more rapidly 
than mercury. The compounds of choice are Arsphenamin (Salvarsan, "606," 
Arsenobenzol, or Diamino-dihydroxy-arseno-benzol hydrochloride) and Neo- 
Arsphenamin (Neo-salvarsan, a mixture of Sodium Arsphenamin-methanal- 
sulphoxylate with inert inorganic salts). These compounds are usually 
administered intravenously, although Neo-arsphenamin is at times given by the 
subcutaneous and intramuscular methods. Arsenical treatment alternated or 
combined with mercurial treatment is more effective. CHAPTER VI 
MUSCLE TISSUE 
Muscle tissue is the tissue mostly concerned in the production of various 
mechanical movements. These movements are brought about by a change of 
shape called the contraction. Muscle tissue occurs 
in masses, known as muscles, attached to the bones 
of the skeleton; it is found also in the walls of the 
hollow viscera, such as the stomach, the intestines and 
bladder, and in the heart. 
The muscle tissue connected to the skeleton is 
under the influence of the will and under the micro- 
scope has a striped appearance. For these reasons it 
is called skeletal, voluntary, or striated muscle. 
The muscle tissue found in the walls of viscera is 
not under the influence of the will and appears smooth 
under the microscope. It is therefore called visceral, 
involuntary, or non-striated or smooth muscle. 
The muscle in the walls of the heart is of a type 
intermediate between the striated and smooth muscle. 
It is called cardiac muscle. 
The Skeletal Muscles.-There are more than five 
hundred muscles in the body. They vary greatly in 
size and shape, but usually consist of a middle por- 
tion, called the belly, tapering toward each extremity 
and merging into a tough, inelastic cord or into a 
membrane of connective tissue called the tendon. The 
active, contractile part consists of the belly, while the 
tendons serve to transmit the movement of contraction 
to the bones. Certain muscles contribute to the for- 
mation of the walls of body cavities, such as the mouth 
and the abdomen. The accompanying illustrations 
will give an idea of the location, arrangement, and 
shape of important muscles (see Figs. 22, 23 and 24). 
Structure of Skeletal Muscle.-A skeletal muscle 
consists of muscle fibers, blood vessels, lymphatics and 
nerves bound together by connective tissue. 
Histology of the Skeletal Muscle Fiber.-The cells that constitute the 
contractile units of the muscle are called muscle fibers. They vary in length 
from 3 to 4 centimeters, and have an average thickness of about 30 These 
fibers are arranged side by side and end to end, lying in the long axis of the 
Fig. 22.-Muscles of the 
back of the hand, forearm, and 
lower half of the arm, as expos- 
ed on dissecting away the skin. 
(Martin-Fitz.) 
31 32 
MUSCLE TISSUE 
Fig. 23.-Left, Back view of the muscles of the trunk. Right, Front view of the muscles of the 
trunk. (Martin-Fitz.) 
Fig. 24.-Side view of the muscles of the face and neck. (Martin-Fitz.) ESSENTIALS OF PHYSIOLOGY 
33 
muscle. Each muscle fiber is cylindrical or prismatic in shape and consists of 
a thin, elastic, transparent membrane, called the sarcolemma, enclosing the 
contractile material. The nuclei are found immediately beneath the sarco- 
lemma. The contractile material is composed of very fine fibers or fibrillae 
running the length of the fiber. These fibrillae are not of uniform thickness 
but are alternately thick and thin, all the thick and thin parts lying opposite 
each other, so that the entire fiber appears to be made up of alternately light and 
dark bands giving it a striped appearance (Fig; 25). The fibrillae are 
surrounded by a transparent fluid called the sarcoplasm. Some histologists 
believe that a membrane runs across the muscle fiber 
through the middle of the light band. 
Physical Properties of Skeletal Muscle; Elastic- 
ity.-Muscle tissue, in common with other tissues, can 
be stretched beyond its natural length; it is therefore 
extensible. If the stretching force has not been too great, 
the muscle will return to its former length. This prop- 
erty, possessed by many bodies, of resuming their orig- 
inal shape after a deforming force has ceased to act, 
is called elasticity. The extensibility and elasticity of 
muscle play important parts in the movements of the 
body. These properties are impaired by fatigue and in- 
sufficient blood supply or any factor interfering with 
the proper nutrition of the muscle. 
Consistency.-When at rest a muscle feels soft and 
yielding. When its tension increases, as occurs during 
contraction, it becomes hard and unyielding. 
Physiological Properties of Muscle. Irritability. 
By this term is meant that property of muscle tissue 
that enables it to respond when stimulated. The re- 
sponse of muscle is a contraction. The irritability of muscle is dependent 
upon a proper supply of nutritive material and of oxygen, the prompt removal 
of waste products, and the proper temperature. 
Conductivity.-This property consists of the ability possessed by the muscle 
substance of propagating a state of excitation through itself. The conduction 
of the excitation process takes place longitudinally. Under normal conditions 
skeletal muscles are stimulated by nerve impulses. A nerve fiber terminates 
upon the center of each muscle cell. The excitation, therefore, takes place at 
the center of the fiber whence it is conducted by the muscle substance to both 
extremities of the fiber. The rate of conduction in human muscles has been 
shown to be from 10 to 13 meters per second. 
Tonicity.-All muscles of the body are in a state of "tone" varying from 
moment to moment. By muscle tone or tonus is understood a slight but 
continuous contraction, giving rise to a state of tension. This property enables 
a muscle, when stimulated, to instantly move the bone to which it is attached. 
As the contraction of muscle, however slight, is accompanied by the liberation 
Fig. 25.-A, diagram of 
arrangement of the contrac- 
tile substance according to 
the view of Rollett; the 
granular figures represent 
the contractile elements,the 
intervening light areas the 
sarcoplasm; B, small 
muscle-fiber of man; the 
corresponding parts in the 
two figures are indicated; 
t, i, I, respectively the trans- 
verse,the intermediate, and 
lateral discs; n, muscle 
nuclei. (Piersol.) 34 
MUSCLE TISSUE 
of heat, the tonicity of the entire musculature is an important means of pro- 
ducing body heat. The tonicity of skeletal muscles is dependent upon the 
arrival of nerve impulses sent out from the spinal cord. 
THE CONTRACTION OF MUSCLE 
When a muscle is stimulated, either in the usual way-i. e., by a nerve 
impulse-or some artificial stimulus, certain phenomena follow that underlie 
and accompany the muscular contraction. The most obvious phenomenon is 
the contraction itself. The muscle changes in shape; from being long and 
narrow it suddenly becomes short and thick, and then resumes its previous 
shape. There is no change in the volume of the muscle. The ultimate mechan- 
ism of the contraction is unknown, although several theories have been offered in 
Fig. 26.-Record of a single muscular contraction, ab, latent period; be, contraction period; cd 
relaxation period. Time record, 100 per second. (G. Bachmann.) 
explanation. It is dependent, however, upon the occurrence of chemical 
changes whereby the potential energy of certain organic compounds is trans- 
formed into kinetic energy. This kinetic energy manifests itself under three 
forms: (i) the mechanical motion of the contraction; (2) the liberation of heat; 
(3) the discharge of electricity. 
Analysis of a Single Contraction.-The most convenient preparation for 
the study of muscular contraction is the gastrocnemius muscle of the frog. 
This muscle can be stimulated indirectly through the sciatic nerve, or directly 
by the application of the stimulus to the muscle substance. If the tendon of 
the muscle be connected to a lever and the point of the lever be made to write 
on a moving blackened surface, a magnified record of the contraction will be 
written by the lever. This record, together with a record of the vibrations of a 
tuning fork and of the time of stimulation, provide the means of analyzing the 
contraction. 
By appropriate means a single electric shock can be sent either into the 
nerve or the muscle; whereupon the muscle will give a single contraction or ESSENTIALS OF PHYSIOLOGY 
35 
twitch (Fig. 26). This analysis of a single contraction shows that it consists 
of three phases: 
(1) A latent period, representing the time that elapses between the appli- 
cation of the stimulus and the beginning of the muscle shortening. This 
period, in the usual manner of recording, seems to occupy 0.01 of a second. 
With very accurate methods the latent period has been reduced to 0.0025 to 
0.004 of a second. 
(2) A contraction period, during which the muscle shortens. This occupies 
about 0.04 of a second. 
(3) A relaxation period, during which the muscle resumes its former 
length. This occupies about 0.05 of a second. 
The Energy Liberated in Muscle.-Of the total energy set free during 
the contraction it has been estimated that from 25 to 40 per cent takes the 
form of mechanical motion. If a weight be lifted by the contracting muscle, 
the muscle will have accomplished work. 
The balance of the energy liberated appears as heat and electricity. The 
amount of heat produced under different conditions can be measured by special 
appliances that need not be described here. Owing to the active metabolism 
taking place at all times in muscle, but more especially during contraction, and 
the great mass of muscle tissue-40 per cent of the body weight-this tissue 
is the most important source of body heat. 
It can be shown by means of special electrical appliances that a change of 
electric potential occurs at each contraction. Inasmuch as the contraction is 
propagated through the muscle substance in the form of a wave, part of the 
muscle must be resting while some other part is in a state of activity. It 
has been shown that the resting part of the muscle is electro-positive to the 
active portion, which is therefore electro-negative. The electric current thus 
established is called the "action current." 
FACTORS MODIFYING THE CONTRACTION 
(a) The Strength of the Stimulus.-Within limits the height of the muscu- 
lar contraction varies with the strength of the stimulus. A weak stimulus 
gives rise to a small contraction; as the stimulus increases the muscular con- 
traction gradually increases in height. When the limit in the height of the con- 
traction has been reached, any further increase in the strength of the stimulus 
has no greater effect (Fig. 27). The explanation of these phenomena lies 
in the fact that weak stimuli affect but few muscle fibers, and that stronger 
stimuli affect an increasingly greater number of fibers until finally all of the 
fibers of the entire muscle are stimulated. 
(fr) Temperature.-The best or optimum temperature at which the frog's 
muscle contracts with maximum efficiency, lies between 2 5°C. and 3O°C. If 
the temperature of the muscle be made to fall gradually the contraction gradu- 
ally declines in height. The phases of the contraction are likewise affected 
in that they are all lengthened (Fig. 28). If the temperature be raised to 4O°C. 
or above the muscle shrinks and becomes permanently stiff, this condition being 36 
MUSCLE TISSUE 
called "heat rigor." At this temperature the proteins of the muscle are 
coagulated. 
(c) Fatigue.-When a muscle is made to contract repeatedly at very short 
intervals, the muscle gradually becomes fatigued. The causes of fatigue are 
Fig. 27.-The effect of a gradual increase in the intensity of a stimulus on muscular contraction. 
ab, submaximal contractions; be, first maximum; de, second maximum. (G. Bachmann.) 
Fig. 28.-Single contractions of the gastrocnemius muscle at different temperatures. Time trac 
ing 200 per second. (Brodie.) 
Fig. 29.-Tracing showing the development of fatigue. Every fiftieth contraction recorded. (G. 
Bachmann.) 
ascribed to the diminution of the energy-yielding compounds on which the 
muscular contraction depends, and to the accumulation of waste products. 
These waste products are mono potassium phosphate, sarcolactic acid, and ESSENTIALS OF PHYSIOLOGY 
37 
carbon dioxide. A fatigued muscle is therefore acid in reaction. The first 
effect of these fatigue products is to increase the vigor of the contraction; 
but as these products continue accumulating the height of the contraction 
gradually diminishes, while, in the frog, there occurs also a lengthening of the 
phases of the contraction (Fig. 29). If the stimulation is continued, the time 
comes when the muscle fails to respond. It has been found experimentally that 
a plentiful supply of oxygen delays considerably the onset of fatigue. 
THE CONTINUOUS CONTRACTION 
The Summation of Muscle Contraction.-The single muscle contraction so 
far mentioned, is not the characteristic activity of muscle. Even very short 
contractions are always sustained; that is, the muscle is continuously contracted. 
Experiments have demonstrated how the normal more or less prolonged and con- 
tinuous contraction, is produced. 
If a muscle be stimulated a second time and the stimulus falls at the begin- 
ning of the relaxation period, a second contraction will occur which is higher than 
the first. A third stimulus may be applied in the same way, and so forth, so that 
the muscle will not have time to relax between the successive stimulations. 
The muscle will shorten more and more until a maximum height has been 
reached which is greater than could be obtained with a single stimulus of maxi- 
mal strength. To this superposition of contractions the term "summation of 
contractions" is given (Fig. 30). 
Tetanus.-By tetanus is meant a more or less continuous contraction of a 
muscle caused by the effect of successive stimuli sent into the muscle at inter- 
vals less than the time of the contraction process. The continuous contraction 
is a state of complete tetanus in which the stimuli are sent into the muscle at such 
close intervals that the muscle cannot relax between the successive stimuli so 
that the muscle remains steadily contracted. When the stimuli fall into the 
muscle at slightly longer intervals the contraction is interrupted by partial 
relaxations. This condition is called "incomplete tetanus" or "clonus" 
(Fig. 31). 
THE CHEMISTRY OF MUSCLE 
A chemical analysis of fresh muscle has shown that it contains the following 
substances: 
Per Cent 
Water 75.00 
Proteins 18.00 
Fat . .. 2.00 
Glycogen 0.90 
Dextrose a trace 
Extractives . 0.40 
Other organic compounds, inorganic salts 1.00 to 2.00 
The proteins of muscle are myosin-a globulin-constituting about one- 
fifth, and myogen or myosinogen-an albumin-constituting the other four- 38 
MUSCLE TISSUE 
Fig. 30.-Tracings illustrating the summation of contractions. (G. Bachmann.) ESSENTIALS OF PHYSIOLOGY 
39 
Fig. 31.-Tracings showing the gradual development of tetanus. The numbers under the curves 
indicate the number of stimuli per second sent into the muscle. (G. Bachmann.) MUSCLE TISSUE 
40 
fifths. These proteins coagulate at different temperatures. They likewise 
undergo coagulation after death, causing thereby the stiffness of the muscles 
known as "rigor mortis." 
The carbohydrates found in muscle are: Glycogen, varying from 0.5 to 1.0 
per cent, depending whether the muscle analyzed was in the resting condition or 
had been active; dextrose is found in traces only when 
the muscle is absolutely fresh. 
Among the non-nitrogenous extractives the most 
important is Sarcolactic Acid. This organic acid is pre- 
sent only in fatigued or dying muscle, and is in all proba- 
bility derived directly from dextrose and indirectly from 
glycogen. The conversion of dextrose to lactic acid is 
doubtless an intermediate step in the metabolism of dex- 
trose, the lactic acid being further oxidized to carbon 
dioxide and water. In the presence of a plentiful supply 
of oxygen lactic acid cannot therefore accumulate. 
The nitrogenous extractives are, in part at least, 
waste products consisting mainly of Creatin, Hypoxan- 
thin, Xanthin, and Uric Acid. Another organic com- 
pound found among the extractives, is Phosphocarnic 
Acid. 
The inorganic Salts are chiefly Potassium Phosphate. 
There are traces of Chlorides and Sulphates of Sodium, 
Magnesium and Calcium. Traces of Iron are also 
found probably in combination with a pigment resem- 
bling Hemoglobin. 
THE INVOLUNTARY OR SMOOTH MUSCLE 
Smooth muscle is found in the walls of hollow viscera 
such as the stomach, intestines, bladder, uterus, arteries, 
veins, etc., as well as in certain structures in the interior 
of the eyeball. It occurs in most places in the form of 
sheets or membranes. On account of its association with 
viscera it is called also visceral muscle, and, since its activ- 
ity is not under control of the will, it is often referred to as 
involuntary muscle. 
Histology of Smooth Muscle.-When the muscle sheet is examined under 
the microscope it is seen to be made up of long, narrow, fusiform cells, measur- 
ing from 40 to 250 /x in length and 4 to 8 m in width. There is in the center of 
each fiber a rod-shaped nucleus (Fig. 32). Each muscle cell is enclosed by a 
membrane resembling the sarcolemma of skeletal muscle fibers. Smooth 
muscle fibers contain delicate fibrillae which may represent the contractile 
material. Some of these fibrillae appear to run from cell to cell, and may, there- 
fore, serve to spread the state of excitation arising at any one point to the entire 
muscVussu^from'the^ 
testinai tract of rabbit, a 
and B, muscle cells in which 
differentiation of the pro- 
topiasrn can be well seen. 
(From Yeo after Ranvier.) ESSENTIALS OF PHYSIOLOGY 
41 
mass of fibers. The bundles of muscle fibers are bound by a delicate network of 
connective tissue (Fig. 33). 
Physical Properties of Smooth Muscle.-The physical properties of smooth 
muscle are virtually identical with those of skeletal muscle. 
Physiological Properties of Smooth Muscle.-The physiological properties, 
as in the case of skeletal muscle, are those of Irritability, Conductivity, and 
Tonicity. 
Smooth muscle shows that it is irritable by responding to adequate stimu- 
lation by a change of form, called the contrac- 
tion, the liberation of heat and of electricity. 
The contraction, however, is very sluggish as 
compared to that of skeletal muscle, all phases 
of the contraction being greatly prolonged 
(Fig. 34). 
The conductivity of smooth muscle is less 
well developed than in skeletal muscle, but 
takes place laterally as well as longitudinally. 
This is doubtless accomplished through the 
intermediation of the fibrillae that pass from 
fiber to fiber. 
Smooth muscle exhibits tone or tonus which, contrary to what is found in 
skeletal muscle, is independent of any action of the central nerve system. The 
nerve system, however, constantly influences this tone in one direction or the 
other, now increasing it and then decreasing it. 
Fig. 33.-Cross section of smooth mus- 
cle fibers from the stomach. X 560. 
a, connective tissue septum; b, section 
of a fiber distal to the nucleus; c, section 
of a fiber through the nucleus. (From 
Lewis and Stohr's Histology.') 
Fig. 34.-Record of the contraction of the pyloric portion of the frogs stomach. (G. Bachmann.) 
Most organs containing smooth muscle in their walls contract rhythmically. 
Smooth muscle, therefore, has the property of rhythmicity. This property is 
probably resident in the muscle itself, although it may be greatly influenced by 
the nerve system. 
The activity of smooth muscle is modified by the strength of the 
stimulus, changes in temperature, and fatigue, and can be made to give tetanic 
contractions. 42 
MUSCLE TISSUE 
CARDIAC MUSCLE 
The structure of cardiac muscle cells is intermediate in type between the 
striated or skeletal muscle and the smooth muscle. Its rapidity of contrac- 
tion, while less than that of skeletal muscle, is greater than that of smooth 
muscle. The property of rhythmicity is one of the outstanding characteristics 
of this type of muscle. 
The anatomical and physiological features of cardiac muscle will be dis- 
cussed in connection with the physiology of the heart. CHAPTER VII 
PHARMACODYNAMICS OF MUSCLE TISSUE 
The functional activity of muscle tissue may be influenced by certain 
drugs which act either directly on the muscle substance or indirectly through 
the nerve system. The drugs mentioned below are the more important agents 
used for their effects on muscle tissue. 
(a) Skeletal, Voluntary or Striated Muscle. Veratrine.1-When a frog 
is poisoned with a small dose of Veratrine (or of Cevadine), it shows very strik- 
ing peculiarities in its muscular movements. Although it can contract its 
muscles with normal rapidity, muscular relaxation is abnormally slow (20-30 
times as long as a normal muscle), so that it is some little time before the 
animal can bend its legs again and pull them up. Experimentation has shown 
that this delayed and prolonged relaxation is not due to loss of muscular elasti- 
city, for the muscles are able to sustain weights during relaxation. Further, 
the facts that more heat is produced during the contraction than in the normal 
muscle, and that contraction takes place against a greater weight than usual, 
show not only that work is being done during the relaxation, but also that 
the absolute strength of the muscles is increased. Hence, it is evident that 
Veratrine is a muscle stimulant. Experiments have also proven that Veratrine 
acts directly on the muscle substance, and not through the nerve system. In 
therapeutic dosage the foregoing effect on muscular relaxation is not seen, but 
distinct stimulation of striated or voluntary muscle is observed. However, no 
important application is made of this action in therapeutics. 
Caffeine.-Experimental work on the laboratory animal, as well as on man, 
has shown that Caffeine increases the functional activity of skeletal muscles 
so that they contract more promptly, more powerfully and more completely, 
and that muscular fatigue is delayed. These effects on the contraction of skele- 
tal muscles are due to a direct action of Caffeine on the muscle substance 
itself whereby the irritability and contractile power are increased. 
The action is enhanced by the fact that Caffeine stimulates the motor 
areas of the brain as shown by the increase in the range and control of voluntary 
acts and the delayed fatigue. 
Advantage is taken of these effects of Caffeine when the drug is used as a 
stimulant or "tonic" in convalescence from acute diseases, such as influenza and 
pneumonia, in loss of muscular tone in states of collapse or in poisoning by 
Morphine, Ether, Chloral Hydrate, and Alcohol, and in physical weariness. 
Poisonous doses of Caffeine, of course, depress skeletal muscles. 
Alcohol.-Human experiments have shown that although Alcohol in 
small quantities increases the power for muscular work, a decrease in muscular 
1 A mixture of alkaloids, chiefly cevadine, obtained from "Sabadilla Seed." 
43 PHARMACODYNAMICS OF MUSCLE TISSUE 
44 
power rapidly follows and fatigue sets in early. Tests made with soldiers 
have shown that, when well fed, those who were receiving no Alcohol were able 
to march farther and were in better condition than those who were furnished 
with Alcohol. However, if underfed, those who were receiving Alcohol could 
endure greater fatigue. It is evident from these experiments that any bene- 
ficial effects on muscle tissue depend not on any stimulation, but on the fact 
that Alcohol, when given in small quantity, is easily and completely oxidized, 
and may act therefore as a source of energy to the body in emergencies. 
Quinine.--This alkaloid first stimulates striated muscle, the irritability 
and contractile power being increased. However, fatigue sets in early so that 
the total amount of work done is less than normal. 
(b) Involuntary or Smooth Muscle. Digitalis.-It has been shown experi- 
mentally that poisonous doses of the active constituents of Digitalis-digitoxin, 
digitalin and digitalein, three glucosides-increase the tone, irritability and 
contractility of the smooth muscle in the walls of the peripheral arteries by direct 
action on the arterial muscle itself. Consequently the arteries, particularly the 
intestinal vessels, are constricted and as a result there follows a rise in arterial 
pressure. However, in therapeutic doses Digitalis usually does not constrict the 
arteries in a measurable degree, and therefore this part of Digitalis action is of 
no great therapeutic importance. The walls of the veins are affected in a simi- 
lar manner. 
Pituitary Extract (Hypophysis Sicca).-This drug stimulates arterial 
muscle itself, as well as the muscles of the intestines, and as a result there is a 
rise in blood pressure due to the arterial constriction, and increased intestinal 
peristalsis. It also stimulates the muscles of the bladder, the ureters, and the 
pregnant uterus. Because of these facts Pituitary Extract is used in shock and 
collapse to raise the blood pressure, in tympanites and intestinal paralysis, and in 
uterine inertia. 
Nitrites, such as Sodium Nitrite and Amyl Nitrite, and substances, such 
as Nitroglycerin, which liberate nitrites in the blood, directly depress arterial 
muscle, and as a consequence, the arteries dilate and the arterial pressure falls. 
They are used in medicine, therefore, to lower abnormally high general arterial 
pressure and to relax the coronary arteries in angina pectoris. The nitrites also 
depress, to a less degree, however, bronchial muscle, so that they are useful in 
relaxing the bronchioles in asthma. 
Quinine, in addition to affecting striated muscle acts also on the smooth 
muscle of the uterus, the contractions of which it seems to augment. For this 
reason it has been employed, under certain conditions, in the second stage of 
labor. The drug also stimulates the smooth muscle of the spleen and possibly 
that of the arteries but the action is not very pronounced. 
Ergotoxine and Ergamine or Histamine, two of the alkaloids found 
in Ergot, strongly stimulate the contractions of uterine muscle by acting 
peripherally on the muscle tissue. This action is enhanced by Tyramine, 
another alkaloid of Ergot, which acts on the nerve supply of the uterus. Ergot, 
in proper dosage, is therefore used in obstetrics to promote postpartum contrac- PHARMACODYNAMICS 
45 
tions of the empty uterus. Since Ergamine is destroyed in the digestive tract, 
it is administered subcutaneously or intravenously. 
Cardiac Muscle. Digitalis.-The active glucosides of Digitalis act directly 
on the cardiac muscle increasing its tone and contractility. (In poisonous doses 
it also directly stimulates arterial muscle which results in constriction and a 
consequent rise in arterial pressure. However, in therapeutic doses the drug 
does not usually produce any measurable general constriction of the systemic 
arteries.) Other cardiac effects of Digitalis will be referred to elsewhere. 
Caffeine, by direct action, increases the irritability, the tone and the con- 
tractility of cardiac muscle, so that there may be a more or less measurable 
increase in the heart's rate and force, and a slight rise in blood pressure. The 
drug may possibly be of some value as an emergency heart stimulant (see p. 159). 
Poisonous doses depress cardiac muscle so that the tone, contractility, and 
consequently the output of blood, are decreased and the blood pressure falls. 
Quinine, in large doses (15 grains upward), directly depresses cardiac 
muscle, and, as a result, the heart is weakened and slowed. In smaller dosage 
there is probably little, if any, measurable direct effect on cardiac muscle, 
although some investigators have reported a primary direct stimulation followed, 
however, by rather early fatigue. CHAPTER VIII 
NERVE TISSUE 
There are two phases of living matter, e. g., active and passive. The 
active phase is illustrated by the moving animal or growing plant; the pas- 
sive by the encysted Ameba or the dormant embryos of seed plants. All 
living organisms, in their active phase of existence, possess the property of 
reacting to stimuli. In the higher animals this reaction takes place chiefly 
through the intermediation of a special tissue called nerve tissue. The 
stimuli calling forth the activity of this tissue may arise either in the external 
world or within the body. The response to external stimuli may consist of 
movements of a defensive or other instinctive nature. The response to 
internal stimuli consists of a co-ordination of the activities of various organs 
associated in the performance of a definite act, i. e., secretion and the move- 
ments of the alimentary canal that occur during digestion; regulation of the 
heart rate and the calibre of the arterioles in the circulation; the maintenance 
of equilibrium and body posture, etc. 
In addition to these fundamental phenomena, the nerve tissue endows the 
individual with a consciousness of the external world. This consciousness is 
built up of the sensations that result from the action of stimuli arising in the 
external world, such sensations as sight, hearing, touch, smell, and taste. The 
retention of the sensory impressions and their subsequent organization, forms 
the basis on which the external world is interpreted and the higher thought 
processes of imagination, judgment, and reasoning built up. These cognitive 
states, being either agreeable or disagreeable, may in turn cause a mental reaction 
termed, an emotion. The cognitive processes and emotional reactions, further- 
more, initiate and control certain movements, such as gesture, speech, loco- 
motion, etc. Nerve tissue serves, therefore, to associate the organs of the body 
with each other and to endow the individual with a consciousness of the external 
world resulting in various adaptive reactions. 
The nerve tissue is arranged into two systems called (i) the cerebrospinal 
or encephalospinal system, consisting of the brain and spinal cord and the 
cranial and spinal nerves, and (2) the sympathetic system, consisting of ganglia 
and sympathetic nerves. 
The Histology of Nerve Tissue.-The histological and physiological unit 
of the nerve system is the neuron. A neuron consists of a nerve cell and its 
various processes. In the brain and spinal cord the neurons are held together 
by a special supporting tissue called neuroglia. The nerves contain nerve 
jibers only and these are bound together by connective tissue. 
The Neuron.-The neuron varies in shape in different parts of the nerve 
system. All neurons, however, present certain features in common, viz., the 
46 ESSENTIALS OF PHYSIOLOGY 
47 
nerve cell, neurocyte, or cell body and its processes of which there are two 
varieties: the axon and the dendrons or dendrites (see Fig. 35). 
The cell body varies greatly in size and shape, having a diameter of from 
4 to 200 /*; and being flask-shaped, fusiform or irregularly stellate. The cyto- 
plasm is finely granular, and contains in addition irregularly shaped granules 
called Nissl or chromophile granules. These granules disappear wholly or in 
part as a result of fatigue. The nerve cell likewise contains a large vesicular 
nucleus and a distinct nucleolus. 
A number of processes spring from the cell body. Some of these processes 
are broad and granular and divide a short distance from the cell body; these are 
called dendrons or dendrites. Another process springs from the cell body and 
Fig. 35.-A, efferent neuron; B, afferent neuron. Found in both spinal and cranial nerves. (Bru- 
baker.) 
passes a long distance from it. This is the axon. There is usually but one axon 
springing from the cell body. 
The dendrons have the same structure as the cell body. They often have a 
fibrillar appearance and have minute lateral projections, termed gemmules. 
The dendrons or dendrites have for their function the transmission of nerve 
impulses to the cell body. 
The axon arises usually from the cell body by a conical projection, devoid of 
Nissl granules, and called the axon hillock. It consists of fine fibrillae 
embedded in a clear semifluid material called the axoplasm or neuroplasm. At 
a distance from the cell body, varying from a few millimeters to one meter, it 
divides into a number of branches-the end arborization or telodendrion. The 
telodendrion may end in minute knots or plates called neuropodia. Aside from 
the end arborization, the axon gives off lateral branches called collaterals. 
These collateral branches are especially numerous in the brain and spinal cord. 
The function of the axon is to transmit impulses from the cell body to the end 
of its branches. 48 
NERVE TISSUE 
The Medullated Nerve Fiber.-At a little distance from the cell body the 
axon acquires a cylindrical sheath of a clear, semifluid substance called myelin. 
This sheath is responsible for the white appearance of nerves and is therefore 
called the myelin sheath, medullary sheath, or white substance of Schwann. 
This is the only sheath covering the axon within the brain or spinal cord. 
Fig. 36.-Section through the dorsal root ganglion of the first thoracic nerve of a cat. The 
ganglion cells contain a large vesicular nucleus, with nucleolus, and are enveloped by a nucleated 
capsule. Several medullated fibers appear among the ganglion cells. (From Barker after Hodge.) 
On leaving the central nerve system the axon receives a second sheath 
consisting of a transparent, elastic membrane called the neurolemma. The axon 
surrounded by the medullary sheath and the neurolemma constitutes a nerve 
fiber. Not all nerve fibers, however, are medullated, and, as already stated, 
the nerve fibers within the central nerve system have no neurolemma. 
Medullated nerve fiber. 
Axis cylinder. 
Nucleus of a tendon cell. 
Fig. 37.-Tendon spindle of an adult cat. (Lewis and Stohr.) 
At short intervals the myelin sheath is entirely interrupted, the apparent 
constriction at this point being called the node of Ranvier. The neurolemma 
and axon are continuous throughout and are in contact with each other at the 
nodes. The portion of the nerve fiber between successive nodes is called the 
intemodal segment or internode. In each internodal segment there is found a 
large nucleus surrounded by a small amount of protoplasm and situated under 
the neurolemma. ESSENTIALS OF PHYSIOLOGY 
49 
The Non-medullated Nerve Fiber.-Many of the fibers of the cranial 
and spinal nerves and the majority of the fibers of the sympathetic nerves are 
Tactile cells. 
Nerve fibrils. 
Connective tis- 
sue sheath. 
Fig. 38.-Tactile corpuscle from a section of the 
skin of a human finger. X 560. (Prepared by van 
der Velde, after the Bielschowsky method.) {After 
Lewis and Stahr.) 
Fig. 39.-Bulbous corpuscle from the human 
conjunctiva. Methylene blue stain. {After 
Dogiel, from Bohm and von Davidoff.) 
non-medullated. These nerve fibers consist of an axon similar to that just 
described, the medullary sheath being absent. A neurolemma, however, with 
many nuclei surrounds the axon. 
Nerve fibers without medullary sheath nor 
neurolemma are found near the terminals of axons 
within the central nerve system or at their peripheral 
end. The olfactory nerves of man consist through- 
out of this type of fibers. 
Varieties of Neurons.-The anatomists dis- 
tinguish several varieties of neurons based upon the 
appearance of the nerve cell and the number and dis- 
tribution of its processes. From a physiological point 
of view, however, it will suffice to name three varie- 
ties; viz., (i) efferent neurons, (2) afferent neurons, 
and (3) associational neurons. 
Efferent neurons are neurons that carry nerve 
impulses toward the periphery of the body. 
Afferent neurons are those that carry nerve im- 
pulses from the periphery into the central nerve 
system. 
Associational neurons are those that distribute 
nerve impulses to various groups of nerve cells. These 
neurons are confined to the central nerve system and 
are called also Golgi's second type of neurons. 
Nerve Centers.-Experiment has shown that 
definite groups of nerve cells exist whose function is to influence definite organs. 
Such groups of nerve cells are called nerve centers. Examples of nerve centers 
are the respiratory center, whose function is to regulate the movements of 
Fig. 40.-A lamellar corpuscle 
from the pleura of a child, a, 
lamellae; b, nerve fiber; c, nerve. 
(After Dogiel.) 50 
NERVE TISSUE 
respiration; the vasomotor center, whose function is to regulate the caliber of 
the blood vessels, etc. 
Aggregations of nerve cells related to different organs are called ganglia. 
Examples of these are the sympathetic ganglia, spinal ganglia, basal ganglia, 
etc. (Fig. 36). 
Sensory nerve fibers." 
Muscle fibers.' 
Motor plate.- 
Medullated nerve fibers. 
Nerve fiber bundle. 
Fig. 41.-Motor nerve endings of intercostal muscle fibers of a rabbit. X 150. (From Lewis and 
Stohr's Histology.) 
Nerve Endings.-The nerve system is composed of a great number of 
neurons lying side by side and connected end to end. The connection beween 
the end arborization of the axon of one neuron and dendritic processes of the 
cell body of another neuron takes place by contact only. The contact may not 
be direct, but is effected through an intermediate substance interposed at that 
Peri- 
neurium. 
Blood vessel 
containing 
corpuscles. 
Endo- 
neurium. 
Axis cylinder 
Medullary 
sheath. 
Fiber sheath. 
Fig. 42.-Medullated nerve. Part of a cross section of the human median nerve. X 220. {From 
Lewis and Stohr's Histology.) 
point. The point of contact between two neurons is called the synapse; 
the intermediate substance is termed the synaptic membrane. 
The endings of peripheral nerve fibers are either in the form of terminal 
fibrils or in connection with special structures called end organs. The accom- 
panying figures illustrate the best known of these endings (see Figs. 37, 38, 39, 
40 and 41). ESSENTIALS OF PHYSIOLOGY 
51 
Structure of Nerve Trunks.-The nerve fibers contained in peripheral 
nerves are united into bundles called nerve trunks or nerves. Each nerve is 
covered by a heavy layer of connective tissue known as the epineurium. 
From this layer, partitions of connective tissue are sent into the nerve. These 
partitions or septa divide the entire nerve into smaller bundles of nerve fibers. 
The connective tissue surrounding these smaller bundles is called the peri- 
neurium. The individual nerve fibers are themselves surrounded by a delicate 
connective tissue termed the endoneurium (Fig. 42). When a nerve trunk 
gives off branches, these are formed by one or more of the smaller bundles 
leaving the parent trunk. The nerve fibers themselves are continuous to 
their termination, that is, until the axon breaks up into naked fibrils. 
The connective tissue of the nerve trunk supports blood vessels, lymphatic 
vessels, and contains numerous lymph spaces. 
PHYSIOLOGICAL PROPERTIES OF NERVES 
Irritability.-Under natural conditions nerve fibers convey nerve impulses 
from one extremity to the other; the efferent fiber conducts from the cell to 
the peripheral end; the afferent fiber from the peripheral to the central end. 
It is possible, however, to stimulate a nerve experimentally at any point in 
its course. Any adequate stimulus, be it mechanical, chemical, thermal, or 
electrical, calls forth nerve impulses which are conducted from the point 
stimulated in both directions. The ability of nerves to respond to the applica- 
tion of stimuli shows that they possess the property of irritability. 
Efferent nerves manifest their irritability by the effects produced in the 
peripheral organs to which they are related. These organs may be skeletal, 
smooth or cardiac muscle, or gland epithelium. The arrival of nerve impulses 
in a skeletal muscle will cause it to contract; in the case of smooth or cardiac 
muscle, types of muscle that are automatic in their contractions, and in gland 
epithelium the nerve impulses may cause either an increase or a decrease in 
the degree of their activity. Those efferent nerves that cause an increase in 
activity are called excitatory; those that cause a decrease or complete cessation 
of activity are called inhibitory. 
Afferent nerves demonstrate their irritability by the effects produced by the 
nerve impulses on reaching the central nerve system. These effects may be a 
sensation or a reflex action. Afferent nerve impulses may not only bring about 
reflex actions but may check reflexes already taking place. There are therefore 
excitatory reflex nerves, and inhibitory reflex nerves. 
Nature of the Nerve Impulse.-The passage of a nerve impulse along a 
nerve is accompanied by a negative electrical change. It has been suggested 
that this electrical change constitutes the nerve impulse. Others believe 
that it is essentially a chemical change propagated by the nerve fiber and that 
it is accompanied by the electrical change just mentioned. The latter view is 
strengthened by the fact that carbon dioxide is liberated when a nerve is stimu- 
lated. Many other views have been offered concerning the nature of the 
nerve impulse, but so far none has proved generally acceptable. NERVE TISSUE 
52 
Conductivity.-A demonstrable amount of time elapses between the 
application of a stimulus to a nerve and the response of the organ to which it is 
related. During this time the nerve impulse is being propagated at a certain 
speed through the nerve. The most exact determinations of the velocity of 
the nerve impulse have been made with efferent nerves innervating skeletal 
muscles. It has been shown that in man the median nerve carries impulses 
at the rate of 117 to 125 meters per second. The velocity of the nerve 
impulse in afferent nerves is difficult of determination; it is usually supposed 
to be the same as in medullated efferent nerves. In non-medullated fibers 
the velocity is much less, being but 8 meters per second in mammals. 
The velocity of the impulse is influenced by temperature; cold diminishes, 
while heat, up to a certain limit, increases the conductivity. The velocity is also 
influenced by the passage of a constant or direct current through the nerve, the 
conductivity being decreased in the neighborhhood of the anode or positive pole. 
Certain chemical substances such as carbon dioxide, the vapor of ether, chloro- 
form, and alcohol, likewise diminish the conductivity of nerve fibers. 
Fatigue in Nerve.-In the discussion of the physiology of muscle tissue it is 
stated that this tissue is subject to fatigue, and that fatigue is brought about 
through an exhaustion of energy-yielding compounds and an accumulation of 
waste products. As intimated in a preceding paragraph, chemical changes 
occur in nerve fibers when they are stimulated. There is, following the appli- 
cation of a stimulus, a very brief period (0.002 to 0.006 of a second) during 
which the nerve will not respond to a second stimulus; this is called the refrac- 
tory period. This period of inexcitability is doubtless the result of the exhaus- 
tion of some compound necessary for the production of the nerve impulse. 
Whatever the nature of this compound, it is promptly rebuilt, and the resulting 
waste is so slight or so readily oxidized that it does not interfere with the function 
of the nerve fiber. It has been shown repeatedly, in fact, that nerve fibers can 
be stimulated for several hours without exhibiting any evident fatigue. 
These statements do not apply, however, to nerve cells. Their metabolism 
is much more considerable than that of nerve fibers; they, therefore, become 
fatigued when excessively stimulated. Histological and chemical changes have 
been shown to occur in nerve cells as the result of prolonged stimulation. It is 
generally believed, however, that the primary seat of fatigue in the central nerve 
system is in the synaptic junction rather than in the cell body. 
The Nutritive or Trophic Influence of Nerve Cells.-If a nerve be divided, 
its peripheral end will undergo degeneration. The process of degeneration con- 
sists essentially of a disintegration and ultimate disappearance of the myelin 
and axis cylinder; the neurolemma remains intact. This phenomenon was 
first studied by Waller and is therefore known as Wallerian Degeneration. 
The portion of the nerve fiber connected to the cell remains virtually intact, 
although later on the cell and its axon will atrophy, probably because of disuse. 
Evidently, the cell body exercises an influence upon its axon that is necessary 
for the maintenance of its nutrition. This influence is referred to as a trophic 
or nutritive action. ESSENTIALS OF PHYSIOLOGY 
53 
CLASSIFICATION OF NERVE FIBERS 
The only function of nerve fibers is to carry nerve impulses. Normally, 
the conduction is either from nerve center to periphery, in which case it is called 
efferent, or from periphery to nerve center, in which case it is called afferent. 
Nerve fibers may, therefore, be divided, functionally, into two great groups; 
viz., efferent and afferent nerve fibers. As already explained in the preceding 
chapter, the nerve impulse, on reaching the organ innervated, may either stimu- 
late it to activity, or decrease or even check an activity already taking place. In 
the first instance the nerve impulse is said to be excitatory; in the second in- 
stance, inhibitory. Since phenomena of excitation and inhibition occur in relation 
with efferent and afferent fibers both groups may be subdivided into excitatory 
and inhibitory. A further basis for classification lies in the type of response as 
determined by the character of the organ innervated. Accordingly nerve 
fibers may be classified as follows: 
Efferent Nerve Fibers 
A. Excitatory: 
i. Motor; this term is usually applied to the efferent nerve fibers going to 
skeletal muscle. 
2. Vasomotor; nerve fibers distributed to the smooth muscle in the walls 
of arterioles. The vasomotor nerve fibers that are excitatory in nature are 
called vaso-constrictors or vaso-augmentors. 
3. Visceromotor; nerve fibers carrying nerve impulses to the smooth muscle 
in the walls of the viscera. Those of an excitatory nature are called viscero- 
augmentor or viscero-accelerator. 
4. Cardiomotor; nerve fibers distributed to the heart and causing an 
increase in the rate and force of its beats. Those fibers that increase the rate of 
the beat are called cardio-accelerator; those that cause an increase in the force 
of the beat are called cardio-augmentor nerve fibers. 
5. Pilomotor; nerve fibers innervating the smooth muscle that, when 
stimulated, cause an erection of the hair. 
6. Secretory; fibers distributed to various glands. These fibers carry nerve 
impulses that cause glands to discharge their secretion. 
B. Inhibitory: 
1. Vasoinhibitor; nerve fibers distributed to the smooth muscle in the 
walls of arteries, whose impulses give rise to dilatation of the blood vessels; 
hence called also vaso-dilatator nerve fibers. 
2. Visceroinhibitor; nerve fibers sending nerve impulses to the smooth 
muscle in the walls of viscera causing a decrease or cessation of their rhythmic 
activity. 
3. Cardioinhibitor; nerve fibers carrying nerve impulses into the heart, 
decreasing the rate and force of the beat. When strongly stimulated these 
nerve fibers may cause a temporary stoppage of the heart's action. 
4. Secretoinhibitor; nerve fibers distributed to glands. When stimulated, 
they cause a decrease or cessation of secretion. 54 
NERVE TISSUE 
Afferent Nerve Fibers 
A. Excitatory: 
i. Sensory or sensorifacient; nerve fibers distributed to the periphery of 
the body; viz., the skin, mucous membranes, special sense organs, muscles, and 
tendons. . The nerve impulses resulting from stimulation of these various parts 
of the periphery are conveyed to the brain where they evoke sensations. The 
sensor nerve fibers may be divided into three groups: 
(a) Special sense; those fibers subserving the senses of hearing, sight, 
taste, smell, touch, pressure, temperature, and pain. 
(&) Muscle sensibility; afferent nerve fibers distributed to muscles and 
tendons and transmitting nerve impulses to the brain where they evoke muscle 
sensations that enable the individual to determine the direction and duration of 
movement, and the relative position of its various parts. 
(c) General sensibility; nerve fibers subserving such ill defined sensations 
as those of comfort or discomfort, hunger, thirst, fatigue, the want of air, etc. 
2. Reflex-excitatory; afferent nerve fibers which carry nerve impulses to 
nerve centers located in the spinal cord and medulla where they excite the 
centers to the discharge of nerve impulses. These nerve impulses are then 
transmitted by efferent nerves to various peripheral organs, e. g., skeletal mus- 
cles, blood vessels, viscera, and glands, which in consequence enter into activity. 
The activity of a peripheral organ brought about in this manner is called 
a reflex action. 
B. Inhibitory: 
i. Reflex-inhibitory; nerve fibers carrying nerve impulses causing an 
inhibition of nerve centers in the spinal cord and medulla. The inhibition of 
these centers results in a decrease in the activity of various peripheral organs. 
Fibers causing an inhibition of sensations have not been demonstrated. CHAPTER IX 
THE NERVE SYSTEM 
In the foregoing chapter the histological and physiological unit of the 
nerve system-the neuron-has been described and its best known properties 
given. It was there stated that the nerve system consists of an enormous 
number of neurons arranged side by side and end to end, and that this system 
can be subdivided into a cerebrospinal and a sympathetic or autonomic system. 
The cerebrospinal system consists of central organs, called the brain 
or encephalon and the spinal cord, and of peripheral organs termed cranial 
and spinal nerves. 
The Central Nerve System.-The brain and spinal cord are located within 
the cranial cavity and the spinal canal respectively. These two parts consti- 
tute the central nerve system and are continuous with each other (see Fig. 43). 
The central organs consist of symmetrical halves united in the median line 
and enclosing cavities called ventricles. The presence of these cavities is readily 
understood when the development of the central nerve system is considered. 
The nerve system begins as a furrow in the external layer of the embryo. This 
furrow is called the neural groove. Later the edges of the groove fuse with 
each other to form the neural tube. On both sides of the tube there appear 
groups of cells which later give rise to the dorsal and sympathetic ganglia. 
The neural tube is at first of uniform calibre but undergoes various dilatations 
and foldings at the head end. The head end ultimately develops into the brain, 
while the tail end becomes the spinal cord. The original cavity of the tube 
persists throughout life as the ventricles. 
The Meninges.-The brain and spinal cord are held in position and pro- 
tected by three membranes called the meninges. The external membrane-- 
the dura mater-is strong and resistant and composed of connective tissue; 
it is attached to the bony walls. The next membrane-the arachnoid-is a 
thin sheet composed of areolar tissue covered on either side by flat endothelial 
cells; delicate bands pass from its inner surface to the underlying membrane. 
The third membrane-the pia mater-is composed of two layers of connective 
tissue; it is closely adherent to the surface of the brain and spinal cord and serves 
as a support for numerous blood vessels and perivascular lymphatics that pene- 
trate into the brain and spinal cord. 
The Cerebro-spinal Fluid.-Folds of the pia mater together with arach- 
noidal tissue, carrying a rich plexus of blood vessels, are found in the cerebral ven- 
tricles where they constitute the Telae Choroideae. The choroid plexuses are cov- 
ered by cuboidal cells giving the entire mass the appearance of an everted gland. 
This gland-like organ secretes a clear liquid called the cerebro-spinal fluid. 
The cerebro-spinal fluid fills the ventricles and surrounds the brain and spinal 
55 56 
THE NERVE SYSTEM 
cord by filling the subarachnoid space. All these spaces communicate with 
each other. 
The cerebro-spinal fluid serves as a water cushion to protect the delicate 
tissue of the central organs of the nerve system; it may act also as a nutritive 
fluid. 
Prosencephalon 
(forebrain) 
Cerebrum 
Mesencephalon 
(midbrain) 
Encephalor 
(brain) 
■Cerebellum 
Olivary body 
Metencephalon 
(hindbrain) 
Rhomben- 
cephalon 
Pons (Varoli) 
Myelencephalon 
(medulla oblongata) 
Pars cervicalis 
Jr ~ Pars thoracalis 
Spinal cord 
(medulla spinalis 
• Pars lumbalis 
Pars sacralis or 
'' conus medullaris 
Fig. 43.-Diagram illustrating the gross divisions of the central nervous system. (From "Morris's 
Human Anatomy ") 
The Peripheral Nerve System.-The peripheral nerve system consists 
of cranial and of spinal nerves. There are twelve pairs of cranial nerves: 
they spring from the brain and leave the cranium by passing through openings 
in its base, hence the name given to these nerves. Some of these nerves are 
composed wholly of efferent, others wholly of afferent, and still others of both 
efferent and afferent fibers. ESSENTIALS OF PHYSIOLOGY 
57 
There are thirty-one pairs of spinal nerves. These originate by two roots, 
one of which is related to the ventral and the other to the dorsal aspect of the 
Clava (nucleus of A 
fasciculus gracilis) ' 
Funiculus cuneatus 
T Olivary body 
* Lateral funiculus 
Decussation of pyramids 
Anterior median fissure 
Posteromedian sulcus 
Cervical 
enlargement 
Section of medulla 
oblongata 
Anterolateral sulcus 
(Line of ventral nerve - 
roots) 
Posterolateral sulcus 
Posterolateral sulcus 
Filum 
terminale 
Anterior median fissure 
Lumbar 
enlargement 
Posteromedian sulcus 
Conus 
medullaris 
Fig. 44.-Posterior and anterior views of the spinal cord. {Modified from Quain.) 
cord. Hence, called the ventral and dorsal roots. The ventral root consists 
of efferent fibers, while the dorsal root is composed of afferent fibers; the spinal 58 
THE NERVE SYSTEM 
nerve formed by the union of the two roots contains, therefore, both classes of 
fibers. The spinal nerves leave the spinal canal through openings in the walls 
of the spinal column. 
The Sympathetic or Autonomic Nerve System.-The sympathetic or 
autonomic nerve system consists essentially of ganglia in relation, on the one 
hand, with the central nerve system, and, on the other hand, with various 
peripheral organs. 
THE SPINAL CORD 
The spinal cord or medulla spinalis is that portion of the central nerve 
system located within the spinal canal. It is cylindrical in shape, though 
slightly flattened ventro-dorsally, and having two 
enlargements, one in the lower cervical and the other 
in the lower lumbar region where the nerves for the 
upper and lower extremities take their origin (see 
Fig. 44). The spinal cord extends from the foramen 
magnum, at the base of the skull, to the second lum- 
bar vertebra where it tapers off and is continued as a 
narrow thread-the filum terminale. It is from 40 to 
45 cm. long, and averages 12 mm. in diameter at the 
cervical and lumbar enlargements. Two fissures 
nearly divide it into two symmetrical halves, one in 
front, called the ventral, the other at the back, called 
the dorsal fissure. 
When the cord is cut across it is shown to be 
composed of gray matter internally and of white 
matter externally. 
The Gray Matter.-The gray matter runs the 
entire length of the cord in the form of a fluted col- 
umn. When seen in cross section it has the appear- 
ance of the letter H. The shape varies in its 
particulars at different levels, but presents every- 
where certain characteristic features. Each half of 
the cord contains a crescentic mass of gray matter. 
The two crescents are joined by a transverse band of 
gray matter, called the gray commissure. The por- 
tion of the crescent turned toward the front is called 
the ventral horn; it is blunt and does not reach the 
surface. The portion of the crescent turned toward the back is called the 
dorsal horn; it is more or less pointed and reaches the surface. The gray matter 
projects laterally in the lower cervical and thoracic regions of the cord to form 
a third horn called the lateral horn. A canal runs through the center of the 
gray commissure and is called the central canal or fifth ventricle (Fig. 45). 
The gray matter consists of groups of nerve cells and their processes sup- 
ported by neuroglia tissue. 
Fig. 45.-Sections througa 
different regions of the spinal 
cord. A, at the level of the sixth 
cervical nerve; B, at the mid- 
dorsal region. C, at the center 
of the lumbar enlargement. I, 
dorsal roots; 2, ventral roots; 3, 
dorsal fissure; 4, central fissure; 
5, central canal. (Morris' 
"Anatomy," after Schwalbe.) ESSENTIALS OF PHYSIOLOGY 
59 
The Nerve Cells.-The nerve cells in the gray matter of the cord are 
arranged in more or less well defined groups that vary in their location at various 
levels. Some of the groups run the length of the cord for greater or less 
distance. In the ventral horn two groups may usually be seen, one called the 
ventro-median group, the other, the ventro-lateral group. Where there is a 
lateral horn, it contains a group of cells known as the intermedio-lateral group. 
In the thoracic region a group of cells occurs at the base and inner side of the 
dorsal horn; it is known as the nucleus dorsalis or Clarke's vesicular column. 
Nerve cells are also found irregularly scattered in the dorsal horn (Fig. 46). 
Fig. 46.-Diagram of a transverse section of the spinal cord showing the main groups of nerve 
cells in the gray matter and the origin of the spinal nerve roots, s.g.c., spinal ganglion cells; d.r., 
dorsal root; d.h.c., dorsal horn cells; n.d. nucleus dorsalis; i.l., intermedio-lateral group of nerve 
cells; v.l., ventro-lateral group of nerve cells; v.m., ventro-median group of nerve cells; v.r., ventral 
root. (G. Bachmann.) 
From a functional point of view all these nerve cells may be divided into 
three classes; viz., afferent or receptive, efferent or emissive and intrinsic or 
associational. 
The afferent or receptive cells receive nerve impulses transmitted from 
the periphery by afferent nerves. These cells are found in the dorsal horn 
and in the nucleus dorsalis. The nerve fibers arising from the cells scattered 
in the dorsal horn carry their nerve impulses to the cerebrum where they evoke 
sensations. The nerve fibers issuing from the nerve cells of the nucleus dorsalis 
go to the cerebellum. Both sets of fibers may directly or indirectly, through 
collaterals, arborize around intrinsic cells or efferent cells for the purpose of 
reflex action. 
The efferent or emissive cells send their axons into the ventral roots of the 
spinal nerves whence they are distributed to muscle tissue and gland epithelium. 
Intrinsic or associational cells give rise to fibers that course up and down 
the cord a variable distance, arborizing at different levels around efferent nerve 60 
THE NERVE SYSTEM 
cells. They therefore serve to associate in their action various levels of the spinal 
cord, on the same or opposite sides. 
The White Matter.-The white matter consists of medullated nerve fibers 
supported by neuroglia. Connective tissue septa, derived from the pia mater 
and supporting blood vessels, penetrate between the nerve fibers. The nerve 
fibers have no neurolemma and run mainly in a longitudinal direction. Each 
side of the white matter of the cord has been divided anatomically into a ventral, 
a lateral, and a dorsal column; the lines of separation, aside from the median 
line, are the ventral and dorsal roots of the spinal nerves. 
The Roots of the Spinal Nerves.-As already stated on page 57 there issue 
from the spinal cord thirty-one pairs of nerves; these nerves take their origin 
from two roots, the ventral and dorsal roots. It has been shown by experiment 
that the ventral root is efferent in function, and that its nerve fibers originate in the 
large multipolar cells situated in the ventral horn of the gray matter as well as 
from the cells of the lateral horn where it exists. Destruction of these cells by 
disease is followed by a degeneration of the nerve fibers of the ventral root; 
section of a ventral root is followed by degeneration of the nerve fibers distal 
to the section. Experiment has shown likewise that the dorsal root is afferent in 
function, and that its fibers originate in cells located in the ganglion seen on 
the root. Section of the fibers of a dorsal root between the ganglion and the 
spinal cord is followed by a degeneration of the fibers passing into the cord; 
section of the fibers below the ganglion is followed by a degeneration of the distal 
end of the fibers. 
The distribution and the function of the fibers of the ventral and dorsal roots 
can be demonstrated by (1) their stimulation and (2) their division. 
Stimulation of the fibers of the ventral root gives rise to: 
(a) Contraction of skeletal muscles. 
(i) Increased contraction of the peripheral arteries. 
(c) Increased contraction or inhibition in the muscle walls of certain viscera. 
(d) Discharge of secretion from glands. 
Division of the fibers of a ventral root is followed by: 
(a) Total loss of movement (paralysis) and relaxation of skeletal muscles. 
(ff) Temporary dilatation of the peripheral arteries. 
(c) Loss of nerve control of certain viscera with temporary derangement of 
their normal activity. 
(d) Abnormal (paralytic) secretion with eventual complete cessation. 
Stimulation of the fibers of a dorsal root results in: (a) Reflex excitation of 
spinal efferent nerve cells followed by contraction of skeletal muscles and blood 
vessels; secretions from glands; variations in the rhythmic activity of certain 
viscera. 
(b) Reflex inhibition of spinal efferent nerve cells followed by decrease in 
the tone of skeletal muscles and blood vessels; cessation of secretion; decreased 
activity of certain viscera. 
(c) Sensations of pain, touch, temperature, and of muscle movements. 
Division of the fibers of a dorsal root is followed by: 61 
ESSENTIALS OF PHYSIOLOGY 
(a) Loss of reflex actions. 
(b) Loss of sensation in all parts supplied by the fibers of that root. 
FUNCTIONS OF THE SPINAL CORD 
The spinal cord may be looked upon as a segmented organ. This point of 
view is best exemplified by referring to the nerve structures that fulfill the same 
Fig. 47.-Diagram of the central nerve 
system of the crayfish, i, supraesopha- 
geal or cerebral ganglion; 2, optic nerve; 
3, antennary nerve; 4, commissure; 5, 
stomatogastric nerve; 6, esophagus; 7, 
subesophageal ganglion; 8, first abdomi- 
nal ganglion. {Modified from Yung and 
Vogt.) 
Fig. 48.-Diagram to show the relation of the neurons 
in the earthworm. Two ganglia and their related seg- 
ments are shown, ep., epidermis; c.m., circular layer of 
muscles; l.m., longitudinal layer of muscles; g.c., ganglion- 
chain; a, afferent or sensor cells from which arise a', affer- 
ent fibers which make synaptic connections with intrinsic 
and efferent neurons in the ganglion chain; i, intrinsic or 
association cells sending their fibers up and down the gan- 
glion chain; e, efferent cells sending their fibers to the mus- 
cles. (G. Bachmann, adapted from Retzius and Schafer.) 
functions in segmented animals such as worms and crustaceans. In these 
animals each segment of the body contains a ganglion with afferent and efferent 
nerve fibers supplying the segment. The ganglia are connected with each other 
by longitudinal nerve fibers. The head ganglion, being related to the sense of 
sight, taste, touch, etc., controls the ganglia in the lower segments of the body 
and serves as brain (Figs. 47 and 48). 62 
THE NERVE SYSTEM 
In the process of evolution the longitudinal fibers have become very 
numerous, and the gray matter has gradually extended into an unbroken column; 
Fig. 49.-Diagram showing the structures involved in the production of reflex actions, r.s., 
receptive surface; af.n., afferent nerve; e.c., emissive or motor cells in the anterior horn of the gray 
matter of the spinal cord, sp.c; ef.n., efferent nerves distributed to responsive organs, e. g., directly 
to skeletal muscles, sk.m., and indirectly through the intermediation of sympathetic ganglia, sym.g., 
to blood-vessels, b.v., and to glands, g. The nerves distributed to viscera are not represented. (G. 
Bachmann.) 
but the segmental arrangement still persists in the origin of the spinal nerves. 
The spinal cord of the higher animals may therefore be regarded as being made 
up of as many segments as there are pairs of spinal 
nerves. The head ganglion has become enormously 
developed and with this great development has assumed 
greater control over the centers of the spinal cord. 
Each spinal segment is related with definite areas 
of the body through the intermediation of its afferent 
and efferent nerves. There is, however, a consider- 
able amount of overlapping, especially as concerns the 
limbs. The spinal segments may accordingly act inde- 
pendently of each other; they may become associated 
in varying numbers owing to the presence of neurons 
distributed to various segments and therefore called 
association neurons. The spinal cord serves also as a 
pathway for impulses entering the cord at various 
levels and destined for the brain, as well as for im- 
pulses sent from the brain to various segments. 
The spinal cord may therefore be regarded as con- 
sisting (i) of more or less independent segments, and 
(2) of a pathway for the conduction of nerve impulses. 
The Spinal Cord as an Independent, Segmented 
Organ.-As stated above, each spinal segment is re- 
lated by afferent as well as efferent nerve fibers to a definite area of the body. 
As a consequence of this relationship, skeletal muscles, blood vessels, glands, 
Fig. 50.-Diagram showing 
the relation of the correlation 
neuron a, to the afferent neur- 
on b, and to the efferent neur- 
ons c, c, c. (After Kolliker.) ESSENTIALS OF PHYSIOLOGY 
63 
etc. may be excited to activity by stimulation of the periphery. Such a phe- 
nomenon is called a reflex action. The characteristics of a reflex action are 
that it takes place independently of the will and as a result of peripheral stim- 
ulation; it may or may not be accompanied by any sensation. Many of the 
reflexes of the body are in fact wholly unconscious. 
The Reflex Arc.-The structures necessary for the production of reflex 
action constitute the reflex arc (Fig. 49). They consist of: 
(1) A sensory surface, called the receptor; e. g., skin, mucous membrane, 
sense organ. 
(2) An afferent neuron. 
(3) An efferent neuron. 
(4) A responsive or effector organ; e. g., muscle, gland, blood vessel, etc. 
Stimulation of the receptor generates nerve impulses in the terminals of the 
afferent nerve fiber; these impulses are transmitted into the spinal cord and pass 
across the synapse into the efferent neuron, from which they are then transmitted 
to the effector organ. If the efferent neuron is excitatory in nature, the result 
will be excitation; if inhibitory, the result will be inhibition. 
A reflex arc, constituted as just described, could give rise to but the 
simplest kind of reflex. Most of the reflexes of the body are, however, very 
complex and necessitate the co-operation of a number of segments of the cord on 
the same and opposite sides of the stimulation. Such reflexes are made possible 
by the interposition of association neurons between the afferent neuron convey- 
ing the impulses from the periphery and the series of efferent neurons related to 
the effector organs (see Fig. 50). 
Reflex Irritability.-Reflex action can be readily studied in the frog after 
destruction of the brain. Immediately upon destruction, and for some little 
time afterwards, the frog passes into a condition during which reflexes are 
unobtainable; this condition is called " spinal shock." After the shock has passed 
away, the frog may be suspended from a hook and various areas of its skin 
stimulated. The response is a contraction of various groups of muscles depend- 
ing on the area of the skin stimulated. The stimulus commonly used is a 
weak solution of sulphuric or acetic acid. The extent and complexity of 
the movements will vary with the strength of the stimulus and the area to 
which it is applied. The movements have the appearance of being purposive, 
and are evidently directed toward the removal of the irritant. Similar reflex 
movements have been observed in warm-blooded animals under proper experi- 
mental conditions. 
Time is required following the application of a stimulus before a reflex 
takes place. This is called the total reflex time. During this time the nerve 
impulses are traveling from the terminals of the afferent nerve fibers in the 
receptor into and through the spinal cord, thence by the efferent neuron to the 
effector organ, which responds after a latent period. When the time required 
for the impulse to pass along the afferent and efferent nerves and for the latent 
period of the effector organ are deducted, the reduced reflex time is obtained; 
it represents the time required for the passage of the impulse through the spinal 64 
THE NERVE SYSTEM 
cord. Most of this time is occupied in the transmission of the impulse across 
the synapse. The reduced reflex time is a measure of the reflex irritability of 
the spinal cord. 
Resistance at the Synapse.-Strong stimuli reduce the reflex time and call 
forth reflex actions of greater intensity and complexity. There are evidently 
synaptic connections of different degrees of resistance; accordingly, weak 
stimuli will pass across the synapses of least resistance and a relatively simple 
reflex will follow. With increasing strength of stimulation the impulses will 
Fig. 51.-Diagram indicating connections and actions of two afferent spinal root-cells, a and all 
in regard to their reflex influence on the extensor and flexor muscles of the two knees; a, root-ce,- 
afferent from skin below knee; a', root-cell afferent from flexor muscle of knee, i. e., in hamstring nerve; 
e and e', efferent neurones to the extensor muscles of the knee, left and right; 6 and 3', efferent neu' 
rones to the flexor muscles; E and E', extensor muscles; F and F', flexor muscles. The ''schalt-zellen"' 
(v. Monakow) probable between the afferent and efferent root-cells are for simplicity omitted. The 
sign + indicates that at the synapse which it marks the afferent fibre a (and a') excites the motor 
neurone to discharging activity, whereas the sign - indicates that at the synapse which it marks 
the afferent fibre a (and a') inhibits the discharging activity of the motor neurones. The effect of 
strychnine and of tetanus toxin is to convert the minus sign into plus sign. (Sherrington, " The 
Integrative Action of the Nervous System,'' Yale University Press.') 
pass across synapses of increasingly higher resistance and reflexes of increasingly 
greater complexity will occur. If, for example, weak irritation be applied 
to an area of the foot of a frog a movement of small extent will take place in the 
leg of the same side. If the irritation be sufficiently increased, not only will the 
movement on the same side be more extensive, but movements of the leg of 
the opposite side will take place also. ESSENTIALS OF PHYSIOLOGY 
65 
Inhibition of Reflexes.-Reflexes may be checked or inhibited by nerve 
impulses coming from higher centers or from another part of the periphery. 
Setschenow's experiment demonstrates the presence of neurons arising in the 
higher centers whose stimulation results in inhibition of spinal reflexes. This 
experiment consists in destroying the cerebral hemispheres of a frog and then 
stimulating the optic lobes with crystals of sodium chloride. So long as the 
crystals remain in contact with the optic lobes, the usual reflexes obtainable 
on stimulation of the skin do not occur. After removing the crystals reflexes 
can be obtained in the usual manner. It is well known that certain reflexes, 
such as sneezing, can be inhibited to a certain extent by an effort of the will. 
The brain, therefore, has an inhibitory influence over reflex actions. A reflex 
act may also be inhibited by stimulating simultaneously two different parts of 
the periphery, as when the reflex act known as sneezing is checked by pressure 
on the upper lip. 
Reciprocal Innervation.-Reflex movements do not consist simply of a 
contraction of certain muscles, but of a simultaneous relaxation of antagonistic 
muscles. Thus, when the leg is reflexly drawn up, the movement is brought 
about by a simultaneous contraction of the flexor and relaxation of the exten- 
sor muscles. The relaxation is brought about by a reflex inhibition of the tone 
of the extensor muscles. The converse holds true: extension takes place through 
a contraction of extensor muscles and a relaxation of flexor muscles (see Fig. 51). 
The same phenomena occur in voluntary movements. Reciprocal innervation 
is observed also in the action of the smooth muscles of the bladder, rectum, 
and iris. 
Muscle Tone.-The skeletal muscles are at all times in a state of slight 
but continuous contraction which is referred to as muscle tone. The immediate 
cause of muscle tone is the continuous discharge of nerve impulses from the spinal 
cord, as it disappears following destruction of the spinal cord or of the efferent 
nerves going to the muscles. 
The phenomenon of muscle tone is a reflex action, the afferent nerve 
impulses arising, in the mammal, mainly in the terminals of the afferent nerve 
fibers distributed in the muscles or tendons. The destruction, therefore, of 
the afferent fibers contained in the dorsal roots of the spinal nerve abolishes 
muscle tone. 
The tonic contraction of muscles enables these to contract without delay 
when stimulated. The slight but constant contraction of muscles, being 
accompanied by the generation of heat, is an efficient means of maintaining 
body temperature, as will be explained more fully in a subsequent chapter. 
THE SPINAL CORD AS A PATHWAY FOR THE CONDUCTION OF NERVE IMPULSES 
The spinal cord acts as a pathway for nerve impulses by virtue of the 
presence of large numbers of nerve fibers. As stated in a preceding paragraph, 
the nerve fibers constitute the essential structure of the white matter, and run 
chiefly in a longitudinal direction. 66 
THE NERVE SYSTEM 
Aside from the division of the white matter on each side of the cord into a 
ventral, a lateral, and a dorsal column by the median septa and the ventral 
and dorsal roots, no further subdivision of the nerve fibers into definite tracts 
is possible on microscopic examination alone. Yet a study of the embry- 
ological development of the cord, as well as of the degeneration of nerve fibers 
that follows their experimental or accidental injury, have shown conclusively 
that the nerve fibers of the cord are arranged in bundles or tracts having various 
origins and destinations (see Fig. 52). 
Classification of the Spinal Tracts.-The tracts-called also fasciculi- 
may be grouped into: association, ascending or afferent, and descending or 
efferent tracts. 
Fig. 52.-Diagram of a transverse section of the spinal cord showing the location and relation 
of the different fasciculi. Associative Fasciculi: 1, fasciculi proprii, ventral, lateral and dorsal; 
x', the comma tract, 1", the septo-marginal tract. The Ascending Fasciculi: 2, the dorso-internai 
(Goll); 3, the dorso-external (Burda ch); 4, the postero-marginal (Lissauer); 5, the dorsal spino- 
cerebellar (Flechsig); 6, the lateral spino-cerebellar (Gower); y, the lateral spino-thalamic; 8, 
the ventral spino-thalamic; 9, the spino-tectal; 10, the spino-olivary. The Descending Fasciculi: 
11, the crossed-pyramidal tract; 12, the direct pyramidal tract (Turek); 15, the rubro-spinal tract 
(Monakow's); 14, the vestibulo-spinal tract. (Brzibaker.) 
The Association Tracts.-These tracts surround the margin of the gray 
matter. As the fibers contained in these tracts are confined entirely to the spinal 
cord, they are termed also fasciculi proprii. There is on each side a ventral, a 
lateral, and a dorsal fasciculus proprius. Their fibers run up and down the 
cord, and make connection by means of collaterals with nerve cells at various 
levels, thus associating in their action more or less distant segments of the cord. 
The Ascending or Afferent Tracts.-Two chief ascending tracts are found in 
the dorsal column of the white matter as follows: ESSENTIALS OF PHYSIOLOGY 
67 
(i) Fasciculus Gracilis (Tract of Goll).-This tract occupies the portion 
of the dorsal column abutting on the mediam septum; it consists of fibers that 
have passed into the cord by way of the dorsal roots. These fibers ascend as far 
as the nucleus gracilis of the medulla around the cells of which they arborize. 
(2) Fasciculus Cuneatus (Tract of Burdach).-This tract is situated in the 
dorsal column close to the dorsal horn of the gray matter. Its fibers are also 
continuations of the dorsal root fibers. They ascend as far as the medulla 
where they arborize around the cells of the nucleus cuneatus. 
The fibers entering the lower portion of the cord by way of the fasciculus 
cuneatus move gradually toward the median line and ultimately occupy the 
position of the fasciculus gracilis. 
For the sake of convenience the ventral and lateral columns will be con- 
sidered together. There are four ascending tracts of importance contained in 
the ventro-lateral column: 
(1) Fasciculus Spinocerebellaris (Dorsal Spinocerebellar Tract, or Tract 
of Flechsig).-This tract lies along the dorso-lateral margin of the white matter. 
It consists of nerve fibers originating in the nerve cells of the nucleus dorsalis 
of the same side. They ascend to the cerebellum where they terminate in the 
vermis after crossing the median line. 
(2) Fasciculus Ventrolateralis Superficialis (Ventro-lateral Spino-cere- 
bellar Tract, or Tract of Gower).-This tract lies immediately in front of the 
preceding one in the position indicated by its name. Like the preceding tract its 
fibers originate in the nerve cells of the nucleus dorsalis of the same side. They 
also ascend to the cerebellum. 
(3) Fasciculus Spinothalamicus Lateralis.-This tract lies immediately 
internal to Gower's Tract. Its fibers originate in nerve cells of the dorsal horn 
of the opposite side. The impulses carried by this tract ultimately reach the 
optic thalamus. 
(4) Fasciculus Spinothalamicus Ventralis.-This tract is situated in front of 
the ventral horn of the gray matter. Its fibers have the same origin and 
destination as those of the preceding tract. 
The Descending or Efferent Tracts.--A number of efferent tracts have been 
described, the most important of which are: 
(1) Fasciculi Cerebrospinalis (Pyramidal Tracts).-The fibers of these 
tracts take their origin in the cells of the motor region of the cerebral cortex. 
They descend through the central part of the brain stem as far as the base of the 
medulla where the majority of the fibers (85 to 90 per cent) cross the midline to 
the opposite side. The tract of fibers thus formed descends the cord in the 
dorsal region of the lateral column. It is known as the fasciculus cerebro- 
spinalis lateralis or Crossed Pyramidal Tract. The fibers terminate at the vari- 
ous levels of the cord around intrinsic cells, whose fibers arborize around the 
efferent cells of the ventral horn of the gray matter of the same side. A direct 
connection with these efferent cells is also possible. 
The remaining fibers (15 to 10 per cent) descend the cord on the same side 
where they are seen in the ventral column along the margin of the ventral 68 
THE NERVE SYSTEM 
fissure. This tract of fibers is called the fasciculus cerebrospinalis ventralis 
or Direct Pyramidal Tract. Some of these fibers make connections with effer- 
ent cells on the same side; some cross the median line through the anterior 
fissure and make connection with the cells of the opposite side. 
(2) Fasciculus Rubrospinalis (Tract of Monakow).-The fibers of this 
tract originate in the cells of the red nucleus of the mid-brain. They shortly 
cross the median line and descend the cord immediately in front of the crossed 
pyramidal tract. The fibers make connections with the cells of the ventral 
horn. 
(3) Fasciculus Vestibulospinalis (Tract of Loewenthal).-The fibers con- 
tained in this tract arise in the cells of Deiters' nucleus in the upper part of the 
medulla. They descend the spinal cord in front of the ventro-lateral spino- 
cerebellar tract and terminate around the cells of the ventral horn. 
Function of the Fiber Tracts.-The general function of nerve fibers is to 
conduct nerve impulses. The effect induced by the nerve impulses will vary 
with their distribution. 
Associative or Intersegmental Conduction.-The nerve impulses distri- 
buted by the association tracts serve the purpose of co-ordinating the various 
segments of the spinal cord so that various parts of the body, more or less distant 
from each other, may enter into co-ordinate activity. This co-ordinate activity 
may be the result of reflex or of voluntary stimulation. 
Ascending or Sensor Conduction.-The nerve impulses that subserve our 
sensations are aroused by stimulation of the endings of the sensor nerves in the 
various parts of the periphery. Some of these nerves are distributed to the skin 
and are therefore called cutaneous nerves. Their stimulation occurs through 
the action of various forces in the external world. The nerve fibers carrying the 
nerve impulses induced in this way may be called exteroceptive. Other nerve 
endings are located in the deeper tissues, more especially in the muscles, tendons, 
etc., and are stimulated by changes in the position of these structures. The 
nerve fibers carrying these nerve impulses are called proprioceptive. 
The cutaneous sensations subserved by the exteroceptive nerve fibers 
have been classified as follows: 
The tactile sense accompanied by the power of localizing the point stimu- 
lated-"one-dimensional localization;" the ability to recognize as separate two 
simultaneous stimulations-"two-dimensional localization" or "tactile discrim- 
ination;" the sense of pain and that of temperature, i. e., heat and cold. 
The sensations subserved by the proprioceptive nerve fibers are (1) the 
muscle sense through which the individual becomes aware of the extent and 
direction of movements and the passive position of parts of the body, and (2) the 
sense of deep pain as in the case of painful pressure and the rupture of a joint. 
The general directions taken by the nerve impulses giving rise to the various 
sensations have been ascertained partly through experimental transverse hemi- 
section of the cord in animals, and partly through a study of the results of 
disease or injury of the spinal cord in man. Such injuries, when occurring in the 
cervical region, are followed by a motor paralysis in the limbs of the same side, ESSENTIALS OF PHYSIOLOGY 
69 
together with a loss of two-dimensional localization and of the muscle sense. 
The fibers for these sensations must therefore ascend the spinal cord on the same 
side as they enter it. The sensations of pain, heat, and cold, as well as that of one- 
Fig. 53.-Diagram of the sensor pathways in the spinal cord enlarged above by fibers of the sensor 
cranial nerves and nerves of special sense. {Brubaker.) 
dimensional localization, are lost in the opposite lower limb, indicating that the 
nerve fibers carrying the impulses for these sensations cross in the spinal cord. 
The first experiments on transverse hemisection of the spinal cord were 
made by Brown-Sequard. The results of the destruction of a lateral half of 
the cord are therefore called the "Brown-Sequard Symptom Complex." 70 
THE NERVE SYSTEM 
The actual tracts containing the nerve fibers subserving the various sensa- 
tions have been ascertained by a detailed study of special experiments on animals 
and of various diseases of the spinal cord occurring in man. These studies 
have shown that the fibers for the muscle sense and two-dimensional localiza- 
Fig. 54.-Diagram of the pyramidal tract or motor path. Ill, common oculo-motor nerve; 
IV, pathetic nerve; V, motor division of the trigeminal nerve; VI, the abducens nerve; VII, facial 
nerve; IX and X, motor divisions of the glosso-pharyngeal and pneumogastric nerves; XI, spinal 
accessory nerve; XII, hypoglossal nerve. (Van Gehuchten.) 
tion (tactile discrimination) ascend in the dorsal tracts of the cord, viz., 
the fasciculi gracilis and cuneatus. These fibers ascend as far as the base of 
the medulla where they terminate around the cells of the nucleus gracilis and 
nucleus cuneatus; from these cells other fibers sweep forward and upward, ESSENTIALS OF PHYSIOLOGY 
71 
crossing the median line at the arcuate decussation. These fibers are then 
continued up to the optic thalamus. 
The fibers for pain and temperature ascend in the fasciculus spinothala- 
micus lateralis and those for touch and one-dimensional localization pass into 
the fasciculus spinothalamicus ventralis. All of these fibers ultimately reach 
the optic thalamus, around the cells of which they terminate. The nerve 
impulses for pain and temperature cross to the side opposite the one they enter 
within five or six segments, while those for touch and one-dimensional localiza- 
tion cross much more gradually, some of these, in fact, not having crossed over 
until the upper cervical segments are reached (Fig. 53). 
The fibers located in the other two important ascending tracts are not 
concerned with sensation. These tracts are the fasciculus spinocerebellaris 
or Tract of Flechsig, and the fasciculus ventrolateralis superficialis or Tract 
of Gower. They convey impulses aroused in the muscles and structures about 
the joints to the cerebellum where they bring into play a co-ordinating mechan- 
ism whereby the skeletal muscles change their tone in adaptation to the needs 
of various postural positions of the body. Division of these tracts is followed 
by a loss of tone and of co-ordinate contraction in the muscles below the lesion. 
Descending or Motor Conduction.-The most important pathway for 
descending nerve impulses is that of the Pyramidal or Cerebrospinal Tracts 
(Fig. 54). These tracts convey the nerve impulses evoked by volition; their 
destruction in the spinal cord is therefore followed by paralysis of the muscles 
on the side below the lesion so that they cannot be made to contract voluntarily. 
A secondary pathway for motor impulses is provided by the Rubrospinal 
Tract. This tract which originates in the red nucleus of the mid-brain is espe- 
cially related to the cerebellum. Experiments have shown that it carries nerve 
impulses that serve to maintain the postural tone of the muscles. 
The Vestibulospinal Tract is likewise related to the mechanism that 
adapts the tone of the muscles to postural changes and thus, serves to maintain 
the equilibrium of the body. CHAPTER X 
THE BRAIN OR ENCEPHALON 
The brain forms the upper part of the cerebro-spinal axis; it is located in 
the cranial cavity which it fills almost completely. It is surrounded by the 
, Prosencephalon 
(forebrain) 
Mesencephalon 
(midbrain) 
Cerebrum 
Encephalon 
(brain) 
Olivary body 
■Cerebellum 
Pons (Varoli) 
M y elencephalon 
(medulla oblongata) 
Metencephalon 
(hindbrain) 
Rhomben- 
cephalon 
■Pars cervicalis 
-Pars thoracalis 
Spinal cord 
(medulla spinalis 
' Pars lumbalis 
Pars sacralis or 
conus medullaris 
Fig. 55.-Diagram illustrating the gross divisions of the central nerve system. (Morris.) 
same membranes that surround the spinal cord and a small amount of cerebro- 
spinal fluid acts as a cushion between its relatively soft mass and the cranial 
wall. The cerebro-spinal fluid likewise fills certain cavities found in the interior 
72 ESSENTIALS OF PHYSIOLOGY 
73 
of the organ-the ventricles. Two of these cavities are found in the cerebrum 
or fore-brain, one in each hemisphere. These cavites are termed the lateral 
ventricles. They communicate with another cavity situated in the diencephalon 
(inter-brain or 'tween-brain) and called the third ventricle. A narrow passage- 
way running through the mid-brain, and termed the Aqueduct of Sylvius, 
forms a means of communication between the third and the fourth ventricles. 
The f ourth ventricle is a space located in the hind-brain between the medulla 
oblongata and the cerebellum. Finally the fourth ventricle communicates with 
the central canal of the spinal cord. 
The Parts of the Brain.-As already intimated the general brain mass 
has been subdivided into a number of parts (see Fig. 55). The various parts 
are named from below upward as follows: 
Medulla oblongata or after-brain 
Pons 
Cerebellum 
hind-brain 
Mesencephalon or mid-brain 
Diencephalon or 'tween-brain 
Cerebrum, prosencephalon or fore-brain 
THE MEDULLA OBLONGATA 
The Medulla Oblongata or Bulb is the upper expanded portion of the spinal 
cord. It is about 38 millimeters long and has the general shape of a truncated 
Fig. 56.-Ventral surface of the brain stem. 
1, decussation of the pyramidal tract; 2, anterior 
pyramid of medulla oblongata; 3, olivary body; 
4, pons; 5, crus cerebri; 6, optic tract. (From 
Brubaker's Textbook of Physiology.) 
Fig. 57.-Dorsal surface of the brain stem, i, 
nucleus gracilis; 2, nucleus cuneatus; 3, restiform 
body; 4, acoustic nerve; 5, inferior peduncle of 
cerebellum; 6, middle peduncle; 7, superior ped- 
uncle; 8, inferior quadrigeminal body; 9, superior 
quadrigeminal body; 10, pineal gland; 11, optic 
thalamus. (From Brubaker's Textbook of Physi- 
ology.) 
cone (see Figs. 56 and 57). As in the case of the spinal cord, it is composed of 
white matter externally and gray matter internally. THE BRAIN OR ENCEPHALON 
74 
The Gray Matter.-Owing to the shifting of various fiber tracts, the gray 
matter of the medulla is not arranged with the regularity seen in the spinal cord. 
In the lower part of the medulla the central canal of the spinal cord is continued 
through the gray matter. At about the middle of the medulla the central 
canal opens on its dorsal surface to become the lower half of the fourth ventricle. 
The floor of the fourth ventricle consists therefore of gray matter covered over 
with the ependyma that lines all the ventricles. Groups of nerve cells are found 
in the gray matter from which arise various efferent cranial nerves. The gray 
Choroid tela of fourth ventricle 
Solitary tract 
Nucleus of vestibular nerve 
Restiform body 
Spinal tract of trigeminus 
Nucleus of cochlear nerve 
Vagus nerve 
Hypoglossal nerve 
Pyramid 
■Spinal tract of trigeminus 
Decussation of pyramids 
Lateral cerebrospinal fasciculus 
(crossed pyramidal tract) 
Ventral cerebrospinal fasciculus 
(direct pyramidal tract) 
Fig. 58.-Diagram showing the decussation of the pyramids. The uppermost level represented is 
near the inferior border of the pons. {Hardesty in Morris' Anatomy.) 
matter of the medulla likewise contains various nerve centers that control 
important functions, e. g., respiration, the activity of the heart, the circulation, 
etc. 
The White Matter.-The white matter consists of the medullated nerve 
fibers that have been described as descending and ascending in the spinal cord. 
The cerebrospinal or pyramidal tract forms an important column of fibers 
from the ventral aspect of the medulla at the base of which the greater number 
of these fibers decussate to the opposite side to assume the position seen in 
the spinal cord (Fig. 58). ESSENTIALS OF PHYSIOLOGY 
75 
Nucleus of spinal 
tract of trigeminus, 
Spinal tract of 
trigeminus 
(Root filament of glosso- 
' pharyngeal nerve 
Restiform body 
Nucleus of ala cinerea 
■Dorsal external arcuate fiber 
Decussation of lemnisci 
-Nucleus of fasciculus cuneatus 
'Nucleus of fasciculus gracilis 
-Fasciculus cuneatus 
-Fasciculus gracilis 
Dorsal spinocerebellar fasciculus 
Dorsal nucleus 
■Gowers' tract 
Fig. 59.-Diagram of the spino-cerebellar fasciculi and the origin and decussation of the medial 
lemnisci. (From Morris' Human Anatomy.) 76 
THE BRAIN OR ENCEPHALON 
The fibers of the dorsal spino-cerebellar tract diverge from their median 
position to enter the restiform body or inferior cerebellar peduncle. The 
restiform body likewise receives some of the fibers from the columns of Goll 
and of Burdach as well as other fibers that pass into it from the deeper parts 
of the medulla. The fibers that arise from the cuneate and gracile nuclei, seen 
at the upper extremity of the dorsal column of the cord, cross to the opposite 
side of the medulla to form the arcuate decussation. These fibers are then 
continued upward as a distinct tract to which the sensor end-nuclei of all the 
afferent nerves of the opposite side (except the auditory nerve) contribute 
additional fibers. This tract contains likewise the ascending fibers from the 
spinal cord. It is called the mesial fillet or lemniscus. The sensor end-nucleus 
of the auditory nerve gives rise to a separate tract of fibers termed the lateral 
fillet or lemniscus (Fig. 59). 
Functions of the Medulla Oblongata.-From the foregoing brief review 
of the best known features of the medulla, it is evident that it constitutes a 
pathway for the conduction of nerve impulses from the higher centers to some 
of its own centers as well as to the spinal cord. Nerve impulses are likewise 
conducted through the medulla from the spinal cord to higher centers. Owing 
to the presence of various special centers, the medulla is also an organ for reflex 
as well as automatic activity. 
(1) The Conduction of Nerve Impulses Through the Medulla.--Since the 
crebro-spinal or pyramidal tract descends through the ventral portion of the 
medulla, volitional nerve impulses are conducted from the cortex of the cerebrum 
to the nuclei of origin of certain cranial nerves as well as to the spinal cord. 
A section of the pyramidal tract of one side, if it is done above the decussation, 
will therefore be followed by a voluntary paralysis of the muscles or hemiplegia 
on the opposite side below the section. 
More dorsally placed is the mesial fillet which conducts afferent nerve 
impulses for the spinal cord as well as from most of the sensor cranial nerves. 
As all of these .fibers ascending on one side are related to the opposite side of 
the body, section of one mesial fillet will be followed by a complete anesthesia 
of the opposite half of the body. 
(2) The Reflex and Automatic Centers of the Medulla.-Since the medulla, 
as well as that portion of the gray matter in the floor of the fourth ventricle 
back of the Pons, contain the nuclei of origin of the greater number of the 
cranial nerves, a number of reflex acts occur similar to those seen to take place 
through the spinal cord. Examples of such reflexes are: movements of facial 
muscles, coughing, and sneezing. 
The special nerve centers located in the gray matter of the floor of the fourth 
ventricle are co-ordinating centers that serve to distribute nerve impulses to 
more or less distant but physiologically related structures, in such a way that 
a definite function may be carried out. These centers may be brought into 
activity reflexly or as a result of a local chemical stimulation. In the latter 
case the center is essentially automatic in action. 
The more important of these centers are as follows: ESSENTIALS OF PHYSIOLOGY 
77 
(a) The Respiratory Center, concerned in the co-ordination of the various 
muscles that produce the respiratory movements. Because of the importance 
of the function of respiration to the life of the individual, destruction of this 
center eventuates in death. For this reason, the area of the medulla containing 
the center is sometimes called 11 the vital spot." 
(b) The Cardiac Centers, viz., a cardio-inhibitor center, whose function is 
to check the heart's action through the intermediation of nerve impulses con- 
ducted to the heart by efferent fibers in the pneumogastric or vagus nerve; 
a cardio-accelerator center, whose function is to increase the frequency and the 
force of the heart beat through nerve impulses carried to the heart by the 
sympathetic nerve. 
(c) The Vaso-motor Center through which the caliber of the blood vessels, 
more especially of the arterioles is regulated. 
(J) The Mastication Center in which the nerve impulses are co-ordinated 
for the orderly sequence of contraction of the muscles necessary for mastication. 
(e) The Deglutition Center, a similar center for the co-ordination of the 
muscles that serve to transfer the food from the mouth to the stomach. 
(/) The Salivary Center, through which nerve impulses are discharged 
for the regulation of the secretion of saliva. 
(g) The Articulation Center, for the co-ordination of the muscles through 
whose activity articulate speech is produced. 
THE CEREBELLUM 
The Cerebellum rests in the inferior fossae of the occipital bone and lies 
immediately under the posterior lobes of the cerebrum from which it is separated 
by a fold of the dura mater called the tentorium cerebelli. It measures approxi- 
mately io cm. from side to side. The organ has been divided into hemis- 
pheres, one on each side, and a central lobe called the vermis. The 
surface is divided into numerous bands or leaves by transverse fissures. Each 
hemisphere is connected with the cerebrum by the superior peduncle-, with the 
pons by the middle peduncle; and with the medulla by the inferior peduncle. 
On section the organ is seen to consist of gray matter externally and of white 
matter internally; masses of gray matter are also found embedded in the white 
matter (Fig. 60). 
The Gray Matter.-A microscopic study of one of the leaves of the cerebel- 
lum shows that the nerve cells in the gray matter are arranged in two layers, 
viz., an external or molecular layer, and an internal or granular layer. Between 
these there is a single layer of large cells called the cells of Purkinje. These 
cells, which are characteristic of the cerebellum, give rise to axons that pass 
into the white matter and terminate around the nerve cells in the masses of 
gray matter found in the interior of the organ (Fig. 61). 
The White Matter.--The nerve fibers composing the white matter are 
associative, afferent, and efferent in function. 
The Association Fibers are the axons arising from the cells of the molecular 
and granular layers; they serve to associate more or less distant parts of the 78 
THE BRAIN OR ENCEPHALON 
cerebellar cortex with each other, and thus provide a co-ordinating mechanism 
through which reflexes of great complexity may occur. 
-Stria medullaris thalamj 
-Third ventricle 
-Column of fornix 
-Anterior commissure 
-Lamina terminalis 
Massa intermedia- 
Thaiamus- 
Pinael body (Epiphysis) 
Corpora quadrigemina. 
Declive 
Cerebral peduncle 
Tuber cinereum 
Recessus infun- 
dibuli 
Hypophysis (pit- 
uitary body) 
Corpus 
medul- 
lare ■ 
Folium of- 
vermis 
Tuber of 
vermis 
■Aquaeductus cerebri (Sylvii) 
Pons 
-Fourth ventricle 
-Tela chorioidea of fourth ventricle 
Medulla oblongata 
Uvula of 
vermis 
Pyramid- 
of vermis 
Fig. 60.-Median section through cerebellum and brain-stem. I, culmen monticuli; 2, superior 
semilunar lobe; 3, inferior semilunar lobe; 4, slender lobe; 5, biventral lobe; 6, tonsil. (Allen Thomp- 
son after Reichert in Morris' Anatomy.) 
Fig. 6i.-Histology of the cerebellum. (From Ob er Steiner.) 
The Afferent Fibers convey nerve impulses coming from different portions 
of the periphery into the organ. Some of these nerve impulses come also from ESSENTIALS OF PHYSIOLOGY 
79 
higher centers and pass into the organ by way of the superior and middle 
peduncles. Other afferent nerve impulses come from the muscles and from the 
vestibular portion of the internal ear, as well as from the semicircular canals. 
These pass into the organ by way of the inferior peduncle. 
The Efferent Fibers issuing from the cerebellum do not originate in the 
cells of the cortex, but in the nuclear masses of the hemispheres. Some of these 
fibers pass by way of the superior peduncle to the red nucleus of the mid-brain 
from which, as already stated, a tract of fibers-the rubrospinal tract-descends 
to the various levels of the spinal cord. Other efferent fibers pass by way of 
the middle peduncle to the nuclei of the pons; while others pass into the inferior 
peduncle to the vestibular nuclei and medulla oblongata. From these nuclei 
various connections are made with higher centers as well as with the spinal cord. 
Function of the Cerebellum.-The function of the cerebellum has been 
deduced from experiments in which various parts of the organ were removed 
and from the study of the effects of destructive disease on the various parts 
of the organ. Following the removal of parts of the organ certain phenomena 
follow which have been grouped into three stages. 
The first stage consists of a number of symptoms explainable on the basis of 
the irritation due to the operation. After a few days these symptoms undergo a 
change and new phenomena appear which indicate the loss of function of the part 
removed. Finally, after a certain time, the animal recovers a part at least of 
the loss of function, this recovery being due apparently to the action of other 
nerve centers which compensate for the loss of cerebellar function. 
The loss of cerebellar function is best illustrated by removing one half 
of the organ. The immediate effects of the operation in the case of mammals is 
to cause various forced and abnormal movements so that the animal is unable to 
stand or walk. If it attempts to do so, it falls toward the injured side. After a 
number of days the animal exhibits the symptoms indicative of loss of function. 
These have been named atonia, astasia, ataxia or asynergia, and asthenia. 
These symptoms are exhibited on the side of the lesion. 
By the term atonia is understood a decrease in the tone of the muscles. 
The muscles lack the firmness they have on the normal side. The muscular 
contractions instead of being smooth and steady, are irregular and unsteady so 
that voluntary movements requiring a certain effort are accompanied by a more 
or less coarse tremor; this is the condition named astasia. There is also a con- 
siderable disturbance in the co-ordination of muscular movements necessary for 
the accomplishment of a definite act. The hand misses its object and the gait is 
staggering. This lack of muscular co-ordination is named asynergia or ataxia. 
Finally, the muscles on the operated side are weaker than on the normal side, 
the condition called asthenia. 
The function of the cerebellum is therefore to maintain the tone of the 
muscles; to regulate the frequency of discharge of the nerve impulses going to 
the muscles so as to insure a smooth and steady contraction; to co-ordinate the 
distribution of nerve impulses so that intended movements will accomplish their 
object; and finally, to reinforce the nerve impulses going to the muscles. 80 
THE BRAIN OR ENCEPHALON 
The recovery that occurs with time, has been shown experimentally to be 
due to the compensatory activity of the opposite cerebral hemisphere. 
The cerebrum constitutes about 85 per cent of the total weight of the ence- 
phalon. It is ovate in shape, and is partly divided by a deep cleft, called the 
THE CEREBRUM 
Fig. 62.-Fissures and gyri on the lateral surface of the left hemi-cerebrum. F, fissure; G, gyrus 
R, ramus. (Spilzka.) 
Fig. 63.-Fissures and gyri of the mesial surface of the left hemi-cerebrum. (Spitzka.) 
great longitudinal fissure, into two masses termed hemispheres. The hemi- 
spheres are joined to each other by a broad band of white matter known as the 
corpus callosum. The surface of each hemisphere is thrown into numerous folds. 
The grooves produced by the infolding of the surface are called fissures or 
sulci, while the exposed surface between the fissures constitutes the convolutions 
or gyri (see Figs. 62 and 63). ESSENTIALS OF PHYSIOLOGY 
81 
The chief fissures are: 
(i) The Fissure of Sylvius which begins at the front and basal portion of the 
cerebrum and extends upward and backward. 
(2) The central Fissure or Fissure of Rolando. It begins near the median 
line, posterior to the center of the great longitudinal fissure and runs forward and 
downward toward the Fissure of Sylvius. 
(3) The Parieto-occipital Fissure, seen on the mesial surface of the hemi- 
sphere, begins as a deep notch on the external surface of the hemisphere and runs 
downward and forward to join another fissure called the Calcarine Fissure. 
(4) The Para-central Fissure, seen also on the mesial surface begins at the 
upper border of the hemisphere back of the central fissure, runs downward and 
forward, and finally upward. 
Numerous other fissures are seen, some of which are constantly present and 
form the boundaries of definite convolutions. 
Fissures 
Convolutions 
The general surface of the hemispheres has been divided, for the sake of 
convenience, into lobes, viz., the frontal, parietal, temporo-sphenoidal, and 
occipital lobes. Each of these lobes contains a number of convolutions as 
follows: 
The frontal lobe is bounded posteriorly by the central fissure, and inferiorly 
by the fissure of Sylvius. It contains four convolutions: the precentral, 
superior frontal, middle frontal, and inferior frontal convolutions. 
The parietal lobe is delimited by the central fissure in front, the parieto- 
occipital fissure behind, and the fissure of Sylvius below. It contains the follow- 
ing convolutions: the posterior central, superior parietal, marginal, and angular 
convolutions. 
The temporo-sphenoidal lobe consists of that portion of the hemisphere 
situated in front of an imaginary line drawn from the parieto-occipital fissure 
to the pre-occipital notch on the inferior border, and below the fissure of 
Sylvius. It contains a superior, middle and inferior temporal convolution. 
The occipital lobe is situated back of the temporo-sphenoidal lobe, and 
below the parietal lobe. It forms the posterior tip of the hemisphere, and con- 
tains a superior, middle, and inferior occipital convolution. 
The Island of Reil or Insula.-A number of convolutions are hidden from 
view by an overlapping of the portion of the hemisphere bordering on the fissure 
of Sylvius. These convolutions constitute the Insula or Island of Reil, and are 
a part of the adjoining lobes. 
The convolutions of the mesial surface are ascribed in part to the lobes 
already mentioned. The chief of these convolutions are the paracentral, 
callosal, hippocampal, inferior calcarine (gyrus lingualis), and inferior collateral. 
The wedge-shaped convolution on the mesial surface of the occipital lobe is 
called the cuneus; while the square-shaped convolution in front and above it 
is called the precuneus or quadrate lobule. 82 
THE BRAIN OR ENCEPHALON 
Structure of the Cerebrum.-The gray matter of the cerebrum forms its 
external layer or cortex. It varies in thickness from 1.25 to 4 millimeters, and 
contains four or five layers of nerve cells of different forms and sizes and prob- 
ably related to different functions (Fig. 64). The axons of these cells acquire 
in due time a medullary sheath, 
and contribute to the formation of 
the white matter which is located 
internally. 
Aside from the gray matter of 
the cortex, two masses of gray mat- 
ter are found in each hemisphere. 
These are called the caudate and 
lenticular nuclei. Important tracts 
of nerve fibers pass between these 
gray masses so that, on cross sec- 
tion, the entire area appears alter- 
nately white and gray or striated, 
hence the name of corpus striatum 
given to this region. Closely related 
to this region is another mass of 
gray matter belonging to the 'tween 
brain and called the thalamus. 
The white matter situated be- 
tween the lenticular nucleus, on the 
one hand, and the caudate nucleus 
and the thalamus, on the other 
hand, is called the internal capsule 
(Fig. 65). Its importance lies in 
the fact that it contains the pyra- 
midal tract of fibers on their way 
from the cortex to the lower centers, 
and the fibers carrying the sensor 
nerve impulses from the thalamus 
to the cortex. Destruction of the 
internal capsule, as by a cerebral 
hemorrhage, will therefore cause a 
paralysis and loss of sensation on 
the opposite side of the body. 
The thalamus, has, in recent years, been shown to be a center for rudimentary 
sensations. Thalamic sensibility differs from the sensibility evoked in the 
cortex of the cerebrum in that it does not enable the individual to recognize 
the different qualities of sensations. An individual deprived of the sensor 
parts of the cortex, becomes merely aware that stimuli have acted upon him, 
but is unable to determine the character of the sensations that similar stimuli 
applied to a normal individual would produce. 
Molecular 
layer. 
Layer of 
small 
pyramidal 
cells. 
Blood 
vessel. 
Layer of 
large 
pyramidal 
cells. 
Layer of 
polymor- 
phous 
nerve cells. 
Fig. ^64.-Vertical section of the cortex (central 
convolution) of an adult. (From Lewis and Stohr's 
Histology.') 83 
ESSENTIALS OF PHYSIOLOGY 
The white matter of the cerebral hemispheres has been classified into three 
systems of fibers: viz., the projection, the association, and the commissural. 
The projection system of fibers serves to connect different parts of the cortex 
with lower portions of the central nerve system; they are either afferent or 
efferent in function. 
Fig. 65.-Horizontal section through the cerebrum showing the natural relations of the various 
structures. (Brubaker.) 
The afferent portion of the projection fibers conveys the nerve impulses 
concerned with the production of sensations, as well as some fibers from the 
cerebellum. The sensor fibers come from the thalamus which is the final 
relay for the afferent impulses coming from the spinal cord and medulla. 
The fibers for the senses of hearing and vision also form a part of the afferent 
projection fibers. 84 
THE BRAIN OR ENCEPHALON 
The efferent portion of the projection fibers consist of the pyramidal fibers 
which take their origin in the large pyramidal or Betz cells of the pre-central 
convolution. They convey voluntary nerve impulses to various levels of the 
mid-brain, medulla and spinal cord. In addition to this important system of 
fibers, other fibers pass from the frontal, occipital, and temporal lobes to the 
nuclei of the pons around the cells of which they terminate. From these cells 
other fibers go to the cerebellum. These tracts are therefore called the fronto- 
cerebellar, and the occipito-temporo-cerebellar tracts. 
The association system of fibers consists of fibers running to neighboring 
as well as distant convolutions of the same hemisphere. There fibers are 
therefore classified as short and long association tracts. 
The commissural system of fibers connects the two hemispheres. The 
most important of these fibers are found in the corpus callosum. Other com- 
missural tracts are the anterior, the posterior and hippocampal commissures. 
FUNCTIONS OF THE CEREBRUM 
Comparative studies have shown that the intelligence displayed by differ- 
ent animals is related to the relative size and complexity of the cerebral 
hemispheres. The greater development of the hemispheres is accompanied 
by increased functional importance, which in turn is associated with a greater 
control over the lower portions of the central nerve system. This development 
finds its highest expression in the brain of man. The average brain weight 
in man is 1360 grams. An estimate of the average brain weight of ninety- 
six distinguished men was made by Spitzka, who found it to be 1473 grams. 
While distinguished mental ability has been usually associated with a large 
brain, instances have been recorded of great mental power associated with a 
brain of average weight. The character of the organization of the hemisphere 
must evidently be of the greatest importance in determining mental capacity. 
Experiments made on different species of animals have demonstrated the 
importance of the hemispheres as organs in which the impressions of past 
events are stored and associated with each other. An animal whose hemi- 
spheres are intact will respond to stimulation in accordance with its memory of 
previous experience. Responses, which on previous occassions have proved 
detrimental, are voluntarily prevented from taking place. The animal is 
therefore able to choose its course of action to befit the circumstances in the 
light of past events. The reactions of an intact animal cannot therefore be 
predicted with certainty, since these reactions will vary with the body of exper- 
ience the animal possesses. An animal whose hemispheres have been removed 
can have no memory, neither can it have any consciousness of its surroundings. 
The reactions exhibited by such an animal are not guided by the intelligence, but 
are merely more or less complex reflex acts. While the animal can move 
about and eat when food is placed in or near the mouth, it exhibits no emotion 
when threatened or caressed and remains at rest in a somnolent condition the 
greater part of the time. ESSENTIALS OF PHYSIOLOGY 
85 
LOCALIZATION OF FUNCTIONS IN THE CEREBRUM 
Animal experiments and the study of the effects of injury and disease of 
the cerebral cortex in man have established the fact that definite areas of the 
cortex are associated with definite functions. It has been shown that certain 
CONCRETE CONCEPT 
Fig. 66.-The areas and centers of the lateral aspect of the human hemicerebrum. (C. K. Mills.') 
Fig. 67.-The areas and centers, of the mesial aspect of the human hemicerebrum. (C. K. Mills.) 
areas are motor and other areas sensor in function. The remaining areas are 
association areas; they are concerned with the language faculty and with the 
higher mental concepts. 
The Motor Areas.-The motor area is located in the precentral convolu- 
tion. This general area is subdivided into smaller areas for the leg, trunk, arm, 
and face (see Figs. 66 and 67). The area for the head and eyes is located in 86 
THE BRAIN OR ENCEPHALON 
the middle and inferior frontal convolutions, immediately in front of the pre- 
central convolution. Each of these have, furthermore, been subdivided into 
still smaller areas for movements of the parts subserved by the larger area, 
such as the thumb, forearm, etc. 
Since these areas contain the nerve cells from which arise the fibers of the 
pyramidal tract, their destruction is followed by a paralysis of volitional move- 
ment on the opposite side of the body, with the exception of certain muscles 
that contract simultaneously with the corresponding muscles of the opposite 
side, as in the case of the respiratory muscles. This paralssis of one half of 
the body is called hemiplegia. Stimulation of any of these areas is followed by 
muscle movements on the opposite side of the body. These movements are 
the result of the co-ordinate contraction of groups of muscles, rather than of 
individual muscles, even when the stimulus is strictly localized. 
The motor area of the cerebral hemispheres is an area of representation for 
definite, and purposeful acts. The greater the variety and complexity of 
movements exhibited by a given region of the body, the larger must be the area 
of representation in the cortex. We find, therefore, that the area for the head and 
face, and the areas for the limbs, are relatively more extensive than the area for 
the trunk. 
The Sensor Areas.-The sensor areas are areas of the cortex in which 
sensations are aroused following the arrival of nerve impulses brought in from 
the periphery. The cortex contains areas for cutaneous sensibility, tempera- 
ture, and pain, the muscle sense, the visual, auditory, olfactory, and gustatory 
senses. 
The Cutaneous and Muscle Sense Areas.-The cutaneous area has been 
stimulated in conscious human beings. The sensations experienced were those 
of touch and numbness. The sensations were referred to different parts of the 
body on stimulation of different areas. Such experiments, together with 
clinical observations, have shown that the cortical representation for the head, 
limbs and trunk is found in the post-central convolution in the same order as the 
motor representation. These areas are concerned with the recognition of 
touch, tactile localization and tactile discrimination. As in the case of the motor 
representation, the area assigned to these various forms of sensibility varies in 
size in accordance with the complexity of the psychic act necessary for the 
recognition of the sensation. 
The areas for the muscle sense is located in the parietal convolutions, while 
that for heat, cold and pain is apparently more diffused, and has been assigned to 
the cortex posterior to the foot of the post-central convolution. 
These cortical areas are stimulated by the nerve impulses brought in from 
the thalamus, which is the last relay station for the impulses carried through the 
spinal cord by the spinothalamic tracts and the tracts of Goll and of Burdach. 
The Visual Area.-The visual area includes that portion of the cortex in 
which the fibers of the optic radiation terminate. These fibers come from nerve 
cells located in the thalamus and in the lateral geniculate body; these cells con- 
stitute a relay in the path of the nerve impulses coming from the retinae and ESSENTIALS OF PHYSIOLOGY 
87 
conveyed by the optic nerves and optic tract. The region of the cortex that 
receives the fibers of the optic radiation lies on the mesial side of the optic lobe, 
around the calcarine fissure. This region constitutes the primary visual area. 
The cuneus together with the occipital convolutions on the lateral aspect of the 
optic lobe constitute a secondary area connected with the primary area/ and 
other portions of the cortex by association fibers. 
In the lower vertebrates the visual area of one hemisphere is related entirely 
to the eye of the opposite side, so that the destruction of one visual area is fol- 
lowed by total blindness of the opposite 
eye. In the mammalia, on the other hand, 
some of the fibers coming from the retina 
of each eye remain on the same side. In 
man, a relatively large proportion of the 
fibers do not cross. Accordingly, destruc- 
tion of the visual area of one side causes 
partial blindness in both eyes. If the 
cortex of the occipital lobe of the right 
side should be destroyed, the retinae of 
both eyes would be blind in their right 
half, indicating, therefore, that about one 
half of the fibers of the optic nerve do not 
cross, and that the fibers that do cross 
are those related to the internal half of 
each retina (see Fig. 68). This half- 
blindness is called lateral homonymous 
hemianopsia. 
The Auditory Area.-The auditory 
area has been located in the superior tem- 
poral convolution and in some of the 
convolutions of the Island of ReiL It 
is in this portion of the cortex that the 
fibers of the auditory radiation terminate. 
The nerve impulses that evoke the sensa- 
tion of sound arise in the terminals of the 
cochlear division of the eighth cranial nerve, and are conducted to the med- 
ulla where they stimulate the cells of the acoustic nuclei. From these 
nuclei nerve impulses ascend the lateral fillet of both sides. These nerve im- 
pulses ultimately reach the internal geniculate body from which they are then 
conveyed by the fibers of the acoustic radiation to the temporal lobe. Since 
there is a partial crossing of the fibers, destruction of one auditory area does not 
result in complete deafness of the ear of the same side. Destruction of both 
of the auditory areas necessarily results in complete deafness. 
This area, as in the case of the visual area, is surrounded by a secondary 
auditory area located in the adjacent convolutions through the medium of which 
various psychic associations occur. 
Fig. 68.-Diagram of the principal components 
of the optic apparatus. (After Cunningham.) 88 
THE BRAIN OR ENCEPHALON 
The Olfactory and Gustatory Areas.-The cortical areas for smell and 
taste are imperfectly known. The area for smell has been assigned to the hippo- 
campal convolution, particularly to its more anterior portion, called the uncus. 
The nerve impulses arise in the terminals of the olfactory nerve in the olfactory 
region of the nasal mucous membrane. The nerve fibers conveying these nerve 
impulses pass through the cribriform plate of the ethmoid bone to reach the 
olfactory bulb around the cells of which they end. From the cells of the olfac- 
tory bulb fibers arise to form the olfactory tract. This tract sends its fibers to 
the hippocampal convolution of the same or the opposite side. 
The area for taste has been located posterior to the area for smell and also 
below it, in the collateral convolution. The nerve impulses arise in the terminals 
of the chorda tympani nerve, supplying the anterior two-thirds, and of the 
glosso-pharyngeal nerve supplying the posterior third, of the tongue. These 
nerves conduct their nerve impulses to nerve cells located in the pons, whence 
other nerve fibers convey them to the gustatory area. 
The Association Areas.-The motor and sensor areas form but a part of the 
cerebral cortex. There remains a considerable cortical surface, stimulation of 
which is not followed by any motor response. Disease of these areas is accom- 
panied, however, by various mental disturbances. They constitute, therefore, 
the physical basis of the individual's mentality. 
There are three regions containing association areas: the anterior or frontal, 
the middle or Island of Reil, and the posterior or parieto-temporal region. The 
frontal association area is concerned mostly with the personality of the individual. 
An atrophy of the nerve cells of this region has been found in cases of dementia. 
The middle and posterior association areas, being related to the auditory, visual, 
and tactile sense areas, are the regions in which the memories of past impressions 
of the external world are stored. These areas are also concerned with the per- 
ception of language, both spoken and written. The association centers for the 
volitional acts necessary to speak or write are situated in front of the general 
motor area in the left cerebral hemisphere only. Destruction of these areas, 
or rather of the association tracts connecting these areas with each other, 
results in a loss of the power to understand and reproduce language. This con- 
dition is called aphasia. Since the acquisition of language is of the greatest 
importance in the development of the intellect, aphasia is accompanied by more 
or less mental deterioration. 
The Cranial Nerves.-The brain gives rise to twelve pairs of nerves, which, 
since they pass through openings in the cranium, are called cranial nerves 
(Fig. 69). Their orign, distribution, and function may be briefly stated as 
follows: 
(1) The First Pair, or Olfactory Nerve arises in the nerve cells found in the 
olfactory area of the nasal mucous membrane. The course of its fibers has been 
traced in the foregoing discussion of the cortical area for the sense of smell. 
Its function is to mediate the sense of smell. 
(2) The Second Pair, or Optic Nerve takes its origin in nerve cells found in 
the retina. The fibers have been traced in the paragraph dealing with the ESSENTIALS OF PHYSIOLOGY 
89 
visual area of the cerebral cortex. It carries nerve impulses which, on reaching 
this area, evoke the sensation of fight and color. 
(3) The Third Pair, or Oculo-motor Nerve arises in the nerve cells of a 
nucleus located in the mid-brain under the floor of the Aqueduct of Sylvius. 
It is distributed to the superior, inferior, and internal recti muscles and to the 
inferior oblique muscle of the eyeball. It likewise sends fibers to the sphincter 
Insula 
Olfactory tract 
Hypophysis 
Anterior perforated 
substances | 
Optic tract 
"N. opticus (II) 
Corpora mammillaria 
• Tuber cinereum 
Cerebral peduncle 
N. oculomotorius 
(HI) 
Lateral geniculate 
body 
Ganglion semi- 
lunar e (Gasseri) 
N. trochlearis (IV) 
"N. masticatorius 
' N. trigeminus (V) 
N abducens (VI) 
■ Brachium pontis 
N. facialis (VII) 
Oblique fasciculus 
N. glossopalatinus 
N. cochlearis and N. 
vestibularis (VIII) 
N. glosso-pharyngeus (IX) 
N. vagus (X) 
N. accessorius (XI) 
(spinal accessory) 
N. hypoglossus (XII 
' Cervical I 
_ Cervical II 
Pyramid7 
Fig. 69.-Surface attachment of the cranial nerves. (After Allen Thomson modified.') 
Decussation of pyramids' 
muscle of the iris and to the ciliary muscle. It is, therefore, entirely motor 
in function. 
(4) The Fourth Pair, or Trochlear Nerve takes its origin from a nucleus 
situated posterior to that of the oculo-motor nerve. Its fibers supply the 
superior oblique muscle of the eyeball. 
(5) The Fifth Pair, or Trigeminal Nerve contains both afferent and efferent 
neurons. The nerve cells from which the afferent fibers arise are located in the 
Gasserian or semilunar ganglion which rests on the apex of the petrous portion 90 
THE BRAIN OR ENCEPHALON 
of the temporal bone. The fibers distributed peripherally are found in three 
large branches called the ophthalmic, superior maxillary, and inferior maxillary 
branches. 
The ophthalmic branch is distributed to the skin of the forehead and nose, 
to the mucous membrane of the nose, to the conjunctiva and skin of the upper 
eyelid, to the cornea, and to the lachrymal gland. 
The superior maxillary branch is distributed to the nose, the cheek and upper 
lip, to the palate, to the teeth of the upper jaw and to the alveolar processes. 
It likewise sends fibers to the skin and conjunctiva of the lower eyelid. 
The inferior maxillary branch is distributed to the side of the head, the 
external auditory meatus, the anterior portion of the tongue, the mucous 
membrane of the mouth, and the arches of the palate, the teeth and alveolar 
processes of the lower jaw, and the skin of the lower part of the face. 
The function of these branches is to endow the parts to which they are 
distributed with sensation. 
The efferent fibers originate in nerve cells found in the medulla under the 
floor of the fourth ventricle. The fibers leave the cranium with the inferior 
maxillary branch, and constitue the motor root of the trigeminal nerve. The 
fibers are distributed to the muscles of mastication, as well as to the tensor 
muscle of the palate and the tensor muscle of the ear-drum. 
(6) The sixth Pair, or Abducens Nerve takes its origin in nerve cells under 
the floor of the fourth ventricle. The fibers are distributed to the external 
rectus muscle of the eyeball. It is, therefore, a motor nerve. 
(7) The Seventh Pair, or Facial Nerve arises similarly in nerve cells found 
under the floor of the fourth ventricle. The fibers are distributed to the super- 
ficial muscles of the face and head. It also gives off branches, stimulation of 
which, causes a dilatation of the blood vessels supplying the submaxillary 
and sublingual glands, as well as a discharge of secretion from these glands. 
One of these branches contains afferent fibers that endow the anterior two- 
thirds of the tongue with the sense of taste. 
(8) The Eighth Pair, or Auditory Nerve consists of two portions: viz., a 
cochlear or acoustic, and a vestibular or equilibratory. The fibers of the cochlear 
portion arise in the nerve cells of the spiral- ganglion situated in the internal 
ear, within the cochlea. The peripheral distribution is, to the organ of Corti 
which is a part of the peripheral mechanism for the reception of sound. The 
central connections of this nerve are given in the discussion of the auditory 
area of the cerebral cortex. 
The vestibular portion takes its origin in the internal ear, from the nerve 
cells of the ganglion of Scarpa. Its peripheral distribution is to the utricle, 
saccule, and semicircular canals. The connections of this portion of the eighth 
nerve to the central nerve system is primarily to the nucleus of Bechterew and 
to the nucleus of Deiters of the medulla. 
(9) The Ninth Pair, or Glossopharyngeal Nerve contains both afferent and 
efferent nerve fibers. The afferent fibers taken their origin in ganglia seen on 
the trunk of the nerve. The fibers are distributed to the posterior third of ESSENTIALS OF PHYSIOLOGY 
91 
the tongue, which they endow with the sense of taste, and to the pharynx, 
soft palate, uvula, and tonsils which mediate ordinary sensation. 
The efferent fibers originate in nerve cells of the medulla beneath the floor 
of the fourth ventricle. They innervate the stylo-pharyngeus and the middle 
constrictor muscles of the pharynx. The glosso-pharyngeal nerve also contains 
fibers which supply the parotid gland and its blood vessels. 
(io) The Tenth Pair, Vagus or Pneumogastric Nerve is likewise a mixed 
nerve containing both afferent and efferent fibers. The afferent fibers take 
their origin from nerve cells in the ganglia on the trunk of the nerve. The 
peripheral distribution of these fibers is very extensive; namely: to the mucous 
membrane of the esophagus, larynx, lungs, stomach, and intestines, as well 
as to the heart and root of the aorta. 
The efferent fibers originate in the medulla in nerve cells located below 
the floor of the fourth ventricle. The efferent fibers are distributed to the 
muscles of the pharynx, the elevator muscle of the palate, the muscle coat 
of the esophagus, to most muscles of the larynx, to the heart, to the muscle 
coat of the bronchial tubes, and to the stomach, intestines, and gall-bladder. 
Other abdominal organs are probably supplied by this nerve also. The 
functions of this nerve will be considered in connection with the functions of 
the organs it innervates. 
(n) The Eleventh Pair, or Spinal Accessory Nerve arises partly from the 
medulla and partly from the spinal cord. Its fibers are distributed to certain 
muscles of the shoulder: viz., the sterno-cleido-mastoid and the trapezius 
muscles. 
(12) The Twelfth Pair, or Hypoglossal Nerve takes its origin from the medul- 
la in nerve cells located beneath the floor of the fourth ventricle. Its fibers 
are distributed to the muscles of the tongue and to muscles that elevate and 
depress the hyoid bone. CHAPTER XI 
PHARMACODYNAMICS OF THE CENTRAL NERVE SYSTEM 
Experimentation has shown that drugs and poisons may cause stimulation 
or depression of nerve structures. This statement must not be construed to 
indicate that there are only two classes of drugs which act on the central 
nerve system, one of which increases while the other depresses the activity of 
the entire central nerve system. Different parts of the central nerve system 
may manifest different susceptibilities to a given drug; and various drugs, 
even though they may be looked upon as affecting only the central nerve 
system, differ much in their actions because of differences in the order of 
development of their effects on various functions. Hence, a great variety 
of effects may be produced in the central nerve system through the agency of 
drugs and poisons. 
The susceptibility of a certain portion of the central nerve system to the 
action of a given drug may be so much more pronounced than those of all other 
parts, that from a practical viewpoint the effects on that one portion only need 
be considered in therapeutics. Thus, in doses of from % to X2 of a grain 
Apomorphine Hydrochloride acts directly on the vomiting center in the medulla 
oblongata and has practically no pronounced effects on the other parts of the 
central nerve system. Further, certain drugs in given dosage may stimulate 
certain centers to increased activity, and depress other centers. For instance, 
in poisoning by Camphor the symptoms may vary from those of moderately 
increased intellectual and motor activity to great excitement, delirium, convul- 
sions, and even coma. Some poisons which first stimulate certain centers later 
cause depression of the same centers. A striking example of this is Hydro- 
cyanic Acid which causes a primary stimulation of the vagus, the vasomotor and 
the respiratory centers, followed by marked depression of the same centers. 
The drugs discussed in this chapter are divided for convenience into two 
groups: (I) Drugs which stimulate portions of the central nerve system, (II) 
Drugs which depress portions of the central nerve system. 
(I) Drugs which stimulate portions of the central nerve system. 
Caffeine, the principal alkaloid of tea, coffee, kola, guar ana, mate, etc., 
produces a general increase in the activity of nerve cells, but particularly those 
of the cerebrum. A large medicinal dose of Caffeine actually produces stimu- 
lation of the intellectual functions, especially the highest ones, i. e., reason, judg- 
ment, will and self-control. There results a greater alertness, keener attention, 
more acute perceptions, and brightened spirits. The drug is thus capable of 
changing a sleepy, inattentive state to a bright, awakeful, active condition. 
Although, following a medicinal dose of Caffeine, there is evidence of increased 
mental ability, as in calculations, a keener and more accurate sense of touch, an 
92 PHARMACODYNAMICS 
93 
increased appreciation of pain, etc., there may be evidence of retarded trans- 
mission of thought into action because of the intervention of judgment, reason 
and self-control. Caffeine also stimulates the motor areas as evidenced by greater 
activity of voluntary motion. Over-dosage produces excessive excitability, 
inability to concentrate, and restlessness. 
Certain structures of the medulla oblongata are also stimulated by 
Caffeine. Although the respiratory center is the structure in this portion of the 
central nerve system most affected, the vagus and the vasomotor centers are also 
mildly stimulated. As a result respiration may be increased both in depth and 
frequency, and occasionally in man there may be a slight slowing of the pulse 
and a moderate rise in the blood pressure. 
By facilitating the passage of nerve impulses through the spinal cord and stimu- 
lating its motor cells, Caffeine increases reflex irritability and tends to improve 
muscle tone. Marked poisoning may, therefore, be characterized by heightened 
reflexes and convulsions. The effects of Caffeine on the spinal cord are similar 
to but much less pronounced than those of Strychnine. 
Caffeine is useful as a central stimulant in depressed mental states, in 
physical weariness, in nervous exhaustion, in convalescence from acute illnesses 
such as influenza; to counteract the cerebral, spinal and respiratory depression 
and loss of muscle tone produced in poisoning by narcotics, such as Alcohol and 
Morphine; and to stimulate respiration in pulmonary edema and respiratory 
depression. 
Strychnine, the most important alkaloid of Nux Vomica, acts on the same 
portions of the central nerve system affected by Caffeine, but the relative 
intensity of its actions on the several structures affected differs. The 
dominant action of Caffeine on the central nerve system is its effect on the 
cerebrum; whereas, the most pronounced action of Strychnine is on the 
spinal cord. 
Although Strychnine stimulates slightly the intellectual functions and the 
motor areas in a manner similar to Caffeine, it is much less pronounced so that 
the drug is not a marked intellectual stimulant and is decidedly less powerful in 
overcoming drowsiness and opposing sleep. The perceptions are stimulated so 
that smell, taste, touch, and hearing are more acute and discriminating, and 
there is an increased susceptibility to pain. 
The respiratory and the vasomotor centers in the medulla oblongata show some 
slight increased excitability following a medicinal dose of Strychnine. Poison- 
ous doses produce very marked effects, followed by depression with final para- 
lysis of these centers. Because of these feeble effects on medullary centers 
Strychnine can only be used as a temporary or emergency remedy in fainting, 
poisoning by such depressant drugs as Chloral Hydrate, Alcohol, Ether, Chloro- 
form, etc., and in markedly depressed conditions of the respiration, as in tuber- 
culosis and pneumonia. 
As already stated, Strychnine produces its most marked effect on the spinal 
cord. If an animal is poisoned with Strychnine, a very slight stimulus, such as a 
touch, will send the animal into convulsions which affect all the voluntary muscles 94 
PHARMACODYNAMICS OF THE CENTRAL NERVE SYSTEM 
of the body, including the diaphragm. The movements are at first rapidly 
intermittent, but soon become tonic resulting in tetanus. Since all the muscles 
are contracted the convulsions are symmetrical, and the stronger muscles of 
opposing sets predominate, which in most locations are the extensors. Accord- 
ingly the body of the animal is arched backward (opisthotonus); the jaws are 
fixed; and, in man, the strong contractions of the face muscles produce a hideous 
grin, called "risus sardonicus." Since the respiratory muscles are involved, 
respiration is arrested and the blood becomes rapidly deoxygenated. In man, 
the skin and lips consequently are blue (cyanosis). Death takes place from 
asphyxia, due either to the continuous spasms of the respiratory muscles, or to 
exhaustion of the respiratory center. 
Experimentation has proved that convulsions in an animal poisoned by 
Strychnine only follow the passage of an impulse from without to the spinal 
cord, and do not occur spontaneously if all sensory impressions are prevented 
from reaching the cord. They are therefore reflex in nature, and are due to the 
greatly increased reflex excitability of the spinal cord. In an unpoisoned 
animal the reflex movement following a given stimulus is always of the same 
kind and is apparently purposeful and definite. Thus, if a leg of a decapitated 
frog is dipped in an acid, it withdraws the leg and attempts to wipeAhe irritating 
substance away with the other leg, by movements involving the contraction of 
certain muscles and the relaxation of their antagonists, i. e., coordination. 
In a frog poisoned with Strychnine a similar experiment not only results in 
stronger and more extensive muscular movements of the legs, but also of all the 
muscles of the body, so that they contract together, there being in the cases 
of opposing sets of muscles no relaxation of antagonists. Thus, the foot which 
was immersed in the acid is extended and thrust against the irritating substance 
instead of being withdrawn from it, i. e., incoordination. 
Experimental data, although not entirely conclusive, indicate that Strych- 
nine affects the nerve cells of both motor and sensory tracts in the spinal 
cord. In an unpoisoned frog an afferent impulse travelling up a nerve 
reaches the cord, and may there pass through a number of paths in each of 
which it is subjected to various resistances, so that different degrees of activity 
may be aroused in different motor cells, or the inhibition of the activity of some 
of them may even occur. Coordinated movement in this way takes place. 
Following a dose of Strychnine the varying resistances disappear, and the 
afferent impulse passes unretarded not only along the paths normally open 
to it but in addition along all available paths. It therefore reaches not only 
a greater number of motor cells but also reaches them in greater force than 
normally, and thus excites a stronger response and a correspondingly more 
powerful muscular contraction. Since the resistance in the different paths is 
essential to the coordination of movements, the muscular contractions following 
a poisonous dose of Strychnine are no longer coordinated and all the muscles 
contract together, the character of the movement being determined by the 
relative strengths of the muscles involved. The action of Strychnine may 
accordingly be explained by supposing that it removes the resistances to the PHARMACODYNAMICS 
95 
passages of afferent impulses through the spinal cord, thus increasing the area 
affected by an afferent impulse and also freeing it from the normal coordinating 
control. 
Since, in therapeutics, it would be undesirable to have an afferent impulse 
affect cells other than the ones usually acted upon, the therapeutic use of 
Strychnine on the spinal cord would be to open up the normal paths in the cord 
when they become depressed, and thus enable an afferent impulse to more 
readily and easily reach the usual motor cell affected. 
The tone of muscles being dependent upon the arrival of nerve impulses 
sent out from the spinal cord, it is evident from the foregoing that Strychnine 
heightens muscle tone by increasing reflex excitability. Most of the therapeutic 
value of Strychnine depends on this property and the drug may be correctly 
called a "tonic." It is useful in debility, convalescence, and atonic conditions of 
organs like the stomach, intestines, uterus, etc. 
In treating poison by Strychnine, beside the use of chemical antidotes, 
such as Tannic Acid and Potassium Permanganate, to precipitate or oxidize 
it, the first aim is to prevent or to lessen the intensity of the convulsions. This 
may be accomplished by quieting the hyperexcitable centers with spinal cord 
depressants or sedatives, such as Ether, Chloroform, Bromides and Chloral 
Hydrate, and by keeping the patient in a darkened, absolutely quiet room 
free from even draughts of air. Artificial respiration and inhalation of oxygen 
are useful in counteracting the effects of the drug on respiration. 
II. Drugs Which DepressPortions of the Central Nerve System.-Drugs 
which depress the central nerve system regularly depress the cerebrum. Since 
consciousness is a function of the cerebral cortex, such drugs are generally 
called narcotics. A narcotic may therefore be defined as a remedy which pro- 
duces a depressed state of consciousness, i. e., narcosis. Although the degree 
of narcosis varies directly with the amount of the narcotic given, the rapidity 
of the onset of narcosis varies greatly with the different members of the group. 
Slight narcosis is evidenced by a tendency to be quiet, while greater degrees 
are shown by a succession of drowsiness, then sleep, stupor, and finally loss 
of consciousness or coma- Stupor is a state of unconsciousness or semiconscious- 
ness from which an individual may be aroused with more or less difficulty. 
Coma is a state of unconsciousness from which the individual cannot be aroused. 
The narcotics may be conveniently grouped into: (a) the general anesthetics; 
(fl) the intoxicants; (c) the hypnotics, or somnifacients; (fl) the analgesics or 
anodynes; (e) the antihysterics. 
(a) The general anesthetics are narcotics which abolish the functions of 
the cerebrum and also those of the spinal cord, while the respiratory center 
in the medulla oblongata is still able to functionate satisfactorily (unless the 
drug is given in overdosage), and the circulation remains comparatively 
unaffected. As a result of these actions, the general anesthetics abolish pain, 
produce unconsciousness, and more or less completely relax the muscles. They are 
therefore extremely valuable for producing anesthesia for surgical operations, to 
set fractures, to reduce dislocations and hernias, to check convulsions, and in 96 
PHARMACODYNAMICS OF THE CENTRAL NERVE SYSTEM 
labor, at the time of the expulsion of the head of the fetus, to stop pain and to 
lessen or abolish the uterine contractions. 
Since the margin between coma and death is not very wide, it is extremely 
important that the dosage of a general anesthetic be controlled quickly and 
accurately. Furthermore, to be useful as a general anesthetic a drug must be 
absorbed very rapidly, must act quickly in inducing narcosis, must be eliminated 
very rapidly, and must produce rather complete muscular relaxation, without 
producing any dangerous depression of the vital medullary centers or permanent 
effects on the central nerve system or other structures. 
Inasmuch as the members of the group are highly volatile and their vapors 
are rapidly absorbed and eliminated largely by the lungs, their administration 
by inhalation is preferred. For the same reason the dosage is more easily con- 
trolled, and anesthesia is more rapidly produced and may be continued for a con- 
siderable period of time. However, sufficient dosage by mouth, rectum, or 
intravenously will likewise produce anesthesia. 
Ether, Chloroform, and Nitrous Oxide are the most important general 
anesthetics. They are usually administered by inhalation, being dropped on 
some sort of inhaler (a cloth held over the nose and mouth by a suitable frame 
or mask), as with Ether and Chloroform, or given by means of a specially 
devised breathing mask, as in the case of Nitrous Oxide. Since Ether and 
Chloroform are more or less irritating locally, their vapors are diluted with air or 
oxygen to avoid dangerous irritation of the respiratory passages, as well as to 
avoid asphyxia. Although Nitrous Oxide has no local action, it too must be 
diluted with oxygen or air because it does not maintain life, and if used pure 
quickly produces asphyxia. 
Ether.-When ether vapor is inhaled it passes rapidly into the blood by 
diffusion and is distributed throughout the body. The anesthetic immediately 
begins to leave the blood for the tissues and, because of apparent special 
affinity for central nerve structures, is taken up especially by the central nerve 
system where it accumulates. After an ether death more of the drug is found in 
the brain than in any other organ. These facts are probably accounted for by 
the greater amount of lipoid substances found in the central nerve system which 
dissolve the Ether and retain it. The flow of ether vapor from the lungs to the 
blood and thence to the tissues continues until the vapor tension is the same in 
each, and the amount of drug in the brain is therefore determined by the 
amount in the blood, which in turn depends on that in the alveoli of the lungs. 
If inhalation of ether vapor is stopped, the tension in the lungs falls and a back- 
ward flow from the brain into the blood and from the blood into the expired air 
results. 
In ether poisoning there is a progressive depression of the central nerve 
system. The higher cerebral functions, such as self-control, reason and judg- 
ment, are the first ones to succumb and as a result the emotions are liberated 
from normal control. Then the emotions, the perceptions, the motor functions, 
and coordination by the cerebellum are depressed, and there is abolition of the 
spinal reflexes. Ultimately the vital centers of the medulla oblongata are PHARMACODYNAMICS 
97 
depressed. Since the sensory centers are affected before the motor, complete 
insensitiveness to surroundings and to pain precedes complete muscular relaxa- 
tion. There is also some depression of the sensory nerve endings. From the 
foregoing it is evident that the effects of Ether on the brain and spinal cord are 
directly antogonistic to those of Caffeine and Strychnine. 
When sufficient Ether is administered to produce a state of coma, with com- 
plete muscular relaxation and the abolition of nearly all reflexes, the condition 
known as complete general or surgical anesthesia is produced. For convenience 
Ether anesthesia is divided into four stages: 
(i) The first stage is characterized by local irritation of the nose, throat, 
and bronchi, producing a choking sensation and an increased flow of mucus 
and saliva, followed by numbness of the lips, nose and throat, ringing in the ears, 
and blunted perceptions. The individual is in a drowsy resigned state but can 
answer questions and may talk. The skin becomes warm and flushed from 
dilatation of the cutaneous arterioles; the pupils are dilated from excitement 
or from irritation of the nose and throat; the heart is rapid; and the blood 
pressure is raised from reflex stimulation of the accelerator and vasoconstrictor 
centers; the respiration is also reflexly stimulated. However, because of the 
irritation of the respiratory tract and the tendency to cough, there is some resis- 
tance to breathing and the respiration may therefore be irregular. 
(2) The second stage is characterized by intoxication or numbness similar to 
that produced by Alcohol. The highest cerebral centers are depressed. As a 
result the emotional and lower animal tendencies are more or less freed from 
normal control, and the patient may sing, shout, rave, or swear. Although the 
perceptions are dulled there is still some sensitiveness to pain. The skin is 
flushed, the pupils dilated and sensitive to light (contract), the heart continues 
rapid, and the blood pressure may be raised. 
(3) The third stage is one of stupor. The pupils contract as in sleep and react 
readily to light, the heart is strong, regular and, although faster than normal, is 
slower than before. The color of the skin is good, and respiration is regular and 
deep. The patient is still sensitive to pain. 
(4) The fourth stage is that of coma, i. e., great muscular relaxation and com- 
plete unconsciousness from which the patient cannot be aroused. Most of the 
voluntary muscles are relaxed, so that an arm or leg raised in the air falls limp. 
The respiratory muscles are not paralyzed. The skin continues flushed and hot, 
and is covered with sweat. Saliva and mucus are abundant. The heart, 
though moderately fast, is regular and strong, and arterial pressure is good. 
Respiration is regular and there may be snoring. (The tongue or the collection of 
the abundant mucus and saliva may impede respiration.) The temperature 
falls, and therefore the patient should be well covered. The pupils are in a 
state of mid-dilatation and react very slowly to light, and the eye reflexes disap- 
pear. All sensation and nearly all reflexes are abolished. This state of com- 
plete general or surgical anesthesia may be continued for a considerable period of 
time if the anesthetic is properly administered. It is recognized when a raised 
arm falls limp (complete relaxation) and by the absence of the eye reflexes. 98 
PHARMACODYNAMICS OF THE CENTRAL NERVE SYSTEM 
If the patient is permitted to go beyond the fourth stage, the pupils 
dilate and do not react to light, the cardiac muscle and the vasoconstrictor 
and respiratory centers are depressed, and the patient passes into a state 
of collapse. 
In recovery from anesthesia the third and second stages may be passed 
through rather slowly. The rapidity of recovery is inverse to the duration 
and manner of the administration. After the withdrawal of the drug, the 
respiration becomes quieter, the eye reflexes reappear, the pupils usually grow 
smaller and dilate readily. There is usually a tendency to remain asleep 
until awakened by nausea, vomiting or coughing. If this occurs it is generally 
followed by sleep lasting several hours. Vomiting, thirst, and distention of 
the stomach and intestines with gas are usual after-effects. 
Chloroform.-The effects of Chloroform on the central nerve system are 
practically those of Ether. However, the cerebral and spinal depression not 
only takes place more rapidly but from a much smaller amount of the drug. 
Thus, while io to 15 minutes may be required to anesthetize a patient with 
Ether, from 2 to 5 minutes are usually required with Chloroform. The amount 
of Ether required is calculated in ounces, while Chloroform is measured in 
drams. In addition to the rapidity of action and smaller dosage chloroform 
is decidedly less irritating locally (when properly diluted), is not inflammable 
or explosive, and is more quickly recovered from. However, in spite of these 
apparent advantages, Chloroform is more dangerous than Ether because it is 
decidedly more depressing to cardiac and arterial muscles and to the vital 
medullary centers, as well as more irritating to the kidneys. Therefore the 
margin of safety between surgical anesthesia and collapse is much smaller with 
Chloroform and restoration of the patient is more difficult after signs of danger 
are manifest. Accordingly Ether is generally preferred. However, when a 
very quick and very transitory effect is desired, as in obsterics and dentistry, 
Chloroform is commonly used. 
The treatment of Ether and Chloroform accidents consists chiefly in artificial 
respiration and the administration of oxygen, artificial heat, hypodermatic 
injections of Atropine (to prevent reflex stoppage of the heart), Caffeine or 
Camphor, intravenous infusion of physiological saline solution containing 
some Epinephrine or Pituitary Extract, and mechanical measures for increasing 
the arterial pressure. 
Nitrous Oxide or Laughing Gas.-After absorption by the lungs Nitrous 
Oxide exists as a simple solution in the blood plasma. It is a distinct narcotic 
and very rapidly produces complete unconsciousness. However, muscular 
relaxation is not complete. When used pure, asphyxia is rapidly produced. 
Therefore, the gas is administered diluted with oxygen. When air is used as 
the diluent, there is always some degree of asphyxia. Although Nitrous- 
Oxide-Oxygen (" Gas-Oxygen") anesthesia is very rapidly induced and recovery 
from it is almost immediate, great skill is required to keep the patient in a 
uniform state of anesthesia of sufficient degree without asphyxia. It is espe- 
cially useful in operations of short duration and in obstetrics and dentistry, PHARMACODYNAMICS 
99 
and is also commonly used as a preliminary to ether anesthesia to avoid the 
disagreeable first two stages. 
(b) Intoxicants.-Ethyl alcohol or "grain alcohol" occupies an intermediate 
position between the general anesthetics and the hypnotics, connecting them 
and belonging as it were, to both classes. Ethyl Alcohol is usually prepared 
by the yeast fermentation of certain sugars. During fermentation when the 
alcoholic content reaches about 18 per cent, fermentation ceases, but may be 
again started by diluting the mixture with water. It is evident from the 
foregoing that the yeast cells are paralyzed by a certain concentration of Alcohol 
in the fermenting liquid. This property of Alcohol to paralyze or depress 
activity holds for all forms of living matter. Chemically Alcohol (C2H5OH) is 
closely related to Ether ((C2H5)2O), so it is not unexpected to find that the 
actions of these two compounds on the central nerve system are more or less 
similar. When given in sufficient amounts Alcohol depresses the highest 
centers of the cerebrum, the intellectual centers; then the lower ones, the motor, 
emotional and animal; then the cerebellum; then the spinal cord; and finally 
the vital centers of the medulla oblongata. 
It is evident therefore, that in acute alcoholic poisoning or drunkenness 
there is more or less freedom from normal restraint, failure of judgment, 
inability to appreciate the likely consequence of given actions, over-confidence 
in the individual's physical and mental powers, and since there is less thought 
and care before speaking, speech is freer. Alcohol, therefore, is an intellectual 
depressant, i. e., a true narcotic, and is directly antagonistic to Caffeine in 
its action on the central nerve system. 
If much alcohol is taken in a short time the stage of intoxication just 
described is followed by muscular inactivity, inattention and mental dulness. 
The gait is staggering because of ataxia or depression of the cerebellum, and 
the speech is thick. Since Alcohol in large dosage depresses the sensory nerve 
endings, there is some anesthesia, so that the intoxicated individual may be 
injured without appreciating pain. The depression of the reflexes results 
in some degree of muscular relaxation which accounts for many escapes from 
fractures in drunken falls. After this stage stuporous sleep may follow with 
slow snoring respiration. If sufficient quantities have been taken serious coma 
leading to collapse and death may be the final result. Although Alcohol pro- 
duces practically the same stages as Ether, they develop much more slowly. 
Continued drinking of large quantities of strong alcoholic liquors may 
ultimately result in serious destructive changes in the nerve system, liver, 
stomach, kidneys, heart, arteries and testicles. Delirium tremens or "the 
horrors" is a special violent form of chronic alcoholism, characterized by horri-j 
ble hallucinations of sight and hearing, which may follow a period of continuous 
heavy drinking. 
Methyl alcohol or "wood alcohol" is not used internally. Although it 
produces an intoxication somewhat similar to that produced by Ethyl 
Alcohol, the onset is slower and the depression or narcosis is more pro- 
longed. Furthermore, it causes atrophy of the optic nerve with permanent PHARMACODYNAMICS OF THE CENTRAL NERVE SYSTEM 
100 
blindness, and marked depression of voluntary and cardiac muscle which results 
in death. 
(c) The hypnotics or somnifacients are remedies employed to induce or to 
maintain sleep. Hypnotic measures include drugs, hot baths, the establishment 
of conditions conducive to sleep, etc. Natural sleep comes because of: (i) les- 
sened irritability, i. e., fatigue, of the cells of the cerebral cortex resulting from 
work; (2) the removal of such external stimuli as light, sound, etc. Narcosis 
however, comes from direct and intentional depression of the cells of the 
cerebral cortex. 
In natural sleep the cells recover from fatigue, and regain their normal 
irritability and capacity for work. In narcosis, however, such restitution 
does not result, but instead the cells lose their irritability and are gradually 
fatigued. Sleep may follow the administration of fa hypnotic drug because of 
the fatigue produced together with the reduction in the excitability of the cells 
of the cerebral cortex which is preventing sleep. It is therefore evident 
that hypnotic drugs do not directly induce normal sleep. If too large a dose is 
given, restorative sleep does not follow the narcosis produced, and the individual 
suffers from mental and physical depression and weariness during the day 
following. 
Hypnotic drugs, then, are narcotics used to induce or to maintain sleep. 
Although their action more or less resembles that of the general anesthetics, they 
are slower to act, less powerful, and more lasting. These drugs act best at the 
usual time for sleep and if the individual is in bed in a quiet dark room. Hyp- 
notics have been often used in insomnia, but because of the peculiar nature of 
this condition the repeated administration of hypnotics may lead to drug habit. 
For convenience of study hypnotic drugs may be classified into two groups: 
viz., (1) those which do not abolish pain, as Chloral Hydrate; (2) those which do 
abolish pain, as Morphine. 
(1) Hypnotics which do not abolish pain. 
Bromides.-The bromides commonly used as hypnotics are those of 
Sodium, Potassium and Ammonium. These salts do not enforce sleep, but in 
fairly large doses act rather by depressing the central nerve system. This 
results in diminished psychic functions and reflexes, and thus establishes con- 
ditions conducive to sleep. The centers of the medulla oblongata are not 
affected. The bromides are particularly valuable in nervous insomnia, hysteria, 
epilepsy, etc., but are of no value against pain. 
The long continued use of large doses of bromides often results in bromide 
acne, mental dulness, physical sluggishness, general ataxia, loss in muscle tone, 
weak memory, tremors, malnutrition and lowered resistance. The treatment of 
this condition, known as bromism, consists of the administration of plenty of water 
to assist in the elimination of the drug in the urine; keeping up body nutrition 
and activity; and counteracting the central depression with Caffeine and 
Strychnine. 
Chloral Hydrate.-Chloral Hydrate is a very reliable hypnotic. In hyp- 
notic doses it very promptly produces mild but prolongued cerebral depression, PHARMACODYNAMICS 
101 
resulting in drowsiness in about 15 minutes and quiet, sound sleep within an 
hour. The respiration and pulse are somewhat slowed, and the blood pressure 
and temperature slightly lowered, but very little more than in natural sleep. 
The sleep usually lasts several hours. The individual can be easily and com- 
pletely aroused and awakens refreshed. There is generally no depressant 
after-effect. 
In acute poisoning by Chloral Hydrate there is pronounced narcosis with 
diminished or abolished reflexes, muscular relaxation, and marked depression of 
the respiration and circulation. The treatment includes artificial respiration and 
oxygen, and the administration of Caffeine, Strychnine, Camphor or 
Atropine. 
Chloral Hydrate should be given well diluted because it is locally irritating. 
It should never be given with alcoholic preparations since the poisonous chloral 
alcoholate formed ("knock-out drops") produces very promptly marked depres- 
sion of the cerebrum and of the medulla oblongata. 
Habit formation is not uncommon. The habitue, gradually becomes thin 
and anemic, suffers from mental and physical depression, skin eruptions, and 
various digestive and nervous disturbances. 
Paraldehyde (CH3CHO)3, Chloretone (CC13C(OH)CH3CH3), Sulphon- 
methane ( (CH3)2C(SO2C2H5)2) or Sulphonal, Sulphonethylmethane (CH3C2H5C 
(SO2C2H5)2) or Trional, Sulphondiethylmethane ( (C2H5)2.C(SO2C2H5)2) or 
Tetronal, and Veronal (C(C2H5)2.CO(CONH)2) or Diethylbarbituric acid are 
other members of this hypnotic group commonly used. 
(2) Hypnotics which abolish pain. 
Morphine.-Morphine, the most abundant alkaloid found in Opium, is 
decidedly the most important. The drug is extraordinary in that it so markedly 
lessens sensibility to pain, i. e., produces analgesia. The effects of Morphine, 
however, differ from those of Ether, Chloroform and Alcohol in that the various 
parts of the central nerve system are affected by it in a different sequence. 
Ether, Chloroform and Alcohol depress first the cerebrum, then the spinal cord, 
and lastly the vital centers of the medulla oblongata such as the respiratory 
center. Morphine, however, produces a depression of certain medullary centers, 
particularly the respiratory center, simultaneously with or even previous to the 
depression of the cerebrum, while the depression it induces in the reflex excita- 
bility of the spinal cord is very much less. It is evident, therefore, that 
Morphine does not produce any essential muscular relaxation and is conse- 
quently useless in treating the convulsions of strychnine poisoning. 
The most important therapeutic use of Morphine is dependent upon the 
fact that certain of the functional tracts of the cerebral cortex show great sensi- 
tiveness to very small doses of Morphine, so that perception of pain is markedly 
decreased by doses which hardly affect the motor centers and which scarcely influence 
the perception of ordinary sensations. (In the cases of the general anesthetics 
and the intoxicants similar analgesic effects are only produced by doses which 
cause unconsciousness.) The respiratory center in the medulla oblongata and 
the closely connected sensory centers which control the cough reflex manifest PHARMACODYNAMICS OF THE CENTRAL NERVE SYSTEM 
102 
a similar sensitiveness to Morphine. In therapeutics small doses of Morphine 
are used to alleviate pain and cough; while hypnotic effects are produced only by 
large doses. Thus a dose as small as 0.003 gm- (about ^0 grain) will lessen 
the perception of pain in an adult who is not habituated to Morphine, while 
0.01 gm. (about grain) is insufficient to produce a hypnotic action in all 
patients. It is evident therefore that Morphine should be used as a hypnotic 
only when pain or cough is preventing sleep. 
Morphinism.-Morphine also relieves fatigue, discomfort, hunger, and 
other disagreeable sensations, euphoria (a feeling of general well-being) result- 
ing. For this reason its use is attended by the great danger of vicious habit 
formation which, if unchecked, results in the physical and moral ruin of the 
individual. 
Acute Poisoning.-Acute poisoning is characterized by drowsiness pro- 
gressing to deep coma, slow pulse but good blood pressure, and pin-point pupils 
(the pupil contracting, vagus and vasoconstrictor centers in the medulla oblon- 
gata being first stimulated by large doses of morphine). The respiration is 
very slow, irregular and shallow. The condition may be distinguished from that 
of alcoholism by the fact that, if the patient can be aroused he brightens up, 
can answer questions intelligently, and can be made to walk. 
Treatment includes washing out the stomach at intervals with Potassium 
Permanganate solution to oxidize the unabsorbed Morphine, as well as that 
which is excreted into the stomach. This excretion takes place whether the 
drug has been given by the stomach or hypodermatically. Strong hot copfee 
by mouth or rectum, or salts of Caffeine hypodermatically, may be used to 
counteract the depression, particularly that of the respiration. The patient 
should be kept awake by constant walking or, if necessary lashing with wet 
towels, for if he relapses into sleep serious ground is lost and chances of recovery 
are lessened. It may be necessary to resort to artificial respiration. 
Codeine.-Codeine (methyl morphine), is another alkaloid found in 
Opium. It is less narcotic, less depressing to the respiration, and less apt to 
induce habituation than Morphine. Codeine is possibly just as effective as 
Morphine in allaying cough, although the dosage is several times as large. 
If too large a dosage is used, restlessness instead of quieting may result because 
of an increase in spinal reflexes. The principal use of Codeine is as a cough 
sedative. 
Heroine (diacetyl morphine) has all the disadvantages of and no advantages 
over Morphine. 
Dionine (ethyl morphine) stands intermediate between Morphine and 
Codeine. It has been used for cough and mild pain. Oculists employ it for 
deep-seated ocular pain, but the drug is capable of producing edema of the 
eyelids. 
Scopolamine or Hyoscine.-Scopolamine, one of the alkaloids found in 
Belladonna, Stramonium, Hyoscyamus, etc., differs markedly in its central 
actions from Atropine and Hyoscyamine, the other two principal alkaloids found 
in the same drugs. Its peripheral actions are qualitatively similar to those PHARMACODYNAMICS 
103 
of Atropine and Hyoscyamine (see page no). While in moderate dosage 
Atropine is excitant, Scopolamine is mainly sedative, usually producing in a 
few minutes fatigue and drowsiness, due to mild, though prolonged, depression 
of the psychic and motor centers. A natural, dreamless sleep lasting several 
hours follows. It possesses the advantages over Morphine and Chloral Hydrate 
of not being habit forming and usually not depressant to the medulla oblongata. 
However, because of its peripheral actions (see page no) being in the main 
similar to the peripheral effects of Atropine, Scopolamine produces a dilatation 
of the pupils, loss of visual accommodation and marked dryness of the mouth. 
Scopolamine is used in medicine as a sedative and a hypnotic especially 
in delirium tremens, tetanus, maniacal excitement, in the treatment of drug addic- 
tions, and as a preliminary to general anesthesia. 
Scopolamine Morphine Anesthesia.-Scopolamine has also been employed 
in combination with Morphine to produce a deep narcosis which will permit 
of major surgical operations. This combination is known as " Scop olamine- 
Morphine Anesthesia," popularly referred to as 11 Twilight Sleep" because of 
its use by some in obstetrics. This use has been largely abandoned on account 
of uncertainty of dosage, and because the great susceptibility of the fetus to 
morphine has resulted in an abnormal number of asphyxiated babies. 
(d) Analgesics or Anodynes.-Drugs which relieve pain without produc- 
ing any material effects on the other sensations are called "Analgesics" or 
" Anodynes. ' ' The more important analgesics are Morphine and its derivatives, 
Acetanilid, Antipyrine, Acetphenetidin ("Phenacetin") Quinine, Salicylic 
Acid and its salts, and Acetylsalicylic Acid ("Aspirin"). 
The analgesic effects of Morphine and its derivatives have been discussed 
on page ioi. 
Acetanilid, Antipyrine, and Acetphenetidin lessen pain, especially that 
from neuralgia or neuritis, lesions of the central nerve system, and headaches. 
The mechanism of their analgesic actions is obscure. Some investigators 
have suggested that the analgesia produced is a result of an action on synapses 
in the pain-conveying tract in the thalamus adjacent to the heat-regulating 
center. Although these drugs are not especially hypnotic, they seem to pro- 
duce a slight partial depression of the cerebral cortex, since doses given at 
bedtime favor the onset and maintenance of sleep. They have, however, 
even in large dosage little, if any, depressant effect on the intellectual functions. 
Quinine has the same analgesic tendencies as Acetanilid, etc., but it is 
decidedly less powerful. 
Salicylic Acid and its salts, such as Sodium Salicylate, also resemble Acetan- 
ilid in their analgesic properties, but are milder. They are, however, almost 
specific in relieving the pain, swelling, etc. of acute articular rheumatism. 
Acetylsalicylic Acid ("Aspirin").-Because of the fact that free Salicylic 
Acid is too irritating for internal use and Sodium Salicylate has a disagreeable, 
nauseating taste, esters of Salicylic Acid, such as Acetylsalicylic Acid, more 
popularly known as "Aspirin," have been introduced which are claimed to be 
less irritating and disagreeable. 104 
PHARMACODYNAMICS OF THE CENTRAL NERVE SYSTEM 
Acetylsalicylic Acid was supposed to pass unchanged through the stomach, 
thereby avoiding irritation of that organ, into the intestine where Salicylic Acid 
would be liberated. Recent investigations have shown that although a part of 
the Acetylsalicylic Acid administered by mouth does undergo the change just 
described, by far the major portion is unaltered. This fact (the absorption of 
unaltered Acetylsalicylic Acid) is probably the reason this drug is so much more 
strongly analgesic than sodium and other salicylates although the mechanism of 
the action is at present obscure. The presence of the unchanged Acetylsalicylic 
Acid is also probably the cause of the occasional acute local or general edema of 
the skin and mucous membranes, eruptions, etc., observed in some individuals 
following the administration of therapeutic doses of this drug. Acetylsalicylic 
Acid is extensively used in headache, neuralgias, toothache, and other pains. 
In amounts somewhat larger than the analgesic doses, Acetanilid, Anti- 
pyrine, Acetphenetidin, Quinine, Salicylates and Acetylsalicylic Acid have the 
power to reduce temperature in fever. They are therefore again referred to in 
the discussion of "Antipyretics" on page 251. 
Counterirritation (see page 27) is frequently resorted to for analgesic 
effect. The use of heat and such irritating substances as the volatile oils (cloves, 
cinnamon, etc.) in toothache, colic, neuralgias, etc. are common illustrations. 
Local Analgesic Anodynes.-Agents, beside the counterirritants, used 
locally to relieve pain and itchings include: Belladonna Ointment, Plaster and 
Liniment (see Atropine, page in); dilute Phenol lotions and ointments (Phenol 
paralyzes the sensory nerve endings}; and Cocaine and its substitutes (see page 
114). 
(e) Antihysterics.-The Antihysterics, "Hysteric Sedatives," or "Anti- 
spasmodics" constitute a group of malodorous drugs which tend to relieve 
hysterical and similar states of nervous instability. Hysteria is a state of nerv- 
vous hyper-excitability and perversion accompanied by numerous imaginary 
symptoms. Although hygienic, psychic and educational measures are doubt- 
less of greater importance in treating these conditions, a number of drugs are 
apparently useful particularly during attacks. The more important drugs in 
this group are Valerian, Asafetida, Musk and Sumbul. All of these drugs 
possess strong, penetrating, rather disagreeable odors and tastes, which are prob- 
ably largely responsible for their frequent effectiveness, i. e., by olfactory and 
psychic reflexes. CHAPTER XII 
THE AUTONOMIC OR SYMPATHETIC NERVE SYSTEM 
The smooth muscle found in the walls 
of the alimentary canal, bladder, uterus, 
arterioles, etc., the heart muscle, and the 
epithelium of glands are not under the influ- 
ence of the will. The system of nerves that 
regulates their activity is for this reason called 
the autonomic nerve system (Fig. 70). This 
term is preferable to the older name of 
"sympathetic."1 
ARRANGEMENT OF THE AUTONOMIC' NERVE 
SYSTEM 
In the autonomic nerve system, two 
neurons are invariably interposed between 
the cerebro-spinal axis and the organ to be 
innervated. The neuron whose cells lies with- 
in the brain or spinal cord is medullated and 
its fiber is of smaller caliber than that of the 
usual neuron. Its terminal arborization is 
located within a sympathetic ganglion more or 
less distant from the central nerve system. 
The fiber that thus issues from the brain or 
spinal cord and ends in a sympathetic gang- 
lion is called a preganglionic fiber. From the 
nerve cells located in the ganglia there issue 
nerve fibers that are non-medullated, and 
that are distributed to the organs to be inner- 
vated. These fibers are called postganglionic 
fibers. The nerve fibers of the autonomic 
nerve system often form intricate meshworks 
designated "plexuses." 
The autonomic nerve system, as is the 
case with the cerebro-spinal nerve system, 
contains both afferent and efferent neurons. 
The afferent neurons, in all likelihood, sub- 
serve certain forms of sensibility although 
little is known on this subject. They are, 
Fig. 70.-Diagram giving a schematic 
representation of the course of the auto- 
nomic (sympathetic) fibers arising from 
the thoracicolumbar and sacral regions of 
the cord. The preganglionic fiber is 
represented in red, the postganglionic in 
black lines. The arrows indicate the 
normal direction of the nerve impulses or 
nerve conduction. S.c., superior cervical 
ganglion; I.c., inferior cervical ganglion; 
T, the first thoracic ganglion; Sp., the 
splanchnic nerve; C., the semilunar or 
celiac ganglion; m., the inferior mesenteric 
ganglion; h„ the hypogastric nerves; 
N.E., the nervus erigens. The numerals 
indicate the corresponding spinal nerves. 
(From Howell, Text-book of Physiology.) 
1 The term "sympathetic" was applied to this sys- 
tem on the belief that the ganglia were centers for reflex 
action, which were formerly called ' 'sympathetic actions." 
105 106 
THE AUTONOMIC OR SYMPATHETIC NERVE SYSTEM 
however, concerned in various reflexes. The efferent neurons are better under- 
stood, and play an important part in the functions of the body. The pregang- 
lionic fibers arise from nerve cells located in: (i) the midbrain; (2) the medulla 
oblongata; (3) the lateral horn of the gray matter of the spinal 
cord between the second thoracic and second or third lumbar 
segments and (4) between the second and the fourth sacral 
segments (Fig. 71). That portion of the autonomic nerve 
system that originates in the mid-brain, the medulla oblongata, 
and the sacral segments of the spinal cord constitutes its 
parasympathetic division; while that portion that springs from 
the thoracic and lumbar segments of the spinal cord constitutes 
its sympathetic division. This subdivision of the autonomic 
nerve system is based on differences in its reaction to drugs. 
The sympathetic ganglia consist of a capsule of connective 
tissue, enclosing numerous nerve cells, together with nerve 
fibers issuing from them or ending in synaptic connections 
around them. The anglia, likewise, contain blood vessels and 
lymphatics. They have been divided by anatomists into 
three groups: viz., the vertebral or lateral, the prevertebral or 
collateral, and the peripheral or terminal. 
The vertebral ganglia form two chains, one on each side 
of the vertebral column on its ventral aspect. There are from 
20 to 22 ganglia in each chain. These ganglia have been group- 
ed in accordance with their relation to the vertebral column, 
as follows: three cervical ganglia-a superior, a middle, and 
an inferior; ten or eleven thoracic ganglia; four lumbar', four 
sacral; and one coccygeal or ganglion impar. 
The prevertebral ganglia are located in the abdominal 
cavity, and include the semilunar, renal, superior and inferior 
mesenteric, and the hypogastric or pelvic ganglia. 
The peripheral ganglia are more or less distantly placed 
or are actually in the walls of the organs innervated. Some 
of these ganglia are in the head, viz., the ciliary or ophthalmic, 
the otic, the spheno-palatine, and the sub-mamillary ganglia. 
Peripheral ganglia are also found in the walls of the heart, 
of the respiratory organs, of the stomach, intestines, etc. 
Functions of the Autonomic Nerve System.--Organs 
containing smooth muscle in their walls are more or less 
automatic in their activity. One of the ways in which this 
activity manifests itself is in the form of a varying, but con- 
tinuous, contraction called tonus. The autonomic nerve 
system has the power of either increasing or decreasing this tonus; it may 
also stimulate the smooth muscle to increased contraction, or inhibit a con- 
traction taking place. Thus, the movements of the stomach and intestines, as 
Fig. 71.-Illus- 
trating the central 
origin of the auto- 
nomic fibers. {Lang- 
^ey.) ESSENTIALS OF PHYSIOLOGY 
107 
well as their tone, are made to increase or decrease through the activity of the 
autonomic nerves supplied to these organs. 
Smooth muscle libers are, likewise, found in the eye, where they serve to 
regulate the refracting power of the lens, and the size of the pupil. The muscles 
concerned in these actions receive autonomic fibers from the mid-brain, through 
the intermediation of the ciliary ganglion. 
The skin contains small muscles, made up of smooth muscle fibers, attached 
to the roots of the hairs. These muscles are under the control of the autonomic 
system, and, when stimulated, cause the hair to stand on end, and to bring about 
the condition called "goose flesh. " The nerves causing these effects are called 
pilomotor nerves. 
In some instances the chief cause of the tonic contraction of smooth muscle is 
the stimulating action of autonomic nerve impulses. This is the case, particu- 
larly, with the smooth muscle found in the walls of blood vessels, more espe- 
cially of the arterioles. The nerves carrying the nerve impulses to the blood 
vessels are called vasomotor nerves. Experiments have demonstrated that there 
are two classes of nerve fibers distributed to the arterioles, one class of fibers 
called vasoconstrictor, causes when stimulated, an increased contraction of the 
vessel; the other class of fibers called vasodilatator, causes when stimulated, a 
decrease in the contraction. 
Similarly the heart, which is a wholly automatic organ, is influenced in 
opposite directions by two sets of fibers belonging to the autonomic system: 
One set of fibers causes, when stimulated, a decrease in the force and the fre- 
quency of the heart beat; these fibers are found in the vagus nerve, which is, 
therefore called the cardio-inhibitor nerve. The other fibers, found in the sym- 
pathetic branches going to the heart, cause when stimulated, an increase in the 
frequency and the force of the heart beat. These neves are, therefore, termed 
the cardio-accelerator and cardio-augmentor nerves. 
The majority of the glands, both of external and of internal secretion, are 
supplied with autonomic nerve fibers. It has been shown, in some cases at least, 
that some of these nerve fibers stimulate the gland epithelium to elaborate the 
material to be secreted; while other nerve fibers bring about the discharge of 
the secretion. 
The nerve fibers supplied to glands are, therefore, called secretor fibers of 
which two kinds exist: viz., secreto-augmentor and secreto-inhibitor. 
The most important factor in the activity of the autonomic nerve system is 
reflex stimulation. While the will cannot influence its activity, the various 
parts of the autonomic nerve system are, nevertheless, under the influence of 
that form of cerebral activity called emotion. The various emotional distur- 
bances are accompanied by stimulation or inhibition of the activity of the organs 
under the control of the autonomic system. 
Hygiene of the Nerve System.-The organs of the nerve system, in 
common with all other organs of the body, require an adequate supply of nutritive 
material for their repair and growth. Any impairment, therefore, in the general 
nutrition of the body will be felt by the nerve system, and will manifest itself in a 108 
THE AUTONOMIC OR SYMPATHETIC NERVE SYSTEM 
lowered capacity for efficient activity. The nerve tissue is, likewise, susceptible 
to fatigue and must, therefore, be given sufficient rest to enable the forces of 
recuperation to come into play. This can be accomplished partly by providing 
short periods of rest in the course of the day, and partly by securing sufficient 
sleep. The number of hours of sleep required varies in different individuals. 
In general, it may be said that an adult requires between seven and eight hours 
of sleep. Children and adolescents require eight or nine hours. Usually people 
who do much mental work require more sleep. 
Since the central organs of the nerve system are constantly subjected to 
streams of afferent nerve impulses, it is obvious that excessive afferent stimulation 
must subject the central nerve system to undue fatigue, which in time may bring 
about a state of nerve exhaustion. Slight defects of the organs of special sense, 
viz., errors of refraction causing eye-strain, irritation about the ears, etc., should 
be corrected, although apparently easy to bear, because of their likelihood of 
causing constant fatigue of the nerve system. The same advice applies to other 
affections that may be the cause of harmful stimulation, e. g., defective teeth, 
painful feet from any cause, hemorrhoids, etc. 
The character of the work in which the individual is engaged influences, 
likewise, the efficiency of the nerve system. Work that is uncongenial, especially 
if accompanied by anxiety or worry, is apt to lower its efficiency and may bring 
about a breakdown that is usually, but erroneously, assigned to overwork. 
Individuals who have inherited a more or less unstable nerve system must 
necessarily observe the greatest care in avoiding all factors that tend to weaken it. 
Exhausting diseases, partly by lowering the general vitality, and partly through 
the action of toxic substances on the delicate structures of the nerve system, 
decrease its capacity for work and must therefore be followed by a careful con- 
valescence until the usual state of health has been regained. 
Attention must be called here to the effect of syphilis on the organs of the 
central nerve system. This disease is the most frequent cause of the most 
serious degenerative diseases of the nerve system, including certain forms of 
insanity. CHAPTER XIII 
PHARMACODYNAMICS OF THE AUTONOMIC NERVE SYSTEM 
The physiological discussion of the autonomic nerve system showed certain 
anatomic and physiologic pecularities of this system. The most striking 
anatomic peculiarity of the autonomic nerves is the fact that they never 
pass directly from the central nerve system to their terminal organs but all 
pass into ganglia, situated outside the central nerve system, from which new 
nerve fibers pass downward to the terminal organs. Physiologically the 
autonomic system includes all the functions which are not under the influence 
of the will-smooth and cardiac muscle and the epithelium of glands. Although 
these structures are capable of functionating automatically when all connections 
with the cerebro-spinal axis are severed, it should be remembered that these 
functions are normally inhibited or augmented by central tonic impulses of 
varying intensity. Pharmacodynamically all autonomic nerves possess one 
common drug reaction. This is their reaction to nicotine. 
The Common Reaction to Nicotine.-Nicotine, an alkaloid found in tobacco, 
paralyzes (usually after a very brief primary stimulation) all the ganglia of 
both the sympathetic and the parasympathetic nerves. This action is specific 
whether the drug is applied locally or injected into the circulation. After the 
absorption or injection of Nicotine into the circulation, stimulation of all 
preganglionic fibers is ineffective, whereas the postganglionic fibers respond 
normally. This shows that the nerve fibers and their peripheral endings 
are still excitable and that Nicotine acts on the ganglia only. 
This reaction of the autonomic system to Nicotine is mentioned not because 
of any important therapeutic applications, but purely because of the fact that 
this action of Nicotine is so specific that it has proved of great value in 
locating the sites of the ganglionic synapses. 
The exact location of the action of the other drugs affecting the autonomic 
nerve system has not yet been satisfactorily decided. It is usually assumed that 
the majority of them act on the myoneural junctions or on a receptive substance 
which exists between the anatomic nerve endings and the contractile elements 
of the muscles or the secretory elements of the glands. The fact that most of 
these drugs continue to produce their effects after the anatomic degeneration 
or the severance of the postganglionic nerve fibers shows that their actions are 
peripheral to the nervous structure. 
Most of the other drugs which act on the autonomic system affect princi- 
pally one or the other divisions of the system. Thus Atropine, Pilocarpine, 
and Physostigmine affect principally the parasympathetic division, whereas 
Epinephrine, Ergotoxine and Cocaine act exclusively on the Sympathetic division. 
This fact is especially interesting because most of the organs possess a double 
109 110 
PHARMACODYNAMICS OF THE AUTONOMIC NERVE SYSTEM 
innervation, one coming from the sympathetic and the other from the 
parasympathetic division. Further, in the majority of such cases this 
double innervation is an antagonistic one, stimulation of the parasym- 
pathetic fibers causing an opposite effect from that produced by stimulation of 
the sympathetic fibers. For example, as stated in the physiological discussion, 
the heart receives two sets of nerve fibers belonging to the autonomic system; 
one from the parasympathetic division-the cardio-inhibitor fibers of the 
vagus nerve, the other from the sympathetic division the cardio-accelerator 
or cardio-augmentor. 
PHARMACODYNAMICS OF THE PARASYMPATHETIC DIVISION 
The most important drugs which chiefly affect the parasympathetic divi- 
sion are (i) Atropine, which depresses or paralyzes the myoneural junctions of 
the nerve endings; (2) Pilocarpine and (3) Physostigmine which stimulate 
them. Therefore, Atropine is antagonistic to Pilocarpine and Physostigmine. 
Atropine.-Atropine, along with the closely related (chemically and phar- 
macodynamically) alkaloids Hyoscyamine and Scopolamine (or Hyoscine), 
occur in varying predominance in Belladonna (nearly all Atropine) , Stramonium 
(mostly Hyoscyamine) and Hyoscyamus (principally Hysocyamine and Scopola- 
mine or Hyoscine). 
Atropine is a highly selective drug depressing the myoneural junctions 
of the following nerve endings whether applied locally or given internally. 
(1) The Secretory Endings.-As a result of strong depression mucous, 
digestive and skin secretions are checked so that the mouth, nose and throat 
become dry, and sweating is checked. The stomach and intestinal secretions 
are somewhat diminished. 
(2) The Motor Endings in the Smooth Muscle of the Viscera (not in striated 
and arterial muscle).-The strong depression tends to allay abnormal contrac- 
tions of the muscles of the bronchi, stomach, imesiines, bile ducts, ureters, etc. 
For this reason the drugs in this group are useful in relieving excessive contrac- 
tions of the bronchial muscles as in spasmodic asthma (by depressing the myo- 
neural junctions of the broncho-motor vagal endings); to overcome spasmodic 
contractions of the pylorus, i. e., pyloric spasm (by paralysis of the myoneural 
junctions of the vagus); to lessen toxic intestinal spasm (as, for example, those 
caused by Pilocarpine and Physostigmine poisoning), intestinal colic, and the 
griping effect of certain purgatives (by depression of the myoneural junctions 
of the vagus, the vagus being the motor nerve of the small intestine); and to 
allay the painful contractions of the bile ducts and ureters which result from 
the passage of calculi ("stones") through these tubes (by paralyzing peripherally 
the innervation of their smooth muscle). 
(3) The Vagus Endings.-The marked depression frees the heart from the 
usual inhibitory vagus control and it therefore beats faster and somewhat 
stronger. This action takes place in spite of the fact that Atropine stimulates 
the vagus center, the central effect being prevented by the peripheral depression. 
The duration of action is, however, short. The vaso-constrictor center is probably PHARMACODYNAMICS 
111 
not directy stimulated, but the increase in the heart's rate may result in a 
slight rise in arterial pressure. 
(4) The Oculo-motor or Third Nerve Endings in the Eye.-Strong depression 
permits the unopposed action of the radial muscles of the iris, which are 
supplied by sympathetic fibers, resulting in dilatation of the pupil. This 
action will be referred to again under the "Pharmacodynamics of the Eye" 
(see page 300). 
The Sensory Endings.-These are moderately affected so that there is a 
slight tendency to lessen pain and sensation. 
Central Action.--In addition to the moderate or slight stimulation of the 
vagus center already mentioned in the preceding paragraphs, Atropine, when 
the respiration is depressed, stimulates the respiratory center, and in poison- 
ous doses stimulates the psychic and motor functions of the cerebrum and the 
reflex excitability of the spinal cord. 
Poisoning by Atropine is characterized by dilated pupils, dry mouth and 
throat, rapid pulse, deep and rapid respiration, and talkativeness and restlessness, 
followed by collapse. Treatment includes evacuation of the stomach, the adminis- 
tration of Potassium Permanganate or Tannic Acid, and central sedatives like 
bromides and whisky {not Morphine, Chloral Hydrate or Chloroform because of 
their depressant effects on respiration). Since Atropine poisoning is dependent 
rather on its cerebral and medullary effects than on its peripheral actions, 
Physostigmine and Pilocarpine, which are peripherally antagonistic, are of no 
great antidotal value. 
Pilocarpine.-Pilocarpine, an alkaloid found in Pilocarpus (" Jaborandi") 
leaflets, stimulates the myoneural junctions of the nerve endings of most smooth 
muscle, of the vagus endings, of the third nerve endings in the internal eye, and 
of the secretory nerve endings of glands. It is therefore antagonistic in these 
respects to A tropine. It does not affect the sensory nerve endings. The principal 
effects of Pilocarpine are therefore: 
(1) An increase in the sweat, saliva, mucus, gastric, pancreatic and intestinal 
juices by stimulation of the myoneural junctions of the secretory nerve endings. 
(2) Increased peristalsis in the alimentary tract, and contraction of the 
bronchi, uterus, and bladder by stimulation of the myoneural junctions of the 
nerve endings governing smooth muscle. 
(3) Contraction of the pupil by stimulation of the myoneural junctions of the 
oculo-motor or third nerve endings. 
(4) Slowing of the heart followed by quickening, due to short primary 
peripheral stimulation succeeded by depression of the vagi. 
All these effects can be prevented by the previous administration of 
Atropine, or checked by its subsequent administration. The chief use of the 
drug in therapeutics is to promote sweating {diaphoretic) in dropsy and in neph- 
ritis with uremia. It is also used locally in the eye to hasten contraction of the 
pupil (myotic) after dilatation produced by drugs like Atropine {mydriatic). 
In poisoning by this drug the pupils are contracted; the skin is flushed and 
covered with profuse sweat; mucus and saliva are abundant; there may be nausea, 112 
PHARMACODYNAMICS OF THE AUTONOMIC NERVE SYSTEM 
vomiting, diarrhea and abdominal cramps. Respiration may be labored and 
asthmatic because of the contraction of the bronchial muscles and the increased 
bronchial secretion, as well as depression of the respiratory center. The most 
important step in treatment is the hypodermatic administration of Atropine to 
overcome the asthmatic breathing, to check bronchial secretion, to lessen abdom- 
inal cramps, and to check the vagus action. 
Physostigmine.-The effects of Physostigmine or "Eserine," the alkaloid 
found in the Physostigma seed ("Calabar Bean") resemble those of Pilocarpine, 
and are therefore also antagonistic to Atropine. The site of action is probably 
the myoneural junctions. Its effect on the nerve endings of smooth muscle 
is strongest in the alimentary tract, so that the drug may be used by mouth 
or hypodermatically as a cathartic. It also tends to produce contractions 
of the bronchi, bladder, and probably the uterus. Physostigmine is used to 
contract the pupil after drugs of the Atropine group, and is usually preferred to 
Pilocarpine for this purpose because its action lasts longer and is more com- 
plete. The glandular stimulation is less marked than with Pilocarpine. The 
symptoms and treatment of poisoning by Physostigmine are practically identical 
with those of Pilocarpine. 
PHARMACODYNAMICS OF THE SYMPATHETIC DIVISION 
Epinephrine.-Epinephrine ("Adrenaline"), a leukomain (animal alkaloid) 
found in the medullary portion of the adrenal glands (see page 275), pro- 
duces a peripheral stimulation limited principally to the sympathetic division of 
the autonomic nerve system. The effect of this drug on a given organ is iden- 
tical with that which follows excitation of the sympathetic nerves which supply 
it. The action is therefore, augmentory or inhibitory, according to whether the 
sympathetic impulses sent to the organ are augmentory or inhibitory. Among 
the principal augmentory sympathetic reactions are: (1) Constriction of most 
of the arteries and a consequent rise in arterial pressure. (2) Stimulation of 
the myoneural junctions of the cardio-accelerator nerves. (3) Stimulation of the 
sympathetic broncho-dilatator nerve endings. (4) Dilatation of the pupils. The 
inhibitory reactions are principally concerned with the tonus and the rhythm of 
the contractions of the alimentary tract, gall-bladder, and urinary bladder. 
From the foregoing it is evident that Epinephrine may produce the follow- 
ing effects: 
(1) When applied locally to a mucous membrane or to a wound or cut 
Epinephrine immediately produces a local constriction of the arterioles which is so 
marked that the blood is almost completely shut off and the tissue conse- 
quently appears blanched and shrunken. Moderate hemorrhage is thus checked. 
These effects are due to stimulation of the myoneural junctions of the vaso-con- 
strictor nerves. However local application and administration by mouth are not 
followed by any systemic effects, either because the marked vaso-constriction 
produced prevents the absorption of the drug, or because the drug is so rapidly 
destroyed at the site of entrance into the tissues that little if any gets into the 
circulation. The vaso-constriction produced by Epinephrine lasts from 15 
minutes to an hour or two. PHARMACODYNAMICS 
113 
Beside producing vaso-constriction, Epinephrine also stimulates peripher- 
ally the vaso-dilatator nerves, so that when the application of the drug is stopped 
and the vaso-constriction, which usually prevails, wears off, the arterioles not 
only return to their normal calibre but may dilate beyond normal, and thus 
possibly overcome the object for using the drug as in hemorrhage. 
A pronounced general constriction of arteries is only obtained following 
the intravenous injection of the drug. Subcutaneous and deep intramuscular 
injections are not as sure nor as pronounced in this respect. 
(2) As a result of the more or less general vaso-constriction produced 
by the intravenous injection of Epinephrine, the arterial pressure rises very 
promptly. Although Epinephrine is the most powerful blood-pressure-rais- 
ing drug used in medicine, its effect on blood pressure lasts only about five 
minutes. 
(3) In small dosage the heart beats faster and stronger as a result of stimula- 
tion of the myoneural junctions of the cardio-accelerator endings. The accelera- 
tion is usually followed by slowing due to reflex stimulation of the vagus center, 
a secondary result of the increased blood pressure which induces congestion 
of the brain and excites the vagus center to activity. 
(4) By stimulation of the myoneural junctions of the sympathetic broncho- 
dilatator nerve endings, Epinephrine produces a decided relaxation of the bronchi. 
This makes the drug valuable in spasmodic asthma due to excessively contracted 
bronchi. 
(5) When dropped in the eye Epinephrine causes a blanching and shrinking 
of the conjunctiva, and may, by 'stimulation of the myoneural junctions of the 
sympathetic nerve endings in the fibers of the radial muscles of the eye, dilate 
the pupil {mydriatic}. 
(6) By stimulation of the myoneural junctions of the splanchnic nerve 
endings (the splanchnic nerves are the inhibitory nerves of the stomach and 
intestines) Epinephrine lessens peristalsis of the stomach and intestines. The 
gall-bladder and urinary bladder are said to be inhibited in the same way. 
(The secretory fibers in the sweat glands, although they are of sympathetic 
origin, are not affected by Epinephrine.) 
The most important medicinal uses of Epinephrine include: (A) Locally,- 
The shrinkage of mucous membranes, as in the nose for hay-fever or acute catarrh, 
and the arrest of small accessible hemorrhages, as in nose-bleed. (B) Hypodermi- 
cally.-The relief of bronchial asthma. (C) Intravenously.-Its use as a 
rapidly acting circulatory stimulant in collapse and shock. 
Epinephrine is also frequently added to solutions of local anesthetics, 
like Cocaine, to prolong the local anesthesia by vaso-constriction which pre- 
vents its rapid removal by the blood stream, and to.prevent local hemorrhage. 
Ergotoxine.-Ergotoxine, an amorphous alkaloid found in Ergot, when 
administered hypodermically or intravenously first stimulates (small dose) and 
then paralyzes (large dose) the myoneural junctions of the vaso-constrictor nerve 
endings, so that with small doses there is a rise in blood pressure, and with large 
doses the primary rise is followed by a fall which cannot be raised by Epinephrine. 114 
PHARMACODYNAMICS OF THE AUTONOMIC NERVE SYSTEM 
This indicates that Ergotoxin in large doses abolishes the response of the aug- 
mentory sympathetic impulses. However, it does not affect the inhibitory 
sympathetic impulses as evidenced by the fact that it does not destroy the 
inhibitory effects of Epinephrine on the intestines and uterus. 
In medicinal doses Ergotoxine slightly stimulates the myoneural junctions of 
the splanchnic nerve endings and causes a diminution in intestinal peristalsis. 
The contraction of smooth muscle, produced by Ergotoxine, especially 
pronounced in that of the uterus, is caused by direct peripheral (myoneural 
junctions) stimulation. This action is made use of in preventing postpartum 
uterine hemorrhage. 
Cocaine.-Cocaine, an alkaloid obtained from the leaves of the Coca 
shrub, is therapeutically important principally because of its action on the 
sensory nerves. 
When Cocaine is applied locally to a mucous membrane or injected sub 
cutaneously, a local constriction of the arterioles follows due to its action on the 
vaso-constrictor nerve endings. Although the part appears shrunken and blood- 
less, the vaso-constriction is not as great as that produced by Epinephrine. 
However, of much greater importance than its vaso-constrictor action is 
the marked paralysis of the sensory nerve endings or their adjacent nerve fibrils 
produced by the local application of Cocaine to a mucous membrane or by its 
subcutaneous injection. The result is a prompt and complete local abolition of 
pain. The most important therapeutic use of Cocaine-that of a local anesthetic 
-depends upon this effect on the sensory endings. 
Cocaine cannot penetrate the unbroken skin, but the drug produces 
anesthesia if applied to any part of the nerve, from the nerve ending to the 
posterior root. Therefore Cocaine anesthesia may be produced by: 
(i) Application of a solution to a mucous membrane. 
(2) Injection of a solution into or beneath the skin (infiltration and subcu- 
taneous anesthesia}, or beneath a mucous membrane. 
(3) Injection aroiind or into a nerve (peri- or intraneural anesthesia}. 
(4) Injection into the spinal canal so that the solution may reach the 
dorsal roots. This method is known as spinal anesthesia or spinal analgesia. 
When this method is resorted to in surgery, or grain of Cocaine Hydro- 
chloride in aqueous solution is injected into the spinal canal by inserting the 
hypodermic needle between the third and fourth lumbar vertebrae into the 
region of the cauda equina. Within a few minutes an anesthesia, beginning 
with the toes, gradually ascends until it reaches the region of the umbilicus, 
all of the body below this being anesthetized. There is little if any muscular 
relaxation; the sense of touch is not completely abolished; and the sensations 
of heat and cold are not appreciably affected. Injections higher up in the 
spinal cord have been made but they are generally considered unsafe. 
The effects of Cocaine on the eye are discussed on page 301. 
Local Anesthetics.-Local anesthesia may be induced by depressing the 
excitability of the sensory nerve endings, called terminal anesthesia, or by pre- 
venting the conduction of nervous impulses in the nerve trunks, termed nerve PHARMACODYNAMICS 
115 
blocking. Blocking may take place anywhere between the point at which the 
dorsal roots enter the spinal cord and the nerve endings. 
Interruption of sensory conductivity by pressure is the oldest method of 
inducing anesthesia. Several decades ago surgeons at times induced anesthesia 
by tightly ligaturing an extremity. The "going to sleep" of a foot or an arm is 
an illustration of anesthesia produced by the accidental compression of nerve 
trunks against bone. 
Local anesthesia may also be produced by extreme cold which depresses the 
excitability of sensory nerve endings as well as that of nerve trunks. This is 
evidenced by the fact that exposure of the extremities to snow and ice causes them 
to become insensitive. The intense local cooling-"freezing"-produced by 
the very rapid evaporation of low-boiling-point liquids, such as Ethyl Chloride 
which boils at i2.5°C., is another illustration of local anesthesia induced by cold. 
Since the penetration of the effects of cold is limited to tissues freely supplied 
with blood, thorough freezing with complete anesthesia is practically attainable 
only in the skin. 
Cocaine is capable of penetrating through the medullary sheath or nerve 
trunks and so depressing their conductivity that the area innervated is anes- 
thetized. This method of nerve blocking is called regional anesthesia. 
Other Local Anesthetics used as substitutes for Cocaine include Procaine or 
Narocaine, Eucaine, Stovaine, Aly pine or Novocaine, and Tropococaine. None of 
these substitutes has the vaso-constrictor effect of Cocaine, but they are less 
toxic. As already stated in the discussion of Epinephrine, the local anesthetics 
are usually combined with Epinephrine which, because of its pronounced vaso- 
constrictor action, prolongs the anesthesia by practically preventing the 
absorption of the local anesthetic into the circulation. 
Although Cocaine is a cerebral stimulant, the fact that it is a vicious habit 
forming drug has caused the abandoning of its therapeutic employment except- 
ing as a local anesthetic. CHAPTER XIV 
THE BLOOD 
The blood is the nutritive fluid of the body. It contains all the material 
that is necessary for the growth and the repair of tissue cells and for the energy 
set free during tissue activity. This material is derived from the food which has 
been elaborated by the alimentary canal and absorbed from it. Oxygen is 
necesssary for the liberation of the energy set free within the tissues; this oxygen 
is taken up by the blood during its passage through the lungs. 
The blood receives also a variety of substances from the tissues, some of which 
cannot be utilized by the body and constitute, therefore, waste material. Other 
substances, however, are capable of utilization for various purposes; among 
these are the internal secretions. The waste material discharged into the blood 
is carried to various organs: viz., the lungs, the kidneys, the large intestines, 
the skin, where it is eliminated from the body. Certain other substances of 
unknown chemical nature are, likewise, found in the blood, and serve the purpose 
of protecting the body from the invasion of micro-organisms. These substances 
are called immunizing substances. 
Aside from supplying the tissues with nutritive material, oxygen, etc., the 
blood serves to regulate the water content of the tissues throughout the body. 
Because of its capacity for absorbing heat, it is, likewise, an important factor in 
the regulation of body temperature. 
The Physical Composition of Blood.-When a thin film of blood is observed 
under the microscope, it is seen to consist of: (i) a clear and colorless, or 
faintly yellow fluid, called the plasma or liquor sanguinis; and, (2) small par- 
ticles called corpuscles, of which there are three types: the red or erythrocytes, 
the white or leukocytes, and the platelets or thrombocytes. 
The Properties of Blood.-(1) Color: The blood found within the arteries 
is a bright scarlet-red; that found in the veins is a dark bluish-red. The color 
imparted to the blood is due to the presence in the red corpuscles of a pigment 
called hemoglobin. This pigment has the property of absorbing and liberating 
oxygen. Its color varies with the quantity of oxygen combined with it, being 
bright red when fully saturated with oxygen, and bluish-red when free from this 
gas. The depth of the color of blood is dependent on the thickness of the layer. 
When a red blood cell is seen singly, it appears of a straw-color. The blood does 
not appear red until numerous red cells are superimposed. 
(2) Odor.-The blood has a peculiar odor which has been attributed to the 
presence in it of a volatile fatty acid combined with a base. The odor can be 
intensified by the addition of concentrated sulphuric acid. 
(3) Taste.-As blood contains mineral salts in solution, the chief of which is 
sodium chloride, it has a salty taste. 
116 ESSENTIALS OF PHYSIOLOGY 
117 
(4) Opacity.-Blood, even in thin layers, will not permit light to pass 
through it. This is due to the shape of the corpuscles, as well as to the difference 
in the refracting power of corpuscles and plasma. Destruction of the corpuscles, 
although it darkens the color, renders the blood transparent. 
(5) Specific Gravity.-The specific gravity of blood varies from 1.050 to 
1.065. It is usually less after a meal and rises after exercise. The changes are 
apparently due to variations in water content. 
(6) Reaction.-The reaction of blood, as determined by physico-chemical 
methods, is slightly alkaline. Its hydrogen-ion concentration varies from 0.35 
Xio-7 to 0.49 X io-7. 
(7) Temperature.-The temperature of the blood varies in different parts 
of the body. In the veins of the liver, for instance, where it is well protected 
from loss of heat, it has a temperature of 39-7°C., while in those vessels near 
the surface of the body, as in the cheek, it may have a temperature of 34.4°C., 
and in the tip of the ear of only 2q°C. 
(8) Viscosity.-Blood does not flow as readily as distilled water at the 
same temperature; it is, therefore, viscid. The viscosity of blood is in part 
due to the presence of substances in solution, but in greater part, to the presence 
of the corpuscles. As compared with distilled water, human blood has a 
viscosity 4.5 times greater. 
THE HISTOLOGY AND FUNCTIONS OF THE BLOOD CORPUSCLES 
The Red Corpuscles or Erythrocytes.-The red corpuscles, as seen under 
the microscope, appear as flat, biconcave discs. As already stated, the red 
Fig. 72.-Red corpuscles forming rouleaux. Fibrin in filaments radiates from the blood^plates. 
(From Da Costa's Clinical Haematology.') 
corpuscles when seen singly are faintly yellow. The average diameter of the 
red corpuscle is 7.5 /z (^,200 of an inch), and the thickness about 2 n. The 
red corpuscles of man, as is the case for all other mammals, has no nucleus 118 
THE BLOOD 
(Fig. 72). There is still some doubt concerning the intimate structure of these 
cells. According to some, the red corpuscle consists of a stroma or meshwork 
of colorless protoplasm in which is held the hemoglobin. According to others, 
the corpuscle consists of a vesicle, the walls of which contain lecithin and 
cholesterol, holding hemoglobin in its interior. 
The red corpuscles are exceedingly numerous. Special methods, however, 
have been devised for the purpose of estimating their number in one cubic 
millimeter of blood. The average number, for men, is 5,000,000 corpuscles per 
c. mm.; and for women, 4,500,000 per c. mm. These averages vary slightly 
under a number of conditions that affect the water content of the blood. Con- 
siderable variations are observed under the influence of altitude, the number 
increasing within a few days after the individual has reached a high altitude. 
The reverse process occurs in passing from a high to a low altitude. 
The Life History of the Red Corpuscles.-The red corpuscles are produced 
in the red marrow of bones from colorless, nucleated cells called erythroblasts. 
During the process of multiplication of these cells they acquire hemoglobin. 
Later on the nucleus is extruded from the cell body, and the cell is gradually 
pushed into the blood stream by the growing mass of cells. 
The length of life of the red corpuscles is unknown, but that they must 
undergo destruction in large numbers daily, is shown by the fact that bile 
pigments are being excreted constantly. The bile pigments are derived 
from the hemoglobin that is set free at the time of the disintegration of the red 
corpuscles. There are reasons for believing that the liver and spleen are espe- 
cially concerned in the destruction of senile red corpuscles. 
Function of the Red Corpuscles.-The function of the red corpuscles is to 
carry oxygen from the lungs to the tissues. The red corpuscles are enabled 
to carry on this function by virtue of the presence in them of hemoglobin. 
This substance is a chromoprotein, possessing the property of uniting with 
oxygen when this gas is under sufficient pressure, and of releasing this gas 
when the pressure decreases. Under suitable chemical treatment, hemoglobin 
splits into a simple prolein, called globin, and a pigment, termed hematin. 
The oxygen-combining property of hemoglobin is related to the presence of 
hematin, in whose molecule there is an atom of iron. When hemoglobin 
has combined with oxygen, it is called oxyhemoglobin : when free from oxygen 
it is called deoxyhemoglobin or reduced hemoglobin. 
Hemoglobin is capable of combining with other gases, notably carbon 
monoxide, a gas found in illuminating gas and occurring as one of the products 
of the imperfect combustion of coal, gasoline, etc. Carbon monoxide, having 
a greater affinity than oxygen, displaces the latter in its combination with 
hemoglobin. This combination of carbon monoxide with hemoglobin is much 
firmer and stable than is the case with oxygen. Hence, carbon monoxide 
poisoning brings about death by depriving the tissues of the oxygen necessary 
for their functions. 
The total quantity of hemoglobin has been estimated at 14 per cent of the 
entire mass of blood. This quantity of hemoglobin is distributed among 20 or ESSENTIALS OF PHYSIOLOGY 
119 
25 trillions of red corpuscles, each of which has a surface area of about 0.000128 
sq. mm. The surface area of hemoglobin exposed to the oxygen in the lungs 
is, therefore, very great and has been estimated at 2,560 to 3,200 sq. m. 
The White Corpuscles or Leukocytes.-When blood is observed under 
the microscope, colorless cells of various sizes may be seen; these are the 
white blood corpuscles or leukocytes. The smallest of these have a diameter 
of 4 u (about ^,000 of an inch), while the larger ones may have a diameter of 
13 M (about Pi g 0 0 of an inch). As these cells are capable of ameboid movements, 
they are irregular in shape unless seen in the resting state, in which case they are 
circular in outline (Fig. 73). 
The greater number of white corpuscles consists of a transparent, apparently 
homogeneous ground substance containing granules of various sizes. Chemi- 
Fig. 73.-Ameboid movements of a white corpuscle from the frog. The form changes occurred 
within ten minutes. The black particles are Chinese ink which had been injected twenty-four hours 
before into the dorsal lymph sac. (Rauber-KopschC) 
cal tests have shown that these granules are composed of protein, lipoid, and 
carbohydrate (glycogen) material. The white corpuscles are nucleated, the 
shape of the nucleus differing in the various types of cells. 
The number of these cells varies between 6,000 and 10,000 per c. mm! of 
blood, there being, therefore, 1 white for every 700 red blood cells. Certain 
physiological, as well as pathological, conditions influence the number of white 
corpuscles. 
Varieties of White Corpuscles.-When a thin film of blood is stained with 
certain dyes, the various white blood cells are seen to react differently. This 
difference in staining properties has enabled investigators to classify these 
cells into five or six different varieties, as follows (see Fig. 74). 
(1) Small Lymphocytes, having a large round nucleus, and a narrow rim of 
cytoplasm. Their diameter varies from 4 /z to 7 u- They make up from 20 
to 25 per cent of all white cells. 
(2) Large Lymphocytes or Hyaline Cells resemble the small lymphocytes, 
except that the nucleus is relatively smaller, and the cytoplasm more abundant. 
Other cells called transitional cells are usually counted with the large lympho- 
cytes, and are distinguished from the latter by the crescentic or indented 120 
THE BLOOD 
nucleus. The large lymphocytes, including transitional forms, are present 
to the number of from 4 to 8 per cent. 
In both types of lymphocytes there are, as a general rule, no granules in 
the cytoplasm. 
(3) Polymorphonuclear Leukocytes.-This variety of white cell owes its 
name to the various shapes possessed by the nucleus in different cells. The 
cytoplasm contains many fine granules, which take a neutral stain. They are 
found to the extent of 60 to 70 per cent of the total number of white cells, and 
vary in size from 7^ to 10/x. 
Fig. 74.-The blood corpuscles (Wright's stain). I, red corpuscles; II, lymphocytes and 
large mononuclear leucocytes; III, neutrophiles; V, myelocytes (not found in normal blood); VI, 
mast cells. (E. F. Faber in Da Costa's Clinical Haematology.) 
(4) Eosinophilic Leukocytes or Eosinophiles.-As in the preceding type, the 
nucleus assumes different shapes. The cytoplasm does not stain, but its limits 
are indicated by the numerous coarse granules that take up the acid dye, such 
as eosin. Normal blood contains but 0.5 to 2 per cent of the total number 
of white cells. 
(5) Basophilic or Mast Cells.-The nucleus of this variety is often irregular. 
The granules vary in size, and react to the basic stain. This form occurs to the 
extent of 0.5 per cent of all white blood cells. 
The Life History of the White Corpuscles.-The most generally accepted 
view of the origin of the leukocytes regards the lymphocytes, both small and ESSENTIALS OF PHYSIOLOGY 
121 
large, as originating in the lymph-adenoid tissues, of the body e. g., the lymph- 
glands, etc. This tissue contains cells, called lymph-corpuscles, that are swept 
into the lymph stream and are thus carried ultimately into the general circu- 
lation. The transitional forms, polymorphonuclear, eosinophilic and basophilic 
leukocytes originate in the bone marrow, where they pass into the blood 
capillaries. 
The duration of their existence is unknown. Their ultimate disintegration 
in the blood stream probably contributes certain necessary materials to the 
blood plasma. , 
Functions of the White Corpuscles.-Little positive is known concerning 
the functions of these cells. A study of their action in certain pathological 
states has shown, however, that they constitute a part 
of the defensive mechanism of the body through which 
a more or less efficient immunity to disease is derived. 
The leukocytes, as already intimated, are capable of 
ameboid movement. This faculty enables them to pass 
through the walls of capillary blood vessels and to 
wander into the surrounding tissue spaces. To this 
phenomenon the term diapedesis is given (Fig. 75). 
By throwing out pseudopodia, the leukocytes are able 
to surround and engulf various foreign particles, includ- 
ing bacteria. This ability to ingest foreign particles is 
called phagocytosis. The micro-organisms thus ingested 
are, under favorable circumstances, destroyed. Poly- 
morphonuclear leukocytes are especially active in this 
respect, and are found in enormous numbers in tissues 
attacked by pus-forming bacteria. These leukocytes, 
when found in such locations, are called pus cells. 
When blood is shed, the leukocytes by their 
disintegration, contribute a part of the material neces- 
sary for its coagulation. 
The Blood Platelets.-A third corpuscle of small 
size (3M in diameter) may be observed in circulating 
blood, as well as in blood collected with special precau- 
tions. These corpuscles, called platelets or plaques, 
are more or less circular in outline, and have a dark granular center, 
usually regarded as a nucleus. These elements undergo rapid destruction 
when exposed to the air, and thus liberate a material necessary in the process 
of coagulation. Their number has been variously estimated at from 200,000 
to 778,000 per c. mm. 
The Blood Plasma.-The blood plasma or liquor sanguinis is the liquid 
portion of the blood. It is a clear, colorless, or faintly yellow liquid, having a 
specific gravity of 1.026 to 1.029 and a slightly alkaline reaction. The general 
discussion of the composition of the blood given at the beginning of this chapter 
gives an idea of the great complexity of the blood plasma. Some of the con- 
Fig. 75.-Diagram illus- 
trating the diapedesis of 
leukocytes. (G. Bachmann.) 122 
THE BLOOD 
stituents are capable of chemical analysis, while others, so far, are known 
through their actions only. 
The average chemical composition of blood plasma is shown in the follow- 
ing table: 
Chemical Composition of Blood Plasma 
Water 00.00 
Plasma-albumin 4.50 
Paraglobulin ... 2.40 
Fibrinogen 0.30 
Proteins 
Fats 0.25 
Sugar 0.10 
Urea 
Uric acid 
Creatin 
Creatinin 
Xanthin 
Hypoxanthin 
Amino-acids 
Cholesterol 
Lecithin 
Extractives 
0.60 
Sodium 
Potassium 
Calcium 
Magnesium 
Chlorides 
Carbonates 
Sulphates 
Phosphates 
Inorganic salts 
as 
o.8s 
In addition to the substances shown in this table, blood plasma contains 
gases in solution (oxygen, carbon dioxide, nitrogen), certain ferments and anti- 
ferments, immune bodies, products of the glands of internal secretion, and a 
number of substances necessary for coagulation. 
Coagulation of the Blood.-When blood is received into a beaker, it is at 
first liquid, but soon becomes viscid and gradullay passes into a semi-solid or 
jelly-like condition. To this change the term coagulation is given. The essen- 
tial phenomenon in the process of coagulation is the appearance of numerous 
fibrils of a protein material called fibrin. If the coagulated blood remains 
undisturbed, the coagulated mass shrinks and squeezes out a yellowish liquid, 
called serum. The fibrin network, in which the blood corpuscles are entangled, 
constitutes the clot. 
The average time it takes for coagulation to be complete varies in different 
animals and under different conditions. In man, the coagulation time is from 4 
to 7 minutes. 
The Cause of Coagulation.-As already stated, the essential process in 
coagulation is the formation of fibrin. Experiments have shown that fibrin is 
derived from fibrinogen under the influence of a ferment-like substance called 
thrombin, and of calcium. Why then does not coagulation occur in the blood 
stream? It has been shown that thrombin does not occur as such in the cir- 
culating blood, but as a precursor called thrombogen or prothrombin. In order 
that the thrombogen or prothrombin may be transformed into the active 
thrombin (a process called activation), it must be acted upon by another 
substance called thrombokinase in the presence of calcium. The thrombokinase ESSENTIALS OF PHYSIOLOGY 
123 
is derived from disintegrated platelets and leukocytes, as well as from any 
tissue cells that have been injured. 
This theory offered by Morawitz may be represented as follows: 
Disintegrated cells yield Thrombokinase 
Thrombokinase->Calcium-»Thrombogen->Thrombin 
Thrombin->Fibrinogen->Fibrin 
According to Howell the reason that prothrombin does not become acti- 
vated in the blood stream is that it is prevented from doing so by being bound 
with another substance called antithrombin. This combination is split under 
the action of the agent called thrombokinase above, but which Howell calls. 
thromboplastin. The prothrombin, being thus liberated, is activated into 
thrombin by calcium. The fibrinogen is then transformed by the thrombin 
into fibrin. Thromboplastin has been shown to be a phosphatid, probably 
kephalin. Howell's theory may be presented as follows: 
ProthrombinOAntithrombin->Thromboplastin-^Prothrombin (free) 
Prothrombin-»Calcium-/Thrombin 
Thrombin->Fibrinogen->Fibrin 
There are pathological conditions in which the blood coagulates very 
slowly, so that slight wounds will bleed for such long periods as to endanger 
the life of the individual. The most typical of these conditions is that called 
hemophilia. An individual so affected is called a "bleeder" or hemophilic. 
From studies made of this disease, it would seem that the chief defect is a 
deficiency in prothrombin. As the prothrombin is derived mainly from the 
blood platelets, and there is no decrease in their number, some change must 
have occurred in them that prevents their disintegration. Hemophilia is a 
congenital disease affecting the male, but transmitted through the female 
only; it is an example of sex-linked inheritance. Bleeders seldom reach middle 
age. 
The Total Quantity of Blood.-The volume of blood in the body has been 
estimated by direct and indirect methods. The direct method, as applied to 
adult man (guillotined criminals), gives a ratio of blood to body weight of i: 13, 
or 7.7 per cent. Indirect methods have given ratios varying from 1:19 to 
1:11, or about 5.25 to 9 per cent. Taking the last figure mentioned, a man 
weighing 70 kilos would have about 6,300 grams of blood; if the specific gravity 
of this blood be considered to be 1.056, then the volume of blood would be 
5,965 cc. 
The total volume of blood is distributed among the different organs as 
follows: 
Heart, lungs, arteries, and veins . 
Liver... M 
Muscles 
Remaining organs THE BLOOD 
124 
Anemia.-Anemia is an abnormal condition characterized by a deficiency 
in the number of red blood cells or in hemoglobin. In many cases a combination 
of these two factors is seen. As a result of the diminution of red blood cells 
and of hemoglobin, the individual is pale, suffers from shortness of breath, 
and from a rapid action of the heart. Anemia may be the result of an extensive 
hemorrhage, or of a slight hemorrhage occurring over a long period of time as 
in the case of bleeding piles and hookworm infection. The red blood cells 
may undergo an abnormal destruction through the action of toxins entering 
the circulation. Red cells are, likewise, destroyed in abnormal numbers, 
or fail to be regenerated, when the individual lives under unhygienic conditions. 
A combination of overwork and lack of fresh air and sun-light, when sufficiently 
prolonged, will give rise to anemia. 
There are other forms of anemia, of graver import, associated with disease 
of the spleen and bone marrow. CHAPTER XV 
PHARMACODYNAMICS OF THE BLOOD 
(i) Physiological Saline Solutions.-The most important and often danger- 
ous alteration of the volume of the blood is acute anemia, a diminution in the 
volume of the blood caused by hemorrhage or by profuse diarrheas. In cases 
of this kind life is often saved by simply increasing the volume of the circulating 
blood by diluting it with a Physiological ("normal"') Saline Solution administered 
by the intravenous (infusion), subcutaneous or rectal method. Experimentation 
has shown that the administration of such a solution after moderate hemorrhage 
so increases the volume of the blood that normal arterial pressure may be 
maintained for a considerable period, and that the coagulation time of the blood 
is shortened thus favoring the stoppage of the hemorrhage. 
The U. S. P. Physiological Saline Solution (Liq. Sodii Chloridi Physiolo- 
gicus) contains 0.85 per cent of Sodium Chloride( about a full teaspoonful to a 
pint). More complex solutions are at times employed, such as Dawson's 
Solution (0.8 per cent NaCl, 0.5 per cent NaHCO3), Locke's Solution (NaCl 
0.9 per cent; KC1 0.042 per cent; CaCl2 0.0024 per cent; NaHCO3 0.03 per cent; 
Dextrose 0.1 per cent), and Ringer's Solution (NaCl 0.7 per cent with small 
amounts of KC1 and CaCl2). The British Bayliss Solution contains 6 per cent 
of Acacia and 0.9 per cent of Sodium Chloride. The Acacia increases the 
viscosity of the blood, and it is claimed, is more effective in counteracting 
low blood pressure in the shock attending wounds. 
(2) Transfusion.-Another method for increasing the volume of blood is 
termed transfusion. This is the transmission of blood from a vessel of one 
person to a vein or an artery of another. It may be carried out by the direct 
method of attaching an artery of the donor to a vein of the recipient; or by 
easier indirect methods. One of the simplest of the indirect methods is to draw 
the blood by means of a syringe into a solution of Sodium Citrate, in such 
proportion that it contains 0.2 per cent of Sodium Citrate, which prevents the 
drawn blood from clotting and permits its subsequent injection into the vein 
of the recipient. Transfusion of blood not only increases the volume of the 
blood but in addition furnishes nutritive material, oxyhemoglobin, and possibly 
antitoxins or antibodies. 
(3) Hematinics.-Hematinics are drugs which tend to increase the 
amount of hemoglobin in the blood. They are therefore useful in certain forms 
of anemia, a condition characterized by a reduction in the amount of hemoglobin 
in the blood, resulting in a diminution in its oxidizing power. In addition to 
drugs it has been found that fresh air and sunlight are valuable agents. 
Iron.-The most important hematinic is Iron, commonly administered in 
the form of Tincture of Ferric Chloride, Pills of Ferrous Carbonate (Blaud's 
Pills), and Syrup of Ferrous Iodide. 
125 126 
PHARMACODYNAMICS OF THE BLOOD 
"Food-iron."-With the exception of rice, white bread, and many fruits, 
the substances used as foods contain Iron in such quantity and in such assimil- 
able form that the ordinary mixed diet supplies enough Iron for ordinary body 
needs. Iron occurs in food exclusively in organic form, generally in combination 
with nucleo-proteins. 
Iron is absorbed mainly from the duodenum, passing into the intestinal 
epithelium. Some of the Iron usually escapes absorption and is eliminated in 
the feces. The absorbed Iron probably then passes directly into the capillaries; 
from the blood the Iron is deposited as granules of the loose organic compound 
called ferratin in the cells of the spleen, liver, red marrow of bone, and slightly 
in the kidney. It is stored in this form until it is used or excreted. The 
liver and spleen seem to be the most important organs for maintaining the 
iron reserve. The stored Iron is transformed into hemoglobin only as needed. 
The administration of Iron is therefore of value only in conditions in which 
there is a deficiency in the normal income or the assimilation of Iron. 
Under the stimulating action of Iron the blood-making organs become more 
active in synthetizing hemoglobin. 
Excretion of Iron is carried out mainly by the large intestine, with traces 
in the bile, urine and gastric juice. 
For a time it was believed that the body could utilize only Iron 
administered in the organic form, but recent investigations have proved that 
inorganic Iron is absorbed, assimilated and converted into hemoglobin exactly 
like food-iron or organic Iron. 
Since Iron preparations are irritating they are administered with plenty of 
water after meals. In the stomach they are converted mostly into Ferrous 
Chloride or Albuminate. On passing into the duodenum the chloride or sul- 
phate probably changes to the carbonate. The Iron enters the blood doubtless 
as carbonate or albuminate. 
Manganese.-Traces of Manganese occur normally in all organs of man and 
animals. When given by mouth it is slightly absorbed and appears to take about 
the same course as Iron. Some investigators are of the opinion that Manganese 
increases the iron reserve of the body. 
Arsenic.-Arsenical compounds, like Arsenic Trioxide, Solution of 
Potassium Arsenite ("Fowler's Solution"), and Sodium Cacodylate, have been 
employed with more or less success in various leucemias and anemias. The 
results are frequently referred to an action, similar to that of Iron, on the bone 
marrow, but in many cases may be parasiticidal. 
(4) Systemic Alkalinizers or Antacids.-Drugs which increase the 
alkalinity of the blood are termed systemic alkalinizers or systemic antacids. 
Sodium Bicarbonate.-When Sodium Bicarbonate is introduced into the 
stomach its effects will vary according to the nature of the gastric contents at 
the time of administration. If given during the active digestive period it 
neutralizes a part of the Hydrochloric Acid of the gastric juice (local antacid), 
thus liberating Carbon Dioxide which acts as a carminative, and is absorbed as 
Sodium Chloride. Therefore, when administered at this time Sodium PHARMACODYNAMICS 
127 
Bicarbonate is purely a local antacid and not a systemic alkalinizer. However, if 
it is given in the resting period (between meals or before meals) Sodium 
Bicarbonate is absorbed as Bicarbonate into the blood to directly increase its 
alkalinity, i. e., is a systemic alkalinizer. Other alkali carbonates have similar 
actions but are less commonly employed. 
Acetates, Citrates, and Tartrates.-Sodium and Potassium Acetates, Sodium, 
Potassium and Lithium Citrates, and Potassium Bitartrate (" Cream of Tartar ") 
and Potassium Sodium Tartrate ("Rochelle Salt") do not neutralize acids, i. e., 
are not local antacids. However, they are oxidized in the tissues and 
absorbed into the blood as bicarbonates, and thus increase the available 
alkalinity of the blood. They, are therefore systemic alkalinizers (as well as 
diuretics). 
Citrates and tartrates are absorbed with some difficulty, and, consequently, 
are more or less laxative or cathartic. The portions absorbed, however, act as 
a systemic alkalinizer. 
(5) Serums and Vaccines.-Since the theories of the nature and formation of 
toxins and antibodies are topics usually discussed in bacteriology, the serums and 
vaccines will be mentioned but briefly here. 
Antitoxins.-The toxins, constituting one of the groups of most powerful 
poisons, are found in animals and plants, and have proved to be the means by 
which many pathogenic microorganisms affect the tissues. As yet none of 
them has been isolated in the pure form, no methods for separating them 
from the proteins of the cells in which they are formed having been perfected. 
Their intimate chemical composition is not satisfactorily understood. 
When animals are injected with small and gradually increasing doses of 
toxins, they finally become insusceptible (immunized) to amounts that would 
prove fatal to an untreated animal. This acquired immunity may persist in a 
greater or less degree for many months or even years. For this reason in many 
diseases, such as smallpox and measles, one attack of the disease confers more or 
less lasting immunity. It is believed that this acquired immunity is due to the 
formation in the animal of antagonistic protective substances-antibodies or 
antitoxins-which prevent the toxin from having any effect by forming a 
loose compound with it which is harmless. Experiment has shown that an 
animal forms a much larger quantity of antibodies than is actually needed to 
neutralize the quantity of toxin injected. This excesss may be obtained by 
bleeding the immunized animal and collecting the blood serum. 
Antitoxic Serums (Antitoxins).-These contain antitoxic substances formed 
by the injection of gradually increasing doses of bacterial toxins into animals, 
usually horses, bleeding the immunized animals, and separating the blood serum. 
When such a serum is injected into a patient it imparts a certain degree of 
immunity to subsequent doses of the original toxin. Certain antitoxic serums 
may be used to protect an individual from the toxin of a bacterial disease 
(prophylactic), if administered early enough, or to cure. The immunity estab- 
lished by the injection of antitoxic serums is a passive immunity to the disease, 128 
PHARMACODYNAMICS OF THE BLOOD 
and the protection usually lasts for only a few weeks or until the antibodies 
are destroyed or eliminated. 
Diphtheria and Tetanus Antitoxins are official and are the ones of greatest 
practical importance. 
Serum Disease.-In many individuals the injection of plain blood serum 
or antitoxic serum is followed in eight or ten days by skin eruptions, mild 
fever, joint pains and swelling of lymph glands. The condition disappears 
spontaneously. 
Anaphylaxis.-This is a more or less rare, peculiar phenomenon of hyper- 
sensitiveness to a foreign protein. Thus, when horse serum is injected into 
certain individuals and a second dose is given ten days or two weeks after the 
first, sudden swelling of the respiratory mucosa, failure of respiration, collapse, 
and even death may result within ten to twenty minutes. 
Vaccines.-Bacterial vaccines are suspensions, extracts or filtrates of killed 
cultures of specific bacteria. A vaccine prepared from organisms obtained from 
the patient himself is termed an autogenous vaccine and is usually looked upon as 
being more effective than "stock vaccines." Stock vaccines are suspensions of 
killed bacteria in salt solution, oil {lipovaccines}, or water, usually containing a 
small amount of a preservative like Phenol or Tricresol. 
Vaccines act by inducing a mild, harmless attack of the disease and thus 
causing the patient himself to manufacture his own specific antibodies. They 
therefore produce active immunity. Their value is most striking in preventing 
the development of disease {prophylaxis}, but they may also be curative. 
Vaccine Virus, used by inoculation {vaccination} to produce active 
immunity against smallpox, is official. Antirabic vaccine, tuberculin, typhoid 
vaccine, and gonococcus vaccine are examples of unofficial bacterial vaccines in 
common use. 
(6) Hemostatics or Styptics.-The hemostatics or styptics have already 
been discussed on page 25. These drugs are of value, however, only in cases 
of relatively small, accessible hemorrhages. Extracts of various tissues- 
"thromboplastins"-especially of the brain and the lungs, hasten the coagulation 
of shed blood and are frequently tried as hemostatics and in hemophilia, etc., 
They act apparently by neutralizing the antithrombin, which, according to 
Howell, exists in freshly shed blood and inhibits the activation of prothrombin 
by calcium (see page 123). CHAPTER XVI 
THE CIRCULATION OF THE BLOOD 
The tissues of the body are dependent for their 
activities on a normal supply of nutritive material 
and of oxygen, as well as on the removal of the 
waste material resulting from their activities. The 
blood not only supplies the tissues with the nutritive 
material they need, but receives also the waste 
material. In order, however, that the blood may 
fulfill this function it is necessary that it be kept 
continuously in movement. The apparatus through 
which the movement of the blood is maintained is 
called the circulatory apparatus. 
The Circulatory Apparatus.-The circulatory 
apparatus consists of (i) a central organ, called the 
heart, by means of which the blood is propelled in a 
definite direction; (2) a system of branching and 
diverging tubes, called arteries, through which the 
blood is distributed to all parts of the body; (3) a 
network of microscopic vessels, having exceedingly 
thin walls, called capillaries, where the exchange of 
material between the blood and the tissues takes 
place; and finally, (4) a system of uniting and con- 
verging tubes, termed veins, which serve to collect 
the blood from the capillaries and return it to the 
heart. The series of vessels through which the 
blood flows constitutes the vascular apparatus (see 
Fig- 76). 
The circulatory apparatus is thus a closed 
system, through which the blood necessarily must 
move in a circle. The movement of the blood 
through this system is, therefore, called the 
circulation. 
From experiments performed on different ani- 
mals, the lime required for a complete circulation of 
the blood has been estimated to be about 23 seconds. 
On this basis a complete circulation of the blood in 
man requires from 26 to 28 heart beats. 
Fig. 76.-Diagram of the 
circulation. 1, heart; 2, lungs; 
3, head and upper extremities; 
4, spleen; 5, intestines; 6, 
kidney; 7, lower extremities; 
8, liver. (After Dalton.') 
129 THE CIRCULATION OF THE BLOOD 
130 
The heart is a hollow, muscular organ, situated in the thorax behind the 
sternum and between the lungs. It is conical or pyramidal in shape, and lies 
obliquely the base being directed upward and to the right, and the apex down- 
ward and to the left. More of the organ lies to the left than to the right of the 
median line. 
The heart is about 5 inches long (about 12.6 cm.), 3^ inches broad, 
(about 8 cm.), and has a miximum thickness of 2^ inches,|(about 6.3 cm.). 
THE HEART 
Fig. 77.-Interior of right auricle and ventricle exposed by the removal of a part of their walls; 
1, superior vena cava; 2, inferior vena cava; 2', hepatic veins; 3, 3', 3", inner wall of right auricle. 
4, 4, cavity of right ventricle; 4', papillary muscle; 5, 5', 5", flaps of tricuspid valve; 6, pulmonary 
artery in the wall of which a window has been cut; 7, on aorta near the ductus arteriosus; 8, 9, aorta 
and its branches; 10, 11, left auricle and ventricle. (From Yeo after Allen Thompson.) 
Its weight in the male is 310 grams (11 ounces.). A muscular partition or 
septum, running through the long axis of the organ divides it into a right and a 
left half. Each half is in turn divided by an incomplete fibrous septum, lying 
transversely, into two chambers. The upper chamber has thin walls and is 
called the atrium or auricle. The lower chamber is thickwalled and is called 
the ventricle (see Figs. 77 and 78). 
The Right Auricle.-The right auricle is a more or less quadrangular 
chamber; a large vein-the superior vena cava-opens into its upper part, return- 
ing the blood from the head and upper limbs; another large vein-the inferior 
vena cava-opens into its lower part, and serves to return the blood from the rest 
of the body. A smaller vein-the coronary sinus-likewise opens into this 
chamber, and returns the blood from the heart muscle itself. ESSENTIALS OF PHYSIOLOGY 
131 
In the septum, separating the right from the left auricle, there is an oval 
depression called the/ossa ovalis. This fossa occupies the position of an opening 
found in embryonic and fetal life-the foramen ovale. 
The Right Ventricle.-The right auricle communicates with the right 
ventricle by an opening, called the right auriculo-ventricular opening, capable 
of being closed by a valve, named the tricuspid valve. This valve consists of 
three roughly triangular-shaped membranes attached to the fibrous tissue 
found at the junction between auricle and ventricle. The valve leaflets hang 
Fig. 78.-The left auricle and ventricle opened and part of their walls removed to show their 
cavities. 1, right pulmonary vein cut short; 1', cavity of left auricle; 3, 3", thick wall of left ven- 
tricle; 4, portion of the same with papillary muscle attached; 5, the other papillary muscles; 6, 6', 
the segments of the mitral valve; 7, in aorta is placed over the semi-lunar valves. (From Yeo after 
Allen Thompson.') 
into the ventricle. The interior of the right ventricle presents numerous 
muscular ridges, termed columnae carneae, and a number of conical muscles 
projecting into the cavity, called papillary muscles. From the tip of each 
papillary muscle there arise tendinous cords-the chordae tendineae-which 
are attached to the under surface of the valve leaflets near their free margin. 
The right ventricle gives rise at its left upper angle to a large vessel called 
the pulmonic artery, through which the blood is conveyed to the lungs. The 
opening of this vessel is provided with a valve composed of three semilunar 
or pocket-shaped membranes. 
The Left Auricle.-The left auricle has the same general shape as the 
right. Four veins open into it; these are the pulmonic veins. They return 132 
THE CIRCULATION OF THE BLOOD 
the blood from the lungs. This auricle communicates with the left ventricle 
through the left auriculo-ventricular opening. 
The Left Ventricle.-As on the right side, the left auriculo-ventricular 
opening is guarded by a valve. This valve consists of two leaflets and thus 
resembles, more or less, a bishop's mitre; for this reason it is generally called 
the mitral valve. The interior of the left ventricle is lined by muscular ridges 
and contains papillary muscles from which chordae tendineae spring to be 
attached to the leaflets of the mitral valve. The left ventricle has considerably 
thicker walls than the right. This is in keeping with the greater amount of 
Fig. 79.-Longitudinal section of a papillary muscle from the human heart. X 240. The 
transverse lines (x) are partly light (where the fiber has broken) and partly dark {intercalated, discs'). 
{From Lewis and Stohr's Histology.) 
work it has to do in propelling the blood throughout the body. The blood is 
conveyed to the general system through a large vessel springing from its upper, 
inner angle, and called the aorta. The opening into this vessel is provided with 
semilunar valves. 
The Endocardium.-The interior of the heart chambers is lined throughout 
by a smooth membrane, called the endocardium, which consists of connective 
and elastic tissue covered with endothelial cells. The valves are composed 
also of fibre-elastic tissue covered on both sides by the endocardium. This 
membrane is continuous with the internal coat of the vessels tha< open into 
the heart chambers. 
The Pericardium.-The pericardium is a fibro-serous sac covering the 
external surface of the heart and the root of the large vessels. From this 
point the sac is reflected and is attached by its external surface to surrounding ESSENTIALS OF PHYSIOLOGY 
133 
structures. This sac consists of fibro-elastic tissue lined on its internal surface 
with endothelial cells. That portion of the pericardium attached to the 
surface of the heart is called the epicardium or visceral layer; while the reflected 
portion of the pericardium is called the parietal layer. A small amount of 
lymph is found between the two layers and serves to diminish friction while the 
heart is contracting and relaxing. The pericardium prevents also, to some 
extent, an over-distension of the heart. 
The Cardiac Muscle and Its Arrangement.-The muscle fibers of which 
the heart is composed are cylindrical, branching cells showing cross and longi- 
tudinal striations. Each cell has a nucleus, but has no sarcolemma. The 
branches of adjacent muscle fibers are bound to each other so that the entire 
muscle mass consists of a net-work of cells or syncytium (Fig. 79). 
The muscle is arranged in sheets which take different courses in the walls 
of the various chambers. The arrangement of these sheets is very complex. 
They take oblique courses and form various loops, which, by their contraction, 
diminish the size of the cavities and force their contained blood in the direction 
imposed by the play of the valves. 
The Cardiac Cycle.-The heart's action consists of an alternate contraction 
and relaxation of its chambers. The contraction is called the systole; the relaxa- 
tion, the diastole. The first act in a heart beat is the contraction of the auricles. 
These two chambers contract virtually at the same time. A little more than 
one-tenth of a second later, the ventricles contract. While the ventricles are 
still in contraction, the auricles have relaxed; in fact the auricular contraction 
is very short, and serves merely to fill the ventricles with blood in addition to 
that which had entered these chambers while the heart was at rest. The 
auricles, therefore, play the part of feed-pumps. The ventricles, on the other 
hand, contract for a much longer time, and force the blood into the arteries 
against a high resistance. These chambers are comparable to force-pumps. 
To the totality of the events that take place in any one heart beat, the term 
cardiac cycle or cardiac revolution is applied (Fig. 80). 
Fig. 8o.-Diagram showing the events in the cardiac cycle. (From Brubaker's Text-book of 
Physiology.) 
It will be convenient, in describing the cardiac cycle and tracing the course 
of the blood through the heart, to begin while the heart is entirely at rest. 
During this time the blood is flowing into the right auricle from the venae 
cavae and coronary sinus and into the right ventricle through the right auriculo- 
ventricular opening. At the same time, blood is entering the left auricle from 
the pulmonic veins, and the left ventricle through the left auriculo-ventricular 
opening. The auricles then suddenly enter in contraction, and force their 134 
THE CIRCULATION OF THE BLOOD 
contained blood into the ventricles, past the auriculo-ventricular valves that 
were floated up by the blood filling the ventricles. Shortly thereafter, the 
ventricles contract. This contraction begins with the papillary muscles, so 
that the auriculo-ventricular valves are braced against the pressure they are 
beginning to feel on their under surface and that causes their sudden closure. 
For a short time after the beginning of the ventricular contraction the ventri- 
cular chambers remain entirely closed. During this time the pressure of their 
contained blood is rising rapidly. As soon as this pressure is greater than that 
in the pulmonic artery on the right side, and in the aorta on the left side, the 
semilunar valves are pushed open and the blood flows into these vessels. It 
continues to flow until the ventricles are almost empty, whereupon they sud- 
denly relax. At this moment the semilunar valves are suddenly closed by 
the pressure of the blood above them. 
In the meantime the auricles, having entered in diastole, have been filling 
with blood, and so the pressure in their interior has been rising. When the 
ventricles have sufficiently relaxed, the pressure of the blood in the auricles 
forces the auriculo-ventricular valves open, and the ventricles fill. The blood 
passing from the auricles into the ventricles is replaced by blood coming from 
the veins. The heart is then ready for another cycle. 
The Course of the Blood through the Heart.-The action of the valves, 
therefore, determines the direction the blood shall take. The general course 
of the blood is as follows: the venous blood that enters the right auricle and then 
the right ventricle, is forced through the closure of the tricuspid valve, occur- 
ring at the time of the ventricular contraction, into the pulmonic artery which 
conveys it to the capillaries of the lungs, where it looses in carbon dioxide 
and gains in oxygen. The blood is then returned from the lungs to the left 
auricle by way of the pulmonic veins. The blood then passes to the left 
ventricle, which on contracting forces it into the aorta, owing to the closure 
of the mitral valve. It is then distributed to capillaries throughout the body; 
there, the blood looses oxygen and gains in carbon dioxide. From these capil- 
laries the blood is returned to the right auricle by way of the venae cavae. That 
the blood is not returned from the arteries to the ventricles while the latter 
are relaxing is due to the fact that the semilunar valves close at the beginning 
of ventricular diastole. 
The Frequency of the Heart Beat.-The average frequency of the heart 
beat in males is 72 per minute, while that of the female is 80 per minute. The 
frequency is also greater in children than in adults, having an average of 95 
per minute in the third year. The frequency is influenced by posture, rising 
in passing from the recumbent to the sitting and then the standing posture from 
66 to 71 and to 81. Exercise, digestion and certain emotions likewise increase 
the frequency of the beat. 
An increase in frequency of sufficient magnitude takes place at the expense 
of the period of rest of the heart, and as the heart muscle is nourished during 
diastole, a rise of frequency, aside from entailing more work, interferes with the 
proper nutrition of the organ. ESSENTIALS OF PHYSIOLOGY 
135 
The Work Done by the Heart.-The blood is at all times under relatively 
high pressure in the arteries. When the ventricles force their contents into 
these vessels against the high blood pressure, they perform a certain amount 
of work. The work done may be estimated by multiplying the weight of blood 
forced out of the ventricles by the resistance opposing them. 
If the average pressure of the blood in the aorta is equivalent to a column 
of blood 1.93 meters in height, and the left ventricle expels 83 grams of blood at 
each beat, the work done will be represented by multiplying the weight of the blood 
by the height to which it is raised, or: 0.083 X 1.93 = 0.16019 kilogrammeter. 
To this must be added the work done in imparting velocity to the blood. 
This, however, is but a small fraction of the above figure. The right ventricle 
performs about one-third of the work of left ventricle. If we suppose that the 
heart beats at an average rate of 72 times per minute, the work done by the 
heart during twenty-four hours would be about 23,60c kilogrammeters. 
This work is enormously increased under any conditions in which the out- 
put of the heart and its frequency are increased. This is the case in muscular 
exercise in which the cardiac output per minute may be three or four times 
as great as during rest. 
The Properties of the Heart Muscle. (1) Irritability.-The heart muscle, 
in common with other forms of living matter, is capable of responding to the 
application of a stimulus; it possesses, therefore, the property of irritability. 
The nature of the natural stimulus is, as yet, unknown. The heart will respond, 
however, to adequate forms of artificial stimuli. 
The irritability of the heart muscle is influenced by temperature: heat 
increasing the irritability within limits, cold having the reverse effect. The 
state of nutrition of the heart, likewise, influences its irritability. 
(2) Conductivity^-By this term is meant the property possessed by living 
matter of transmitting a state of excitation through its substance. The 
stimulus, or excitatory process, arises in the mammalian heart in a remains of an 
embryonic chamber opening into the right auricle and called the sinus venosus. 
A sinus venosus persists throughout life in the lower vertebrates, but in mammals 
becomes merged into the right auricle. A small remnant of this chamber 
is found at the junction of the superior vena cava with the right auricle and is 
termed the sino-auricular node. It has been shown experimentally that the 
natural stimulus arises spontaneously in this node. The stimulus, or excitatory 
process, is transmitted rapidly to the muscle fibers of the auricular walls. 
It spreads also to the ventricles by way of a special structure called the atrio- 
ventricular bundle. This structure consists of muscle fibers of a more primitive 
type than the cardiac muscle. The atrio-ventricular bundle is found on the 
right side of the interauricular septum, and divides at the auriculo-ventricular 
junction into two branches, one for each ventricle. These branches break up 
into a network of fibers spreading under the endocardium, and making connec- 
tions with the cardiac muscle. This mechanism insures a rapid spread of the 
excitatory process to the muscular mass of the ventricles. The time required 136 
THE CIRCULATION OF THE BLOOD 
for the conduction of the excitatory process from the right auricle to the 
ventricle is about 0.12 second (Fig. 81). 
Experimental compression of the atrio-ventricular bundle interferes with 
the conduction of the excitatory process to the ventricles. The degree of inter- 
ference is proportional to the amount of the compression, passing from a mere 
delay in the time of conduction to a condition in which the excitatory wave 
coming down from the auricles is unable to pass the obstacle and thus fails to 
excite the ventricles. The ventricles, therefore, beat at a lower rate than the 
auricles. This condition is called heart-block (Fig. 82). 
(3) Rhythmicity.-As each beat of the heart occupies a definite period of 
time, the heart possesses the property or rhythmicity. The frequency of the 
Fig. 81.-Record of the contraction of the right auricle (Aur.) and right ventricle (Vent.) of the 
dog's heart. The A - V interval is approximately 0.08 sec. (G. Bachmann.) 
rhythm, however, varies in the different chambers. In those animals that have a 
sinus venosus it is found that this chamber exhibits the highest frequency of 
rhythm; that the auricles are next in order; and that the ventricle when entirely 
detached from the rest of the heart is incapable of developing a rhythm of its 
own. The mammalian heart exhibits similar differences, the sino-auricular 
node having the highest rhythm, knd the right auricle coming next in its power 
of producing rhythmical contractions. The ventricles, contrary to what is 
found in the case of cold-blooded animals, will develop their own rhythm when 
separated physiologically from the auricles. The frequency of the rhythm, 
however, is only about one-third that of the sino-auricular node. 
(4) Tonicity.-Cardiac muscle, in common with other kinds of muscle, 
exhibits the phenomenon of tone or tonus. By this is meant a more or less con- 
tinuous but slight degree of contraction. 
(5) Automaticity.-The heart is an automatic organ. By this is meant that 
whatever the nature of the stimulus may be, it arises within the organ itself. 
According to some investigators, the stimulus arises in nerve cells located 
within the walls of the right auricle, more particularly within or in the neigh- 
borhood of the sino-auricular node. From these cells the stimulus is conducted ESSENTIALS OF PHYSIOLOGY 
137 
by way of nerve fibers to all parts of the organ. This view constitutes the 
neurogenic theory of the heart beat. 
A more generally accepted view considers that the stimulus for the heart 
beat originates in and is conducted by muscle tissue. This conception of the 
origin and conduction of the stimulus constitutes the myogenic theory of the 
heart beat. 
Fig. 82.-Tracing of the heart's action in heart-block induced in a dog by clamping the atrio-ven- 
tricular bundle. (G. Bachmann.) 
THE NERVE REGULATION OF THE HEART BEAT 
The heart, being an automatic organ, does not depend on the arrival of 
nerve impulses from the central nerve system for its beat. Nevertheless, the 
force and the frequency of the heart's action are made to vary from time to time 
in accordance with the needs of the other organs through the intermediation of 
the central nerve system. Two sets of nerves are distributed to the heart: 
the vagus and the sympathetic (see Fig. 83). 
The Origin and Distribution of the Cardiac Fibers of the Vagus Nerve.- 
The cardiac fibers of the vagus nerve are a part of the autonomic nerve system. 
They originate in nerve cells located in the medulla oblongata. The nerve 
fibers arising from these cells pass into the trunk of the vagus and leave it in the 
neighborhood of the heart to contribute to the formation of the cardiac plexus. 
Ultimately they pass under the epicardium and terminate around the ganglion 138 
THE CIRCULATION OF THE BLOOD 
cells found in groups throughout the sino-auricular junction, as well as in 
the atrio-ventricular bundle. From these ganglion cells other fibers arise that 
end, in all probability, on the muscle fibers of the sino-auricular node, as well 
as on those of the beginning of the atrio-ventricular bundle. 
The Origin and Distribution of the Cardiac Sympathetic Nerve.-The 
preganglionic fibers of this nerve arise, it is believed, in nerve cells located in the 
Emotional Centers 
Exhilarating (blue) 
Depressing (aeo) 
Cardio-Inhibitor Center 
Cardio -Accelerator Center 
lagas Nerve 
Aff^^^ti^citutor (bluc) 
Afferent inhibitor [gLU£) 
Efftnni ^Inhibitor(be0) 
Ganglion Stellatam 
Sympath etl c Ne roes' 
Accelerator ^Augmentor 
Inlra-CardiacNeroe Cells 
Fig. 83.-^Diagram of the nerve mechanism of the heart. (G. Bachmann, in Brubaker's Physiology.) 
medulla oblongata. These fibers descend in the lateral column of the spinal cord 
as far as the second, third, and sometimes the fourth thoracic segments. They 
leave the spinal cord with the corresponding spinal nerves, and pass into the 
vertebral chain to end ultimately around the nerve cells of the first thoracic 
ganglion, or ganglion stellatum. From these cells postganglionic fibers pass into 
the cardiac plexus, and thence into the heart. ESSENTIALS OF PHYSIOLOGY 
139 
Fig. 84.--Tracing from the dog's heart showing the effect of stimulation of the peripheral end 
of the divided right vagus. Observe the complete arrest of auricular and ventricular beats. The 
first auricular beat, on recovery, is of large size and is followed by a marked depression of contractility. 
(G. Bachmann.) 
Fig. 85.-Tracing from the dog's heart showing the effect of stimulation of the peripheral end 
of the divided left vagus. There is but slight slowing of the auricles; an incomplete heart-block is 
the most evident result of the stimulation, the ventricles responding to every other auricular beat 
only. (G. Bachmann.) 140 
THE CIRCULATION OF THE BLOOD 
The Function of the Cardiac Fibers of the Vagus.-The action of the vagus 
nerve can be disclosed by dividing it and stimulating its peripheral end. With 
a stimulus of sufficient intensity the heart will come to a complete standstill in 
diastole. With weaker stimulation the heart will beat less frequently, and the 
force of the beat will be diminished. The vagus nerve serves, therefore, to 
check or inhibit the activity of the heart; it is the cardio-inhibitor nerve. In 
mammals a complete cessation of the heart beat cannot be maintained for more 
than a few seconds, despite a continuance of the stimulation. Stimulation of the 
vagus nerve, in addition to diminishing the force and frequency of the beat, 
likewise diminishes the conductivity of the heart muscle. This effect is, how- 
ever, more pronounced on stimulation of the left, than on that of the right vagus. 
(Figs. 84 and 85.) 
Fig. 86.-Tracings showing the effects on the heart-beat of the frog from stimulation of the 
sympathetic nerves prior to their union with the vagus nerve. The upper tracing shows an increase in 
the rate, which before stimulation was 15 per minute and during stimulation 30 per minute. Before 
stimulation the height of the ventricular beat was 9 mm. and during the stimulation it was 12 mm. 
The lowest tracing shows a similar series of effects, the differences being only of degree. {Brodie.) 
If a section of both vagi be made, it will be observed that the heart rate 
instantly rises. This indicates that, normally, the nerve cells that give rise to 
the vagus fibers are at all times discharging nerve impulses that course to the 
heart to check its activity. This group of nerve cells is called the cardio- 
inhibitor center. This center is, therefore, tonically active. Its activity may be 
increased or decreased through the arrival of reflex nerve impulses, or through 
the influence of emotional disturbances. 
The Function of the Cardiac Sympathetic Nerve.-Stimulation of the sym- 
pathetic fibers causes an increase in the frequency and in the force of the heart 
beat. The acceleration of the heart's activity varies from 58 to 100 per cent, 
while the augmentation in the force of the beat may be well defined or wholly 
lacking. For this reason the sympathetic nerves are believed to contain two ESSENTIALS OF PHYSIOLOGY 
141 
classes of fibers, viz., cardio-accelerator and cardio-augmentor fibers. The 
augmentor fibers are generally found in the left nerve (Fig. 86). 
The nerve cells in the medulla that give rise to the preganglionic fibers 
constitute the cardio-accelerator center. This center, like the cardio-inhibitor 
center, is in a state of tonic activity. 
The heart is thus under the control of two sets of nerves having opposite 
effects on its activity. The frequency and the force of the heart's action at any 
moment will vary, therefore, according as one or the other of these two sets of 
nerves will preponderate in its action. CHAPTER XVII 
THE VASCULAR APPARATUS 
The vascular apparatus consists of arteries, 
capillaries and veins. It is generally divided into a 
systemic and a pulmonic portion. The systemic 
apparatus includes the vessels that begin at the left 
ventricle with the aorta and end at the right auricle 
with the superior and inferior venae cavae. The 
pulmonic apparatus consists of the vessels that 
begin at the right ventricle with the pulmonic 
artery and end at the left auricle with the pulmonic 
veins (see Fig. 86). 
In these divisions of the vascular apparatus 
there is generally but one set of capillaries between 
arteries and veins. In the abdomen, however, there 
is a double set of capillaries intervening between the 
arteries and the veins. The vein that receives the 
blood from the capillaries of the stomach, intestines 
and spleen passes to the liver, where it again 
breaks up into capillaries. These capillaries dis- 
charge their blood into the hepatic veins, which 
empty into the inferior vena cava. As the vein that 
enters the liver is called the portal vein, this portion of 
the general circulation is called the portal circulation. 
THE STRUCTURE OF THE BLOOD VESSELS 
(i) Arteries.-An artery of average size consists 
of three coats: an internal or tunica intima; a middle 
or tunica media; and an external or tunica adventitia, 
(Fig. 87). 
The internal coat is composed ot a layer of smooth 
endothelial cells resting on an elastic basement mem- 
brane. The middle coat consists of number of layers 
of non-striated muscle fibers arranged circularly, and 
held by elastic connective tissue fibers. The external 
coat is made up of white fibrous and yellow elastic 
connective tissue. 
In the larger arteries the elastic tissue predominates greatly, and the 
muscle tissue is relatively much less abundant. The external coat is also well 
Fig. 86.-Diagram of the 
circulation, i, heart; 2, lungs; 
3, head and upper extremities; 
4, spleen; 5, intestines; 6, kid- 
ney; 7, lower extremities; 8, 
liver. (After Dalton.) 
142 ESSENTIALS OF PHYSIOLOGY 
143 
developed. As the arteries decrease in size, the muscle tissue does not decrease 
in thickness to the same extent as the connective tissue, so that relatively to the 
other coats, the muscle coat of the small arteries is well developed. The very 
fine, microscopic arteries preceding the capillary network are called arterioles. 
Since the arteries contain both elastic and muscle tissue in their walls, they 
possess the properties of elasticity and contractility. 
(2) Capillaries.-Beyond the arterioles the vessel walls gradually decrease in 
thickness through an attenuation of the external and middle coats. Ultimately 
there remains in the vessel wall but a single layer of endothelial cells. At this 
point the true capillaries are reached (Fig. 88). These microscopic vessels vary 
Fig. 87.-Coats of a small artery, a. 
Endothelium; b, internal elastic lamina; c, 
circular muscular fibers of the middle coat; 
d, the outer coat. (Landois and Stirling.) 
Fig. 88.-Capillaries. The outlines of 
the nucleated endothelial cells with the cement 
blackened by the action of silver nitrate. 
(Landois and Stirling.') 
in size in different tissues from 4.5/z to 7.5^, and will, therefore, allow red blood 
cells to pass in single file only. These vessels form networks, the length of the 
individual vessels varying from 0.5 mm. to 1.0 mm. 
The capillaries permit the passage through their walls of a variety of sub- 
stances found in the blood stream, as well as in the tissue spaces; that they are 
capable of fulfilling this function is due to their property of permeability. 
(3) Veins.-The network of capillaries empties into microscopic vessels, 
called venules. These are small veins corresponding to the arterioles on the 
arterial side of the capillaries. The venules unite to form larger and larger 
vessels, called veins. The walls of these vessels have the same coats as the 
arteries, but neither the elastic nor the muscle tissue are found in as large an 
amount. For this reason a vein collapses when empty, whereas an artery retains 
its cylindrical form. 144 
THE VASCULAR APPARATUS 
The veins, like the arteries, are endowed with the properties of elasticity and 
contractility. The elastic and contractile tissues being less abundant, these 
properties are less well developed. 
The large veins of the extremities possess valves consisting of two semilunar 
leaflets formed by a folding of the internal coat strengthened by fibrous tissue 
(Fig. 89). They open toward the heart, and close whenever there is any obstruc- 
tion to the forward flow of blood thus preventing, temporarily at least, a 
Fig. 89.-The pocket valves in the veins. On the right is shown the external appearance of 
the vein at the valves when the latter are closed; on the left, a vein slit lengthwise and opened; in 
the middle, a longitudinal section of a vein. (Hough and Sedgwick.) 
damming back of the blood in the capillary region. These valves are found also 
at the entrance of the large veins into the abdominal and thoracic cavities. 
(i) Arteries.-At every contraction of the left ventricle there is forced about 
80 cc. of blood into th e already full arterial system. This blood is accommodated 
by the distension of the aorta. As soon as the contraction of the heart has 
ended, the distended aorta recoils upon the blood and propels it onward. The 
elasticity of the arteries enables these vessels to transform the intermittent 
outflow from the heart into a remittent flow in the arteries and ultimately a 
continuous flow into the capillaries and veins beyond. 
If an artery be severed, it will be observed that the blood comes out of it in 
spurts and that it is projected to a considerable distance. The arterial blood is, 
therefore, under high pressure. This fact can be illustrated by inserting a long 
vertical glass tube into an artery. In an experiment of this sort made on a horse 
the blood ascended to a height of 8 feet and 3 inches. In man, a similar experi- 
ment would yield a pressure of about 6 feet, 6 inches of blood, or if a mercury 
manometer were used, a pressure of 120 mm. Hg. 
The causes of the high arterial pressure are, first, the driving force of the heart; 
and second, the resistance which the blood encounters while flowing through 
the entire vascular apparatus, but more especially, the high resistance found in 
the arteriole region. These vessels are tonically contracted, and thus narrow the 
stream bed at the end of the arterial system. As a consequence, the resistance 
at this point is high, and the pressure ahead, i. e., in the arteries, is correspond- 
ingly high. Owing to the intermittent action of the heart and the elasticity of 
the arterial wall, the arterial pressure undergoes oscillations between a relatively 
high level during the systole; and a lower level seen during the diastole at 
THE FUNCTIONS OF THE BLOOD VESSELS ESSENTIALS OF PHYSIOLOGY 
145 
which time the blood is passing into the capillaries. The extent to which 
the pressure will fall during the diastole will necessarily be determined by 
the degree of contraction of the arterioles. Normally this factor is so adjusted 
that the diastolic level of pressure is about 80 mm. Hg. The pressure seen 
during systole is, in young men, about 120 mm. Hg. The arterial pressure 
thus oscillates with every heart beat between 80 and 120 mm. Hg. The 
increase of pressure between the diastolic and the systolic level travels through 
the arterial system in the form of a wave called the pulse wave; hence, the differ- 
ence between the diastolic and the systolic level is called the pulse pressure. 
This pressure, in the instance just mentioned would, therefore, be 40 mm. Hg. 
It is the passage of the pulse wave along the arteries that gives rise to the alter- 
nate expansion and recoil of their walls that is called the pulse. 
The height of the arterial pressure increases with age. The chief cause of 
this change is the gradual decrease in the elasticity of the arteries. 
The property of contractility possessed in high degree by the arterioles thus 
serves to maintain the high resistance in this region, which as previously 
explained, is responsible for the high arterial pressure necesssary for an effective 
circulation. In addition to this function of the arteriole muscle, it affords a 
means of regulating the amount of blood to be distributed to various organs in 
accordance' with their needs. This is accomplished by a contraction of the 
arterioles in the less active tissues, and a dilatation of the arterioles supplying 
organs in a state of functional activity. 
(2) Capillaries.-The object of the circulation is to supply the tissues with 
oxygen and nutritive material, and to remove waste. This object is accomp- 
lished in the capillary region of the vascular apparatus. That the capillaries 
are capable of fulfilling this function is due to their extremely thin and 
permeable wall. The forces responsible for the passage of the material through 
the capillary wall are those of difusion, osmosis, dialysis, and filtration. The 
action of these forces is modified in the various tissues by differences in the 
degree of permeability of the capillary wall. 
The exchange of material between the blood within the capillaries and 
the lymph found in the tissue spaces is conditioned by the amount of blood 
flowing through the capillaries, its pressure, its velocity, and the constancy 
of its flow. The average pressure of the blood within the capillaries is about 
20 mm. Hg. 
Owing to their small size, a hemorrhage from these vessels is characterized 
by an oozing of the bloo,d from the wound. 
(3) Veins.-The veins return the blood from the capillary areas to the heart. 
The pressure in these vessels is low, being but 10 mm. Hg. in the small veins on 
the back of the hand, and 0.5 mm. Hg. in the external jugular vein. When a 
vein is cut, therefore, the blood does not come out with the force seen in arteries, 
but merely wells out of the vessel. Aside from this difference, the color of the 
blood in arteries is a bright scarlet-red, whereas in the veins it is a deep purple. 
The relative height of the blood pressure in the three divisions of the vascular 
apparatus is represented graphically in Fig. 90. 146 
THE VASCULAR APPARATUS 
The return flow through the veins is aided by accessory forces. These 
consist of: (r) The contraction of the skeletal and visceral muscles which, by 
compressing the veins, force the blood onward; a backward flow toward the 
capillaries cannot take place owing to the closure of the venous valves. (2) 
The movements of respiration. At the end of expiration the pressure within the 
thorax is below that of the atmosphere. This negative pressure, being felt by 
the great veins, causes the blood in the veins outside the thorax to be aspirated 
toward the heart. During inspiration the pressure within the thorax becomes 
still lower; the blood is, therefore drawn with increasing speed into the large 
veins that empty into the right auricle. This action is aided by a simultaneous 
rise of intra-abdominal pressure, caused by the descent of the diaphragm. This 
Line of 
-SYSTOLIC PRESSURE 
Line of 
MEAN PRESSURE 
Line of 
DIASTOLIC - 
PRESSURE 
PULSE PRESSURE 
The difference between 
DIASTOLIC 
and 
SYSTOLIC PRESSURE 
Fig. 90.-A diagram designed to show the magnitude and the relation of the blood-pressure in 
the three divisions of the vascular apparatus, as well as the relation of the diastolic, the mean, and 
the systolic pressures in the arterial system. Based on experiments made on dogs. H, heart; A, 
arteries; C, capillaries; V, large veins; O, O, being the zero line ( = atmospheric pressure), the pressure 
is indicated by the height of the curve. The numbers on the left give the pressure (approximately) 
in millimeters of mercury, h, pressure in heart; a, arteriole region showing sudden fall of pressure; 
c, the fall of pressure in the capillaries; v, the negative pressure in the large veins. (From Brubaker's 
Textbook of Physiology.) 
rise of pressure forces the blood of the inferior vena cava into the heart. 
During expiration the pressure within the thorax returns to its former level, and 
the quantity of blood flowing into the heart diminishes. 
The Velocity of the Blood.-The velocity of the blood is relatively high in 
the arteries, but gradually diminishes as these vessels branch out, and becomes 
least in the capillary region. This diminution in the velocity is due to the large 
increase in the width of the stream bed which accompanies the repeated divisions 
of the vessels. The velocity of the blood in the capillaries has been shown to be 
between 0.5 mm. and 1.0 mm. per second. As the vessels converge to form ven- 
ules and veins, the stream bed again narrows and the velocity increases, although 
it does not return to what it was in the arteries because the total area of cross 
section of the venous bed is greater than that of the arterial bed. In fact the 
capacity of the venous system is so much greater than that of the arterial system, 
that all the blood of the body could be stored in the veins. ESSENTIALS OF PHYSIOLOGY 
147 
THE NERVE REGULATION OF THE BLOOD VESSELS 
In discussing the functions of the arteries it has been stated that the 
arterioles are at all times in a state of slight but continuous contraction, and 
that this tonic contraction is necessary to maintain the relative pressures found 
in the different parts of the vascular apparatus. The chief cause of the tonic con- 
traction of the arterioles is the constant arrival of nerve impulses into their 
muscular coat. The changes of caliber seen in these vessels when changes in the 
distribution of blood to various organs take place, are likewise occasioned by 
nerve impulses which determine an increase in the contraction, or a relaxation 
of their muscle coat. 
The system of nerves that regulates the caliber of the blood vessels, 
especially that of the arterioles, is called the vaso-motor system; it is a part of 
the autonomic nerve system. Those nerve fibers that increase the contraction 
are called vaso-constrictor or vaso-augmentor; those that decrease the con- 
traction, and thus cause a dilatation of the vessel, are called vaso-dilatator or 
vaso-inhibitor. 
The Vaso-constrictor Nerves.-The vaso-constrictor nerves, being a part 
of the autonomic nerve system, consist of two neurons: a preganglionic and a 
postganglionic neuron. The preganglionic fibers arise in nerve cells in the 
lateral horn of the gray matter of the thoracic and lumbar segments of the spinal 
cord. These fibers terminate around the cells of sympathetic ganglia of the 
vertebral and prevertebral chains. From these cells postganglionic fibers arise 
that pass to the blood vessels. One of the most important of the vaso-con- 
strictor nerves of the body is the splanchnic nerve. It supplies the blood 
vessels of the majority of the abdominal organs. As this vascular area is large, 
stimulation of the splanchnic nerve induces a marked rise in the general arte- 
rial pressure, white its section causes a fall in the general arterial pressure. 
The Vaso-motor Center.-The activity of the vaso-constrictor nerves 
throughout the body is under the control of a group of nerve cells situated in 
the medulla oblongata. To this group of nerve cells the term vaso-motor 
center is given. This center sends nerve fibers to the thoracic and lumbar seg- 
ments of the spinal cord, from which the preganglionic fibers of the vaso-con- 
strictor nerves arise. 
The vaso-motor center is in a state of tonic activity, as can be demonstrated 
by a section of the spinal cord that interrupts the nerve fibers descending from 
the center. Such a section is immediately followed by a wide dilatation of all 
the arterioles and a marked fall of arterial pressure. 
The tonic activity of the vaso-motor center is caused, in part, by the stimu- 
lating action of the acid products of metabolism, more especially of carbon 
dioxide. A rise in the H-ion concentration of the blood stimulates the center 
to increased activity, and the arterial pressure rises. This phenomenon occurs 
typically in asphyxia. The vaso-motor center is also under the influence of 
reflex nerve impulses. 
The effect produced by the reflex nerve impulses discharged into the center 
varies with the afferent nerve stimulated. The majority of afferent nerves 148 
THE VASCULAR APPARATUS 
cause an increase in the activity of the center. As the effect that follows, is a 
rise in the arterial pressure, the afferent nerve fibers conveying the impulses 
to the center are called pressor nerve fibers. Other afferent nerves, when stimu- 
lated, inhibit the activity of the vaso-motor center, and thus bring about a fall 
of arterial pressure. The afferent nerve fibers causing this effect are called 
depressor nerve fibers. 
The application of cold to the skin causes a blanching brought about by a 
constriction of the arterioles supplying the skin. This phenomenon is a reflex 
action, the result of stimulation of pressor nerve fibers. Conversely, the appli- 
cation of heat causes a dilatation of the blood vessels of the skin owing to a 
stimulation of depressor nerve fibers. The vaso-motor mechanism is, therefore, 
an important means of regulating body heat. / 
The vagus nerve contains depressor nerve fibers distributed peripherally 
to the root of the aorta, and possibly to the ventricles as well. When, for any 
reason, the arterial pressure rises to an abnormal height, nerve impulses ascend 
this nerve and inhibit the vaso-motor center; nerve impulses are likewise trans- 
mitted by this nerve to the cardio-inhibitor center which they stimulate. The 
result is a dilatation of the arterioles throughout the body, and a diminution 
in the force and frequency of the heart beat. These two factors cause the 
arterial pressure to fall. 
The activity of the vaso-motor center may be modified also as a result of 
emotional disturbances. Since the emotions arise in the cerebrum, there must 
be nerve fibers descending from the cerebrum to the center. The emotion 
of shame or embarrassment causes a flushing, while great fear causes a blanch- 
ing of the skin. 
The Vaso-dilatator Nerves.-The trunks of the spinal nerves contain 
fibers whose stimulation gives rise to a dilatation of the arterioles. Experiments 
have demonstrated that these nerve fibers, cqntrary to what might be expected, 
are not efferent but afferent nerve fibers. This being the case, these fibers 
carry nerve impulses in a direction opposite to that usually observed in other 
afferent fibers; for this reason they are called antidromic nerve Ubers. 
There are reasons for believing that these fibers branch near their peripheral 
end, one branch going to the skin or mucous membrane, the other to the wall 
of the blood vessels. It has been shown also that a reflex action may occur 
through the point at which the branching occurs. Such a reflex action is 
called an axon reflex. 
Other vaso-dilatator nerve fibers which are, however, purely efferent in 
function, are found in the trunks of the facial and of the glosso-pharyngeal, 
on the one hand, and in some of the sacral nerves, on the other hand. The 
vaso-dilatator nerve fibers found in the facial and glosso-pharyngeal are 
distributed, through the intermediation of sympathetic ganglia, to the blood 
vessels of the mucous membrane of the naso-pharynx, cheek and gums, and 
of the submaxillary, sublingual, and parotid glands. The sacral vaso-dila- 
tator nerve fibers are' found in the nervus erigens and are distributed to the 
blood vessels of the sexual organs. Stimulation of these fibers gives rise to ESSENTIALS OF PHYSIOLOGY 
149 
an engorgement of the organs of generation such as occurs during sexual 
excitement. 
The vaso-dilatator nerve fibers are not tonically active; neither are they 
under the control of a general center. The nerve cells from which the medul- 
lary and sacral vaso-dilatator nerves arise are capable, however, of being 
stimulated reflexly, as well as through the influence of various emotions. 
Vaso-motor Nerves to the Capillaries and Veins.-In the preceding 
discussion, all vaso-motor reactions have been described as taking place in 
the arterioles. It is probable, however, that the capillaries and the veins are 
supplied with vaso-motor fibers. The distribution of blood in accordance with 
the needs of the tissues is accomplished, therefore, not only by changes in the 
caliber of the arterioles, but by appropriate changes taking place simultaneously 
in the capillaries and in the veins. Recent studies have shown that during 
rest the capillaries found in muscle are in part so firmly contracted that the blood 
cannot pass through them. Only about one-fourth of the capillaries, it has 
been estimated, are open to the blood stream. When the muscle enters into 
activity, the capillaries that were constricted dilate and permit a considerable 
increase in the quantity of blood flowing through the muscle. It has been shown 
that these changes in the caliber of the capillaries are not merely passive, but 
are the result in part of chemical action, and in part of nervous regulation. 
Some Facts Relative to the Hygiene of the Circulation.-Certain infectious 
diseases, notably acute rheumatic fever, tonsillitis, and syphilis, may cause an 
inflammation of the endocardium. As the valves of the heart are formed by a 
folding of the endocardium strengthened by connective tissue, they suffer 
more or less extensively. In the course of time there results a shrinking of the 
valve leaflets, so that the opening they guard no longer closes completely. 
The blood, therefore, flows in part in the direction whence it came or regurgitates, 
a condition called regurgitation. At other times, the valve leaflets adhere 
permanently to each other and are incapable of opening as fully as formerly. 
This condition is called stenosis. In this case the blood encounters a high 
resistance in passing into the chamber or vessel for which it is destined. In 
any event, one or more of the heart chambers has more work to perform. 
If the nutrition of the heart muscle is adequate, the wall of the chamber affected 
responds by increasing in thickness, giving rise to what is known as a hyper- 
trophy of the chamber. The reserve power of the heart is, however, encroached 
upon so that the organ is not as able to meet unusual demands. If, for any 
reason, the nutrition of the heart muscle declines, or the organ is subjected to 
continued strain, the heart muscle gradually looses its tone and dilates. The 
heart is no longer capable of maintaining a sufficiently high arterial pressure; 
the blood accumulates in the capillaries and veins; the tissues suffer in their 
nutrition; and constituents of the blood plasma escapfe in the tissue spaces, 
giving rise to edema. Instead of a gradual dilatation, a diseased heart may under 
unusual strain dilate suddenly and fail to contract again. 
The seriousness of valvular disease varies in accordance with the valve 
affected. In any case, precautions should be taken to avoid those infections 150 
THE VASCULAR APPARATUS 
which are known to cause heart disease. If, however, one should be so unfor- 
tunate as to contract such a disease, it is imperative that treatment should be 
prompt and effective. An essential part of the treatment is rest in bed in order 
to decrease the work of the heart. 
Since the supply of blood available for the needs of the body is limited, 
any increased supply to a sufficiently large area must be accompanied by a 
decreased supply to all other areas of the body. During mental activity blood 
must flow to the brain in larger quantities. There are reasons for believing 
that the blood vessels of the brain are not provided with vaso-motor nerves. 
A greater volume of blood is made to flow through the cerebral vessels, however, 
through a general constriction of the arterioles, more especially those supplying 
the skin. The effect is a general rise in arterial pressure which causes a diver- 
sion of the blood to the brain. Conversely, during sleep the blood vessels 
of the skin dilate; blood is, therefore, withdrawn from the brain and its activity 
declines so that sleep sets in. When the vessels of the skin are constricted by 
cold, it is more difficult to fall asleep. Insufficient covering, therefore, inter- 
feres with restful sleep. 
Unconsciousness, such as is seen in fainting, is primarily due to withdrawal 
of blood from the brain. An unconscious individual should, therefore, be made 
to lie on his back, the head lower than the feet, that the circulation through 
the brain may be aided by the force of gravity. 
During digestion a larger amount of blood flows through the alimentary 
canal and its associated glands. This continues for a variable time depending 
on the quantity and character of the food. In this case, also, the increased 
quantity of blood flowing through the organs of digestion is compensated for 
by a constriction of the vessels of the skin. In cool weather it is not uncommon 
for an individual to feel chilly after a meal. Mental work is difficult also for 
some time after eating. These considerations indicate the need for rest for at 
least half an hour after eating. Muscular or mental work cannot be done at the 
height of digestion without interfering with a function that is of the greatest 
importance to the health of the individual. CHAPTER XVIII 
THE LYMPH 
The blood does not come in intimate contact with the tissue cells. The 
liver and the spleen, however, are exceptions to this general rule. Generally, 
certain parts of the blood pass through the capillary wall into spaces found in 
the tissues, and constitue the lymph or tissue fluid. The tissue cells select 
what material they need out of the lymph for their growth, repair, and energy, 
and discharge into it their waste products. 
Fig. 91.-Diagram of the main lymph vessels, p lymph vessels from the head and neck; 2, 
lymph vessels from the upper extremity; 3, lymph vessels of the thorax; 4, intestinal lymph vessels; 
5, lymph vessels from the lower extremity; c.c., cisterna chyli; t.d., thoracic duct; r.l.d., right lymph- 
atic duct; l.j.v., left jugular vein; l.s.v., left subclavian vein. (G. Bachmann.) 
Aside from the spaces found within the tissues, larger spaces, lined by endo- 
thelial cells, contain a fluid resembling lymph. These spaces are called serous 
cavities. Among these are the pericardial, pleural, abdominal, and synovial 
cavities. 
The Lymphatic System.-If the irritability of the tissue cells is to continue 
unimpaired, it is necessary that the lymph should continue to be formed in 
151 THE LYMPH 
152 
proper amounts, and that the lymph that has received the waste products 
be continuously removed. This is accomplished by a system of vessels which, 
beginning in the tissue or lymph spaces, carries the lymph into the venous blood 
stream. To this system the term lymphatic system is given (see Fig. 91). 
The lymphatic system begins in lymph capillaries. These are micro- 
scopic tubes whose wall consists of a single layer of endothelial cells. They 
form a meshwork in the tissues, and end blindly. The lymph capillaries empty 
into gradually enlarging vessels called lymph vessels, possessing three coats 
similar to those seen in veins. These vessels, however, are provided with a 
greater number of valves than the veins. For this reason the lymph vessels, 
when full, have a beaded appearance. 
The lymph vessels of the lower extremities, abdominal organs, trunk, 
left arm, and left side of the head, discharge their lymph into a larger vessel 
Fig. 92.-Diagrammatic section of lymphatic gland, a.l., afferent; e.l., efferent lymphatics; 
C, cortical substance; l.h., lymphoid tissue; l.s., lymph-path; c., fibrous capsule sending in trabeculae, 
r, into the substance of the gland. (Sharpey.) 
called the thoracic duct. This large lymph vessel-about 18 inches long- 
begins in the abdominal cavity in a dilated portion called the receptaculum chyli 
or cisterna chyli; it then passes through the aortic opening of the diaphragm 
into the thoracic cavity, which it ascends as far as the root of the neck where 
it terminates by opening into the left innominate vein at the junction of the 
internal jugular and subclavian vein. 
The remaining parts of the body empty into a very short lymph vessel 
called the right lymphatic duct, opening at a similar point on the right side. 
Lymph-nodes or Glands.-The course of the lymph vessels is interrupted 
by small, rounded structures called lymph-nodes or glands (Fig. 92). The 
lymph passes through these bodies in spaces called lymph sinuses, but as 
the lymph flows through these sinuses, some of the cells that form the pulp of ESSENTIALS OF PHYSIOLOGY 
153 
the lymph gland are washed out into the lymph stream, where they are called 
lymph corpuscles. These later on, pass into the blood stream where they are 
known as lymphocytes. The lymph-nodes act as filters and serve to stop any 
foreign material that may have passed into the lymph. When bacteria are 
held in these structures, they may induce an inflammatory reaction which is 
accompanied by a painful swelling. In this way an infection may remain local- 
ized; but if for any reason the bacteria are able to spread beyond the lymph 
glands, a general infection results. 
The Composition of Lymph.-Lymph varies in composition in different 
tissues. Since it is discharged into the thoracic duct, the lymph obtained from 
this vessel represents its average composition. This lymph, in the intervals of 
digestion, is a clear, colorless fluid, having a specific gravity of about 1.020. 
When tested with litmus paper, it gives an alkaline reaction. If allowed to 
stand lymph coagulates; the clot, however, is not as firm as that of blood. 
Lymph consists of water holding in solution about 4 per cent of proteins 
(serum-albumin, fibrinogen, serum globulin), 0.1 per cent of dextrose, 0.8 to 0.9 
per cent of inorganic salts, and ether-soluble extractives. During the time of 
absorption of food from the alimentary canal, the lymph of the thoracic duct 
contains a high percentage of fat, and has then a milky appearance. 
From its composition, lymph may be regarded as a dilute blood plasma. 
Formation of Lymph.-Numerous experiments have shown that a rise in 
the pressure of the blood within the capillaries is accompanied by an increased 
production of lymph. This rise in pressure may be accomplished by compression 
of the veins or by the injection of certain substances, like sugar and neutral 
salts, that cause an absorption into the blood stream of large amounts of water 
from the tissue spaces. The constituents of lymph pass, therefore, through the 
walls of the blood capillaries, in part at least, by the process of filtration. 
It has been found also that the permeability of the blood capillaries varies 
in different situations, the capillaries of the limbs being the least permeable, 
while those of the liver are the most permeable. Under similar conditions more 
lymph will be formed in the liver than in the limbs. The permeability of the 
capillaries can be increased by certain poisons, such as peptone and an extract 
from the leech, as well as extracts from certain shell fish. These substances are 
called lymphagogues. Some investigators, believing that lymph is formed 
through the secretory activity of the endothelial cells of the blood capillaries, 
interpret these results on the basis of stimulation of the endothelial cells. 
The activity of the tissues influences greatly the production of lymph. 
The cause of the increased production of lymph observed under this condition is 
related to the discharge of the products of metabolism of the tissues into the 
lymph. These metabolic products raise the osmotic pressure of the lymph; as a 
consequence, water passes from the blood into the lymph. The process of 
osmosis plays, therefore, an important part in the formation of lymph. 
The physical forces of filtration and osmosis, modified by the degree of 
permeability of the capillary wall, would seem to be sufficient to account for the 
production of lymph. 154 
THE LYMPH 
The Flow of Lymph.-The primary factor in the flow of lymph is a differ- 
ence in pressure between the tissue spaces and the end of the thoracic duct. The 
pressure of the lymph in the lymph spaces may be as high as 40 mm. Hg; while 
that in the great veins at the mouth of the thoracic duct is usually below that of 
the atmosphere to the extent, at least, of-5 mm. Hg. In addition, the same 
forces that aid in the flow of the venous blood, contribute materially to the 
flow of lymph. These are: (1) the contractions of skeletal and visceral muscle, 
which compress the lymph vessels and propel the lymph forward, owing to the 
presence of numerous valves. (2) The changes in intrathoracic and intra- 
abdominal pressures that occur during respiration. A certain amount of suction 
may likewise occur, owing to the flow of the venous blood across the mouth 
of the thoracic duct. CHAPTER XIX 
PHARMACODYNAMICS OF THE CIRCULATION 
An exhaustive study of the large number of drugs known to affect the circu- 
latory apparatus would be out of place in a textbook of this character. There- 
fore only a few drugs of major therapeutic importance will be briefly discussed. 
For convenience the remedies whose principal actions are on the circulation 
may be divided into the following groups: 
(i) Circulatory Stimulants.-In addition to the drugs discussed below other 
remedial measures are frequently resorted to in the treatment of failing circu- 
lation. These include dietetic measures, such as the restriction of liquids and the 
elimination of fermenting articles of food from the diet, rest in bed, light, saline 
baths, cold baths, cold air, exercise, etc. The drugs of major importance follow. 
Digitalis.-The circulatory effects of Digitalis are brought about through 
its action on five structures, viz., the sino-auricular node, the cardiac muscle, the 
atrio-ventricular bundle, the coronary arteries, and the systemic arteries. 
(a) The sino-auricular node (see page 135) is the structure in which the 
natural stimuli arise that determine the rate of the heart beat, and is therefore 
looked upon as the pacemaker of the heart's action. One of the effects of Digi- 
talis is to retard or inhibit the projection of impulses by the sino-auricular node. 
As a consequence the heart's rate is slowed. The slowing is due mainly to direct 
stimulation of the vagus center. Atropine (see page no) abolishes the slowing 
produced by Digitalis. 
(&) The effects of Digitalis on the cardiac muscle have been discussed on 
page 45. It will be recalled that Digitalis increases the tone and contractility 
of the cardiac muscle resulting in an increased output of blood. The increased 
output of the heart may result in a rise in the blood pressure. 
(c) The atrio-ventricular bundle (see page 135) performs the function of 
conducting the excitatory impulses from the right auricle to the ventricles so that 
normally the ventricular beat follows that of the auricles in from 0.12 to 0.2 of a 
second. Digitalis may retard or prevent conduction by this bundle. Since Atro- 
pine may prevent this action of Digitalis, it is probably usually due to vagus 
stimulation. However,' in some cases Atropine fails to prevent the effect of 
Digitalis on the conductivity of this bundle. In such cases Digitalis presumably 
has a direct action on the bundle proper or the junctions of its ramifications with 
the proper muscles of the ventricles. 
If the auriculo-ventricular interval is prolonged to three-tenths or three- 
fifths of a second it is called "incipient heart block." Interference with 
conduction which results in the frequent or occasional failure of the ventricles 
to beat in response to the auricles is termed "partial heart-block." Either of 
155 156 
PHARMACODYNAMICS OF THE CIRCULATION 
these conditions may be brought about by Digitalis, although the latter is 
infrequent. More rarely "complete heart-block" may result, the ventricles, 
receiving no adequate stimulus from the auricles, beat at a lower rate (see 
page 136). 
(d) The coronary arteries are probably unaffected by Digitalis excepting in 
poisoning when constriction of these vessels may take place. However, as a 
result of the effects of Digitalis on the cardiac tone and contractility the coronary 
circulation is invigorated through the increased pressure in the aorta. The pro- 
longed diastole, resulting from the slowing in rate, permits the coronary flow to 
last longer. The increased contraction in systole promotes the emptying of the 
coronary veins. Because of the foregoing effects there is an increase in the 
amount of oxygen, food and the drug itself supplied to the heart. Thus 
increased cardiac oxygenation and nutrition, and a recuperation of the heart are 
affected by Digitalis. 
(e) The effects of Digitalis on the systemic arteries were discussed on 
page 44. In therapeutic doses usually no marked constriction of the arteries 
takes place, although the intestinal vessels may form an exception to this general 
statement. The kidney vessels, it is claimed, tend to dilate (see page 160). 
In poisoning the direct stimulation of arterial muscle, already mentioned, 
causes constriction of all the arteries. 
Digitalis is used in medicine when cardiac decompensation has occurred. 
Its most striking effects are observed in auricular fibrillation and when there is 
venous engorgment. 
For intravenous administration, Strophanihin, as well as Ouabain, which 
have similar circulatory effects but are more rapid and less irritating locally, 
are used. They are, however, more toxic. 
Epinephrine.-The stimulation of the myoneural junctions of the vaso- 
constrictor nerves, with the consequent rise in arterial pressure, and of the cardio- 
accelerator nerves, with resulting primary acceleration followed by slowing due 
to reflex stimulation of the vagus center, have already been discussed on page 
112. It should be remembered that the systemic effects are very brief and 
effectively produced only by intravenous injection. By this method the drug 
is used as a very rapidly acting emergency circulatory stimulant in collapse 
or shock. 
Pituitary Extract {Hypophysis Sicca) .-The stimulation of arterial muscle, 
with resulting rise in arterial pressure, produced by this preparation, has been 
discussed on page 44. It is used by the intravenous method in shock. 
Ammonia.-Ammonium compounds which liberate the irritating gas ammo- 
nia, such as Ammonia Water, Ammonium Carbonate and Aromatic Spirit of 
Ammonia, when given by inhalation or by mouth produce a prompt rise in 
arterial pressure by reflex stimulation of the vasoconstrictor center. At the 
same time there occurs also a reflex stimulation of the vagus and accelerator 
centers, but the effects are variable depending upon which action predominates. 
After absorption, as from the hypodermic administration, there is a slight direct 
stimulation of the vasoconstrictor and the vagus centers and of the cardiac PHARMACODYNAMICS 
157 
muscle resulting in increased arterial pressure. The action, although very brief 
because of rapid conversion of the compound to urea, is nevertheless useful in 
overcoming mild, transient circulatory depression as in fainting and mild 
collapse. Very large doses are rapidly depressant to cardiac muscle. 
Caffeine.-The increase in the tone, strength and irritability of cardiac 
muscle produced by Caffeine were mentioned on page 45. ' It moderately 
stimulates the vasoconstrictor center, but may produce a peripheral vasodila- 
tator action due to peripheral depression of the vasoconstrictor mechanism which 
tends to neutralize the central effect. Caffeine as a circulatory stimulant is a 
rather unreliable agent. It does not possess the permanent, tonic action of 
Digitalis. 
(2) Cardiac Depressants.-Aconite and Veratrum are the only drugs to be 
mentioned in this discussion. 
Aconite.-Aconite M onkshood") owes its activity to Aconitine, an 
extremely active alkaloid given in average dose of 0 °f & grain. The tincture 
is, however, the galenical preparation usually employed in medicine. 
In therapeutic dosage Aconite may slow the heart's rate, the diastolic pause 
being prolonged, and the strength of systole being reduced. Consequently, 
less work is done by the heart; the resting period of the organ is longer; there is a 
decrease in the output of blood; and a gradual fall in blood pressure takes place. 
These actions are the result mainly of stimulation of the vagus center, for if the 
vagi are cut or Atropine is administered they do not take place. 
Slowing of the circulation by Aconite has been tried in hypertension, and in 
certain cardiac diseases and fevers attended by an "over-active heart." 
When introduced into the mouth Aconite, even in very dilute solutions, 
produces a warm, tingling sensation followed by numbness and partial local 
anesthesia. There is also a reflex flow of saliva. That there is no local irritat- 
ing action is shown by the fact that there is no redness, pain or swelling. The 
effect, therefore, is purely sensory due to primary stimulation followed by 
depression of the sensory nerve endings. Similar effects may be produced on 
the skin by local application, or even by the systemic administration of large 
doses, thus showing the selective action of the drug. Therapeutic use of the 
local action of Aconite is made for the relief of toothache, neuralgia, rheuma- 
tism, lumbago, and muscular pains. 
Veratrum.-Various species of Veratrum {Green and White Hellebore), 
have been recognized at different times in the U. S. Pharmacopoeia. " Vera- 
trine," a mixture of alkaloids obtained from Sabadilla seed, is also official. 
Because of the foregoing facts much confusion has arisen concerning the con- 
stituents of these agents. Both varieties of Veratrum probably owe their 
activity mainly to the alkaloid Protoveratrine, although there is considerable 
difference of opinion as to the constituents of the green variety. Veratrine 
contains Cevadine as its principal active constituent. 
Protoveratrine resembles Aconite in its effects on the circulation, but is 
more toxic. It strongly stimulates the vagus center so that the heart's rate is 
slowed and the blood pressure thus lowered. 158 
PHARMACODYNAMICS OF THE CIRCULATION 
Cevadine is less toxic than Protoveratrine. It also resembles Aconite 
in that it stimulates the vagus center slowing the pulse and lowering the blood 
pressure. 
The actions of Veratrine and Cevadine on striated muscle were discussed on 
page 43. Protoveratrine does not produce the prolonged relaxation charac- 
teristic of Cevadine, neither is it as irritating locally. 
In medicine Veratrum is probably the most reliable cardiac depressant. 
The tincture is used by many in conditions of high blood pressure, especially 
eclampsia, and to slow a rapid heart. Since Veratrum is a central, circulatory 
and muscular depressant, collapse may be more or less readily produced by the 
administration of large doses for two or three days. 
Veratrine, being decidedly irritating when applied locally, has been employed 
as a counterirritant in muscular pains, and neuralgia. However, absorption 
has resulted in severe and dangerous gastroenteritis. 
(3) Drugs Which Affect the Caliber of Vessels.-In the physiological dis- 
cussion of the Vascular Apparatus (page 145) attention was called to the 
fact that the property of contractility, possessed in a marked degree by arterial 
muscle, serves to maintain the high resistance found in the arterioles, which 
is responsible for the high arterial pressure necessary for an effective circulation. 
The variable contraction of the arterioles affords a means of regulating the 
amount of blood to be distributed to the various organs according to their needs. 
Also that the vessels, like the heart, have two sets of nerves having opposite 
effects on their caliber, i. e., the vasoconstrictor and the vasodilatator nerves 
which constitute the vasomotor nerve system, a part of the autonomic nerve 
system. 
It is evident that as a result of this double innervation, dilatation of the 
vessels may be brought about in two ways, viz., by depression of vasoconstric- 
tors or by stimulation of the vasodilatators. Similarly, vascular constriction 
may be accomplished either by stimulation of the vasoconstrictors or depression 
of the vasodilatators. Alterations in the caliber of vessels may also be effected 
by direct action on arterial muscle. 
(a) Centrally Acting Vasoconstrictor Drugs.-Strychnine may slightly 
augment the excitability of the vasomotor center in the same way in which 
reflex excitability of the spinal cord is heightened by this drug (see page 93). 
This vasomotor action is, however, only marked in poisoning. Experience 
has shown that therapeutic doses of Strychnine either produce no effect what- 
soever, or a very slight rise in the blood pressure. This shows that stimulation 
of the vasomotor center by Strychnine is slight or doubtful. The cardiac 
contractions are not changed, proving that in medicinal dosage the drug is 
not a cardiac muscle stimulant. Poisonous doses, however, strongly stimulate 
the vasomotor center, this being one of the causes of the high blood pressure seen 
during strychnine convulsions. The vascular system is not equally affected; 
thus, the splanchnic vessels in poisoning are markedly contracted, while the 
vessels of the skin and cerebrum are dilated. PHARMACODYNAMICS 
159 
From the foregoing it is evident that Strychnine is not a direct cardiac 
stimulant. In general weakness the improved general muscular tone brought 
about by Strychnine may have a good effect on the circulation. Strychnine, as 
far as any circulatory effects are concerned, is, therefore, only an emergency 
or temporary remedy to tide a patient over a crisis. 
Caffeine moderately stimulates the vasomotor and vagus centers so that 
the arteries may contract, the blood pressure may rise, and the pulse may be 
slowed. Some investigators have reported a peripheral depression of the 
vasoconstrictor mechanism resulting in vasodilatation, particularly marked 
in the kidney vessels. In animals, because of the fact that Caffeine increases 
the irritability, the tone, and the contractility of the heart muscle itself, the 
drug usually produces a greater or less increase in the heart's rate and generally 
a slight rise in pressure. It is frequently tried as an emergency cardiac 
stimulant when a quick effect is desired, as in fainting and collapse, but is 
rather unreliable as such. 
Atropine probably does not directly stimulate the vasomotor center, 
but the increase in the heart's rate may cause a rise in arterial pressure. 
The latter is doubtless the major factor in the production of an increased blood 
pressure by this drug. 
Alcohol.-Upon ingesting a strong alcoholic liquor, like whisky or brandy, 
there may be an immediate rise in the arterial pressure and an increase in the 
heart's rate. The action, however, lasts but a few minutes, but nevertheless 
may be made use of in mild forms of circulatory collapse like fainting 
and shock. Since well diluted alcoholic liquors do not produce this effect, it 
is doubtless a reflex stimulation from the mouth. 
Similar reflex stimulation is produced by Ether (Spirit of Ether), Camphor 
(Spirit of Camphor), and Ammonia (Aromatic Spirit of Ammonia by mouth, 
or Ammonia by inhalation). 
The cutaneous vessels are dilated even by small doses of Alcohol, but the 
constriction of the splanchnic vessels probably compensates for the peripheral 
vasodilatation. 
After the absorption of intoxicating amounts of Alcohol, there is depression 
of the vasomotor center and of the cardiac muscle with consequent fall in blood 
pressure. 
(If) Centrally Acting Vasodilatator Drugs.-Narcotics, like Alcohol, Chloro- 
form, Morphine, etc., in large or toxic doses, cause a gradual diminution in 
the excitability and ultimately a paralysis of the vasomotor center, the blood 
pressure consequently falling and the heart's rate becoming slowed. The 
same is true of bacterial toxins like diphtheria toxin. 
(A Peripherally Acting Vasoconstrictor Drugs.-The vasoconstrictor effects 
of Epinephrine, Cocaine and Ergotoxine have been discussed on page 112. 
Digitalis in therapeutic dosage may produce a vasoconstriction involving 
mainly the intestinal vessels, due to a direct peripheral action on the arterial 
muscle, even though the blood pressure does not rise. The vasomotor center 
is little, if at all, affected. The kidney vessels are said to dilate because of an 
elective dilatator action (see "Diuretics," page 265). 160 
PHARMACODYNAMICS OF THE CIRCULATION 
(J) Peripherally Acting Vasodilatator Drugs.-The Nitrite Group, which 
includes Amyl, Ethyl and Sodium Nitrites, and certain organic nitrates, like 
Nitroglycerin and Erythrol Tetranitrate which are reduced to nitrites in the 
body, lessen the tone of the unstriated muscle of the arteries and veins, thus 
causing vasodilatation and consequent fall in blood pressure. Amyl Nitrite, 
given by inhalation, is most rapid but is too fleeting for use excepting in 
emergencies. Nitroglycerin and Sodium Nitrite, although less prompt, produce 
effects of longer duration. These agents are used to lower abnormally high 
pressure and in angina pectoris. 
Digitalis and Caffeine and its allies like Theobromine, are said to exert a 
local elective dilatator effect on the renal vessels particularly (see " Diuretics "), 
but recent investigations have shown no significant changes in the vessels. CHAPTER XX 
RESPIRATION 
Respiration is the process whereby an exchange of gases takes place between 
an organism and its environment. In animals, oxygen is transferred from the 
surrounding medium to the tissues, and carbon dioxide from the tissues into the 
surrounding medium. The oxygen is utilized in the tissues for those oxidative 
processes that underlie the liberation of the energy locked up in the food material; 
the carbon dioxide, which is one of the products of oxidation, must be con- 
stantly removed if the normal irritability of the tissues is to be maintained. 
In the higher vertebrates the general process of respiration includes two 
phases: one phase in which oxygen passes from the atmosphere into the blood, 
and carbon dioxide passes from the blood into the atmosphere and called external 
respiration; the other phase in which oxygen passes from the blood into the tissues, 
and carbon dioxide from the tissues into the blood and termed internal 
respiration. 
The series of organs that subserve the function of external respiration con- 
stitute the respiratory apparatus. 
The Respiratory Apparatus.-The respiratory apparatus consists of (i) 
The lungs and the air-passages connecting them to the exterior, viz., the nasal 
chambers, the mouth, the pharynx, the larynx, trachea, and bronchi. (2) The 
thorax and the muscles attached to it. 
The Air-passages.-The nasal chambers are the natural passage-way for the 
entrance and the exit of the air in breathing. The presence of the turbinate bones 
covered with a vascular, moist mucous membrane retards the movement of the 
inspired air which thereby increases in temperature and moisture. This rise of 
temperature and moisture safeguards the lower respiratory passage-ways from 
the irritation caused by cold and dry air. While the mouth is often used for 
respiration, this is not its normal function. The nasal chambers and the mouth 
open posteriorly into the pharynx. The pharynx is continued inferiorly into 
both the larynx and the esophagus. 
The larynx is a cartilaginous structure developed, primarily, for the pro- 
duction of sounds. The cavity of the larynx is narrowed owing to the presence 
of the vocal bands. The space between these bands is triangular in shape and 
is called the rima glottidis. Food particles are prevented from entering the 
larynx during deglutition through the closure of its upper opening by the 
epiglottis, and a momentary inhibition of respiration. 
The trachea is a tube about four and a half inches long and one inch in 
diameter. It consists of C-shaped, or incomplete rings of cartilage held by fibrous 
tissue. The trachea is lined by a mucous membrane covered by stratified 
161 162 
RESPIRATION 
columnar, ciliated epithelial cells. Numerous mucous glands, secreting mucus, 
are embedded in the submucous tissue. The mucus entangles dust particles 
that may have gained entrance, and are gradually moved toward the larynx and 
pharynx by the waving of the cilia. The extremities of the C-shaped cartilages 
are turned toward the back and are bridged over by a sheet of smooth muscle, 
called the tracheal muscle. 
At the level of the fifth thoracic vertebra the trachea divides into a right and 
a left bronchus. Each of these subdivides in turn into two or three branches 
that pass into the corresponding lung. 
The Lungs.-Within the lungs the bronchi continue to branch out, all the 
while diminishing in size (Fig. 93). At the same time the cartilaginous rings 
Fig. 93.-Diagram showing the larnyx, trachea, bronchi, and lungs; the ramification of the bronchi, 
and their division into lobules. {Brubaker.) 
become gradually thinner and smaller, and a layer of smooth muscle fibers, 
arranged circularly, makes its appearance. This is the bronchial muscle. 
When the bronchus has become i.o mm. in diameter, it is called a terminal bron- 
chus or bronchiole. From the bronchiole arises the pulmonary lobule, the histo- 
logical unit of the lung. 
The bronchiole gives rise to a number of branches which acquire alveoli or 
air-cells; they are then called respiratory bronchioles. The respiratory bron- 
chioles open into wider tubes called alveolar ducts, surrounded by saccules with 
air-cells. The alveolar ducts, in turn, open into from three to six short and 
broad spaces, called atria. These then open into from two to five air-sacs, or 
infundibula, the walls of which bulge out to form pulmonary alveoli or air-cells 
(Fig. 94). 
Ciliated epithelium lines the bronchial tubes as far as the bronchioles, 
occasionally as far as the respiratory bronchioles. Gradually, however, the ESSENTIALS OF PHYSIOLOGY 
163 
epithelial cells decrease in height and become more and more flattened and non- 
ciliated. In the alveoli the epithelium is greatly flattened and includes many 
non-nucleated plates. This epithelium is known as the respiratory epithelium. 
The structures making up the lungs are held together by connective tissue 
containing a large percentage of elastic fibers. 
The venous blood is brought into the lungs by the pulmonic artery. A 
branch of this vessel penetrates each lung at the place of entrance of the bron- 
chial tubes. Ultimately the vessel, after many subdivisions, forms an extensive 
Fig. 94.-Diagram of the three pulmonary lobules connected with a terminal bronchiole (TB). 
The middle lobule is stippled. BR, bronchiole; RB, respiratory bronchiole of the first order; TB, 
respiratory bronchiole of the second order (terminal bronchiole); I, II, III, alveolar ducts; 1, 2, and 3 
a, b, c and d, atria; As, Alveolar sacs with pulmonary alveoli or air-cells. (Jordan and Ferguson, 
after Miller.) 
meshwork of broad capillaries surrounding the air-cells. As the air-cells of 
neighboring air-sacs are very close to each other, the capillary network is 
exposed to the air of two air-cells, the blood being separated from the air only by 
the endothelium of the 'capillary and the epithelium of the air-cell. The capil- 
laries merge to form the pulmonic veins which carry the blood from the lungs into 
the left auricle of the heart. 
The bronchial muscle, particularly that of the bronchioles, may by its con- 
traction regulate the quantity of air passing in and out of the pulmonic lobules. 
It may also by a maximum contraction shut off the entrance of air into the lobu- 
les ; this may happen when the bronchial muscle is reflexly stimulated through 
the action of irritating gases, as well as in certain forms of asthma. The bronchial 164 
RESPIRATION 
muscle is supplied by the autonomic nerve system by two sets of fibers, viz., 
broncho-constrictors, found in the trunk of the vagus, and br oncho-dilatator s, 
probably derived from the thoracic portion of the sympathetic. 
The lungs fill the thoracic cavity, with the exception of the space between 
them which is occupied by the heart, great vessels, and other structures. Each 
lung is separately covered by a serous membrane consisting of endothelial cells 
resting on connective tissue. This membrane is called the pleura; it is reflected 
Superior thoracic aperture 
True ribs 
■False ribs 
Subcostal angle 
Fig. 95.-The thorax. (Front view.) (From "Morris' Human Anatomy. 
Floating ribs 
over the structures lying between the lungs, the inner wall of the thorax, and the 
superior surface of the diaphragm. A thin layer of a lymph-like fluid is found 
between the two layers of the pleura, and serves to diminish friction during 
the movements of the lungs and chest wall. 
The Thorax.-The thorax consists of a bony framework, formed by the 
thoracic vertebrae, the ribs, the costal cartilages, and the sternum, and of 
muscles, fascia and skin. 
The ribs are bony arches articulating posteriorly with the vertebrae and 
anteriorly with the sternum through their cartilages. The last two or "floating 165 
ESSENTIALS OF PHYSIOLOGY 
ribs" do not articulate with the sternum. The ribs are slightly twisted upon 
themselves, and lie obliquely from above downward and forward (Fig. 95). 
The muscles of respiration entering in the formation of the thorax are: the 
diaphragm, the external and internal intercostals, the levatores costarum, the tri- 
Fig. 96.-The diaphragm, viewed from in front. (Teslut.) 
Ext. Intercostal 
Int. Intercostal 
Iitercartilayine^ 
Levatores Costarum 
ErtJntercosfat 
IntJntereostal 
Fig. 97.-Showing the situation, the 
points o f attachment, and. direction of the 
intercostal muscles. 1, the intercostales ex- 
tern!; 2, the intercostales interni; 3, the 
intercartilaginei. (From Brubaker's Text-book 
of Physiology.) 
Fig. 98.-View from behind of four dorsal 
vertebrae and three attached ribs, showing the 
attachment of the elevator muscles of the ribs 
and the intercostals. (After Allen Thomson.) 
angularis sterni, and the infra-costales. The origin and insertion of some of 
these muscles are of special interest in a study of the respiratory movements. 
The diaphragm is a double muscle which, with its central tendon, forms, a 
dome-shaped partition separating the thoracic from the abdominal cavity. It 166 
RESPIRATION 
arises from the first three or four lumbar vertebrae and certain adjacent liga- 
mentous structures; from the border of the six lower ribs; and from the ensiform 
cartilage. The muscle fibers pass toward a common center to be inserted into 
the central tendon (Fig. 96). 
The external intercostals consist of short muscle fibers situated between the 
ribs. They run obliquely from above downward and from behind forward. 
The internal intercostals are likewise situated between the ribs and pursue 
an oblique direction opposite to that of the preceding muscles (see Figs. 97 
and 98). 
THE MOVEMENTS OF RESPIRATION 
In order that the exchange of gases may take place readily it is necessary 
that the lungs be constantly ventilated. This is accomplished by an alternate 
increase and decrease in the size of the thorax. (The lungs follow the variations 
in size of the thorax in a purely passive manner. 
Inspiration.-In inspiration the thorax increases in all its diameters. The 
vertical diameter is increased by the contraction of the diaphragm. When this 
double muscle contracts, its arch flattens and there is a slight descent of the 
central tendon toward the abdominal cavity. As a consequence, the vertical 
diameter of the thorax is enlarged and the abdominal wall bulges forward. 
The antero-posterior and transverse diameters of the thorax are increased 
by the contraction of those muscles that elevate the ribs. At the beginning of 
inspiration the upper part of the thorax is held rigidly by the contraction of 
the scaleni muscles which spring from the transverse processes of the cervical 
vertebrae and are attached to the first and second ribs. The thorax being thus 
fixed, the contraction of the external intercostal muscles raises the ribs. As 
the ribs run obliquely downward and forward from their vertebral articulation, 
their elevation causes the sternum to move forward, thus increasing the antero- 
posterior diameter of the thorax. There is also at the same time an outward 
rotation of the ribs which causes the transverse diameter of the thorax to be 
increased. 
In quiet inspiration, therefore, the diaphragm and the external intercostal 
muscles are the muscles that come chiefly into play. There is at the same 
time a slight lateral movement of the vocal cords that facilitates the entrance 
of air into the lungs. In forced inspiration other muscles assist those already 
mentioned in enlarging the thorax. Among these may be mentioned the 
pectoral muscles, the sternomastoid, the trapezius, and the rhomboid muscles. 
Expiration.-The movement of expiration is a purely passive process, 
and is brought about by the elastic recoil of the abdominal wall and of the chest 
wall, which asserts itself the moment the muscles of inspiration relax. In 
forced expiration the thoracic cavity is further decreased by the contraction 
of the internal intercostal muscles, the triangularis sterni, and the muscles of the 
abdominal wall. 
The Lungs.-As the lungs are contained within a completely closed cavity, 
and as they are elastic, they follow passively all changes in the size of the thoracic ESSENTIALS OF PHYSIOLOGY 
167 
cavity; in other words, the lungs follow the descent of the diaphragm and the 
outward movement of the chest wall during inspiration, and return to their 
former position, with the return of the diaphragm and of the chest wall to their 
position of rest, during expiration. 
The lungs are at all times distended and occupy all availabe space. The 
pressure that causes their distension is that of the air within. This is called 
the intra-pulmonic pressure; at the end of expiration it is that of the atmosphere, 
which at the sea level is 760 mm. Hg. (see Fig. 99). During inspiration, 
the lungs expand rapidly, and as a consequence the intra-pulmonic pressure 
falls about 2 mm. Hg. The atmospheric pressure being higher, air rushes into 
the lungs until the intra-pulmonic pressure at the end of inspiration is again 
that of the atmosphere. 
Fig. 99.-Section of the thorax of a dog with the lungs, heart, and principal vessels. 5, catheter 
introduced into the pleural space and connected with a manometer. (Brubaker after Moral and 
Doyon.) 
During expiration, the lungs are pressed upon by the recoiling chest wall 
and the ascending diaphragm so that their contained air is compressed and its 
pressure rises about 3 mm. Hg. The intra-pulmonic pressure being now 
higher than that of the atmosphere, air leaves the lungs and continues to do so 
until the intra-pulmonic pressure again equals that of the atmosphere. This 
is the condition that obtains at the end of expiration. 
These variations of pressure taking place within the lungs are dependent 
in part on the rapidity and extent of the respiratory movements, and in part 
also on the resistance which the air encounters in passing through the respira- 
tory passageways. 
As the lungs are highly elastic and are at all times distended, they are 
constantly endeavoring to recoil upon themselves. This, however, they cannot 
do owing to the fact that the thoracic wall is rigid and does not permit the 168 
RESPIRATION 
pressure of the atmosphere to act on the external surface of the lungs. That 
this is the case, can be readily demonstrated by making an opening in the thoracic 
wall. When this is done, the atmospheric pressure acting outside neutralizes 
that acting inside the lungs; the elastic tissue of the lungs, therefore, recoils, 
and the lung collapses. 
This recoil force of the lung tissue neutralizes a part of the intra-pulmonic 
pressure, so that the structures within the thorax outside the lungs, such as the 
heart and large vessels, do not feel the full intra-pulmonic pressure. The 
pressure outside the lungs is called the intra-thoracic pressure; it is the intra- 
pulmonic pressure minus the recoil force of the lung tissue at any particular 
moment. Since the recoil force of an elastic body will be proportionate to the 
extent to which it is stretched, the intra-thoracic pressure will vary during 
respiration. At the end of expiration, the thorax 
being at rest, the intra-thoracic is about 6 mm. 
Hg. below that of the atmosphere. At the end 
of a quiet inspiration, the lungs being moderately 
distended, the intra-thoracic pressure is about 9 
mm. Hg. below that of the atmosphere. Naturally 
in deep inspiration the intra-thoracic pressure will 
become materially less. If it be remembered that 
at that time the diaphragm has descended and 
raised the intra-abdominal pressure, it can readily 
be seen that the movement of inspiration facili- 
tates greatly the flow of venous blood and of 
lymph toward the thoracic cavity. 
During expiration the intra-thoracic pressure 
returns to the value it had preceding inspiration. 
The Quantity of Air Breathed.-The quant- 
ity of air entering and leaving the lungs will vary 
with the depth of the respirations. This quantity 
can be determined by means of an apparatus, 
called a spirometer, which is a modified gasometer (Fig. 100). 
With the spirometer the volumes of air breathed under different conditions 
have been estimated as follows: 
(a) The tidal air, which is the volume of air flowing into and out of the 
lungs with each quiet inspiration and expiration, averages about 500 cc. (30 
cu. in.). 
(i) The complemental air, the volume of air flowing into the lungs in addi- 
tion to the tidal air as a result of the deepest possible inspiration. This volume 
is about 1600 cc. (100 cu. in.). 
(c) The reserve or supplemental air is the volume of air flowing out of the 
lungs, in addition to the tidal air, as a result of the most forcible expiration. It 
averages about 1600 cc. (100 cu. in.). 
((f) The Residual Air.-Even after the most forcible expiration there still 
remains in the lungs a certain volume of air that fills the alveolar passages, the 
Fig. ioo.-A spirometer. 
(Boruttau.) ESSENTIALS OF PHYSIOLOGY 
169 
bronchial tubes, and the trachea. This air is called the residual air, and has 
been variously estimated at from 800 to 1600 cc., the average being 1200 cc. 
(75 cu. in.). 
The Respiratory or Vital Capacity of the Lungs.-The respiratory or vital 
capacity of the lungs can be determined by ascertaining the volume of air 
that can be expelled by the most forcible expiration following the deepest 
possible inspiration. This volume includes, therefore, the tidal, complemental, 
and reserve volumes. It consequently averages about 3700 cc. 
The Frequency of Respiration.-The number of respirations per minute 
varies with age. Numerous observations have shown that the average rate 
of respiration at various ages is as follows: 
Age 
Respirations per Minute (Quetelet) 
o- i year 
44 
5 years 
26 
15-20 years 
20 
20-25 years 
18.7 
25-30 years 
15 
30-50 years 
17 
During sleep the respirations decrease in frequency as well as in depth. 
A rise in the temperature of the blood, as in fever, increases the respiratory rate. 
A deficiency of oxygen in the blood, such as may occur in anemia or when the 
air breathed is deficient in this gas, likewise causes an increased frequency of 
respiration. The same result follows an abnormal accumulation of carbon 
dioxide in the blood, as occurs during violent exercise or as a result of inter- 
ference with the exchange of gases. An increase in frequency and depth of 
respiration is termed hyperpnea. When the conditions that cause hyperpnea 
become intensified, breathing becomes labored and difficult, a condition called 
dyspnea. There are reasons for believing that carbon dioxide is the normal 
stimulus to respiration. When the percentage of this gas in the blood is greatly 
diminished, as can be done by rapid and forcible breathing for a few minutes, 
the individual ceases breathing for some little time. To this temporary cessa- 
tion of breathing the term apnea is given. The respirations return gradually, 
at first in a more or less periodical manner, when the carbon dioxide has accumu- 
lated in the blood in sufficient quantities. 
When for any reason the lungs cannot be ventilated, as when an individual 
is confined in a small airtight space or the respiratory passageways are blocked, 
the individual passes rapidly through the stages of hyperpnea and dyspnea 
into the condition called asphyxia, which if not promptly relieved eventuates 
in death. 
Respiratory Sounds.-If the ear be applied to the chest over the position 
of the trachea and bronchi a blowing, somewhat harsh sound is heard during 
both inspiration and expiration. This sound is produced by the vibrations of 
the air as it passes between the vocal bands. A different sound is heard over 
the lungs proper; it is a faint, rustling sound supposedly due to the expansion 
of the air-cells. It may, however, be the bronchial sound modified by its 
passage through the porous, vesicular structure of the lungs. CHAPTER XXI 
THE CHEMISTRY OF RESPIRATION 
Changes in the Composition of the Air.-An examination of the air 
breathed shows that in the short time it stays in the lungs it undergoes changes 
in chemical composition, in temperature, and in volume. The significance of 
the changes in chemical composition becomes evident on comparing the com- 
position of inspired with that of expired air. 
Oxygen 20.80 
Carbon dioxide traces 
Nitrogen 79.20 
Water vapor variable 
Inspired Air 
Oxygen 16.02 
Carbon dioxide 4-38 
Nitrogen 79.60 
Water vapor saturated 
Organic matter a trace 
Expired air 
100 vols. 
100 vols. 
From this table, it is evident that the air loses 4.78 per cent of oxygen 
and gains 4.38 per cent of carbon dioxide. The small gain in nitrogen is 
probably due to the absorption from the intestines of nitrogen-holding 
gases produced by putrefaction. The expired air is likewise more or less 
completely saturated with water vapor, and is also warmer than the inspired 
air. At the average room temperature (21 °C. or 7o°F.) the expired air has 
the temperature of the body (37°C. or 98.6°F.). 
A small amount of organic matter, consisting of mucous and epithelial 
debris from the respiratory passages, is likewise found in the expired air. 
The Total Respiratory Exchange.--The entire amount of air passing 
through the lungs in twenty-four hours may readily be calculated on the basis of 
a tidal volume of 500 cc. and an average respiratory rate of 18 per minute. 
Under such conditions the total amount of air breathed will be 12,960 liters. If 
the percentage loss of oxygen is 4.78, the amount of oxygen absorbed in the body 
in twenty-four hours will be: 
ioo:4.78::i2,96o: x = 620 liters. 
In the same manner the amount of carbon dioxide liberated from the body 
in twenty-four hours can be calculated, if with each expiration the air gains 4.38 
per cent of this gas. 
100:4.38:112,960: x = 567 liters of carbon dioxide. 
These figures reveal the interesting fact that, undera verage conditions, the 
volume of carbon dioxide exhaled is less than that of the oxygen absorbed. This 
would not be the case if all the oxygen taken into the body were utilized to 
oxidize carbon. Since more water leaves the body than is ingested, it is evident 
that a portion of the oxygen absorbed is utilized to oxidize hydrogen. The 
170 ESSENTIALS OF PHYSIOLOGY 
171 
hydrogen so oxidized is contained in the fats of the food. The ratio of the 
volume of carbon dioxide exhaled to the volume of oxygen absorbed represents, 
therefore, the proportion of the oxygen that is used in oxidizing carbon. This 
• • 11 j i . CO2 
ratio is called the respiratory quotient, and is written ~ • 
O2 
The respiratory quotient varies with the character of the diet, which is in 
turn affected by exercise and the external temperature. On a pure carbo- 
hydrate diet, there is enough oxygen in the carbohydrate molecule to combine 
with the hydrogen, all the oxygen utilized combines therefore with the carbon, 
and the respiratory quotient is 1. In the case of an exclusively protein diet, a 
portion of the oxygen combines with the excess of hydrogen in the protein mole- 
cule, so that the respiratory quotient is 0.82; while with a diet of fat, a still 
greater proportion of oxygen must combine with hydrogen, and the respiratory 
quotient is still lower, viz., 0.71. 
In the example given of the volumes of oxygen absorbed and carbon dioxide 
exhaled, the respiratory quotient is 0.916; an indication, therefore, that the diet 
was rich in carbohydrates. 
When the volume of the expired air is compared with that of the inspired 
air, it is found to be smaller by about one two-hundred and fiftieth. 
The Composition of the Alveolar Air.-The analysis of expired air men- 
tioned in the introductory paragraph shows, naturally, the average composition 
of the air as it comes partly from the lungs and partly from the respiratory 
passages, viz., the bronchi, trachea, pharynx, and nasal chambers. The air con- 
tained in the respiratory passages does not undergo any material change in com- 
position, and therefore dilutes the air coming from the alveoli in which the 
exchange of oxygen and carbon dioxide takes place. An analysis of the alveolar 
air is, therefore, necessary to obtain an idea of the intensity of these changes. 
This has been accomplished by the use of specially devised apparatus. The 
alveolar air has been shown to contain less oxygen and more carbon dioxide than 
the average expired air. The alveolar air contains but 13 to 15 per cent of 
oxygen, and from 5 to 6 per cent of carbon dioxide. 
Ventilation of the Alveoli.-The respiratory movements, with their accom- 
panying changes in volume of the lungs, do not do more than ventilate the 
respiratory passageways including a part of the finer subdivisions of the bronchi. 
The oxygen must therefore find its way to*the depth of the alveoli, and the carbon 
dioxide pass from the alveoli into the bronchi, through some other force. This 
force is that of diffusion as determined by the difference in pressure of these 
gases at these points. ' The pressure of any one gas in a mixture of gases is pro- 
portional to the percentage in which the gas is present in the mixture. If the 
pressure of atmospheric air is 760 mm. Hg., the respective pressures of its 
oxygen and carbon dioxide will be 158 mm. Hg. and 0.3 mm. Hg. The pressure 
of the oxygen in the trachea will therefore be approximately 158 mm. Hg., while 
in the alveoli it may be only 106 mm. Hg.; it is obvious, therefore, that the 
oxygen will rapidly diffuse toward the alveoli. But as the oxygen is constantly 
passing into the blood, a state of equilibrium can never be established. Simil- 172 
THE CHEMISTRY OF RESPIRATION 
arly, the pressure of the carbon dioxide in the alveoli is about 40 mm. Hg., while 
in the trachea it may be nearly 0.3 mm. Hg.; hence diffusion will take place 
from the alveoli toward the trachea. Here, again, equilibrium cannot take 
place, since carbon dioxide is continually passing out of the blood into the 
alveoli. 
Changes in the Composition of the Blood.-The blood conveyed by the 
pulmonic artery into the lungs is purple, while that passing out of the lungs into 
the pulmonic veins is a bright scarlet red. This change in color takes place con- 
comitantly with the disappearance of oxygen from the alveolar air, and the 
appearance of carbon dioxide in the alveolar air. This phenomenon indicated, 
therefore, that the blood is changed from the venous to the arterial condition by 
a gain in oxygen and a loss in carbon dioxide. The converse phenomenon, viz., 
the change of the blood from the arterial into the venous condition, occurs as the 
blood is flowing through the capillaries of the body. Here, therefore, oxygen 
must leave the blood and carbon dioxide pass into it. 
That the blood holds these gases can be readily demonstrated by subjecting 
it to the high vacuum of the mercurial air-pump. Every 100 volumes of blood 
contains an average of 60 volumes of gases at the standard pressure of 760 mm. 
Hg., and temperature of o°C. These gases are distributed in arterial and 
venous blood as follows: 
Oxygen 20 vols. 
Carbon dioxide 40 vols. 
Nitrogen 1-2 vols. 
Oxygen. 12 vols. 
Carbon dioxide 45 vols. 
Nitrogen 1-2 vols. 
Arterial blood 
Venous blood 
The air in the alveoli of the lungs is separated from the blood of the 
pulmonic capillaries by the thin alveolar epithelium and the thin endothelial 
cells of the capillaries. This cellular mem- 
brane is moist and readily permits the 
passage of gases through it. It is believed 
that oxygen and carbon dioxide pass 
through this membrane by the process of 
diffusion. Indeed, the difference in pres- 
sure of the oxygen in the venous blood 
entering the lungs and of the oxygen pre- 
sent in the alveoli is sufficiently great to 
account for the volume of this gas pass- 
ing into the blood by diffusion. The 
presssure of the oxygen in the venous 
blood is about 40 mm. Hg., while that of 
the oxygen in the alveoli is about 106 mm. 
of Hg. As the oxygen passes into the 
blood, it combines chemically with hemoglobin and thus ceases to exert any 
pressure. This chemical combination is, however, unstable and is dependent 
on the pressure of the oxygen dissolved in the plasma. When the blood passes 
into the tissue capillaries and comes in diffusion relations with the tissue cells 
where the oxygen pressure is nil, the oxygen instantly leaves the blood and 
Fig. ioi.-The exchange of oxygen and car- 
bon dioxide between the blood and the lymph 
in the tissues. {Hough and Sedgwick.} ESSENTIALS OF PHYSIOLOGY 
173 
combines with some constituent of the tissue cells (Fig. ioi). In the short 
time that the blood flows through the capillaries the oxygen pressure falls from 
106 mm. Hg. to about 40 mm. Hg. 
The difference in pressure of carbon dioxide in the venous blood and in the 
alveoli is not as great as in the case of oxygen. The pressure of the carbon diox- 
ide in the venous blood is about 43 mm. Hg., while that of the carbon dioxide 
in the alveoli is about 40 mm. Hg.; there is therefore but a difference of 3 mm. 
Hg. The rate of diffusion of carbon dioxide through a moist membrane is, 
however, 25 times greater than that of oxygen, so that though the difference in 
pressure is slight, it is also sufficient to account for the passage of carbon dioxide 
by the simple process of diffusion. 
Similarly, the pressure of carbon dioxide in the tissues lies between 45 and 
68 mm. Hg., while that of the carbon dioxide in the arterial blood is about 40 
mm. Hg. The carbon dioxide, therefore, passes readily from the tissues into 
the blood. 
The manner in which carbon dioxide is held in the blood is not fully under- 
stood. It is believed, however, that it is held in three ways: (1) in solution; 
(2) in combination with alkaline bases, such as NaHCO3; and (3) in combina- 
tion with the proteins of the plasma and of the red corpuscles. CHAPTER XXII 
THE NERVE CONTROL OF RESPIRATION 
The rhythmic movements of respiration, caused by alternate contractions 
and relaxations of the respiratory muscles, are determined and co-ordinated 
insp. c. 
-■/ned.ob. 
p.u.r. 
\eic. 
\inh. 
sp. c. 
\dtap/ira<f7n 
Fig. 102.-Diagram showing the relation of the pulmonic fibers of the vagus to the inspiratory 
center and the connections of the latter with the phrenic and intercostal nerve centers and their 
related muscles, med.ob., Medulla oblongata; sp.c., spinal cord; p.v.r., pulmonic vagus nerve, exci- 
tator and inhibitor; insp.c., inspiratory center; phr.c., phrenic nerve-centers; phr.n., phrenic nerve; 
int.n.c., intercostal nerve-centers; int.c.n., intercostal nerves; ext.int.c.m., external intercostal muscles. 
(G. Bachmann, in Brubaker's Physiology.') 
through the activity of a nerve center, called the respiratory center. This 
center is situated in the gray matter under the floor of the fourth ventricle. 
The nerve cells of this center discharge nerve impulses rhythmically to the 
various groups of nerve cells from which arise the efferent nerve fibers innervat- 
ing the respiratory muscles. These efferent nerves are the vagus, supplying the 
174 ESSENTIALS OF PHYSIOLOGY 
175 
muscles of the larynx, the cervical nerves, sending fibers to the muscles of the 
neck, the intercostal nerves, supplying the intercostal muscles, and the phrenic 
nerves, innervating the diaphragm. 
The Respiratory Center.-The respiratory center is a double one, there 
being a group of nerve cells on each side of the median fine (see Fig. 102). As 
in the case of other nerve centers, it is susceptible of stimulation or inhibition 
through the action of reflex nerve impulses. But, while this is the case, the 
respiratory center is believed by many to be essentially automatic in its action, 
inasmuch. as severance of reflex paths does not abolish, although it greatly 
diminishes its activity. 
The Relation of the Vagus Nerve to the Respiratory Center.-The chief 
afferent fibers capable of reflexly influencing the respiratory center are contained 
in the vagus nerves. If both vagi are cut, the respiratory movements decrease 
markedly in frequency; the inspirations become deeper and are more or less 
spasmodic in type. Stimulation of the central end of one of the severed vagi 
with weak induced electric currents, is followed by an increased frequency and a 
diminution in the depth of the respiratory movements. The vagus nerves 
apparently contain inhibitory fibers for the respiratory center, which on 
stimulation cause expiration to occur sooner than would otherwise be the case. 
Experiments have shown that the peripheral terfninals of these fibers of the 
vagus are in the alveolar wall, and that they can be stimulated by mechanical 
distention of these walls. 
Stimulation of the central end of the divided vagus with stronger currents 
may also produce the reverse effect, viz., an increase in the extent of the 
inspiratory movement which gradually passes into a condition of forced inspi- 
ration. The vagus nerves, therefore, contain also another class of afferent nerve 
fibers whose stimulation causes an augmentation in the activity of the respira- 
tory center which leads to a tetanic contraction of the muscles of inspiration. 
The terminals of these fibers are likewise in the alveolar wall, and can be 
stimulated by aspirating air from the lungs, so that the alveoli are more or less 
collapsed. 
From these results it would seem that, normally, the distention of the alve- 
oli taking place during inspiration, generates nerve impulses in the vagus nerve 
which, on reaching the respiratory center, inhibit its activity. This leads to an 
expiration; the ensuing collapse of the alveoli generates nerve impulses in 
another set of vagus fibers which, on reaching the respiratory center, stimulate it 
to activity, so that an inspiration takes place. 
Studies made during quiet breathing have shown, however, that nerve 
impulses travel up the vagus nerve during inspiration only. These are the 
inhibitory nerve impulses that check the activity of the respiratory center, 
so that expiration occurs sooner than otherwise. The following inspiration, it is 
believed, is caused by the stimulating action of carbon dioxide which has 
accumulated during expiration. 
Influence of Other Afferent Nerves.-The activity of the respiratory 
center may also be modified by nerve impulses coming from other regions of 176 
THE NERVE CONTROL OF RESPIRATION 
the body. Painful stimuli usually stimulate the center so that hyperpnea is 
induced. The afferent nerves distributed to the upper respiratory passageways 
produce, when stimulated, an inhibition of respiration. These nerves are stimu- 
lated when irritating vapors, such as those of chlorine, ammonia, and sulphur 
dioxide, are accidentally inhaled. There is simultaneously with the stoppage of 
respiration a reflex contraction of the muscles that close the glottis. Stimula- 
tion of the sensor fibers supplied to the mucous membrane of the larynx, as by 
the presence of a foreign body, not only inhibits inspiration, but causes also 
violent expiratory movements with the apparent purpose of expelling the irritat- 
ing object. 
Influence of Higher Centers.-The respiratory center is likewise in rela- 
tion with the cerebrum, as shown by the well-known effect of emotional dis- 
turbances on the frequency and depth of the respiratory movements. 
Violent muscular exercise influences the activity of the respiratory center 
even before there has been time for changes in the composition of the blood. 
Evidently, the nerve impulses conveyed by the pyramidal tract fibers on their 
way to the various levels of the spinal cord, overflow and increase the activity 
of the center. 
The brain controls also, within limits, the activity of the respiratory center. 
The respiratory movements may be made to take place with more or less fre- 
quency and depth as a result of volitional efforts. The breath, however, 
cannot be held indefinitely; a time soon comes when the irritability of the 
respiratory center becomes so great that it discharges nerve impulses despite 
any inhibitory effort. 
THE CHEMICAL CONTROL OF RESPIRATION 
As brought out in preceding paragraphs, the respiratory center while 
essentially automatic in its action is constantly being played upon by reflex 
nerve impulses. The automatic stimulus is generally believed to be the carbon 
dioxide present in the blood supplied to the center. While carbon dioxide 
is the normal stimulus, a decrease in the percentage of oxygen supplied to the 
center will act as a stimulus also. 
Carbon Dioxide.-The effect of carbon dioxide on the respiratory center 
can be demonstrated by breathing air containing 2 per cent of carbon dioxide. 
The respiratory movements increase notably in depth as well as in frequency. 
The amount of air passing through the lungs may be doubled or trebled. 
A stimulation of the respiratory center occurs during muscular exercise 
owing to the large amount of carbon dioxide produced by the contracting mus- 
cles and absorbed into the blood. The carbon dioxide stimulates the respira- 
tory center so that the respiratory movements become more frequent and deeper, 
and remove the large amount of carbon dioxide as fast as it is formed. That 
this is the case, is shown by the fact that there is but a slight increase in the 
pressure of the carbon dioxide in the blood and alveolar air during exercise. 
A decrease in the amount of carbon dioxide in the blood below the normal 
level is attended by a decrease in the activity of the respiratory center. If ESSENTIALS OF PHYSIOLOGY 
177 
the decrease is sufficiently great, the respiratory center ceases to act temporarily. 
This is the explanation of the apnea caused by excessive breathing. The return 
of respiration is due to the gradual accumulation of carbon dioxide to a level 
sufficient to stimulate the center. 
Carbon dioxide acts as a stimulus to the respiratory center by virtue 
of its combination with the water of the blood plasma with its consequent 
change into carbonic acid. It is therefore the increase in hydrogen ion con- 
centration that stimulates the center. Accordingly, other acids that may be 
produced by the metabolism of the tissues may stimulate the center. Such 
acids as lactic acid and beta-oxybutyric acid may, under certain conditions, 
so stimulate the center that the percentage of carbon dioxide in the blood and 
in the alveolar air falls markedly. 
Oxygen.-A decrease in the percentage of oxygen in the air breathed will, 
likewise, lead to an increase in the respiratory movements. The average 
percentage of oxygen in the alveolar air is about 15 per cent; it is not until 
the percentage of this gas has been decreased to less than 8 per cent that the 
respiratory center becomes more active. The skin and mucous membranes, 
at the same time, become blue (cyanosis), and the individual may feel dizzy 
and may even lose consciousness. 
The stimulation of the respiratory center under such conditions is not due 
directly to the lack of oxygen but to the accumulation of such acids of metabo- 
lism as lactic acid, and therefore to the increase in the hydrogen ion concentra- 
tion of the blood. With an adequate supply of oxygen the lactic acid is 
oxidized to carbon dioxide and water. 
Breathing an excess of oxygen has no effect in normal individuals. It 
enables more muscular work to be done, however, owing to the more complete 
oxidation of the lactic acid produced by the muscles. So long, therefore, 
as the supply of oxygen is ample, the activity of the respiratory center will 
be determined, in part at least, by the percentage of carbon dioxide in the 
blood. 
Ventilation.-The purpose of ventilation is so to adjust indoor conditions 
that the comfort and the health of the individual may be maintained. Contrary 
to common belief, the evil effects of badly ventilated rooms are not due either 
to a deficiency of oxygen or an accumulation of carbon dioxide. The discharge 
of organic substances into the air of ill-ventilated rooms has been shown by 
careful experiments not to be responsible for the evil effects experienced by the 
individual. The discomfort and headache, which may pass on to more serious 
disturbances, have been shown to be due to an interference with the loss of heat 
from the body. The decreased ability of the body to lose heat as fast as it is 
produced in the tissues, is caused by the increase in the humidity and heat of 
the atmosphere observed in crowded places. As a consequence of this inter- 
ference with heat loss, there arises a mild fever. The mucous membrane of 
the respiratory passageways swells and becomes boggy. If under such condi- 
tions the individual passes into cool air, or is exposed to a draught that rapidly 
cools the surface of the body, the blood supply to the respiratory passages 178 
THE NERVE CONTROL OF RESPIRATION 
becomes greatly diminished, the resistance to bacterial infection is lowered, 
and the individual develops a "cold." 
The evil effects of poor ventilation may therefore be counteracted by 
supplying cool, dry air in sufficient volume, or by favoring heat loss by keeping 
the air in motion by electric fans. The best way of warming a room is by 
radiant heat, near the floor, as can be done with a grate fire. 
Artificial Respiration.-When an individual has been asphyxiated from 
drowning or from breathing some irrespirable gas, or when the respiratory 
Fig. 103.-This illustrates the two principal positions, A and B, in performing Schafer's method of 
artificial respiration. {Halliburton.) 
center has been strongly inhibited as by an electric shock, it is sometimes 
possible to revive him by bringing about respiratory movements by artificial 
means. Several methods of artificial respiration have been devised. The 
method of Schafer is effective and easy of application (Fig. 103). Schafer's 
description of his method is as follows: "The method consists in laying the sub- 
ject in the prone posture, preferably on the ground, with a thick folded garment 
underneath the chest and epigastrium. The operator puts himself athwart 
or at the side of the subject, facing his head, and places his hands on each 
side over the lower part of the back (lowest ribs). He then slowly throws ESSENTIALS OF PHYSIOLOGY 
179 
the weight of his body forward to bear upon his own arms, and thus presses 
upon the thorax of the subject and forces air out of theilungs. This being 
effected, he gradually relaxes the pressure by bringing his own body up again 
to a more erect position, but without moving the hands. " These movements 
up and down should take place at the rate of about 15 times per minute until 
Fig. 104.-*' The Lungmotor.' ' 
normal breathing has returned. It is sometimes necessary to maintain artificial 
respiration for an hour and a half before the asphyxiated person breathes again. 
Certain devices, such as the lungmotor, or "pulmotor, " are used also for 
artificial respiration. With these devices, air, or a mixture of air and oxygen, 
is forced into the lungs under appropriate pressure (Fig. 104). CHAPTER XXIII 
PHARMACODYNAMICS OF THE RESPIRATION 
Oxygen Inhalations.-The inhalation of air containing an abnormal 
percentage (above 20.80 per cent) of oxygen or even undiluted oxygen, produces 
no appreciable effect on the respiratory apparatus under normal conditions. 
If, however, the supply of oxygen is deficient from any cause, inhalations of 
the gas will promptly relieve the asphyxial symptoms. The results are most 
effective in those conditions in which the access of oxygen to the blood is hin- 
dered by mechanical interference with respiration as in drowning, suffocation, 
croup, etc., by vitiated air of mines and wells, by diminished absorbing surface 
as in pneumonia, and by depressed respiration as in collapse. In the foregoing 
cases the hemoglobin is not saturated with oxygen. The inhalation of air rich 
in oxygen therefore promotes saturation. 
In asphyxial conditions resulting from a deficiency in hemoglobin as in 
anemias, the inhalation of oxygen cannot increase the amount of oxygen carried 
by the hemoglobin. In such cases improvement must be due to an increase in 
the small amount of oxygen present in simple solution in the blood plasma, the 
result of the direct increase in the percentage of oxygen in the alveolar air. 
Carbon Dioxide.-The role played by carbon dioxide in the chemical control 
of respiration has been discussed on page 176. 
As already stated in the discussion of the nerve control of respiration 
(see page 174), the rhythmic movements of respiration are determined and 
coordinated through the activity of the respiratory center. This center is 
susceptible to stimulation or inhibition through reflex nerve impulses as well as 
through the action of drugs. 
Respiratory Stimulants.-The number of drugs which directly stimulate 
the respiratory center is very large. Practically all highly volatile drugs stim- 
ulate the respiration, but the only ones of practical therapeutic importance are 
Alcohol, Ether and Ammonia. 
Alcohol.-Although the effects of therapeutic doses of Alcohol are some- 
what variable and usually rather small, most investigators are of the opinion that 
medicinal amounts of this drug may increase the frequency and the depth 
of respiration by direct stimulation of the respiratory center. It is probably true 
that a part of its action on the respiration is reflex from local irritation. In- 
toxicating doses ultimately depress the respiratory center. The respiratory 
stimulating effect of Alcohol is at times employed in the treatment of collapse. 
Ether.-When administered, sufficiently diluted to avoid local irritation, 
by mouth (Spirit of Ether and Compound Spirit of Ether), or by inhalation, 
Ether directly stimulates the respiratory center so that respiration is somewhat 
180 PHARMACODYNAMICS 
181 
deeper and more rapid. The drug will also produce this effect by subcutaneous 
administration. If the drug irritates the mouth, stomach or respiratory 
passages, reflex stimulation augments the direct action. If the irritation is 
intense, temporary stoppage of respiration may result (see page 176). 
If large amounts of Ether are absorbed the respiratory center is rapidly 
depressed, paralysis of the center ultimately taking place. 
The preparations of Ether mentioned above are at times employed to 
relieve bronchial and cardiac dyspnea or that due to an over-distention of the 
stomach. 
Ammonia.-Inhalations of ammonia gas or strong solutions by mouth, 
through local irritation produce a momentary standstill (see page 176) and then a 
reflex stimulation of the respiration. If the drug is absorbed there is direct 
stimulation of the center. It is commonly used in the form of smelling salts 
(ammonium carbonate in lavender, violet or other perfumed solution) by inhal- 
ation, or as Aromatic Spirit of Ammonia by mouth for its respiratory and 
circulatory effects in. fainting, collapse, etc. 
A number of non-volatile drugs also stimulate the respiratory center. Those 
of greatest therapeutic importance are Caffeine and Strychnine. 
Atropine.-A hypodermic dose of Atropine is followed by an increase in the 
rate and frequently the depth of respiration, in various conditions of marked 
respiratory depression. This is largely due to stimulation of the respiratory 
center, and is made use of in treating poisoning by drugs which depress respira- 
tion, such as the narcotics, as well as in general anesthesia and in pneumonia. 
Atropine also peripherally paralyzes the innervation of the bronchial muscles 
and glands, and as a result the bronchi are dilated and dried. This action is 
employed in the treatment of bronchial asthma. 
Caffeine.-By the hypodermic method Caffeine stimulates the respiratory 
center. By mouth the action is less pronounced. The drug is used as a respira- 
tory stimulant in narcotic poisoning and collapse. It should be remembered 
that overdoses of respiratory stimulants are finally depressant to the center. 
Strychnine.-In therapeutic doses Strychnine produces little if any respira- 
tory effects excepting some increase in the respiratory rate, due to increased 
sensitiveness of the respiratory center. The action is more pronounced in con- 
ditions of depressed respiratory sensitiveness, as in poisoning by narcotic drugs. 
Strychnine is less valuable as an emergency respiratory stimulant than 
Caffeine. 
Respiratory Sedatives or Depressants.-In therapeutics it is probably true 
that indications for quieting and regulating the respiration are more common 
than conditions calling for stimulation. One of the most common conditions in 
which a respiratory sedative or depressant is frequently indicated is troublesome 
or painful cough. Although all drugs which depress the central nerve system 
i. e., the narcotics, usually decrease the excitability of the respiratory center, 
there are decided differences in their respiratory effects. Thus, the anesthetics 
all depress the respiratory center but their action on the respiratory center is 
produced by more or less toxic doses, and are consequently unsuitable for this 182 
PHARMACODYNAMICS OF THE RESPIRATION 
purpose. Members of the hypnotic group, such as Morphine, Chloral Hydrate, 
and the bromides, may be effective as respiratory sedatives in doses which pro- 
duce only very moderate hypnotic effects. 
Morphine.-As already stated on page ioi the sensitiveness of the respira- 
tory center and the closely related sensory centers which control the cough reflex 
is markedly diminished by Morphine. This action appears to be so specific that 
it is produced by doses so small that there is little ii any other sedative action. 
After very small doses of Morphine respiration is usually slowed and deep- 
ened. Thus, respiration although slowed is more efficient, and the patient's 
strength, a matter of great importance in cardiac and high fever cases, is saved. 
Morphine diminishes the excitability of the cough reflex centers more rapidly 
and readily than that of the respiratory center proper. The foregoing actions, 
therefore, make Morphine of value in relieving troublesome, painful, ineffective 
cough with little expectoration, and to relieve laryngeal irritation and inflam- 
matory conditions which are aggravated by repeated coughing. 
Morphine Derivatives.-Codeine is usually preferred as a respiratory seda- 
tive in place of Morphine because it is less narcotic, less constipating, and less 
apt to induce habituation; yet it is probably just as effective in allaying cough. 
Dionine and Heroine have also been used as cough sedatives but possess no 
advantages over Codeine. 
Chloral Hydrate produces respiratory effects similar to those of Morphine, 
and is used at times as a sedative in whooping-cough and other coughs. 
Bromides, such as Sodium Bromide, also diminish the cough reflex and are 
at times employed in sedative cough mixtures. 
Expectorants.--Drugs which facilitate the expulsion of mucus from the 
respiratory organs are termed expectorants, and are therefore useful in treating 
productive coughs. The exact manner in which the expectorants act is not 
clearly understood. Some of them produce their effects possibly by accelerating 
and strengthening the movements of the ciliated respiratory epithelium and an 
upward peristaltic movement of bronchial muscle, thus facilitating the trans- 
portation and expulsion of respiratory mucus. Others are probably helpful 
in acute inflammatory respiratory conditions principally by stimulating the 
secretion of mucus which tends to protect and soothe the inflamed areas. 
They are conveniently subdivided into the following groups: 
(i) Sedative Expectorants.-These include the nauseant expectorants, such as 
Apomorphine, Ipecac, and Antimony and Potassium Tartrate; the demulcent expec- 
torants, like Acacia, Licorice, Glycerin, etc.; and the saline expectorants, such 
as Ammonium Chloride, Ammonium Carbonate and Potassium Iodide. They 
are helpful in acute respiratory inflammation, especially in the first stages of 
bronchitis. 
(2) Stimulating Expectorants.-Expectorants in this group produce a mild 
degree of irritation of the respiratory mucous membrane which tends to stimu- 
late repair and to diminish excessive secretion. They may be accordingly 
particularly helpful in subacute and chronic bronchitis. Most of them are 
aromatic, volatile compounds, such as Terpene Hydrate, Creosote, Cubeb, Balsam PHARMACODYNAMICS 
183 
of Peru, Balsam of Tolu, Santol, Guaiacol, Tar, Benzoates, etc. Squill and 
Senega, irritant drugs, are also classed here. 
(3) Anodyne Expectorants.-Morphine, its preparations like Paregoric, and 
its derivatives, especially Codeine, in small doses depress excessive cough reflex 
and probably diminish respiratory mucus by delaying its expulsion and thereby 
permitting it to dry. These drugs appear to be especially useful if the secretion 
is scanty. They should not be used if the respiratory mucus is excessive, as 
they would more or less seriously interfere with its prompt expulsion. Small 
doses of Chloroform are also used. 
From the foregoing it is apparent that expectorants should be carefully 
chosen to meet those special indications of the different stages of respiratory con- 
gestion and inflammation. These conditions can be recognized only by the 
physician after thorough examination of the chest, throat, larynx, nose and ears. 
Counterirritants.-Pain, by interfering with the movements of the thorax 
on one or both sides, may cause respiration to become shallow and rapid. 
By applying mild counterirritants, such as mustard plasters, flaxseed poultices, 
Tincture of Iodine, Chloroform Liniment, Spirit of Camphor, hot water bottles, 
etc. the pain is relieved, respiration is deepened and improved, and inflammatory 
conditions of the respiratory tract, as in bronchitis, pleurisy, pneumonia, etc., 
may be relieved. 
Antiasthmatics.-The manner of action and the use of Atropine, Epine- 
phrine and the Nitrite Group (see pages 44 no, 112,) in the treatment of 
bronchial asthma have already been mentioned. 
Iodides, such as Sodium and Potassuim Iodides, are perhaps the most 
successful agents used in preventing the recurrence of asthma. Since most 
cases of asthma are possibly due to some affection of the air passages, the 
iodides are valuable probably because they are stimulants to the mucous mem- 
branes of the nose, throat, and bronchi. If an iodide is administered in any 
chronic disturbance located in these mucous membranes, the drug tends to 
increase the exudate from these membranes and to make the mucus much 
more liquid. Although at first apparently irritating, the iodide soon relieves 
any congestion of these membranes, and often ultimately cures the chronic 
congestion and causes the membrane to become healthy ("alterative"). How- 
ever, the use of an iodide for the relief of asthma should be carried out only upon 
the advice of a physician for should the patient have pulmonary tuberculosis, 
the administration of an iodide would be likely to cause the absorption of the 
caseous (cheesy) areas in the lung tissue and set free the tubercle bacilli con- 
tained in them, thus spreading the infection and promoting the expectoration 
of these organisms. In addition, the arterioles in the caseous areas, being 
deprived of their supporting tissues, might rupture and cause hemorrhage. CHAPTER XXIV 
FOODS 
Functions and Definition of Food.-The activities of the organs and tissues 
of the body are characterized by a transformation of energy. The complex 
molecules of the living and food materials are constantly undergoing disinteg- 
ration, and are ultimately oxidized more or less completely. As a result, the 
energy locked up in the living matter and the food material is set free and 
appears as motion, heat, and electricity. The products of oxidation, being 
of no further use to the body, constitute waste which is eliminated by the lungs, 
kidneys, liver, and skin. 
If the organs and tissues of the body are to continue fulfilling their function, 
it is necessary that they be supplied with new material for their growth, repair 
and the liberation of energy. This material must obviously be similar in 
composition to that of the tissues. As it serves to maintain the nutrition of the 
tissues, it is called nutritive material or food. A food may therefore be defined 
as any substance that can yield energy or supply material for the growth and repair 
of the living matter, or that contributes material necessary for the maintenance of the 
normal composition of the body. 
Hunger and Thirst.-The individual is made aware of the need to supply 
the tissues with food material by the sensations of hunger and thirst. Numer- 
ous experiments have demonstrated that the immediate cause of the sensation 
of hunger is a periodical contraction of the musculature of the stomach. The 
sensation of thirst occurs when the water content of the body tissues has 
decreased below the normal limit. At that time the mouth and fauces feel 
dry, and the characteristic sensation of thirst arises. 
Classification of Food Principles.-Not all of the material found in articles 
of diet is capable of being digested and absorbed or of being utilized by the 
body tissues. Those substances in foods that are capable of contributing to 
the nutrition of the body are called nutrients or food principles. The food 
principles consist of inorganic and organic substances: they may be grouped 
as follows: 
A. Inorganic 
Water 
Sodium and potassium chloride 
Sodium, potassium and calcium phosphates and 
carbonates 
Iron 
Principle 
Where Found 
In nearly all animal and vegetable foods. 
184 ESSENTIALS OF PHYSIOLOGY 
185 
Principle 
Where Found 
B. Organic 
Dextrose or grape-sugar. 
Levulose or fruit-sugar 
1. Carbohydrates 
Lactose of milk-sugar :. Milk. 
Saccharose or cane-sugar Sugar-cane, beet roots. 
Maltose Malt and malted foods. 
Starch Cereals, tuberous roots, and leguminous plants. 
Glycogen Liver, muscles. 
In fruits. 
2. Proteins 
Myosin Flesh of animals. 
Albumin, vitellin White of egg, yolk of egg. 
Caseinogen Milk. 
Serum albumin, fibrin Blood contained in meat. 
Gliadin and glutinin Grains of wheat and some cereals. 
Vegetable albumin Soft-growing vegetables. 
Legumin Peas, beans, lentils, etc. 
3. Fats 
Animal fats . In adipose tissue of animals. 
Vegetable fats In seeds, grains, nuts, fruits, and other vegetable 
tissues. 
Citric, tartaric, acetic, malic In fruits and vegetables. 
4. Vegetable Acids 
5. Vitamins 
Vitamin A In milk, butter, egg yolk, cabbage, spinach, 
carrots, the germ of cereals, and green leaves of 
plants ("salads"). 
Vitamin B : In yeast, milk, cheese, eggs, liver, pancreas, 
beans, peas, the germ of cereals, oranges, 
tomatoes, lemons, apples, grapes, honey, pota- 
toes, carrots, turnips, and nuts. 
Vitamin C In raw cabbage, lemons, oranges, tomatoes, 
potatoes, carrots, bananas, apples, turnips, 
lettuce and watercress. 
Vitamin D In milk, butter, cod-liver oil. 
6. Accessory Articles of Diet 
Tea, coffee, cocoa, condiments, flavors. 
The carbohydrates, as shown in the table, are mainly starches and sugars. 
Their molecule consists of carbon, hydrogen, and oxygen. The carbon occurs in 
the proportion of six atoms, or some multiple of this number, and the hydrogen 
and oxygen are present in the molecule in the same proportion in which they 
exist in water, viz., as 2: i. 
The proteins are found in both animal and vegetable tissues. Their 
molecule contains carbon, hydrogen, oxygen, nitrogen, and sulphur. These 
elements occur in varying proportions in different proteins. The molecule, 
likewise, differs in complexity in different proteins. On hydrolysis the pro- 
teins are reduced to simpler bodies which, namedin the order of their complexity, 
are: proteoses, peptones, peptides, diamino-acids and amino-acids. 
The fats occur in the tissues of vegetables and animals. Their molecule 
consists of carbon, hydrogen, and oxygen. The proportion of hydrogen and 186 
FOODS 
carbon atoms is relatively large. The fat of animals is a mixture differing 
in its proportions in different animals of three fats called stearin, palmitin and 
olein. When hydrolyzed, fats are split into glycerin and a fatty acid, the proc- 
ess being called saponification. 
COMPOSITION OF FOODS 
The various foods entering into the diet of man are obtained from both 
the animal and vegetable world. Their nutritive value depends on the amount 
of the food principles they contain, as well as their digestibility. 
The following table, taken from Atwater and Bryant, shows the percentage 
composition of typical foods: 
Food 
Water, 
per 
cent 
Carbo- 
hydrates, 
per cent 
Fat, 
per 
cent 
Proteins, 
per 
cent 
Indiges- 
tible 
portion, 
per cent 
Ash, 
per 
cent 
Beef, loin, lean 
67.0 
12.1 
19.1 
1.2 
1.0 
Mutton, leg 
62.8 
17.1 
17.9 
i-7 
0.8 
Pork, loin chops 
52-0 
28.6 
16.1 
2.2 
0.8 
Mackerel 
73-4 
6-7 
18.1 
i-3 
0.9 
Milk 
87.0 
5-o 
3-8 
3-2 
o-5 
05 
Eggs 
73-2 
11.4 
12.8 
1.2 
0.6 
Whole wheat bread 
38.4 
49-i 
0.8 
7-5 
3-2 
1.0 
White bread 
35-3 
52.3 
1.2 
7-i 
3-3 
0.8 
Corn meal 
12.5 
73-5 
1.7 
7-5 
4.0 
0.8 
Rice 
12.3 
76.9 
0-3 
6-5 
3-7 
o-3 
Beans, lima, dried 
10.4 
65.6 
i-4 
12.8 
6-7 
3-i 
Beans, string, cooked 
95-3 
1.9 
1.0 
0.6 
o-5 
0.7 
Peas, green, cooked 
73-8 
14-4 
3-i 
5-i 
2-5 
1.1 
Potatoes, boiled, cooked 
75-5 
20.0 
0.1 
1.9 
i-7 
0.8 
Potatoes, sweet 
5i-9 
40.3 
1.9 
2.2 
3° 
0.7 
Beets, cooked 
88.6 
7-2 
0.1 
i-7 
1.2 
1.2 
Cabbage 
91-5 
5-5 
03 
1.2 
0.7 
0.8 
Tomatoes 
94-3 
3-8 
0.4 
0.7 
0.4 
0.4 
Spinach 
92.3 
3-2 
0.3 
1.6 
1.0 
1.6 
Asparagus 
91.6 
2.1 
3-0 
i-7 
1.0 
0.6 
A comparison of the articles of diet contained in the table shows that the 
animal foods are rich in protein material. The percentage of fat contained in 
meat is relatively small, except in pork and mutton. The inorganic salts con- 
tained in animal food are chiefly potassium phosphate and sodium chloride. 
During the process of cooking meats, flavors are developed that render 
the meat more palatable. Moreover, the connective tissue is converted into 
gelatin so that the meat is more easily masticated and digested. The heat 
of cooking is usually sufficiently great to destroy bacteria or animal parasites 
that may be present in the meat. 
Cereals are rich in carbohydrates and contain also a fairly high percentage 
of proteins. The indigestible portion consists of cellulose. When the husk 187 
ESSENTIALS OF PHYSIOLOGY 
is removed from wheat, in the preparation of white flour, the greater part of 
the gluten is removed together with the vitamins. For this reason white bread 
is not as nutritious as whole wheat bread. The salts contained in wheat flour 
are principally potassium and magnesium phosphates. 
The vegetable foods differ greatly in their nutritive value. This is in part 
due to the difference in the percentage of food principles they contain, and in 
part to the amount of cellulose present. Beans and peas contain much protein 
and starch and are, therefore, highly nutritious. While the green vegetables 
contain but small amount of food principles, they are nevertheless valuable 
articles of diet in that they contain inorganic and organic salts, as well as 
vitamins necessary for the maintenance of health. CHAPTER XXV 
DIGESTION 
Definition.-Digestion is the process through which the food principles 
are prepared for absorption. While during digestion the food is subjected to 
various mechanical actions, the process 
is essentially chemical in nature. Dur- 
ing digestion the food principles are liber- 
ated from the indigestible material, such 
as tough connective tissue and cellulose; 
the food principles are then acted upon 
chemically and transformed into sub- 
stances suitable for absorption. 
The Digestive Apparatus.-The ser- 
ies of organs concerned in the function of 
digestion constitutes the digestive appar- 
atus. It includes the alimentary canal 
and its appendages, viz., the lips, teeth, 
tongue, salivary glands, gastric and in- 
testinal glands, pancreas, and liver. 
The alimentary canal begins at the 
mouth and ends at the anus. It is a mus- 
culo-membranous tube about 9 meters (30 
feet) in length, and includes the following 
parts: the mouth, pharynx, esophagus, 
stomach,, small and large intestines (see 
Fig. 105). 
The glands in relation to the alimen- 
tary canal discharge into its interior a 
number of digestive fluids. These diges- 
tive fluids are: the saliva] the gastric, in- 
testinal, and pancreatic juices, and the bile. 
All of these fluids, except the bile, cause 
chemical changes in the food principles, 
chiefly through the action of specific sub- 
stances called jerments or enzymes. The 
transformed food principles are then ab- 
sorbed; the indigestible material, together with certain waste products, pass 
gradually into the large intestine and are finally expelled from the body. 
Ferments or Enzymes.-Ferments are substances elaborated by living cells. 
They may produce their action within the cells, and are then called intracellular 
Fig. 105.-Diagram of the digestive appar- 
atus. Sal.g., salivary glands; Phar., pharynx 
Es., esophagus; Stom., stomach; Tr., trachea 
Liv., liver; G.b., gall-bladder; Duod., duoden- 
um; Pane., pancreas; L.int., large intestine 
S.int., small intestine; Sigm., sigmoid; Red. 
rectum; V. app., vermiform appendix. (G 
Bachmann, after Landois.) 
188 ESSENTIALS OF PHYSIOLOGY 
189 
enzymes. In other instances, ferments may be discharged from the cell so that 
their action takes place outside the cell; such ferments are called extra-cellular 
enzymes. The ultimate chemical constitution of enzymes is unknown although 
they are probably organic in nature. As they do not enter in the end-products 
of the chemical changes they induce and are not destroyed, ferments are believed 
to be catalyzers. Catalyzers act by virtue of their mere presence; they do not 
initiate but accelerate a chemical reaction that would otherwise take place 
although exceedingly slowly. 
Enzyme action is very susceptible to temperature changes. At o°C. 
enzymes are unable to induce any change. The velocity of their action gradu- 
ally rises as the temperature increases until a temperature of 4O°C. to 5o°C. 
is reached, when they are capable of producing their maximum effect. This 
is called the optimun temperature. The velocity of their action declines when 
the temperature rises about 5o°C. At 6o°C. their action stops, while at roo°C. 
enzymes are destroyed, particularly if water is present. 
When the products of enzymic action are not removed as fast as formed, 
the enzyme recombines them into the original substances. This is termed 
reversibility of action. Here again the enzyme does not initiate the process 
but merely accelerates it. 
Enzymes are specific in their nature. An enzyme that acts upon a given 
carbohydrate has no action upon even a closely related carbohydrate, nor 
upon fat or protein. In other words, each enzyme is adapted to act upon but 
one substance only. 
The name given to a given enzyme usually indicates the substance upon 
which it acts, for example, an enzyme acting on starch is called amylase, one 
acting on fat is called lipase, one acting on maltose is termed maltase, etc. 
The action of enzymes is indicated whenever possible by adding the suffix-lytic 
to a prefix indicative of the name of the substance acted upon, as proteolytic or 
protein-splitting; lipolytic or fat-splitting; amylolytic or starch-splitting. 
Enzymes are secreted in an inactive form; the material is then called a 
zymogen or proferment. Preferments are converted into active enzymes by 
substances termed activators or kinases. 
Stages of Digestion.-While digestion is a continuous process, it has been 
divided for purposes of study into the following stages: mouth digestion, includ- 
ing mastication and insalivation, deglutition, gastric digestion, and intestinal 
digestion. 
MOUTH DIGESTION 
Mastication.-The object of mastication or chewing is to subdivide the 
food so that the digestive fluids may the more readily act upon it. This is 
accomplished by the action of the teeth and the movements of the lower jaw 
and of the tongue. At the same time that the food is being comminuted the 
first digestive fluid-saliva-is incorporated with it. 
The Teeth.-In man, two sets of teeth are developed. The first set are 
called deciduous or milk teeth. The second set are the permanent teeth. 190 
DIGESTION 
The deciduous or milk teeth are twenty in number, ten in each jaw. They 
consist of four incisors, two cuspids or canines, and four molars for each jaw. 
There are thirty-two permanent teeth, sixteen in each jaw, which include 
four incisors, two cuspids or canines, and four bicuspids or premolars, and six 
molars. The last permanent molars are called the wisdom teeth. 
Three distinct parts are recognizable in all teeth: (1) the crown, or part 
projecting beyond the gums; (2) the root or fang, or part found in the alveolar 
socket; (3) the neck, situated between these two parts, and surrounded by 
the free edge of the gum. 
The crown of the incisors is chisel-shaped. Their sharp edges are espe- 
cially adapted for cutting the food. The cuspids or canines have a more or less 
Fig. 106X.-Teeth of adult, lingual surfaces. Fig. 106B.-Teeth of adult, labial and buccal 
(Broomell and Fischelis.) surfaces. (Broomell and Fischelis.) 
conical crown with a central point or cusp on the cutting edge. These teeth 
are highly developed in the carnivora in whom they are used for seizing and 
holding the prey. The bicuspids or premolars have a somewhat cuboidal 
crown and two cusps; one of the cusps is turned toward the cheek, while the 
other faces the interior of the mouth. The molar teeth have large and 
broad crowns possessing four or five tubercles that make their surface uneven 
and adapts them for grinding the food (Fig. 106). 
The Structure of the Teeth.-When a longitudinal section of a tooth is 
examined it is seen to consist of three distinct layers, viz., the enamel, the 
dentine, and the cementum (Fig. 107). In the center of the tooth there is a 
cavity, varying in shape in different teeth, filled by the pulp. 
The enamel covers the dentine on the crown. It consists of dense cylinders, 
hexagonal in shape and held together by cement substance. In unworn teeth, 
the enamel is covered by a thin horny membrane called the cuticle or membrane 
of Nasmyth. 
The demine, or ivory, forms the greater part of the bulk of the tooth. 
It consists of connective tissue fibers in a ground substance, in both of which ESSENTIALS OF PHYSIOLOGY 
191 
lime salts have been deposited. Fine canals, the dentine canals or tubules, 
permeate the dentine. These tubules radiate from the pulp cavity and end 
in fine branches which open into irregular spaces called interglobular spaces, 
which lie under the cementum and enamel. The dentine lining the tubules 
is denser and constitutes the dentinal sheath or Neumann's sheath. 
The cementum resembles bone in that is contains lacunae and canaliculi. 
The pulp consists of connective tissue supporting the blood vessels and 
nerves that penetrate into the pulp cavity through a foramen seen at the apex 
of the root. The external surface of the pulp is covered with a layer of large 
spherical cells, termed odontoblasts. From these 
cells, processes extend into the pulp as well as 
into the dentine tubules. These processes are 
called dentine fibers. Enough space is present 
between the dentine fibers and the wall of the 
tubules for a free circulation of lymph between 
the pulp cavity and the interglobular spaces, as 
well as the lacunae of the cementum. 
The teeth are bound firmly in their sockets 
by a fibrous membrane supplied with blood ves- 
sels and nerves and called the peridental mem- 
brane. The fibers of this membrane run between 
the alveolar process and the cementum. 
The Movements of Mastication.-During 
the time that the food stays in the mouth, it is 
subjected to the cutting and grinding action of 
the teeth and is being mixed with saliva. The 
act of chewing, or mastication, takes place through 
movements of the lower jaw, which owing to its 
peculiar articulation is able to move up and down, 
and to slide forward and sideways. A combina- 
tion of these sliding movements produces a grind- 
ing action between the lower and upper teeth. 
The muscles that move the lower jaw are striated skeletal muscles and are, 
therefore, under the control of the will. The food is kept between the teeth by 
movements of the lips, cheeks, and tongue. 
The Nerve Mechanism of Mastication.-The nerve cells from which the 
efferent fibers innervating the muscles of mastication arise, are located in the 
medulla oblongata. The nerve fibers leave by way of (i) the trigeminal or 
fifth cranial nerve to be distributed to the muscles that move the lower jaw; 
(2) the facial or seventh cranial nerve to be distributed to the muscles of the face 
and cheeks; and (3) the hypoglossal or twelfth cranial nerve, to supply the 
muscles of the tongue. 
The nerve cells from which these efferent nerves arise may be stimulated by 
nerve impulses descending from the cerebral cortex by way of the pyramidal 
tract. They may likewise be stimulated by reflex nerve impulses following 
Fig. 107.-Vertical section of tooth 
in jaw. E., enamel; D., dentine; 
pulp cavity; C., cement; B., bone of 
lower jaw; V., vein; a., artery; N., 
nerve. 192 
DIGESTION 
stimulation of the terminals of afferent nerves in the mucous membrane of the 
tongue and mouth. While the beginning of mastication is a voluntary act, 
the continuance of the movements is dependent upon the action of the reflex 
mechanism. The afferent portion of the reflex arc consists of the buccal and 
lingual branches of the trigeminal nerve; of the lingual branches of the glosso- 
pharyngeal, and of the chorda tympani nerves. 
Insalivation.-The saliva that is mixed with the food during mastication 
consists of the secretions of the parotid, submaxillary, and sublingual glands 
and of the mucous glands of the mouth (Fig. 108). 
Accessory parotid. 
Duct of accessory 
parotid 
Duct of parotid 
Bristle inserted 
into duct 
Frenulum linguae. 
Major sublingual 
duct 
Sublingual gland' 
-Parotid gland 
-Masseter muscle 
_ Sternomastoid 
muscle 
Posterior belly of 
■ digastric muscle 
-Lingual nerve 
Submaxillary 
- gland, 
drawn backward 
-Loop of fascia 
-Hyoid bone 
Duct of submaxil- - 
lary gland - 
Mylohyoid muscle 
Anterior belly of/ 
digastric muscle 
Fig. 108.-The salivary glands. (Morris' Anatomy.') 
Deep portion of submaxillary gland 
The parotid gland is located in front of and below the external ear. From 
its anterior border there passes out a duct-Stensen's duct-which extends for- 
ward, pierces the muscle of the cheek, and opens opposite the second upper 
molar tooth at the tip of a papilla. 
The submaxillary gland lies on the inner surface of the lower jaw. Its 
duct, known as Wharton's duct, opens on the side of the tongue. 
The sublingual gland is located immediately under the mucous memb rane 
in the anterior part of the mouth where it causes a protuberance between the 
gums and tongue, called the sublingual plica. About twelve ducts, known as 
the ducts of Rivinus, emerge from the upper part of the gland and open on the 
edge of the sublingual plica. 
Structure of the Salivary Glands.-The salivary glands are compound 
tubulo-alveolar glands. The alveoli or acini are more or less tubular in shape, 
and consist of a single layer of polygonal epithelial cells resting on a basement ESSENTIALS OF PHYSIOLOGY 
193 
membrane. The acini are surrounded by a network of blood vessels, the spaces 
between which and the basement membrane are filled with lymph. Each acinus 
opens into a narrow duct lined by flat cells (Fig. 109). These small ducts, by 
their union, form a larger duct called the secretory tubule. The secretory 
Fig. 109.-The origin of the duct of a gland in alveoli, togther with the'connective tissue and blood 
vessels. (Hough and Sedgwick.) 
tubules, in turn, unite to form a much larger duct-the excretory duct-through 
which the saliva is carried into the mouth. This duct is lined by tall, columnar 
epithelial cells. 
The salivary glands have been divided into two classes in accordance with 
the character of the secretion they produce. Those salivary glands that produce 
Fig. no.-Parotid gland at rest. 1,1, acini; 
2, duct; 3,3, albuminous cells filled with fine gran- 
ules; 4,4, nuclei almost concealed. (Semi-dia- 
grammatic.) (Brubaker.) 
Fig. hi.-Parotid gland after prolonged ac- 
tivity. 1,1, acini; 2, duct; 3,3, albuminous cells 
almost free of granules; 4, nuclei clear and well 
defined. (Semi-diagrammatic.) (Brubaker.) 
a watery secretion are called serous or albuminous, while those that produce a 
thick, viscid secretion are called mucous glands. The serous or albuminous 
glands include the parotid, part of the submaxillary, and part of the glands 
of the tongue. The mucous glands include the sublingual, part of the submaxil- DIGESTION 
194 
lary, and part of the glands of the tongue, the glands of the lips, cheeks, palate, 
and pharynx. 
In the intervals of secretion, the epithelial cells of the serous glands are 
swollen and filled with dark'granules. During the time that the gland is secret- 
Fig. 112.-Submaxillary gland at rest. 1,1, 
acini; 2, duct; 3,3, mucous cells containing mucin; 
4,4, nuclei, flattened and dispersed toward the 
base of the cells; 5,5, crescents of Giannuzzi. 
{After Vialleton.) 
Fig. 113.-Submaxillary gland after prolonged 
activity. 1,1, acini; 2, duct; 3,3, mucous cells 
free of mucin and filled with fine granules; 4,4, 
nuclei rounded and returned to the center of the 
cell; 5,5, cells of Giannuzzi, large and distinct. 
{After Vialleton.) 
ing, the granules disappear from the external border of the cells and move toward 
the internal border and into the lumen of the acinus. At the same time the 
cells shrink and become clear. The granules are believed to be the material 
Fig. i 14.-Scheme of the nerves involved in the secretion of saliva. {G. Bachmann, in Brubaker's 
Physiology.) 
from which the ferment of the saliva is derived; they are therefore called 
zymogen granules (Figs, no and in). 
In the mucous glands, during rest, the epithelial cells are likewise swollen 
and filled with highly refractive globules. These globules constitute the material ESSENTIALS OF PHYSIOLOGY 
195 
that gives rise to the mucin, characteristic of the secretion of the mucous glands. 
This material is therefore called mucigen (Figs. 112 and 113). As the mucigen 
globules are discharged into the lumen of the acinus, the cells diminish in size. 
On the basis of these observations it is believed that during the intervals of 
secretion, the gland cells are engaged in elaborating the material found in the 
granules out of substances supplied to them by the lymph, which in turn is 
derived from the blood. During the act of secretion the blood vessels dilate 
widely, a larger amount of lymph is produced, and the gland cells discharge 
water, inorganic salts, and their organic material into the lumen of the acinus. 
The saliva thus formed is led by the ducts into the mouth. 
Both the gland cells and blood vessels of the salivary glands are supplied 
with nerve fibers issuing from sympathetic ganglia. The changes just described 
are therefore mediated through the nerve system. 
The Nerve Mechanism of Salivary Secretion.-The salivary glands, being 
supplied by the sympathetic, are not under the control of the will. The secre- 
tory activity of these glands is determined, however, by reflex action (Fig. 114). 
It is influenced also by various mental states. 
The afferent nerves of the reflex arc consist of the taste fibers of the chorda 
tympani, similar fibers of the glosso-pharyngeal, and the fibers of the lingual and 
buccal branches of the trigeminal nerve. 
The nerve cells from which the efferent fibers arise that supply the gland 
cells with secretory fibers, and the blood vessels with dilatator fibers, are located 
in the medulla oblongata where they constitute a center called the nucleus 
salivatorius. 
The efferent nerves are contained in the chorda tympani. The fibers of this 
nerve terminate around the sympathetic ganglion cells of the submaxillary and 
sublingual ganglia, whence postganglionic fibers pass to the glands of the same 
name. Other efferent fibers pass by way of the glosso-pharyngeal nerve to the 
otic ganglion, whence postganglionic fibers pass to the parotid gland and its 
vessels. 
Aside from these efferent nerves all salivary glands are supplied by sym- 
pathetic fibers arising from the cells of the superior cervical ganglion. 
Stimulation of the chorda tympani and glosso-pharyngeal nerves on the one 
hand, and of the sympathetic on the other hand, yields different results. When 
the chorda tympani or the glosso-pharyngeal nerve is stimulated, an abundant 
flow of watery saliva takes place; at the same time the blood vessels supplying 
the glands dilate widely. Stimulation of the sympathetic, however, is not 
followed by any secretion or, at best, gives rise to but a scanty flow of thick 
saliva. There is also a marked constriction of the blood vessels. While stimu- 
lation of the sympathetic does not cause an outpouring of secretion, it neverthe- 
less excites the gland cells to accumulate inorganic as well as organic material, 
as shown by the larger amount of these substances that appear on the sub- 
sequent stimulation of the chorda tympani or glosso-pharyngeal nerve. 
Reflex stimulation of the various efferent nerves is apparently determined 
by differences in the character of the peripheral stimuli. 196 
DIGESTION 
Mental states induced by the odor, the sight, or even the thought of 
appetizing food, likewise, exercise a stimulating influence on the salivary center 
from which the efferent fibers arise. The free flow of saliva thus brought about, 
is commonly referred to as "watering of the mouth." 
The Composition of Saliva.-As already intimated, the saliva collected from 
the different glands varies in composition. The saliva found in the mouth is a 
mixture of the secretions of all the salivary glands. Mixed saliva is a slightly 
turbid, opalescent, and somewhat viscid fluid that frothes readily when mixed 
with air. Its specific gravity lies between 1.002 and 1.006. It is normally 
alkaline in reaction to litmus, although the presence of fermenting food par- 
ticles in the mouth may render it neutral or even acid. Under the microscope 
the saliva is seen to contain corpuscles resembling leukocytes, epithelial cells, 
and a great variety of micro-organisms. 
Chemically, the saliva consists of: 
Water 994.20 
Epithelium 2.20 
Soluble organic matter (mucin, globulin and serum albumin) . 1.40 
Potassium Sulphocyanide 0.04 
Inorganic salts (sodium and potassium chloride, sodium and calcium carbonate, potassium 
sulphate, calcium phosphate) 2.20 
1000.04 
(Hammerbacker.) 
The quantity of saliva secreted during twenty-four hours has been estimated 
at between 1300 cc. and 1500 cc. The quantity will vary with the character 
of the food, the length of time it is masticated, and the water content of the 
body. 
The quantity of saliva poured out by the different glands is determined by 
the character of the food. When the food is dry, a relatively larger amount of 
parotid saliva is secreted. With food the consistency of meat, there is a rela- 
tively greater activity of the submaxillary gland. 
The Functions of Saliva.-The saliva has a physical and a chemical 
function. Physically it serves to soften the food and to bind its particles into a 
single mass that can be readily swallowed. This function is subserved by the 
water and mucin. 
Chemically, it contributes to the digestion of starches, which during the 
process of cooking have been liberated from the wall of cellulose surrounding 
the starch granules and have, furthermore, absorbed water. This function is 
carried out through the presence in saliva of a ferment called ptyalin. This 
ferment acts more readily on cooked than on raw starch. 
The first change that cccurs in starch under the action of the ptyalin of 
saliva is its conversion into soluble starch. This, then becomes changed into 
erythrodextrin and maltose. The erythrodextrin is further changed into a differ- 
ent variety of dextrin called achroddextrin and maltose. The achrobdextrin is 
itself ultimately converted into maltose. ESSENTIALS OF PHYSIOLOGY 
197 
These changes may be represented, schematically, as follows: 
Erythrodextrin - 
Maltose 
Achrobdextrin = Maltose 
Maltose 
Starch = Soluble Starch = 
The action of the ptyalin is therefore to change the starch into dextrin and 
maltose. This conversion is accomplished by a process of hydrolysis as shown 
in the following formula: 
3(C6H10O5) + H20 -» Ci2H22Ou + C6H,o06 
Starch Water Maltose Dextrin 
The saliva contains also a small amount of another ferment called maltase 
which has the property of converting maltose into dextrose. 
DEGLUTITION 
Deglutition, or the act of swallowing, consists of the transference of the 
food from the mouth into the stomach. The structures through which 
Fig. 115.-Vertical section of the nasal fossa and mouth. I, left nares; 2, lateral cartilage of the 
nose; 3, position of the internal alar cartilage forming the skeleton of the lower part; 4, superior 
meatus; 5, middle meatus; 6, inferior meatus; 7, sphenoidal sinuses; 8, external boundary of the poste- 
rior nares; 9, internal elliptical opening of the Eustachian tube; 10, soft palate; 11, vestibule of the 
mouth; 12, vault of palate; 13, genioglossus muscle; 14, geniohyoid muscle; 15, cut margin of the 
mylohyoid muscle; 16, anterior pillar of the palate (anterior half-arch), presenting a triangular figure 
with the base inferiorly, covering partly the tonsil; 17, posterior pillar (posterior half-arch) of the 
palate; 18, tonsil; 19, follicular (mucous) glands at the base of the tongue; 20, cavity of the larynx; 
21, ventricle of the larynx; 22, epiglottis; 23, cut os hyoides; 24, cut thyroid cartilage; 25, thyrohyoid 
membrane; 26, section of posterior portion of the cricoid cartilage; 27, section of the anterior portion 
of the same cartilage; 28, crico-thyroid membrane. (Sappey.) 
the food must pass constitute the deglutitory canal and include the mouth, the 
pharynx, and the esophagus (see Fig. 115). 
The Mouth.-The cavity proper of the mouth is delimited in front and on 
the sides by the dental arches. Its roof is formed by the hard palate, and its 198 
DIGESTION 
floor by the tongue. The mouth opens posteriorly into the pharynx by an 
opening termed the isthmus of the fauces. This opening is bounded at the sides 
by the glosso-palatine arches, above by the soft palate, and below by the tongue. 
The glosso-palatine arches are two folds of mucous membrane on each side 
investing muscles. A lymphatic structure, called the tonsil, is located between 
the arches. 
The Pharynx.-The pharynx or throat, is a more or less conical structure 
about 12.5 cm. (5 in.) in length. It contains in its walls three pairs of striated 
muscles-the superior, the middle and the inferior constrictors. The pharynx 
communicates through a number of openings with the nasal chambers, the mouth, 
and the larynx, as well as with the Eustachian tubes which lead into the middle ear. 
The Esophagus.-The pharynx is continued into the esophagus or gullet, 
a musculo-membranous tube about 25 cm. (10 in.) long. The muscle coat 
consists of an external layer of longitudinal fibers, and of an internal layer 
of more or less circularly arranged fibers. The upper third of the fibers are 
striated; the middle third contains both striated and non-striated fibers; while 
the lower third are exclusively non-striated. At the opening between the 
esophagus and stomach the muscle fibers form a complete ring to which the name 
of sphincter cardiac muscle has been given. 
The mouth, pharynx and esophagus are lined by mucous membrane. 
The Act of Deglutition.-Three stages are recognized in the act of degluti- 
tion, viz., (1) The passage of the food from the mouth into the pharynx; (2) 
The passage of the food through the pharynx into the esophagus; (3) The pas- 
sage of the food through the esophagus into the stomach. 
In the first stage, the food formed into a bolus is placed upon the tongue. 
The mouth is then closed and respiration temporarily inhibited. The tongue 
is raised from before backward against the hard palate, and the contraction 
of certain muscles of the tongue and of the floor of the mouth pushes the bolus 
through the isthmus of the fauces into the pharynx. This part of the act of 
deglutition is voluntary in character. 
When the bolus of food is of firm consistence, the second and third stages 
are accomplished by a progressive wave of contraction back of the bolus, pre- 
ceded by a wave of relaxation in front of the bolus. This wave-like movement 
is called peristalsis. In this manner a firm bolus is transferred, through the 
pharynx and the esophagus into the stomach in about six seconds. 
When the food is liquid, the sudden rise of pressure that occurs under the 
action of the tongue and floor of the mouth propels the food with great rapidity 
to the end of the esophagus. Experiments have shown that it takes but 0.1 
second for liquids to pass from the mouth to the end of the esophagus. This 
is followed by a peristaltic wave which carries any particles of food onward, 
and finally forces the food into the stomach. 
If food is swallowed at intervals of less than one second the peristaltic 
wave and the opening of the cardiac sphincter are inhibited until after the last 
act of swallowing. In such a case, the accumulation of food at the end of the 
esophagus may give rise to pain radiating along the esophagus. ESSENTIALS OF PHYSIOLOGY 
199 
Owing to the sudden rise of pressure that occurs in the first stage of degluti- 
tion, food, especially liquids, might be forced into the nasal or laryngeal cavities 
were it not for their timely closure. The posterior nasal openings are closed 
by the elevation and tension of the soft palate through the action of certain 
muscles. The opening into the larynx is closed by the elevation of the larynx 
and the downward and backward movement of the epiglottis which applies 
itself upon the larynx as a lid. The passage of food into the larynx is further- 
more prevented by a reflex inhibition of respiration that takes place when 
the mucous membrane of the soft palate and pharynx are stimulated by the 
passing food. 
The Nerve Mechanism of Deglutition.-Aside from the first stage, which 
is essentially voluntary, deglutition is a reflex action. The afferent pathway 
is probably along the glosso-pharyngeal nerve. The efferent portion of the 
reflex arc consists of groups of nerve cells in the medulla oblongata from which 
arise the nerve fibers that innervate the muscles of deglutition. The efferent 
nerves for the voluntary part of the act are the trigeminal for the muscles of 
the floor of the mouth, and the hypoglossal for the muscles of the tongue. 
The efferent nerves for the purely reflex part of the act, are the glosso-pharyn- 
geal and vagus nerves for the muscles of the pharynx, and the vagus nerves 
for the esophagus. 
GASTRIC DIGESTION 
Following the entrance of the food into the stomach it undergoes further 
physical and chemical changes until it is finally reduced to a liquid or semi- 
liquid condition. 
fisophayo-yastric orifice 
Functus 
Incisura annularis 
Sphincter cardial. 
Cardiac portion 
or 
Body 
Pyloric sphincter 
Pylorus 
Pyloric canal 
Sulcus interenedius 
Vestibule 
Gastro duodenal constriction 
Fig. 116.-Diagram showing the anatomic features of the stomach. (From Brubaker's Text-book of 
Physiology.) 
The Stomach.-The stomach-a dilated and specialized portion of the 
alimentary canal-varies considerably in shape according to the extent to which 
it is filled. When slightly distended, it is more or less piriform in shape (Fig. 
116). Its position within the abdomen varies with the quantity of food it 
contains and the position of the body. When full, and the individual is in 200 
DIGESTION 
the erect posture, the stomach lies vertically and extends from beneath the 
diaphragm on the left side to the level of the umbilicus where it turns toward 
the right to end in the small intestine. The capacity of the stomach varies from 
1500 cc. to 1700 cc. 
The opening at the junction between the esophagus and stomach is called 
the esophago-gastric or cardiac orifice. The opening at the junction between the 
stomach and intestines is termed the pylorus. At the point where the stomach 
turns toward the right there is an indentation on its upper curve called the 
incisura angularis. A line drawn from this indentation to the opposite edge of the 
stomach divides the organ into a pyloric portion to the right, and a cardiac portion 
to the left. Similarly, a line drawn transversely across the organ from the car- 
diac orifice to the greater curved edge of the stomach divides the cardiac portion 
into the fundus above the line, and the main body of the stomach below it. 
The wall of the stomach is thin over the fundic and cardiac portions, and 
thick over the pyloric portion. The pyloric portion is divided into two parts: 
the antrum or more spacious part, and the pyloric canal leading to the pylorus. 
The Structure of the Stomach.-The walls of the stomach consists of four 
coats bound together by areolar connective tissue. These coats named from 
without inward are the serous, muscle, submucous, and mucous. , 
The serous coat is a thin membrane covered with endothelial cells. It is a 
part of the peritoneum, a serous membrane that covers more or less completely 
the abdominal and pelvic organs and that is reflected on the inner surface of the 
abdominal wall. It secretes a small amount of fluid and serves the purpose of 
diminishing friction. 
The muscle coat is composed of three layers of smooth muscle fibers 
arranged in sheets having a longitudinal, circular, and oblique direction. The 
circularly arranged muscle fibers are especially well developed at the esophago- 
gastric opening, where they constitute the sphincter cardiac. Another local 
thickening of the circular fibers is found along the line of division of the cardiac 
and pyloric portions. This circular muscle is known as the sphincter antri 
pylorici. The circular fibers are likewise well developed over the antrum, where 
they constitute the antral muscle. There is also a well defined thickening of the 
circular fibers at the pylorus known as the sphincter pylori. The longitudinal 
fibers over the latter region have been named the dilatator pylori. 
The submucous coat is composed of areolar connective tissue supporting 
blood vessels, lymphatics, and nerves. A thin layer of smooth muscle, called 
the muscularis mucosae supports the mucous membrane. 
The mucous coat in the empty stomach is thrown into numerous folds 
termed rugae, which however disappear when the stomach is distended. It is 
smooth and velvety, and when the stomach is at rest is covered with a layer of 
mucus. A circular fold of the mucous membrane is found at the pyloric open- 
ing and is known as the pyloric valve. The surface of the mucous membrane is 
covered with a layer of tall, columnar epithelial cells. 
The mucous coat contains an enormous number of tubular glands which 
open on the surface by wide-mouthed ducts. These glands are known as gastric ESSENTIALS OF PHYSIOLOGY 
201 
glands and are of two types, viz., the fundus or cardiac glands and the pyloric 
glands. 
The fundus or cardiac glands are branched, tubular glands possessing short 
ducts (Fig. 117). The secreting portion of the gland is from five to eight times 
the length of the duct, and is lined by two types of cells, the chief and the parietal 
cells. The chief, central or peptic cells are granular, cuboidal cells. The gran- 
ules are zymogen granules which disappear during active secretion. The par- 
ietal, border or oxyntic cells are large ovoid cells that stain deeply with acid dyes. 
Fig. 117.-Cardiac gland, m, mouth of duct; 
n, neck; f, fundus; c, central cells; p, parietal 
cells. {Landois and Stirling.') 
Fig. 118.-Pyloric gland of the stomach, m 
mouth of duct; n, neck. (Landois.) 
They are clear or finely granular and are situated in the external portion of the 
gland wall. These cells possess an elaborate system of fine canals which open 
into the lumen of the gland through a minute passageway. The greater number 
of these glands is found in the middle zone of the stomach. 
The pyloric glands are branched, convoluted, tubular glands with relatively 
long ducts (Fig. 118). The cells lining this type of gland are tall and columnar; 
their cytoplasm is clear and appears to contain a mucus-like material. The 
pyloric glands, as their name indicates, are found in the pyloric portion of the 
stomach. 
The arteries of the stomach are derived from branches of the aorta. They 
pass beneath the serous coat and send ramifications into the muscle, submucous, 
and mucous coat. From the capillaries, arise veins which ultimately follow the DIGESTION 
202 
course of the arteries and empty into the portal vein. The various coats of the 
stomach contain likewise numerous lymphatic vessels. 
The nerve supply to the organ is partly intrinsic and partly extrinsic. The 
intrinsic part consists of two plexuses of nerve fibers and ganglion cells. These 
plexuses are known as the plexus of Auerbach, or myenteric plexus, located in the 
muscle coat, and the plexus of Meissner or submucous plexus, situated in the 
submucous coat. 
The extrinsic part of the nerve supply consists of fibers from the vagus nerve 
and from the great splanchnic nerve. 
The Gastric Juice.-The secretion produced 
by the gastric glands is termed the gastric juice. 
This secretion may be obtained in a pure state, 
from an animal, by making a miniature stomach 
out of the main stomach, and stitching the open- 
ing of the miniature stomach to an opening in the 
abdominal wall. This miniature stomach is known 
as Pavlov's pouch (Fig. 119). Gastric juice has 
been obtained from men having an artificial open- 
ing through the abdominal wall into the stomach as 
a result of injury or of a necessary operative pro- 
cedure. The gastric juice can be collected in a nor- 
mal individual also by passing a rubber tube through 
the esophagus into the stomach, and aspirating the 
secretion. 
By these various means, sufficient gastric 
juice has been collected for chemical analysis. The 
juice, when free from admixture with food and mucus, is a clear, colorless fluid, 
having a saline and acid taste. It consists of about 99 per cent of water hold- 
ing a number of substances in solution. According to Carlson, it has a specific 
gravity of 1.006 to 1.009, and the following composition: 
Fig. 119.-Diagram showing the 
relation of the natural stomach to 
the miniature stomach or pouch 
made according to the procedure 
devised by Pavlov. V., the natural 
stomach; S., the miniature stomach; 
e, e., the septum formed by the mu- 
cous membrane. A, A., the abdo- 
minal walls. (From Brubaker's 
Text-book of Physiology.) 
Acidity 
Free hydrochloric acid 0.4 to 0.5 percent 
Total acidity 0.45 to 0.6 per cent 
Solids 
Organic • 0.42 to 0.46 per cent 
Inorganic 0.13 to 0.14 per cent 
The organic substances are chiefly mucin and a protein; the inorganic sub- 
stances consist of chlorides of sodium, potassium, calcium and magnesium, and 
small amounts of the phosphates of calcium, magnesium and iron. 
The enzyme or ferment of the gastric juice is pepsin. This ferment is 
elaborated in the chief cells of the glands, not in an active form but as a zymogen 
termed propepsin or pepsinogen. The pepsinogen is converted into the active 
pepsin by the hydrochloric acid of the secretion. 
The Hydrochloric acid is the normal acid of the gastric juice. Other 
acids present, such as lactic and acetic acids, are the result of fermentative 
changes taking place in the food under the action of bacteria. The hydro- ESSENTIALS OF PHYSIOLOGY 
203 
chloric acid is produced by the parietal or oxyntic cells by an interaction within 
the cell between sodium acid-phosphate and sodium chloride as follows: 
NaH2PO4 + NaCl HC1 + Na2HPO4 
The disodium phosphate is then reconverted into sodium acid-phosphate by a 
reaction between carbon dioxide and water: 
Na2HPO4 + C02 + H20 NaH2PO4 + NaHCO3 
The sodium bicarbonate passes into the circulation where it increases the alkaline 
reserve of the blood, which in turn leads to the decrease in the acidity of the 
urine observed during digestion. 
The amount of gastric juice secreted every twenty-four hours has been 
estimated as being not less than 1500 cc. With a meal of average quantity and 
composition about 700 cc. of gastric juice is believed to be secreted. 
The Secretion of Gastric Juice.-Numerous observations made on man 
have shown that the stomach contains at all times a variable amount of true 
gastric juice. Estimates vary greatly from 10 cc. to 180 cc.; the greater 
number of observations have yielded, in the morning before breakfast an aver- 
age of 50 cc. 
The exciting causes of the secretion of the gastric juice required for diges- 
tion are of two kinds: a nerve excitation, and a chemical excitation. The first 
stimulus to secretion is the result of the effect of the sight, odor, and taste of 
the food. The food acting on the special senses subserving the sensations just 
mentioned sets into play a reflex mechanism which, acting through the efferent 
fibers of the vagus nerve, causes the gastric glands to discharge their secretion. 
The secretion thus induced, is called the psychic or appetite juice. 
The amount of gastric juice secreted in this way, is relatively small, and is 
readily affected by emotional states, painful or depressing emotions inhibiting 
the flow, while agreeable emotions aid it. 
Once the food has entered the stomach the chief factor in maintaining an 
active secretion is chemical in nature. It is generally believed that under 
the action of certain foods, e. g., meat broths, dextrin, etc., a chemical substance 
is produced in the mucous membrane of the pyloric region which passes into 
the blood and is distributed to the gastric glands which it stimulates to activity. 
This stimulating agent is called the gastric hormone or gastric secretin. 
There is some evidence that the character of the secretin excited by the 
gastric hormone varies in composition in accordance with the character of the 
food. Apparently, the hormone produced during the digestion of meat excites 
a gastric juice having a high percentage of hydrochloric acid and a medium 
amount of pepsin; while with bread, the percentage of hydrochloric acid is low 
and the amount of pepsin high. This so-called qualitative adaptation may, 
however, be the result of different rates of secretion (Carlson). 
The Functions of the Gastric Juice.-The foods that enter the stomach 
are a mixture of nutritive and indigestible materials that have been more or less 
finely subdivided. In the short time that the ptyalin of the saliva has acted DIGESTION 
204 
upon the starch, but a small amount of it has been converted into dextrin and 
maltose. Free hydrochloric acid destroys the activity of the ptyalin, but 
since this acid does not accumulate in sufficient amount within about half an 
hour of the onset of gastric digestion, the action of ptyalin may go on within 
the stomach for this length of time. The food principles in combination with the 
indigestible material are set free by the solvent action of the gastric juice 
whose chief function is to reduce the proteins to simpler compounds, and thus 
to disintegrate and liquify the food. 
Under the action of hydrochloric acid and pepsin the protein molecules 
undergo hydrolysis and are split into simpler and more soluble molecules. 
The first change effected is the conversion of protein into acid-metaprotein, 
which by hydrolysis is split into various proteoses, and finally, into peptones. 
These various stages in the gastric digestion of protein may be represented 
by the following schema: 
Protein 
Acid-metaprotein 
Primary proteoses 
Secondary proteoses 
Peptones 
The protein of the food is not entirely converted into peptone before the stomach 
contents pass into the small intestine. 
Gastric juice acts also upon caseinogen, a phospho-protein of milk, and con- 
verts it into a solid substance, casein. This action of gastric juice is commonly 
ascribed to a ferment termed rennin, but there are reasons for believing that 
it is due to the action of pepsin. The process whereby the liquid caseinogen 
is transformed into the solid casein resembles the coagulation of blood, and, as 
in the latter, calcium salts are necessary. The general process may be repre- 
sented as follows: 
Caseinogen -* Rennin (or pepsin) -> Soluble Casein 
Soluble Casein -> Calcium salts -> Casein 
The casein, like other proteins, is then converted into proteoses and peptone. 
Fais in the form of a fine emulsion, as found in milk and the yolk of egg, 
are split into glycerin and fatty acids. The ferment that accomplishes this 
cleavage is called lipase. It is in all likelihood derived from pancreatic juice 
which has passed into the stomach by regurgitation from the intestines. Fat 
globules are set free during gastric digestion by the digestion of the connective 
tissue that surrounds them. 
The vegetable proteins undergo the same changes as the animal proteins, 
but they are more difficult of digestion. ESSENTIALS OF PHYSIOLOGY 
205 
The Movements of the Stomach.-During the time the food remains in 
the stomach it is kept in motion by peristalic movements of the stomach wall 
(see Fig. 120). These movements bring about a thorough admixture of the 
gastric juice with the food, and at the proper time eject the semiliquid material 
into the intestine. 
By mixing bismuth subcarbonate or barium sulphate with the food, it is 
possible with the X-ray to observe the movements of the stomach in animals 
and in man as well. The food is confined within the 
stomach by a tonic contraction of the cardiac and pyloric 
sphincters. The fundus and cardiac portions of the 
stomach contract tonically and thus press upon the gas- 
tric contents. At the same time peristaltic waves origi- 
nate at the beginning of the antrum and travel toward 
the pylorus. These waves recur every 15 or 20 seconds 
and move so slowly that several of them may be seen at 
any one time. So long as the pylorus remains closed 
while peristalic waves are advancing toward it, the food 
is forced to return in a central stream toward the car- 
diac portion. From time to time, however, the pyloric 
sphincter relaxes and allows the passage of liquified mater- 
ial into the intestine. Thereupon the mass of food 
contained in the fundus and cardiac portion advances 
under their steady contraction into the pyloric region, 
where it is in turn subjected to the churning action just 
described. As the food gradually leaves the stomach the 
organ assumes more and more a tubular shape. 
Duration of Gastric Digestion.-The time that food 
remains in- the stomach varies with its nature, its capac- 
ity for absorbing hydrochloric acids, and it state of 
subdivision. 
According to Cannon, the contraction and relaxa- 
tion of the pyloric sphincter depend on the respective 
chemical reactions of the contents of the pyloric part of the 
stomach and of the small intestine. The relaxation of the 
sphincter depends in part also on the degree of fluidity of the food on the stomach 
side, hard food causing it to remain contracted for a longer period than fluid food. 
Cannon's experiments on the cat would seem to show that when free hydro- 
chloric acid appears in the pyloric contents, the sphincter relaxes and the 
advancing waves of peristalsis drive the acid contents into the intestines. The 
acid acting upon the intestine presumably causes the sphincter to contract. 
The sphincter remains contracted so long as the intestinal contents remain acid. 
When these contents have been fully neutralized and free acid appears on the 
pyloric side of the sphincter, it again relaxes and permits the passage of semi- 
liquid material into the intestine. 
Fig. 12 o.-Shadow- 
sketches of the outlines of 
the stomach of a cat im- 
mediately after a meal 
(n.o), and at various in- 
tervals afterward (at 12.0, 
at 2.0, 3.30, 4.30). (W.B. 
Cannon.) 206 
DIGESTION 
In accordance with this view, the proteins, having a large capacity for 
absorbing hydrochloric acid, remain In the stomach an appreciable time. The 
first discharge takes place in about half an hour and continues from time to time 
during the several hours needed for their digestion. As fats delay the secretion 
of gastric juice, they leave the stomach with extreme slowness. Carbo- 
hydrates, on the other hand, having but little absorbing capacity for hydro- 
chloric acid, leave the stomach early and rapidly. Water likewise leaves the 
stomach early. 
More recent work, however, has shown that this view, which has gained wide 
acceptance, cannot be held any longer. The relaxation of the sphincter pylori 
has been observed to take place within a few minutes of the ingestion of any of 
the various food principles. The relaxation of the sphincter occurs whenever a 
peristaltic wave reaches the antrum no matter what the reaction of the gastric 
or intestinal contents may be. There seems to be some relationship between 
the state of fluidity of the gastric contents and their ready passage into the 
intestine. The subsequent occurrence of peristaltic waves over the intestine 
carrying the material injected into it, likewise influences the emptying of the 
stomach. 
With an average meal the stomach empties itself within four or five hours, 
although this time may be very much shortened following a period of fasting. 
Absorption in the Stomach.-The stomach being, primarily, a reservoir in 
which a substantial amount of food may be stored while undergoing preliminary 
digestion, permits of little if any absorption. 
Experiments with various salts and sugars would indicate that these sub- 
stances are not absorbed unless present in concentrations higher than found in an 
ordinary meal. Neither water, peptones, nor fats are absorbed. 
The Nerve Mechanism of the Stomach.-The muscle wall of the stomach 
contains a plexus of nerve fibers and nerve cells (Auerbach's plexus) which may 
serve as a co-ordinating mechanism. The activity of the muscle wall is likewise 
regulated by two sets of nerves, viz., the vagus and splanchnic. Section of the 
vagus nerves is followed by a loss of muscle tone. Stimulation of the vagus 
causes an augmentation in the force of the contraction of the pyloric muscles 
and an increase in the tone of the fundus muscle, of the sphincter pylori, and of 
the sphincter cardiae. 
Stimulation of the splanchnic nerve causes an inhibition of peristaltic 
movement and a loss of muscle tonus. The peristaltic movements of the 
stomach and the maintenance of its tonus are therefore under the control of two 
oppositely acting nerves. One-the vagus, increasing, the other-the splan- 
chnic, inhibiting these muscular activities. 
Vomiting.-The act of vomiting is preceded by a feeling of nausea, a free 
flow of saliva, and sighing inspirations. Just before the ejection of the stomach 
contents, waves of peristalsis run from the pyloric end of the stomach toward the 
cardiac end. The sphincter cardiae relaxes, an inspiration takes place and the 
glottis closes; the diaphragm then suddenly contracts and forces the stomach 
downward, while at the same time the abdominal muscles contract and compress ESSENTIALS OF PHYSIOLOGY 
207 
the stomach against the diaphragm. As a consequence, the stomach contents 
are expelled past the relaxed sphincter of the cardiac end into the esophagus, 
pharynx, and out of the mouth. 
Vomiting is a reflex act. The afferent nerves concerned may be widely 
distributed, but are mainly the trigeminal, glosso-pharyngeal, and the vagus. 
For the co-ordination of the outgoing impulses to the muscles concerned in 
the act of vomiting, a co-ordinating center would seem to be necessary. Such a 
center has been located in the medulla oblongata and is known as the vomiting 
center. The efferent nerves are the vagi to the muscles of the stomach, the 
phrenic nerves to the diaphragm, and the spinal nerves distributed to the 
abdominal muscles. 
The vomiting center may be stimulated also by nerve impulses descending 
from the cerebrum and cerebellum. 
INTESTINAL DIGESTION 
The partially digested material that passes from the stomach into the intes- 
tine is called chyme. Chyme is a semiliquid mixture of substances consisting 
of water, inorganic salts, starch, dextrin, maltose, saccharose, dextrose, lactose, 
acid meta-protein, proteoses, peptones, fat, and the indigestible portions of 
vegetables, meats, and fruits. As the chyme enters the intestine it excites a 
secretion of the digestive fluids necessary to complete digestion, viz., the 
pancreatic juice, bile, and intestinal juice. These secretions have an alkaline 
reaction and, therefore, neutralize the acid constituents of the chyme, following 
which intestinal digestion begins. 
The Small Intestine.-The small intestine is a musculo-membranous tube 
extending from the end of the stomach to the beginning of the large intestine. 
As the small intestine is about six meters (20 ft.) in length and the space it 
occupies is restricted, it is thrown into many folds or convolutions. 
The small intestine is divided into three parts, viz.,the duodenum, about 
eleven inches long, the jejunum, comprising the upper two-fifth, and the 
ileum, the lower three-fifths. 
Structure of the Small Intestine.-The intestinal wall is made up of 
four coats which, from without inward, are the serous, muscle, submucous, 
and mucous coats (Fig. 121). 
The serous coat consists of the peritoneal membrane already described 
as covering the greater number of the abdominal organs. 
The muscle coat is composed of two layers of smooth muscle fibers, the 
external of which is arranged longitudinally, while the internal one runs cir- 
cularly. The circularly arranged fibers are the more numerous. At the junc- 
tion of the small with the large intestine the circular fibers are well developed 
and constitute the sphincter muscle known as the ileo-colic sphincter. Its func- 
tion is to control the passage of material from the small into the large intestine. 
The submucous coat consists of areolar connective tissue; it binds the 
muscle to the mucous coat, at the junction of which a thin layer of smooth 
muscle fibers, the muscularis mucosae, is found. 208 
DIGESTION 
Sections of villi. 
Epthielium.. 
Tunica 
propria." 
Tunica 
propria. 
Muscularis 
mucosae.- 
Submucosa. 
Intestinal glands. 
Oblique sections of intestinal glands. 
Fig. 121.-Vertical section of the mucous membrane of the jejunum of an adult man. X 80. 
The space, a, between the tunica propria and the epithelium of the villus is perhaps the result of the 
shrinking action of the fixing fluid. At b the epithelium has been artificially ruptured. The goblet 
cells have been drawn on one side of the villus on the right. 
Villi ■ 
Epithelium. 
Plica circularis. 
Tunica 
propria. 
Intestinal glands. 
'Submucosa. 
Submucosa. 
Circular muscle 
Plexus 
myen- 
tericus. 
Longitudinal 
muscle. 
Serosa' 
Fig. 122.-Vertical longitudinal section of the jejunum of an adult man. X 16. The plica 
circularis on the right supports two small solitary nodules, which do not extend into the submucosa; 
one of them exhibits a germinal center, x. The epithelium is slightly loosened from the connective 
tissue core of many of the villi, so that a clear space, xx, exists between the two. The isolated bodies 
lying near the villi (more numerous to the left of the plicae circulares) are sections of villi that were 
bent, so that their ends were cut off in sectioning. (From Lewis and Stohr's Histology.} ESSENTIALS OF PHYSIOLOGY 
209 
The mucous coat has the soft and velvety appearance already described 
in the stomach. Its surface is lined with a single layer of columnar epithelial 
cells. Numerous small, conical structures, called villi, project from the general 
surface. Aside from these projections the mucous membrane is thrown into 
numerous transverse folds, termed valvulae conniventes. These folds, however, 
are not seen in the upper part of the duodenum nor in the lower half of the ileum. 
The valvulae conniventes increase the amount of surface available for secre- 
tion and absorption, and retard the onward movement of the food. 
Fig. 123.-A, diagram of the blood vessels of the small intestine; the arteries appear as coarse 
black lines; the capillaries as fine ones, and the veins are shaded. {After Mall.) B, Diagram of the 
lymphatic vessels. {After Mall.) C, diagram of the nerves, based upon Golgi preparations. {After 
Cajal.) The layers of the intestine are m., mucosa; m. m., muscularis mucosae; s. m., submucosa; 
c. m., circular muscle; i. c., intermuscular connective tissue; 1. m., longitudinal muscle; s., serosa; 
c. 1., central lymphatic; n., nodule; s. pl., submucous plexus; m. pl., myenteric plexus. {From Lewis 
and Stohr's Histology.) 
The Intestinal Glands.-The mucous membrane of the intestine contains 
innumerable small tubular glands known as the intestinal glands or Glands 
of Lieberkuhn (Fig. 122). They are lined with columnar epithelium resting 
on a basement membrane and open on the surface between the bases of the 
villi. Some of the cells of these glands become distended by mucin and are 
then called mucous or goblet cells. The intestinal glands secrete the greater 
part of the intestinal juice. 
In the upper half of the mucous membrane of the duodenum another type 
of gland occurs. These are called the duodenal glands or Glands of Brunner. 
They are small acinotubular glands branching in the submucous coat and 
resemble somewhat the pyloric glands of the stomach. Their openings lie 
between those of the intestinal glands. 210 
DIGESTION 
At about the middle of the duodenum, namely 3^ or 4 inches below the 
pylorus, the pancreatic and bile ducts open by a common orifice situated at 
the tip of a papilla. 
Blood and Nerve Supply.-Numerous arteries derived from the superior 
mesenteric artery pass between the folds of the peritoneal membrane to be dis- 
tributed to the intestinal wall (see Fig. 123). From the capillary net-work 
in the intestinal wall, veins arise that form the superior mesenteric vein. This 
vein joins with the splenic and gastric vein to form the portal vein. 
Lymphatic vessels, arising in the mucous and muscle coat, likewise unite 
to form larger vessels that pass between the layers of the peritoneum and 
ultimately empty into the thoracic duct. 
Fig. 124.-An island of the pancreas with the surrounding alveoli, from an adult. X 400. (From 
Lewis and Stohr's Histology.') 
The two plexuses of nerve fibers and nerve cells already described in con- 
nection with the structure of the stomach are likewise found in the intestinal 
wall. Meissner's plexus, it will be recalled, lies in the submucous coat, while 
Auerbach's plexus lies between the layers of the muscle coat. The latter is 
called also the myenteric plexus. 
The Pancreas.-The pancreas is an elongated and flattened gland lying 
on the posterior abdominal wall just behind the stomach. It is from twelve 
and a half to fifteen centimeters (5 to 6 in.) long, six centimeters (about 2^ in.) 
wide. It is customarily divided into a head, body, and tail. The head lies to 
the right within the curve of the duodenum; the tail lies to the left and reaches 
to the spleen. As previously stated, the pancreatic duct opens into the duo- 
denum together with the bile duct. The pancreatic duct begins at the tail 
and runs in a tortuous course throughout the length of the gland. 
Structure of the Pancreas.-The structure of the pancreas is similar to 
that of a serous salivary gland. It is an acino-tubular gland, the acini or ESSENTIALS OF PHYSIOLOGY 
211 
alveoli of which consist of a layer of more or less polygonal epithelial cells 
(Fig. 124). The end of the cells turned toward the lumen is filled with num- 
erous granules, while the base of the cells is clear. During the intervals of 
digestion the granular layer increases in extent; after active secretion the 
granular layer is very narrow. 
Aside from the secreting alveoli the pancreas contains another type of 
structure located between the acini. These structures are spheroidal and are 
made up of columns of globular cells between which are found large sinus- 
like capillary blood vessels. These structures are entirely separated from the 
acini by connective tissue. They likewise, do not communicate by any duct 
system with the rest of the gland. They are known as the Islands or Islets 
of Langerhans. The material elaborated by their cells passes directly into 
the blood and plays an important part in the metabolism of dextrose. 
The pancreas receives an abundant blood supply. It is innervated 
chiefly by the vagus nerves through the semilunar ganglion. 
The Pancreatic Juice.-The pancreatic juice may be obtained by intro- 
ducing a cannula into the pancreatic duct, and securing it through an opening 
in the abdominal wall. Human pancreatic juice is a clear, limpid fluid, having 
a strong alkaline reaction, and a specific gravity of 1.007. It is composed of 
water, holding in solution nucleoprotein, enzymes or their pro-enzymes, and 
inorganic salts, chiefly sodium carbonate and sodium chloride. The enzymes 
found in the secretion are trypsin, amylase or amylopsin, and lipase or steapsin. 
The amount of pancreatic juice obtained daily in a case of human fistula 
of the duct varied from 420 cc. to 884 cc. 
The Secretion of Pancreatic Juice.-The first factor in the discharge of 
pancreatic juice is the psychic state induced by the sight, odor, and taste of 
appetizing food. This brings about a discharge of nerve impulses which are 
transmitted by the vagus nerves to the cells of the acini. The amount of 
pancreatic juice secreted following stimulation of the vagus nerve is, however, 
small, but it is richer in ferments and poorer in sodium carbonate than the 
juice secreted later. 
The greater amount of pancreatic juice is poured out when the contents of 
the stomach are passing into the duodenum. Since pancreatic juice may be 
made to appear by introducing a weak solution of hydrochloric acid into the 
duodenum, it is believed that the acid of the gastric contents is the factor 
concerned in exciting the secretion. As this action occurs even when all nerve 
connections have been destroyed, it cannot be reflex in nature. The stimulus 
must therefore be chemical in character, and has been shown to consist of a 
chemical substance developed in the mucous membrane of the duodenum under 
the action of hydrochloric acid. This substance, called secretin, is absorbed 
in the blood and carried to the cells of the pancreatic acini which it stimulates 
to secretory activity. 
The pancreatic juice poured out during digestion is almost entirely the 
result of the stimulating action of secretin. It has been found that those foods 
which like milk, do not stimulate an abundant flow of gastric juice, delay 212 
DIGESTION 
the appearance and cause but a small discharge of pancreatic juice; conversely 
foods which, like meat and bread, excite a large flow of gastric juice likewise 
excite an early and abundant flow of pancreatic juice. 
The Functions of the Pancreatic Juice.-The pancreatic juice contains 
enzymes that have the power of acting on the three food principles, viz., pro- 
tein, starch, and fats. 
The Action on Proteins.-Pancreatic juice obtained from the pancreatic 
duct, without having come in contact with the intestinal mucous membrane, 
has no action on protein. If the pancreatic juice is permitted to flow over the 
duodenal mucous membrane or is mixed with intestinal juice, it becomes 
strongly active as a proteolytic agent. It is accordingly believed that the 
pancreatic juice, when secreted, does not contain the active enzyme but an 
inactive precursor known as trypsinogen. This proenzyme becomes activated 
under the action of an activator present in the intestinal juice and called 
entero-kinase. The fully formed ferment is called trypsin. Under its action 
the proteins undergo a hydrolytic cleavage. Since the medium is alkaline 
in reaction the first change is a conversion of the protein into alkali meta- 
protein, instead of acid meta-protein as in peptic digestion. The successive 
steps in the hydrolytic cleavage of the protein molecule may be represented 
as follows: 
Protein 
Alkali meta-protein 
Primary proteoses 
Secondary proteoses 
Peptones 
Polypeptides and Amino-acids. 
Tryptic differs from peptic digestion in that the early stages take place 
more rapidly, so that only small amounts of primary proteoses may be found. 
Furthermore, the peptones are themselves split into simpler .substances com- 
posed of two or more groupings of amino-acids known as polypeptides, and 
into individual amino-acids. Since the intestinal juice contains a ferment 
termed erepsin that has the power of converting peptones into amino-acids, 
it is believed by some that the similar action of the pancreatic juice is due to 
the presence in it of erepsin. 
The Action on Starch.-Pancreatic juice contains another enzyme known 
as amylase or amylopsin that has the power of converting starch into maltose. 
This enzyme therefore resembles in its action that of the ptyalin of the saliva; 
it is however much more rapid and powerful in its action. The same stages 
occur in the process of conversion as those already mentioned in salivary 
digestion. ESSENTIALS OF PHYSIOLOGY 
213 
The Action on Fats.-Neutral fats, such as olein, palmitin or stearin, are 
decomposed under the action of pancreatic juice into fatty acids and glycerin. 
The enzyme causing this change is termed lipase or steapsin. The fatty acids 
Fig. 125.-The under surface of the liver. 1, lobus hepatis sinister; 2, lobus hepatis dexter; 
3, quadrate lobe; 4, caudate lobe; 5, lobus caudatus; 6, hepatic artery; 7, portal vein; 8, fossa ductus 
venosi; 9, fossa vesicae fellae; 10, cystic duct; 11, hepatic duct; 12, fossa venae cavae; 13, vena cava. 
combine with the alkaline salts present to form soaps, following which the 
undigested neutral oil becomes divided through the movements of the intestines 
into microscopic globules which are held in suspension in the soap solution, 
Fig. 126.-Liver of a pig. The lobules have artificially shrunken from the interlobular tissue, 
a; b, bile duct; c, hepatic artery; d, interlobular vein (a branch of the portal); e, trabeculae; f, 
central vein. (From Radasch's Histology.) 
thus forming an emulsion. The fat in the emulsified state offers a greater 
surface for the action of the enzyme. 
The activity of the pancreatic enzymes is greatest under the conditions 
that obtain in the duodenum. These conditions are: (i) a Virtual neutraliza- 214 
DIGESTION 
tion of the pancreatic and intestinal juices; (2) the presence of bile. Bile is 
especially influential in raising the activity of the fat-splitting enzyme. 
The Liver.-The fiver is the largest gland in the body (Fig. 125). It 
weighs in the adult from 1500 to 1650 grams (about 3 to 3^ pounds), and is 
situated in the upper right side of the abdominal cavity, immediately under 
the diaphragm where it is maintained in position chiefly by folds of the peri- 
toneal membrane. The organ is enclosed by a membrane of connective tissue 
known as Glisson's capsule; connective tissue partitions penetrate the interior 
Fig. 127.-Schemic representation of a portion of a hepatic lobule, i, branch of the portal vein 
breaking, within the lobule, into the network 3; 4, branch of the hepatic artery which empties into the 
portal capillaries at 5. The blood of the portal vein and of the hepatic artery empties into the 
central vein, 2; 7 and 8, biliary capillaries; 6, perilobular biliary canaliculi; 10, perilobular lymph 
vessels receiving lymphatics 11, from the interior of the lobule. (G. Bachmann, after Testut.) 
of the liver and subdivide it into minute lobules. The liver is divided into 
lobes of various sizes by five grooves. Its blood supply is obtained in part from 
the hepatic artery and in part from the portal vein. These vessels penetrate 
into the interior of the organ at the transverse fissure or hilum. Numerous 
nerve fibers derived from the vagus and the splanchnic nerves, likewise pass into 
the organ. 
The Structure of the Liver.-The unit of structure is the lobule. These 
lobules, present in enormous numbers, vary in diameter from i to 2 mm. 
(^5 to X2 in-)- They are more or less polygonal in shape, and are separated 
from each other by a thin layer of connective tissue supporting blood vessels, ESSENTIALS OF PHYSIOLOGY 
215 
lymphatics and bile ducts. The epithelial cells (hepatic cells) making up the 
lobule are polygonal in shape and are arranged radially from the circumference 
to the center of the lobule (see Fig. 126). Their bioplasm contains granules 
which have been shown to consist of glycogen, fat and protein, as well as 
various pigments. The row of cells are separated by capillary blood vessels 
derived chiefly from the portal system, by lymph spaces, and bile capillaries 
(Fig. 127). From both the bile and blood capillaries minute canals pass into 
the interior of the hepatic cells. The blood plasma, therefore, brings the mate- 
rial for secretion directly into the cells, and the bile formed is readily discharged 
into the biliary channels. 
The blood capillaries passing from the periphery to the center of the lobule 
discharge their contents into a vein passing through the center of the lobule and 
therefore called the central vein. The central veins in turn discharge their blood 
into veins located under the lobules, termed sublobular veins, and these finally 
unite to form the hepatic veins which empty into the inferior vena cava. 
The blood conveyed by the hepatic artery serves the purpose of nourishing 
the walls of the portal vessels and of the bile ducts, the connective tissue, etc. 
The branches of the hepatic artery end in the branches of the portal vein as they 
pass into the liver lobules. 
As the bile capillaries issue from the lobules they open into larger vessels 
called interlobular bile ducts. These ducts by their repeated union ultimately 
form a right and left chief ducts which by their junction within the hilum form 
the hepatic duct. 
The secretion of bile is a continuous process; in the intervals of digestion it is 
stored into a reservoir termed the gall-bladder. This reservoir communicates 
with the hepatic duct through the cystic duct. The junction of these two ducts 
forms the common bile duct which unites with the pancreatic duct to form a short, 
flask-shaped duct called the ampulla of Vater. The ampulla opens in the interior 
of the duodenum at the tip of a papilla, as mentioned elsewhere. The biliary 
passages are lined by mucous membrane and contain smooth muscle in their 
walls. Circularly arranged muscle fibers are especially well developed at the 
end of the common bile duct where they act as a sphincter. 
General Functions of the Liver.-The liver fulfills a number of functions as 
follows: 
(1) It elaborates and excretes bile. 
(2) It converts and stores dextrose in the form of glycogen, and reconverts 
the latter into the former in accordance with the needs of the body. 
(3) It plays an important part in the metabolism of proteins in that it 
forms urea. 
(4) It stores fat, particularly during pregnancy and lactation. 
(5) It transforms putrefactive products of protein fermentation into harm- 
less substances by conjugation into ethereal salts. 
The Bile.-Bile may be obtained either from the hepatic duct or from the 
gall-bladder. Samples from these two sources differ chiefly in the degree of 
their fluidity, that from the hepatic duct being thin and fluid, while that from 216 
DIGESTION 
the gall-bladder is viscid and otherwise thicker, depending on the time it was 
stored before collection. The specific gravity of human bile lies between i.oio 
to 1.030. The chemical reaction is alkaline owing to the presence of sodium 
carbonate and phosphate. It varies in color from yellow to green and has a 
bitter taste. The viscidity of human bile is due to the presence of mucin. 
Composition of Bile.-Owing to the loss of water, the secretion of mucin and 
possibly of cholesterol from the gall-bladder, the bile obtained from this 
reservoir after death, differs in composition from that collected from a fistula of 
the bile duct or gall-bladder during life, as shown in the table below. 
Parts per hundred 
Bile from 
Gall-bladder 
Fistula 
W ater 
86 . oo 
97.00 
Solids . 
14.00 
3 00 
T... . I Sodium glycocholate \ 
Bile salts i , । 
9.00 
0.9 -1.8 
1 Sodium taurocholate J 
Mucin and bile pigments 
3 00 
■50 
Cholesterol 
0.20 
0.06 -• 0.16 
Lecithin and fat ...... 
0.5-1.0 
0.02 - O.OQ 
Inorganic salts 
0.80 
0.70 - 0.80 
The Bile Salts.-The bile salts are sodium salts of the organic acids known as 
glycocholic and taurocholic acids. Both acids are compounds of cholic acid with 
an amino-acid; these amino-acids being glycine in the case of glycocholic acid, 
and taurine in the case of taurocholic acid. Cholic acid is probably related to 
cholesterol; glycine is a simple amino-acid formed during protein digestion; 
while taurine is derived from cystine, a sulphur compound found in various 
tissues. 
The bile salts serve to hold cholesterol in solution. After their passage into 
the intestines the greater part of these salts is absorbed into the portal 
blood, and is thus returned to the liver to be once again excreted in the bile. 
During their passage through the liver cells they act as stimulating agents in the 
production of bile. They are therefore cholagogues. 
Cholesterol.-Cholesterol is a monatomic alcohol of the terpene series. It is 
especially abundant in the myelin of nerve fibers and in the stroma of red blood 
cells. Its source is therefore from these cellular elements as well as from various 
foods. Most gall-stones are composed almost entirely of cholesterol. This 
substance is normally discharged in the feces. 
Lecithin.-Lecithin is a lipoid entering into the composition of many tissues, 
more especially of nerve tissue, blood corpuscles, and semen. It is found also 
in milk and the yolk of eggs. 
The Bile Pigments.-The bile pigments are named bilirubin and biliverdin. 
These pigments are derived from the hemoglobin set free during the disinteg- 
ration of senile red blood cells. This disintegration takes place in part in the ESSENTIALS OF PHYSIOLOGY 
217 
liver. As the hemoglobin is liberated it is split off into hematin and globin. 
The hematin is then converted by the loss of its iron and a combination with 
water into bilirubin. The oxidation of bilirubin gives rise to biliverdin. 
The bile pigments are decomposed in the large intestine under the action of 
bacteria into stercobilin, which imparts color to the feces. Some stercobilin is 
absorbed into the blood and eliminated in the urine in the form of urobilin, the 
chief pigment of the urine. 
The Secretion of Bile.-As stated in a preceding paragraph, bile is con- 
tinuously secreted and accumulates in the gall-bladder in the intervals of diges- 
tion. The ingestion of a meal is accompanied by a slight discharge of bile into 
the duodenum. But the gall-bladder does not empty itself until about the 
second or third hour after a meal. Thereafter, bile continues to pass into the 
duodenum until digestion has ended, whereupon it once again is stored in 
the gall-bladder. Only small quantities of bile pass periodically into the 
intestines in the intervals of digestion. 
The exciting agents responsible for the secretion of bile have been shown 
experimentally to be (i) the reabsorbed bile salts, and (2) the secretin formed 
under the action of the acid chyme upon the intestinal mucous membrane. 
Secretin, therefore, not only stimulates the secretion of pancreatic juice, but 
that of bile as well. 
The discharge of bile is brought about by a simultaneous contraction of the 
gall-bladder and the larger bile ducts, together with a relaxation of the sphincter. 
The discharge of bile is a reflex action. The afferent fibers, it is believed, ascend 
in the trunk of the vagus; the efferent fibers are contained in the splanchnic 
nerve. 
The total quantity of bile produced daily has been variously estimated at 
from 500 to 800 cc. 
Functions of the Bile.-Bile is not a digestive fluid, but it materially 
increases the activity of the enzymes of the pancreatic juice. This is especially the 
case with lipase whose capacity to split fats is increased fourfold. Bile likewise 
promotes the absorption of the digested food material. As bile has laxative proper- 
ties, it prevents the stagnation of food and thus limits the amount of putrefaction 
taking place in the intestinal canal. Finally, the bile serves as a means of 
excreting certain waste material, such as cholesterol and bile pigments. 
The Intestinal Juice.-The digestive fluid secreted by the glands of 
Lieberkuhn is called the intestinal juice. As obtained from an isolated loop of 
intestine with blood and nerve supply intact; it is a watery, slightly opalescent 
liquid of a faint yellow color, alkaline in reaction, and of a specific gravity of 
1.010. It consists of water holding in solution inorganic salts, mainly sodium 
chloride and sodium carbonate, and organic substances comprising chiefly 
serum-albumin, serum-globulin, mucin, and enzymes. 
The Functions of the Intestinal Juice.-The intestinal juice acts on (1) 
sugars (disaccharides); (2) proteoses and peptones; and (3) activates trypsinogen. 
The disaccharides acted upon by the ferments of the intestinal juice are 
saccharose, maltose, and lactose. Saccharose is converted under the action of 218 
DIGESTION 
the ferment invertase or saccharase into dextrose and levulose. A mixture of these 
two monosaccharides is known as "invert sugar." The maltose is hydrolyzed 
by the enzyme maltase into dextrose; while the lactose is split under the action of 
lactase into dextrose and galactose. 
The final stage in the hydrolysis of the protein food takes place through the 
activity of the enzyme termed erepsin, which has the property of splitting pro- 
teoses and peptones into amino-acids. 
As stated above, the intestinal juice contains an organic activator which 
transforms the inactive trypsinogen of the pancreatic juice into the active 
enzyme, trypsin. 
How far the changes just enumerated take place in the lumen of the 
intestines, or as the food material passes through the epithelial cells lining the 
mucous membrane, is still an open question. 
Some of the ferments mentioned as present in 
the intestinal juice are believed by some to 
be located within the epithelial cells, in which 
case their actions would take place within 
the cells rather than in the intestinal lumen. 
The Movements of the Small Intes- 
tine.-While the food is undergoing digestion 
in the small intestine certain movements of 
the intestinal wall take place whereby the 
digestive fluids are thoroughly mixed with the 
food, and the latter is gradually propelled 
toward the large intestine. 
Rhythmic Segmentation.-The movements 
that serve to mix the intestinal contents con- 
sist of a series of annular constrictions occurr- 
ing at regular distances from each other, 
which divide the food into short segments. A relaxation of the constricted 
parts then takes place, while a new series of constrictions appears over the cen- 
ter of the first series of segments. Neighboring halves of segments of food 
are thus brought together, and the process is repeated for a varying time last- 
ing from half to three-quarters of an hour (see Fig. 128). These movements 
are non-progressive, take place in variable lengths of intestine, and occur at the 
rate of ten to twenty segmentations per minute, the rate being more frequent in 
the upper than in the lower part of the intestine. 
Aside from serving to mix food with the digestive fluids, these movements 
promote absorption and accelerate the movement of lymph and blood through 
the intestinal wall. 
Peristalsis.--The food is carried onward to new portions of intestine by 
peristaltic waves. This wave, already described in connection with the move- 
ments of the stomach, consists of a ring of contraction immediately preceded by 
a zone of relaxation, the two traveling toward the large intestine at the rate of 
one to two centimeters per minute. After the food has been carried a variable 
Fig. i28.--Ihe divisive or segmenting 
movements of the small intestine. A, sur- 
face of a portion of the intestine, showing 
six constrictions which divide the contents 
into five segments, as shown in B; as these 
constrictions pass away new ones come in 
between them and divide each segment 
of the contents into two, the adjoining 
halves of neighboring segments fusing to 
make the new segments shown in C. Re- 
petition of this process results in the con- 
dition shown in D. (Modified, after Hough 
and Sedgwick, The Human Mechanism.) ESSENTIALS OF PHYSIOLOGY 
219 
distance, the peristaltic wave disappears and the food is then subjected to the 
movements of rhythmic segmentation. These two classes of movements recur a 
number of times before the food reaches the large intestine. 
Following the administration of purgatives a more rapid peristaltic wave 
makes its appearance. In the rabbit, a wave of peristalsis has been observed, 
under such condition, to pass from the duodenum to the large intestine at one 
sweep, in the course of 15 seconds. This form of peristalsis is known as rush 
peristalsis. In this case a long section of intestine relaxes in front of the advanc- 
ing wave of constriction. 
Nerve Mechanism.-Various experiments have demonstrated that the 
movements of rhythmic segmentation are not dependent on nerve impulses as 
they take place after section of the vagus and splanchnic nerves and the 
myenteric plexus. They are, therefore, said to be myogenic in nature, and 
occur under the stimulus of the distending food. 
The peristaltic wave, on the other hand, is caused by the co-ordinate activity 
of the myenteric plexus. The vigor of the movement of peristalsis may, how- 
ever, be influenced by the central nerve system through the vagus and splan- 
chnic nerves. Stimulation of the vagus is followed by an augmentation of the 
movement, while stimulation of the splanchnic is followed by its inhibition. 
The ileo-colic sphincter is in a state of tonic contraction so that the contents 
of the small intestine accumulates before it. When an advancing wave of 
peristalsis reaches the ileo-colic junction, the sphincter relaxes and the accumu- 
lated material passes into the large intestine. 
The contractions of the ileo-colic sphincter are under the control of the 
splanchnic nerve, whose stimulation augments the contraction; and of the vagus 
nerve, whose stimulation inhibits the contraction. 
The Large Intestine.-The large intestine includes that portion of the 
alimentary canal located between the end of the ileum and the anus. It meas- 
ures from 1.8 to 1.95 meters (5 to 5^ feet), and varies in diameter from 3^ 
to 7 cm. (about to 2% in.). The large intestine is divided into the cecum, 
the colon-ascending, transverse, and descending-and the rectum. 
The cecum is the blind extremity situated below the opening of the small 
intestine. It is located in the right, lower portion of the abdominal cavity. 
Springing from its extremity is a slender process of variable length termed the 
vermiform appendix. The opening of the small intestine is guarded by two folds 
of mucous membrane which plays the part of a valve-the ileo-cecal valve. 
The ascending colon extends as far as the under surface of the liver. The 
colon then crosses the abdominal cavity to the spleen, thus forming its trans- 
verse portion. From the spleen the colon-descending colon-passes to the lower 
left side of the abdominal cavity where it bends upon itself to form the sigmoid 
flexure. This portion of the intestine is then continued into the rectum, situated 
against the posterior wall of the pelvis and ending at the anus. 
The large intestine has the coats already described as present in the small 
intestine, viz., serous, muscle, submucous, and mucous. The longitudinal 
smooth muscle fibers occur in the form of three bands except over the rectum 220 
DIGESTION 
where they cover the entire circumference. The longitudinal bands being 
shorter than the intestine, the intestinal wall is thrown into folds so that the 
intestine appears sacculated. The saccules are called haustra. 
The circularly arranged muscle fibers are uniformly distributed, and are 
especially well developed over the rectum where they form, at a distance 
of 2 or 3 cm. from the anus, a sphincter muscle called the internal sphincter. 
Another sphincter, composed of striated muscle fibers, surrounds the anal 
opening-the external sphincter. 
The mucous membrane of the large intestine has neither villi nor valvulae 
conniventes. It, however, contains innumerable tubules resembling the glands 
of Lieberkuhn. (Fig. 129). The secretion elaborated by these glands is thick 
and viscid from the presence of mucin; it does not contain any digestive ferments. 
Fig. 129.-Cross-section of segment of colon, a, mucous coat; b, submucous coat; c, muscular 
coat; d, fibrous coat; e, columnar cell;/, goblet cell; g, basement membrane; h, tunica propria; i, inner 
circular layer of muscularis mucosae; k, outer longitudinal layer of muscularis mucosae; I, inner 
circular layer of muscular coat; m, outer longitudinal layer of muscular coat. {Radasch.) 
The vermiform appendix and the ascending and transverse colons are 
supplied with blood by brandies of the superior mesenteric artery; the descending 
colon, by branches of the inferior mesenteric artery; and the rectum by the 
hemorrhoidal arteries. The blood is returned by veins having corresponding 
names. 
As in the case of the stomach and small intestine, plexuses of nerve fibers 
and nerve cells are located in the submucous coat and between the muscle layers. 
The large intestine receives inhibitory nerve fibers issuing from the lumbar region 
of the spinal cord as pre-ganglionic fibers. The post-ganglionic fibers arise 
in the cells of the inferior mesenteric ganglion and are distributed to the muscle 
coat. Augmentor fibers arise in the sacral portion of the spinal cord, and are 
distributed by way of pelvic ganglia to the muscle coat. 
Functions of the Large Intestines.-The material passing into the large 
intestine is semiliquid and contains but very small amounts of nutritive sub- 
stances. The contents of the large intestine are chiefly indigestible material, ESSENTIALS OF PHYSIOLOGY 
221 
such as cellulose, together with waste products, as cholesterol, bile pigments, 
etc., portions of the digestive juices that have failed of resorption, water, 
mucus, and numerous bacteria. 
The chief function of the large intestine is to absorb water. As the water 
becomes absorbed, the material contained in the large intestine assumes grad- 
ually the consistency and appearance of feces. 
The bacteria found in the intestinal contents induce certain changes in 
the undigested material which result in the formation of a variety of substances. 
Cellulose is changed into methane (marsh gas), fatty acids, hydrogen, and 
carbon dioxide. The protein that has escaped digestion is decomposed into 
indol, skatol, phenol and cresol. These aromatic bodies are absorbed into the 
blood and carried by the portal vein into the liver, where they are transformed 
into ethereal sulphates. The object of this change is to render these substances 
non-toxic. They then pass into the general circulation and are eliminated in 
the urine. The most readily recognizable of these substances is indol which 
appears in the urine as potassium indoxyl sulphate or indican. The amount 
of this substance present in the urine serves as an index to the extent of putre- 
factive changes going on in the intestine. Other products of protein fermen- 
tation are such gases as hydrogen sulphide, ammonium sulphide, and ammonia. 
The large intestine may act also as an organ of excretion. The substances 
commonly excreted are iron, calcium, and magnesium phosphate. Certain 
drugs, as mercury, may also be excreted by the large intestine. 
The Movements of the Large Intestine.-As observed under the X-ray 
in man, the movements of the large intestine result from the distension that 
accompanies the accumulation of material passing through the ileo-colic orifice. 
A wave of contraction, not preceded by any relaxation, begins near the junction 
between the ascending and transverse colon and moves slowly toward the cecum. 
A number of similar waves follow each other with the result that the contents 
of the ascending colon are stirred, and the absorption of water is facilitated. 
These waves are called anti-peristaltic waves. The material is prevented from 
passing back into the small intestine through the action of the ileo-colic valve 
and the tonic contraction of the sphincter. 
From time to time-usually three or four times a day-the contents of 
the ascending colon are transferred to the transverse and descending colon 
through rapidly-moving peristaltic waves. These movements commonly 
occur at the time that the food enters the stomach. The material transferred 
by the peristaltic waves accumulates in the sigmoid flexure. 
When the feces gradually pass from the sigmoid flexure into the rectum, 
they cause by their distention a sensation that evokes the desire for defecation. 
The act of defecation is essentially a reflex action, which through education 
has come under control of the will. Defecation occurs through a relaxation 
of the sphincter ani and contractions of the walls of the sigmoid flexure and rec- 
tum. It is materially aided by the rise of pressure caused by voluntary contrac- 
tions of the abdominal and pelvic muscles following a deep inspiration and a 
closure of the glottis. DIGESTION 
222 
The nerves concerned in the reflex part of the act of defecation have been 
mentioned in a preceding paragraph. 
The Hygiene of Digestion.-The importance of thorough mastication 
can readily be understood since by this means a greater surface of food is 
exposed to the action of ferments, and its subsequent digestion can proceed 
more rapidly. Since efficient mastication depends on sound teeth, it is neces- 
sary to prevent their decay. Tooth decay is due to the action of bacteria con- 
stantly present in the mouth; recent work has shown that dental caries is 
caused by the Lactobacillus odontolyticus. This bacillus through its action 
on food particles produces acids which decalcify and dissolve the hard layers 
of the teeth. A thorough brushing of the teeth and gums with a suitable 
dentifrice, preferably after each meal, and periodic visits to the dentist are there- 
fore necessary if the teeth and gums are to be kept free from disease. 
The importance of mastication lies, furthermore, in the fact brought out 
in the discussion of gastric digestion, that the tasting of appetizing food causes 
a flow of gastric juice-the so-called appetite juice. Pavlov's experiments 
have shown also that depressing emotions inhibit the flow of gastric juice as 
well as the movements of the stomach and intestines. These findings have been 
confirmed on man by various methods. Good digestion therefore depends 
not only on properly prepared and appetizing food, but also on the proper mental 
attitude, an atmosphere of enjoyment being especially conducive to this end. 
One of the most common ailments of civilization is constipation. This 
condition, which may lead to more serious disturbances, can be avoided (i) by 
drinking water in suitable quantities; (2) by including a sufficient amount of 
food containing indigestible material, particularly cellulose; (3) by taking a 
sufficient amount of physical exercise; and (4) by the observance of regularity 
in emptying the bowels. 
The amount of water to be drunk in twenty-four hours will naturally vary 
with its loss in perspiration. The drinking of water with the meals does not 
interfere with digestion provided it is not used to swallow food insufficiently 
masticated. Indigestible material prevents constipation by providing bulk 
to the contents of the large intestine, and so, by its distention, brings about 
the peristaltic movements that precede defecation. 
Physical exercise, by raising the general tone of the body and improving 
the circulation, favorably influences the movements of the gastro-intestinal 
tract. Finally, the movements of the large intestine are susceptible to that 
form of education that results in habit formation. The assignment of a regular 
time to empty the bowels is therefore a necessary part of the hygienic rules 
for the avoidance of constipation. A convenient time is immediately after 
breakfast as the movements of the body that follow on arising and the par- 
taking of a meal have been shown by the X-ray to induce a peristalsis in the colon 
which carries the feces into the rectum. CHAPTER XXVI 
PHARMACODYNAMICS OF DIGESTION 
Sialogogues.-Drugs which increase the flow of saliva are termed sial- 
ogogues. In the discussion of the nerve mechanism of salivary secretion on 
page 195 attention was called to the fact that the salivary glands are not under 
the control of the will, that their activity is determined by reflex action and 
also influenced by mental states, such as stimulation of the appetite, disgust, or 
nausea. The water content of the blood and the tissues directly influences 
salivary secretion. If the water content is low, as after profuse sweating or 
diarrhea, the salivary secretion stops. The activity of the salivary glands 
may also be influenced directly or indirectly by certain drugs. 
Sialogogues may act reflexly, as in the case of acids, bitters, and aromatic or 
irritant substances like Peppermint and Mustard, which, by their action on the 
mucous membrane of the mouth, reflexly stimulate the salivary glands. 
Other drugs increase salivation by direct action on some portion of the nerve 
mechanism of the salivary glands. 
Pilocarpine (see page in) increases the activity of the salivary glands by 
stimulation of the myoneural junctions of the secretory nerve endings. 
Mercury salts at times produce a profuse flow of saliva ("salivation" or 
"ptyalism") which is probably partially due to direct irritation of some portion 
or portions of the salivary mechanism. The exact mode of action is not clearly 
understood. 
There are very few, if any, therapeutic uses for sialogogues. 
Antisialogogues.-Drug which decrease the flow of saliva are called 
antisial0gogues. Atropine and its allies (see page no) are the most impor- 
tant members of this group. It will be recalled that Atropine by strongly 
depressing the myoneural junctions of the secretory endings checks most body 
secretions including saliva. Therefore, after a dose of Atropine, preparations 
of Belladonna, etc., the mouth and throat become more or less dry. 
Excretion of Drugs in the Saliva.-Iodides, Bromides, Mercury Salts, 
Hexamethylenamine ("Urotropin"), and some alkaloids, such as Quinine and 
Strychnine, are partially eliminated by the salivary glands, and chemical tests 
may be used to establish their presence in the saliva. 
Stomachics.-Numerous drugs which promote appetite and digestion are 
loosely grouped together as stomachics. The more important subgroups follow. 
(1) Bitters.-These are drugs having bitter tastes which are administered 
ten or fifteen minutes before meals to stimulate the taste buds (see page 286) 
and thereby promote the appetite and the flow of the "appetite" gastric juice 
(see page 203). Since the appetite juice is of great importance in starting 
gastric digestion, and since the bitters favor its secretion, they are frequently 
223 224 
PHARMACODYNAMICS OF DIGESTION 
of value in treating loss of appetite. As the bitters are dependent upon their 
taste for their action, no attempt to disguise the bitter taste should be made. 
If the appetite is normal the bitters will not increase it. Bitters are usually 
classified as follows: 
(a) Simple Bitters, substances which owe their activity simply to their 
bitter taste, and are practically without systemic action. Examples are 
Gentian, Calumba, Taraxacum ("Dandelion"), and Quassia. (Certain alka- 
loids in very small dosage, such as Strychnine and Quinine, are at times employed 
as simple bitters.) 
(6) Aromatic Bitters possess volatile oils in addition to the bitter principles. 
They include Bitter Orange Peel, Anthemis ("English or Roman Chamomile") 
Matricaria ("German Chamomile"), and Calamus, Compound Tincture of 
Gentian (made from Gentian, Cardamon and Bitter Orange Peel) and Compound 
Tincture of Cinchona (made from Red Cinchona, Bitter Orange Peel and Serpen- 
taria) . 
(c) Astringent Bitters contain tannin in addition to the bitter principles. 
More important members of the group are Cinchona, Cimicifuga ("Black 
Cohosh"), Condurango and Serpentaria ("Virginia Snakeroot"). 
(2) Aromatics.-These are drugs like Mustard, Pepper, Peppermint, etc. 
which act in a manner similar to the bitters because of their taste, but also 
produce a mild irritating action which has led to the employment of some of 
them as condiments, and others as carminatives. 
Carminatives.-Remedies which tend to overcome distention of the 
stomach or colon with gas ("flatulency") and to diminish colic pains are termed 
carminatives. They depend for their action upon volatile oils, resinous or 
other irritating constituents, which possess "warm," aromatic tastes, and pro- 
duce a mild degree of irritation on the mucous membrane of the digestive tract. 
They give rise to a feeling of warmth or well-being in the region of the stomach, 
stimulate motor activity and the expulsion of gas. Their mode of action in reliev- 
ing colic is not well understood. They are often added to irritating cathartics 
to prevent "griping." 
The carminatives more commonly used include Anise, Ginger, Peppermint, 
Capsicum, Aromatic Spirit of Ammonia, and Compound Spirit of Ether 
("Hoffman's Anodyne"). 
Digestive Ferments or Enzymes.-The physiological discussion of digestion 
brought out the fact that the digestion of food in the alimentary tract is accom- 
plished principally by the aid of certain catalytic substances called digestive fer- 
ments or enzymes, the ultimate chemical composition of which is unknown. The 
commercial digestive ferments or enzymes are purified extracts which are either 
dried or preserved in glycerin. Pepsin, Pancreatin, and Diastase are official. 
Pepsin.-Pepsin is a proteolytic extract usually obtained from the fresh 
mucous membrane of the stomach of the hog. The U. S. P. requires that it be 
capable of converting 3000 times its own weight of coagulated egg-albumin into 
soluble protein. Pepsin acts in weakly acid medium, and is destroyed by alka- 
lies, strong acids, metallic salts and tannin. PHARMACOD YN AMICS 
225 
Because of the fact that it is a comparatively rare occurrence to find the 
human gastric contents deficient in its specific ferments, Pepsin is not a very 
important therapeutic agent and its use in most cases of gastric disturbances is 
superfluous. 
Pancreatin.-Pancreatin is a mixture containing the specific enzymes of the 
pancreas, chiefly amylopsin, trypsin, and steapsin, obtained from the fresh pan- 
creas of the hog or ox. It acts best in faintly alkaline or neutral medium, and 
is destroyed by very weak acidity. The Pharmacopoeia requires Pancreatin to 
be capable of converting 25 times its own weight of starch into sugars. It also 
specifies that 1 grain of Pancreatin with 5 grains of Sodium Bicarbonate must be 
capable of peptonizing completely 3 ounces of cow's milk at io4°F. (4O°C.) 
in thirty minutes. 
Pancreatin is not commonly indicated in medicine and is therefore not an 
important drug. 
Diastase.-Diastase is a mixture, containing amylolytic enzymes, prepared 
from an infusion of barley malt. The U. S. P. requires that it be capable of 
converting 50 times it own weight of potato starch into sugars. It is active in a 
neutral medium, and is retarded in its activity by acids and alkalies. Malt and 
Extract of Malt contain Diastase but are less active. This ferment is also seldom 
needed in therapeutics. 
Predigested foods, prepared by artificial digestion outside the body are of 
doubtful value, not only because the digestive products formed are irritating and 
not identical with those of normal digestion, but also because digestive distur- 
bances usually involve the motor functions and absorption more commonly than 
the chemical reactions of digestion. 
Antacids.-So-called hyperacidity of the gastric juice is frequently found to 
be either a condition more correctly called hypersecretion, or a deficiency in the 
motility of the stomach with the consequent fermentation of the food and the 
formation of organic acids. The usual results of the foregoing conditions are 
gastric discomfort or pain, regurgitation of stomach contents into the mouth, 
"heartburn," etc. These symptoms are relieved by the Local Antacids (see 
page 126), such as Sodium Bicarbonate, Prepared Chalk (CaCO3), Lime Water 
(Ca(OH)2), and Milk of Magnesia (Mg(OH)2). 
Emetics.-Emetics are drugs which are capable of inducing emesis or 
vomiting. The coordination of several mechanisms is necessary for the pro- 
duction of emesis: viz., closure of the pylorus, opening of the cardia, contraction 
or fixation of the diaphragm, and contraction of the abdominal muscles. This 
coordination is accomplished through the intermediation of the vomiting center, 
located in the medulla oblongata. The vomiting center is highly sensitive to 
certain sensory impulses from the pharynx and stomach, and may also be 
directly stimulated by certain substances introduced into the blood stream. 
The emetics are usually classified as (a) Central Emetics and (6) Local or Reflex 
Emetics. 
(a) Central Emetics.-The drug most commonly used as a central emetic is 
Apomorphine, the hydrochloride usually being employed. This drug acts 226 
PHARMACODYNAMICS OF DIGESTION 
directly on the vomiting center, increasing its excitability. It may be given 
by mouth or by the hypodermic method, the latter method being preferred 
since absorption is much more rapid and consequently emesis more promptly 
induced. 
Ipecac acts also directly on the vomiting center. Having a local irritating 
action, it acts more promptly when given by mouth than subcutaneously. It is, 
therefore, generally classed as a local emetic. 
Certain other drugs, such as Digitalis, Squill, and the Salicylates, act also 
directly on the vomiting center, but are never used as emetics because doses 
large enough to induce vomiting would probably prove toxic. 
(b) Local or Reflex Emetics.-The afferent paths which may reflexly stimu- 
late the vomiting center are numerous, but in therapeutics only those of the 
pharynx and the mucosa of the stomach are employed. The local or reflex 
emetics act by irritating the pharynx or the stomach and thereby reflexly stimu- 
lating the vomiting center. Thus, all irritating drugs are capable of producing 
vomiting, but most of them are not available for practical use because of the 
degree of the severity of their irritating action. Those available for emetic 
purposes are usually not absorbed, and therefore produce no systemic effects. 
The most important are: Copper Sulphate, Zinc Sulphate, Mustard, Ipecac 
(see "Central Emetics"), and Alum. Tickling the throat with a feather or 
sticking the finger down the throat may also be effective. 
The emetics are useful in cases of acute poisoning (excepting by narcotics 
which narcotize the vomiting center), acute indigestion, to remove solid objects 
from the esophagus, pharynx and upper respiratory passages, and to relieve spasm or 
congestion in the respiratory passages as in croup or asthma. 
Antemetics.-These are measures for relieving nausea and vomiting. If 
the condition is due to hyperacidity, the local antacids, such as Sodium Bicarbon- 
ate and Milk of Magnesia may be useful. Insoluble and non-irritating salts, like 
Bismuth Subnitrate or Subcarbonate and Cerium Oxalate, may be effective by 
mechanically preventing irritation of the mucous membrane. 
Local Sedatives, such as Atropine, Cocaine, Phenol, and cold (ice), may act as 
antemetics by depressing the sensory nerve endings or their myoneural 
junctions. 
Central Sedatives, like Chloral Hydrate, Codeine, Bromides, and Morphine, 
may prove effective by depressing or decreasing the sensitiveness of the vomit- 
ing center. 
Counter irritants to the epigastrium, such as a mustard plaster or hot water 
bag, are frequently effective in relieving and checking obstinate vomiting. 
Cathartics.-Drugs which induce defecation are termed cathartics. 
They are employed to correct constipation, to remove irritating and other harm- 
ful substances from the intestines, as in food-poisoning and certain diarrheas, 
to relieve the kidneys in nephritis by removing fluid, to remove excessive fluids 
from the body, as in dropsy and cerebral congestion, to lower temperature in 
fevers, and to soften the stools in hemorrhoidal conditions. The importance 
of proper regulation of the bowels has already been mentioned. PHARMACODYNAMICS 
227 
Classification of the Cathartics.-Cathartic drugs may be classified accord- 
ing to the intensity of their effects. It should be remembered, however, that 
the effect varies with the size of the dose. 
(A) Laxatives or Aperients are cathartic drugs which only moderately 
increase peristalsis, producing soft stools of about normal frequency, causing 
little, if any, irritation. They act by (i) Mechanical stimulation as in the cases 
of seeds of fruit and the husks like cereals; (2) increasing the bulk of the intesti- 
nal contents, as with vegetables and salads which contain considerable quantities 
of indigestible cellulose; (3) chemical stimulation, as in the cases of the organic 
acids and salts, sugars, etc. of fruits like prunes, figs, dates, etc., or the unabsorbed 
fats and oils or their soaps, as with Olive and Cottonseed Oils, Soap, Glycerin 
and Cocoa-butter suppositories; also Liquid Petrolatum, Sulphur and Agar-agar. 
Small doses of Cascara, Rhubarb, Senna and Castor Oil are laxative also. 
Mechanical Measures, such as exercise, massage, and simple enemas, are included 
in this class. 
{B} Purgatives are cathartic drugs which actively increase peristalsis, 
producing copious soft, semiliquid, or fluid stools. They may be subdivided 
as follows: 
(a) Simple Purgatives, such as Aloes, Cascara, Rhubarb, Senna, Castor Oil, 
Phenolphthalein, and Calomel, act by producing more or less irritation. They 
frequently cause griping or cramps as a result of spasmodic contractions of 
the intestines at the site of the irritation instead of coordinate peristalsis. 
Aloes, Cascara, Rhubarb and Senna contain glucosidal substances which are 
hydrolyzed or oxidized in the intestine yielding irritating compounds such 
as emodin and chrysophanic acid. Castor oil is saponified in the small intestines 
forming the irritating soap-Sodium Ricinoleate. Calomel upon reaching the 
intestines is converted into an irritant grey mixture consisting of the carbonate, 
oxide or hydroxide of mercury and probably metallic mercury. This change 
is brought about by the presence of alkali carbonates in the intestinal contents. 
The grey mixture is somewhat antiseptic. Phenolphthalein is mildly irritating 
to the intestines. 
(Z>) Saline Purgatives, such as Magnesium Sulphate ("Epsom Salt"), 
Magnesium Citrate, Magma of Magnesia ("Milk of Magnesia"), Sodium 
Phosphate, Sodium Sulphate ("Glauber's Salt"), Potassium Bitartrate ("Cream 
of Tartar"), Potassium Sodium Tartrate ("Rochelle Salt"), etc., produce 
profuse watery stools without irritation or griping. These salts act as cathartics 
because they are absorbed with difficulty, and consequently remain for the 
most part in solution in the intestines thus increasing the bulk and the fluidity 
of the intestinal contents. Any portion of the salt which is absorbed is excreted 
by the kidneys. They act very rapidly if given on an empty stomach, prefer- 
ably about a half hour before breakfast. Solution of Magnesium Citrate, 
Compound Effervescing Powder ("Seidlitz Powder"), and Effervescing Sodium 
Phosphate are less disagreeable to take. 
(C) Drastics are harsh, very irritating cathartics which produce profuse, 
watery stools, and tend to cause violent inflammation in large doses. Their 228 
PHARMACODYNAMICS OF DIGESTION 
active constituents are either irritating, resinous glucosides, such as Jalapin 
in Jalap, Colocynthin in Colocynth, or acids, such as Crotonic Acid in Croton 
Oil. This class includes Jalap, Colocynth, Podophyllum, Croton Oil, Elaterium, 
Scammony, Gamboge, and Compound Cathartic Pills ("C C Pills-containing 
Calomel, Compound Extract of Colocynth, Resin of Jalap, and Gamboge). 
If absorption of the active principles of the drastic purges occurs, elimina- 
tion is accomplished by the kidneys which are severely irritated. This, 
together with the fact that the drugs are extremely irritating to the intestines, 
limits their usefulness. They should be administered only upon the advice 
of a physician, and because of their emmenagogue and abortifacient properties 
should not be used during menstruation and pregnancy. Neither should they 
be used in nephritis, hemorrhoids, or inflamed conditions of the intestines. 
(D) Hydragogues are cathartics which produce watery movements, 
i. e., the Saline Purgatives and the Drastics. 
(Ef Cholagogues are cathartics which are thought to increase the flow of 
bile. However, investigation has shown that there are very few substances 
which in therapeutic amounts have this action. Bile salts (Sodium Glyco- 
chelate and Sodium Taurocholate) which increase the amount of bile because 
of their ready excretion by the liver cells, and Oxgall, because of its bile'salts, 
are practically the only available true cholagogues. Salicylates possibly 
increase the amount of bile to a very slight extent. 
(F) Cathartics Acting by Special Affinity are: Physostigmine (see page 112) 
which stimulates the myoneural junctions of the endings of the vagus or motor 
nerves of the intestines, and Pituitary Extract (see page 44) which is directly 
stimulating to intestinal muscle. 
Localization of Action.-Calomel increases peristalsis both in the small and 
large intestine. Castor Oil, Salines, and Colocynth stimulate peristalsis mainly in 
the small intestine. Senna, Cascara, Rhubarb, Aloes, and probably Bile Salts 
and Phenolphthalein act mainly on the large intestine. Combinations of cathartic 
drugs are accordingly frequently used in an attempt to activate the entire 
intestinal tract. 
Rapidity of Action.-The usual time of response for the more important 
cathartics follows: 
(a) Saline Purgatives: one-half to one hour if given on an empty stomach; if 
the patient is in bed, two to four hours. 
(&) Castor Oil: one to two hours if given on an empty stomach. 
(c) Jalap: two to three hours. 
(d) Senna, Rhubarb, Cascara, Aloes, and Phenolphthalein: four to twelve 
hours. 
(e) Podophyllum: ten to fifteen hours. 
Antidiarrheics.-In the discussion of Astringents on page 2 5 attention was 
called to the fact that in the intestines the coagulated proteins (produced by 
a reaction between the proteins of the intestinal contents and of the tissue cells 
with the astringent), form a protecting layer which lessens irritability and thus 
retards intestinal movements. As a consequence any inflammation is lessened, PHARMACODYNAMICS 
229 
and, since there is more time for the absorption of liquids from the intestinal con- 
tents, constipation may result. One of the most common applications of this 
action of the astringents is made in the treatment of diarrheas. Usually the 
treatment is begun with a rapidly acting cathartic to get rid of the irritating sub- 
stances in the intestines responsible for the diarrhea. After the cathartic has 
acted the antidiarrheic is administered. 
The more important antidiarrheics are: Bismuth Subcarbonate, Subnitrate 
and Subgallate, Cerium Oxalate, Prepared Chalk (CaCO3), Lead Acetate, the 
Vegetable Astringents (see page 25), Opium, and Camphor. With the excep- 
tion of Opium and Camphor all the foregoing drugs act partly by virtue of their 
astringency, but also by mechanically affording a protecting layer over the walls 
of the intestines. In the cases of tannin-containing vegetable drugs, such as 
Catechu, Kino, Nutgall, Gambir, Witchhazel, etc., the galenical preparations are 
preferred because the colloidal matter present in them retards chemical 
changes and absorption of the Tannic Acid, thus enhancing the direct local 
astringent action. 
Opium acts as an antidiarrheic because the constituent Morphine prolongs 
the time the food remains in the stomach and intestines. The extended sojourn 
in the stomach is produced by a prolonged contracture of the pyloric and cardiac 
sphincters. The food remains in the fundus several hours longer than normally; 
the intestines are, therefore, at rest for a longer time. The food passes through 
the small intestine slowly, and makes a lengthy stay in the cecum and ascend- 
ing colon. The delay in the large intestine is the chief factor in the constipation 
produced by Opium and its preparations. 
Camphor is believed by some to be of value as an antidiarrheic through its 
inhibitory action on intestinal secretion. This point, however, has not been 
definitely established. 
The Sun Cholera Mixture, N. F. (containing Tinctures of Opium, of 
Capsicum, and of Rhubarb, and Spirits of Camphor and of Peppermint) and 
Squibb's Diarrhea Remedy, N. F., (containing Tinctures of Opium and of 
Capsicum, Spirits of Camphor and Chloroform) are widely used antidiarrheics. 
Anthelmintics.--An anthelmintic is a drug used to expel ("vermifuge") or 
to paralyze or kill ("vermicide") intestinal worms. Active intestinal peristalsis 
tends to mechanically remove those intestinal worms which do not cling to the 
intestinal wall, such as the pin- or thread-worms. However, there are varieties 
of intestinal worms which fix themselves to the walls of the intestines, by means 
of suckers, hooks, etc., In such cases it is necessary to employ remedies which 
will at least paralyze', if not kill, the parasites so that they may be more readily 
removed by the subsequent administration of an active cathartic, such as a 
saline or Calomel. 
Most of the anthelmintics employed to paralyze intestinal worms are not 
only toxic to the parasite, but are toxic also to man if absorbed in sufficient 
quantities. Fortunately most of them are absorbed with more or less difficulty 
by the intestines, and the cathartic administered sometime after the worm 
remedy causes the expulsion of the unabsorbed poisonous anthelmintic. 230 
PHARMACODYNAMICS OF DIGESTION 
Before administering the anthelmintic drug the patient is usually starved 
for about twelve hours and is then given a brisk cathartic, such as a saline or 
Castor Oil. The object of this preliminary treatment is to empty the bowel in 
order that the intestinal worms may be more completely exposed to the action of 
the drug used. The drug is then administered, and is followed in four or five 
hours by a rapidly acting cathartic, such as a saline, to expel the parasites and 
the unabsorbed drug. Castor Oil at this step in the treatment is usually 
avoided because an oily medium may dissolve the poisonous constituents of 
most anthelmintics and thus promote their absorption. 
Infection by intestinal worms usually takes place through: (a) eating 
insufficiently cooked meats which contain the eggs or the embryonic form of the 
parasites, as in the cases of tapeworms and Trichinas; (&) eating uncooked, 
insufficiently washed vegetables grown on sewage-contaminated soil containing 
the eggs, or drinking sewage-contaminated water, as in the cases of thread- 
worms and round-worms. Infection with the Trichinas though more rare, is 
probably incurable since these parasites do not remain in the intestines but mig- 
rate to the muscles which they irritate and paralyze. The various kinds of 
intestinal worms require different anthelmintic treatment. Because of the 
toxicity of most of the anthelmintics and the necessity for insuring the removal 
of all worms, the treatments should be carried out under the supervision of a 
physician. 
(i) Pin- or Thread-worms (Oxyuris).-These parasites are tiny, thread-like 
worms usually inhabiting the colon. Since they do not cling to the intestinal 
wall and are found chiefly in the mucus, they are easily expelled by means of 
cathartics or by rectal injections of mildly irritating solutions. 
The cathartics most commonly used are Calomel and Castor Oil. Solutions 
of Tannic Acid or Alum (30 gr. to a pint), Quinine Bisulphate (1-2000), Soap- 
suds containing one half ounce of Oil of Turpentine to a quart; Phenol (0.25 per 
cent), Lime Water, and Infusion of Quassia are frequently employed for colon 
injections. If the organisms penetrate into the small intestine the administra- 
tion of more active drugs by mouth, such as Santonin, Thymol or Oil of Chenopo- 
dium, becomes necessary. 
(2) Common Round-worms {Ascaris}.-The common round worm is usually 
found in the small intestine and grows to from six to about twelve inches in 
length. The chief remedies are Oil of Chenopodium, Santonin and Spigelia. 
They are at times called 11 Ascaricides. " 
(3) Hookworms (Uncinaria, Necator or Ankylostoma').-(a) Oil of Cheno- 
podium.-The routine treatment of the Rockefeller Hookworm Commission 
(1917) consists in a light supper, followed by a dose of Magnesium Sulphate. 
Some milk is given the patient in the morning, followed by three doses of 
Oil of Chenopodium an hour apart. Another dose of Magnesium Sulphate 
is given two hours after the last dose of the oil. The treatment is repeated 
every 3 to 5 days until the parasites have disappeared from the feces. 
QQ Thymol.-The U. S. Public Health Service (Bulletin # 32) recommends 
a dose of Magnesium Sulphate at night, followed by one-half the dose of PHARMACODYNAMICS 
231 
Thymol at 6:oo A. M., and the other half at 8:oo A. M. Another dose of 
Magnesium Sulphate is given at 10:00 A. M. The treatment is repeated once 
in a week until cured. 
(4) Tape-worms.-The tape-worms most common in America are the 
varieties found in (a) beef, Taenia saginata; (&) in fish, Dibothriocephalus 
latus; and the dwarf tape-worm, Hymenolepis nana. The tape-worm remedies 
are commonly called "Teniacides" and "Teniafuges." 
The most efficient teniacides are Oleoresin of Aspidium ("Male Fern"), 
Amorphous Filicic Acid (one of the active constituents of Aspidium), and 
Pelletierine Tannate (a mixture of the tannates of the alkaloids of the bark of 
Pomegranate root and stem). Infusions of Granatum ("Pomegranate"), 
Cusso and Kamala are used also. CHAPTER XXVII 
ABSORPTION 
The final products of digestion are separated from the body fluids by a 
layer of epithelial cells. Before the digested food can play its part in the body, 
it must first pass through the epithelial layer. The process through which this 
is effected, is called absorption. 
Fig. 130.-Longitudinal section of a villus 
from intestine of the dog highly magnified. 
a, columnar epithelium containing goblet-cells 
(&), and migratory leukocytes (A); c, basement 
membrane; d, plate-like connective-tissue ele- 
ments of core; e,e, blood-vessels;/, absorbent 
radical or lacteal. {Piersol.) 
Fig. 131.-Diagram of the portal system. H., 
heart;/.., liver; T. C., transverse colon; A. C., ascend- 
ing colon; 5.1., small intestine; St., stomach, (turned 
upward); Sp., spleen; P., pancreas; D.C., descend- 
ing colon; Sig., sigmoid; R., rectum; i.v.c., inferior 
vena cava; hep. v., hepatic veins; p.v., portal vein; 
s.m.v., superior mesenteric vein; r.g.-e.v., right gas- 
tro-epiploic vein; l.g.-e.v., left gastroepiploic vein; 
c.v., coronary vien; sp.v., splenic vein; i.m.v., infer- 
ior mesenteric vein; hem.v., hemorrhoidal veins. 
(G. Bachmann.) 
Of the fully digested material present in the stomach but little is absorbed. 
The chief organ of absorption of the products of digestion is the small intestine. 
This function is carried out by innumerable conical processes projecting from 
the general surface of the intestinal mucous membrane and termed villi. Vir- 
tually all digested food has been absorbed by the time the intestinal contents 
have reached the lower end of the ileum. 
232 ESSENTIALS OF PHYSIOLOGY 
233 
Structure of a Villus.-A villus consists of a filiform or finger-like process 
from 0.5 to 1 mm. in length, and from 0.2 to 0.5 mm. in width (Fig. 130). 
It consists of a core of retiform connective tissue covered by a basement mem- 
brane upon which rest tall, columnar epithelial cells whose free end is striated. 
The connective tissue supports arteries, capillaries and veins, and contains in 
its meshes numerous lymphoid corpuscles. In the center of the villus there 
is a lymph vessel, the central lacteal, ending in a blind extremity and communi- 
cating with the lymph vessels of the submucosa. Valves are present at the 
point of junction of the central lacteal with the underlying lymph vessels. 
The core of the villus contains also smooth muscle fibers springing from the 
muscularis mucosae and attached to the basement membrane, near the apex 
of the villus, and to the lacteal vessel. 
The Portal Vein.-The arterioles supplying the villi are derived from the 
superior mesenteric artery. The veins, arising from the capillary network, 
return the blood by way of the superior mesenteric vein which joins with the 
splenic and gastric vein to form the portal vein (see Fig. 131). The superior 
mesenteric vein returns blood from the greater portion of the large intestine, 
also. As the inferior mesenteric vein, which drains the rest of the large intestine 
empties into the splenic vein, it will be seen that the blood returning from the 
whole of the gastro-intestinal tract must pass through the liver by way of the 
portal vein. 
The Absorption of the Products of Digestion.-The mechanism through 
which the end-products of digestion are made to pass through the epithelial 
cells lining the villi to reach the circulating fluids, is not fully understood. 
While the physical laws of diffusion and osmosis may play a part in the process, 
they are insufficient by themselves to account for it. This is demonstrated by 
the fact that the intestine will absorb the animal's own blood serum. 
The process of absorption depends on some property of the living epithelial 
cells which enables them to select appropriate material from the intestinal con- 
tents and transfer it into the interior of the villi. When the epithelial lining of 
the intestine has been killed, absorption then takes place entirely in accordance 
with the laws of diffusion and osmosis. During the passage of the material 
through the epithelium certain changes may occur in it through the action of 
ferments found within the cells. 
The Absorption of Water and Inorganic Salts.-Water and inorganic salts are 
transferred through the epithelial cells into the lymph spaces of the villi, and 
thence through the walls of the capillary blood vessles from which they gain 
the portal vein. After circulating through the liver, they enter the general 
circulation and are distributed to all the tissues. 
A bsorption of Sugar.-All carbohydrates are changed during digestion into 
the monosaccharides, dextrose and levulose, and a small amount of galactose. 
The greater portion of the sugar to be absorbed, is in the form of dextrose. All 
sugar passes into the capillary blood vessels of the villi to be carried by the portal 
vein into the liver. There is, therefore, a decided increase in the percentage of 
dextrose in the portal blood during absorption. If, during this time, however, 234 
ABSORPTION 
the blood of the systemic circulation is analyzed it will be found to contain but 
little if any increase in dextrose. 
Evidently, during the passage of the portal blood through the liver, this 
organ must remove the excess of dextrose present. This function of the liver is 
accomplished by an enzyme capable of transforming dextrose by a process of 
dehydration into a starch-like, non-diffusible substance called glycogen. The 
glycogen is stored in the liver cells in the form of granules, and constitutes a 
reserve of carbohydrate from which the tissues may draw whenever the need 
arises. 
Absorption of the End-products of Protein Digestion.-Under the action of the 
trypsin of the pancreatic juice, the proteins have been split into polypeptides 
and a variable amount of amino-acids. It has been shown conclusively that the 
proteins are absorbed into the blood in the form of amino-acids. Since the 
intestinal contents contain proteoses, peptones, and polypeptides, these sub- 
stances must be converted into amino-acids while passing through the epithe- 
lium of the villi. This conversion is brought about by a ferment found within 
the cells, called erepsin. 
The amino-acids enter the blood capillaries of the villi as such and are 
carried to the liver. They ultimately reach the general circulation where they 
can be detected by chemical means before being taken up by the tissues. 
Absorption of Fat.-The fats are split during digestion into fatty acids and 
glycerin. A portion of the fatty acids combines with bases to form soaps while 
the rest remains in solution with the aid of the bile salts. After entering the 
epithelial cells the fatty acids are set free from their combination and are 
resynthesized with the glycerin to form neutral fats characteristic of the 
animal. 
The fat, therefore, appears as microscopic globules permeating the epithe- 
lial cells. These globules reach the interior of the villus and pass into the central 
lacteal. The transference of the fat globules is apparently accomplished by the 
leukocytes present in the lymph spaces. The central lacteal is emptied into the 
subjacent lymph vessels by the contraction of the smooth muscle that causes a 
rhythmical shortening of the villus. During absorption, the lymph flowing 
through the intestines becomes loaded with fat which, being in an emulsified 
state, imparts to the transparent lymph vessels a milky appearance, hence the 
name of lacteal being given to these vessels. This lymph loaded with fat is 
called chyle. It is carried by the lymph vessels of the mesentery into the 
receptaculum chyli-the beginning of the thoracic duct. The chyle is ultimately 
discharged into the blood at the junction of the internal jugular and subclavian 
veins (see page 152). 
The routes taken by the absorbed foods are illustrated in Fig. 132. 
Absorption of Drugs.-It is usually assumed that if a drug is soluble in 
water it will be readily absorbed when introduced into the alimentary canal or 
injected subcutaneously or intramusularly. Recent investigations, however, 
have shown that the relation between the solubility in water and the absorb- 
ability of a drug is not as simple in all cases as the foregoing statement implies. ESSENTIALS OE PHYSIOLOGY 
235 
Owing to the many complex problems involved which have not yet been entirely 
satisfactorily solved, the subject is still unsettled. It has been taken for granted 
that if a certain compound of a drug is readily soluble in water, it is more readly 
absorbed than other compounds of the same drug which are relatively insoluble. 
Fig. 132.-Diagram showing the routes by which the absorbed foods reach the blood of the gen- 
eral circulation, l.i., loop of small intestine; int. v., intestinal veins converging to form in part; p.v., 
the portal vein, which enters the liver and by repeated branchings assists in the formation of the 
hepatic capillary plexus; h.v., the hepatic veins carrying blood from the liver and discharging it into, 
inf. v. c., the inferior vena cava; int. I. v., the intestinal lymph vessels converging to discharge their 
contents, chyle, into rec. c., the receptaculum chyli, the lower expanded part of the thoracic duct; 
th. d., the thoracid duct discharging lymph and chyle into the blood at the junction of the internal 
jugular and subclavian veins; sup. v. c., the superior vena cava. (G. Bachmann, in Brubaker's Physi- 
ology.) 
The fluid of the digestive tract is not water, but is a complex solution of 
various substances some of which are capable of increasing the solubility of 
many drugs. Thus, the free hydrochloric acid present in the stomach contents 236 
ABSORPTION 
and in the first portion of the duodenum is capable of converting free alkaloids 
or alkaloidal salts which are relatively insoluble into alkaloidal hydrochlorides 
which are readily soluble. It is probable, therefore, that many alkaloids are 
absorbed in the form of hydrochlorides, irrespective of the form in which they 
are administered. Quinine sulphate (i to 725). Quinine Hydrochloride (1 to 
18) and the free alkaloid Quinine (1 to 1560) differ widely in their solubility in 
water, although it has been shown that all three substances are absorbed with 
about the same facility and rapidity. About 9,000 cc. of fluid per day are 
passed into the alimentary canal, a quantity which is doubtless sufficient to dis- 
solve a large amount of a relatively insoluble drug, even though it may not have 
undergone any changes which increased its solubility. On the other hand 
Ouabain, which is quite soluble, is very poorly absorbed from the digestive tract, 
while Digitoxin, which is relatively insoluble, is readily absorbed. From the 
foregoing facts it is evident that the solubility of a drug in water bears no 
necessary relation to the rapidity and facility of its absorption from the gastro- 
intestinal tract. 
Rate of Absorption of Drugs.-It is possible to determine the rate of absorp- 
tion of certain drugs, given by mouth, in several ways. If the drug produces 
demonstrable definite actions, the interval to the appearance of such actions may 
be taken as a measure of the absorption rate. Another method is the determi- 
nation of the time of the appearance of the drug or its derivatives in the urine, 
or in the saliva, or in both. The rapidity of the appearance of a drug in the 
blood after subcutaneous injection may also be determined. These methods 
have been applied to a few drugs like the Iodides, the Salicylates, and the active 
constituents of Digitalis and of Cinchona. The importance of such knowledge 
to the therapeutic applications of drugs, their dosage and the frequency of 
dosage is apparent. CHAPTER XXVIII 
METABOLISM 
The food principles absorbed into the blood are carried to the tissues where 
they are, in part at least, transformed into living material. The activity of the 
living cells is accompanied by the liberation of the energy locked up in the food 
material stored in the cells. This takes place through a disintegration and sub- 
sequent oxidation of the large complex molecules with the result that simpler 
substances are formed which, being of no further use to the body, are excreted 
as waste products. 
The constructive changes whereby the food material is built up into the com- 
plex molecules of living matter are called anabolism. The disintegrative changes 
accompanying the liberation of energy and resulting in the production of waste 
matter, are termed catabolism. The sum total of all chemical changes included 
in the two forms of activity just mentioned, is termed metabolism. 
METABOLISM OF CARBOHYDRATES 
The greater part of the carbohydrate food is absorbed in the form of 
dextrose. The dextrose enters the portal blood and is carried to the liver where 
it is converted into glycogen and stored in the liver cells. This function of the 
liver is called its glycogenic function. This function is shared by the muscles. 
Glycogen has the same chemical formula as starch and is equally non- 
diffusible. On hydrolysis it yields dextrose. This reconversion of glycogen 
into dextrose occurs in the liver under the action of a ferment called glycogenase. 
The object of this reconversion of glycogen into dextrose is to maintain the per- 
centage of sugar naturally present in the blood, at its average level. Blood 
plasma contains from o.i to 0.15 per cent of dextrose. Dextrose is the most 
readily available substance from which the muscles may obtain the energy 
necessary for their contraction. Whenever, therefore, the muscles become 
active they utilize dextrose in quantities proportional to their activity. Under 
these circumstances, the percentage of dextrose found in the blood would fall, 
were it not for the fact that glycogen is at the same time undergoing conversion 
into dextrose. The transformation of glycogen into dextrose is termed 
glycogenolysis. 
The Control of Glycogenolysis.-The ultimate mechanism that prevents the 
glycogenase of the liver from continuously transforming glycogen into dextrose 
is not fully understood. Certain factors, however, influence the glycogenolytic 
process either directly or indirectly. 
When the floor of the fourth ventricle of the medulla oblongata is stimu- 
lated by a puncture, a rapid conversion of glycogen follows. As a consequence 
sugar accumulates in the blood producing the condition known as hyperglycemia. 
237 238 
METABOLISM 
This in turn leads to an excretion of sugar in the urine, a phenomenon termed 
glycosuria. After a time that varies in different animals, these phenomena dis- 
appear. A group of nerve cells controlling glycogenolysis exists, therefore, in 
the medulla; to this group of cells the name diabetic center has been given. 
The manner in which the nerve control of the conversion of glycogen takes 
place in the normal body is not understood. It has been suggested, on the basis 
of certain experiments and clinical observations, that emotional disturbances 
accompanied by worry and nerve strain may lead to a glycosuria owing to 
excessive stimulation of the diabetic center. A repetition of such nerve strain 
may in time cause a true diabetes, but it is more likely, however, that errors of 
diet or disease of certain organs of internal secretion are the usual causes of 
diabetes. 
The Utilization of Dextrose in the Tissues. {Glycolysis).-The dextrose 
found in the blood is distributed to the tissues, more especially to the muscles, 
where it is oxidized and yields its energy. The ultimate products of oxidation 
are carbon dioxide and water. The decomposition of dextrose into these simple 
compounds takes place, however, in successive steps, or intermediate stages, 
which are not fully understood. There are reasons for believing, however, that 
lactic acid and pyruvic acid are the intermediate products in the process of disin- 
tegration of the dextrose molecule. The process through which dextrose is 
destroyed in the tissues to liberate its energy, is called glycolysis. 
A portion of the sugar supplied to the tissues is transformed, especially in 
herbivora, into/aL 
The Influence of the Pancreas on Glycolysis.-When the pancreas is removed 
from the body of an animal a marked hyperglycemia and glycosuria occur. The 
hyperglycemia and glycosuria are permanent and persist even after the glycogen 
of the liver has been exhausted and all carbohydrate food has been withdrawn 
from the diet. It has been demonstrated that the source of the sugar is then to 
be sought in the proteins of the diet and of the animal's own tissues. Some of 
the sugar formed in the body is possibly derived also from the glycerin split off 
from the body fats. As a consequence of these changes the animal loses rapidly 
in weight and exhibits symptoms similar to those seen in severe cases of diabetes 
in man. The chief difficulty arising from the removal of the pancreas is an 
inability on the part of the tissues to utilize the sugar brought to them by the 
blood. 
Many experiments and clinical observations have established that the 
Islands of Langerhans produce a material-a hormone-which is discharged into 
the blood and is distributed to the tissues. There, in some as yet unknown 
manner, it fulfills an essential function in the process of glycolysis. 
Aside from the changes already described, pancreatic diabetes is accom- 
panied by an accumulation in the blood and tissues of aceto-acetic and beta- 
oxy-butyric acids. This condition is called acidosis or ketosis. In the course 
of a few weeks the accumulation of these acids brings about a state of coma 
which eventuates in death. The production of these acids is due to an imper- 
fect oxidation of fat in the animal's body. ESSENTIALS OF PHYSIOLOGY 
239 
Recently, extracts of the pancreas prepared from organs whose ducts had 
been tied some weeks previously, have been used in the treatment of experi- 
mental and clinical diabetes. Such an extract is capable of bringing about an 
oxidation of sugar in the tissues of diabetic individuals simultaneously with a 
decrease in the amount of sugar in the blood and the urine. A similar reduction 
of blood sugar has been induced also in normal animals. This extract has been 
named " I nsulin." 
Aside from the influence of the hormone of the pancreas, other hormones 
produced by other glands of internal secretion play a part in the metabolism 
of the carbohydrates. These glands are the adrenals, parathyroids, and pituitary 
body. The manner in which the hormones produced by these organs effect 
sugar consumption is not fully understood. 
Assimilation Limit of Carbohydrates.-The ability of the body to dispose of 
carbohydrates is limited. Whenever this limit is overstepped an excess of 
sugar appears in the blood, a condition already referred to as hyperglycemia. 
This excess in turn leads to an excretion of sugar by the kidneys; a glycosuria 
ensues. In determining the assimilation limit for various carbohydrates the 
test is made from 12 to 16 hours after the last meal in order to make sure that the 
gastro-intestinal tract is empty. The urine should be analyzed every one and a 
half hours. 
The assimilation limit is highest for starches. Very large quantities of 
rice or potatoes may be eaten without giving rise to more than a trace of sugar 
in the urine. On the other hand, the assimilation limit is lower for dextrose; 
it varies between 150 and 250 grams. It would seem to be lowest for lactose, 
for which it has been found to be 100 grams (Macleod). The administration 
of these sugars on an empty stomach beyond the figures mentioned leads to a 
hyperglycemia and glycosuria. 
METABOLISM OF FAT 
The fat resynthesized during the process of absorption is carried by the 
thoracic duct into the blood stream. After a meal rich in fat the percentage 
of fat in the blood rises much beyond the normal average which has been 
variously estimated at from o.i to 0.6 per cent. The fat is carried by the blood 
to (1) certain depots such as the subcutaneous and retroperitoneal tissues, (2) 
the liver, and (3) the tissues generally. In each of these situations the fat differs 
slightly in composition. 
The Origin of Body Fat.-The fat present in the body is not only derived 
from the fat of the food, but also from the carbohydrates. If an animal be 
fed on larger amounts of carbohydrates than is actually necessary for its energy 
requirements, a portion of the carbohydrates will be transformed into fat and 
stored for future use. Careful experiments to determine whether fat could be 
formed from protein have yielded negative results. 
The Utilization of Fat by the Tissues.-The large fat molecule breaks down 
through a number of successive steps which result in the formation of fatty acids, 
such as stearic, palmitic and oleic acids, and glycerin. These fatty acids are 240 
METABOLISM 
then reduced to simpler acids such as butyric acid, which then undergoes 
oxidation to form beta-oxybutyric acid. A further oxidation produces aceto- 
acetic acid which by losing carbon dioxide becomes transformed into acetone. 
As oxidation proceeds the acetone ultimately is converted into carbon dioxide 
and water. These successive oxidations require an abundant supply of oxygen, 
as well as a simultaneous oxidation of dextrose. 
METABOLISM OF PROTEIN 
The proteins are absorbed into the blood in the form of amino-acids. The 
various amino-acids are of unequal importance, in that they cannot all be 
utilized for the repair and growth of the tissues. Only those found in the body- 
proteins can be so utilized. Those amino-acids that have no representation in 
the body-proteins or that are in excess of the present needs of the body are 
nevertheless utilized for the store of energy they contain. 
The Utilization of Amino-acids by the Tissues.-Those amino-acids capable 
of entering in the formation of body-proteins are rapidly taken up by the tissues 
and synthesized into protein characteristic of the tissue. The excess of these 
amino-acids, as well as the foreign amino-acids, undergo a different change. 
This consists of a cleavage of the amine radical ( -NH2), and of the carboxy] 
radical ( -COOH), from the amino-acid molecule. This deaminization of 
amino-acids takes place chiefly in the liver, although it doubtless occurs in 
the other tissues. The amine radical then combines with hydrogen and carbon 
dioxide to form ammonium carbonate and ammonium carbamate which are 
then transformed in the liver into urea by a process of dehydration. The 
carboxyl radical is oxidized to carbon dioxide and water with the liberation of 
heat. Direct experiments have shown that some amino-acids may be trans- 
formed into dextrose. 
The protein of the tissues during its catabolism is ultimately reconverted 
into amino-acids which may be utilized, as in starvation, by those tissues most 
in need of them. They do not seem to undergo any further cleavage and 
oxidation, although a certain loss of body-protein occurs in the form of creatinine. 
This substance occurs chiefly in the voluntary muscle. 
The Metabolism of the Nucleo-proteins.-The nucleo-proteins are the 
chief constituents of the nuclei of cells, both animal and vegetable. During 
their digestion, they are split into nuclein and a protein; the nuclein is, further- 
more, changed into nucleic acid which is then absorbed. On reaching the 
tissues the nucleic acid is split by successive enzymes into a number of complex 
bodies which, ultimately yield uric acid. Other articles of diet such as coffee, 
tea, and cocoa must be mentioned as sources of uric acid owing to the presence 
in them of caffeine, theophylline and theobromine, respectively. As the uric 
acid derived from the food is of external origin, it is called the exogenous uric 
acid. The exogenous uric acid will naturally vary with the character of 
the food. Any food containing large amounts of nucleic acid such as liver, 
sweet-breads, and kidneys, will give rise to correspondingly large amounts of 
uric acid. ESSENTIALS OF PHYSIOLOGY 
241 
In the catabolism of the tissues, the nucleo-proteins of the cells undergo 
similar changes. A portion, therefore, of the uric acid excreted has an internal 
origin. This uric acid is termed endogenous. 
ENERGY REQUIREMENTS AND DIET 
The animal body may be considered as a machine for the performance of 
work and the liberation of heat. If the stock of energy constantly expended is 
to be renewed, it is necessary that the body be supplied with energy-yielding 
material. This material consists of the food principles found in the diet. 
The various foods are derived directly or indirectly from vegetable matter 
built up by living plants from inorganic substances under the action of the sun's 
Window 
CALORIMETER 
CHAMBER 
Oxygen 
Rotary pump 
H2S0+ 
Soda Lime 
S 0^ 
Fig. 133.-Diagram to show the principle of the Atwater-Benedict calorimeter. (From Brubaker's 
Text-book of Physiology.) 
rays. The energy supplied by the sun's rays is transformed into potential 
energy in the form of various organic compounds. When assimilated in the 
animal body, these organic compounds, i. e., the food principles, undergo 
subsequent oxidation with a liberation of their contained potential energy 
into kinetic energy, which appears, chiefly, in the form of heat and muscular 
work. 
As stated previously, a portion of the food is utilized also to repair the 
waste of the tissues and, in the young, to supply material for new growth. 
The Food Principles as the Source of Energy.-As the various forms of 
energy are interconvertible it is possible to express the total amount of energy 
set free in the body in any one form. The most convenient form is that of 
heat. The unit of measurement is called the Calorie, and may be described 
as the amount of heat necessary to raise the temperature of one kilogram of 
water i° centigrade. The amount of heat set free from the body can be 
ascertained by placing the individual in a calorimeter (Fig. 133). The work 242 
METABOLISM 
done by the muscles of respiration, visceral muscles, etc., is computed and 
expressed in terms of heat. 
The amount of heat liberated is lowest in the morning, fourteen to sixteen 
hours after the last meal, the individual being at rest in the recumbent position. 
This measures the basal metabolism. It varies with the surface area of the body, 
with sex, and age. In adult man it has an average of 39.7 Calories per square 
meter of body surface, per hour. A man of average height and weight would 
thus, liberate about 1680 Calories of heat a day. Individuals who do light 
work set free about 3000 Calories of heat, while those who do severe muscular 
work liberate from 4000 to 5000 Calories or more. 
The diet must accordingly contain sufficient energy to replace that lost. 
It is, therefore, necessary to known the energy or heat value of the different 
food principles. This can be determined by burning a definite amount of any 
given food principle, say one gram, in a calorimeter and measuring the amount 
of heat liberated. As carbohydrates and fats are oxidized in the body to carbon 
dioxide and water, these food principles yield the same amount of heat within 
the body that they do when oxidized in a calorimeter. Proteins, however, 
are but incompletely oxidixed in the body, namely to the stage of urea, so that 
their oxidation in the calorimeter yields more heat than in the body. The 
physiologic heat value of protein can be readily estimated, however, by deduct- 
ing the heat value of the urea to which it gives rise. Some of the food ingested 
moreover escapes digestion. The amount so lost is normally slight but must 
be deducted. 
The energy or heat value of the various food principles is as follows: 
1 gm. of protein 4.1 Calories 
1 gm. of carbohydrate 4.1 Calories 
1 gm. of fat 9.3 Calories 
From these figures, a diet can be worked out containing the food principles 
in amounts sufficient to replace the energy lost daily. An average diet, with 
its energy equivalent, is represented in the table below. 
Protein 100 gm. X 4.1 = 410 Calories 
Fat 60 gm. X 9.3 = 558 Calories 
Carbohydrate 500 gm. X 4.1 = 2050 Calories 
Total 3018 Calories 
Construction of a Diet.--It would seem from the tables just presented, 
that the energy requirements of the body could be supplied by any other 
proportion of the various food principles. This, however, is not the case, for 
if protein alone were to be taken, for instance, it would require more than three 
pounds of lean meat a day to supply the required energy. This amount of 
meat would not only overtax the digestive capacity of the individual, but 
likewise put a severe strain on the excretory organs. 
A balanced diet can be established by ascertaining whether the end-products 
of metabolism balance the intake. The carbon in carbohydrate and fat and a ESSENTIALS OF PHYSIOLOGY 
243 
portion of that in protein is discharged through the lungs in the form of carbon 
dioxide. The nitrogen of protein appears in the urine as urea, uric acid, etc. 
As it requires 6.25 gm. of protein to yield 1 gm. of nitrogen to the urine, the 
amount of protein used in the body can readily be calculated. The relative 
amount of carbon in the carbohydrate and the fat oxidized in the body can 
also be readily calculated by determining the respiratory quotient. 
When the carbon eliminated exactly balances the amount in the food, the 
individual is said to be in a state of carbon equilibrium. Similarly, when the 
amount of nitrogen eliminated is equal in amount to that ingested, the indivi- 
ual is said to be in a state of nitrogen equilibrium. The individual in such 
a case neither gains nor loses in weight, and is said to be in nutritive equilibrium. 
An individual may increase in weight owing to a retention of carbon in 
the form of fat or carbohydrates, or to a retention of nitrogen in the form 
of protein. If he loses weight more carbon or nitrogen will be eliminated 
than are ingested with the food. 
The following table, from Ranke, shows the balance between the income 
and the outcome in a man weighing 70 kilograms, in a state of nutritive 
equilibrium: 
Income 
Grams 
N 
c ! 
Outcome 
Grams 
N 
C 
Protein 
IOO 
i5 5 
530 
Urea 
31-5 
14-4 
6.16 
Fat 
IOO 
79 •0 
Uric acid 
0 ■ 5 
Carbohydrate 
250 
93-o 
Feces 
1.1 
10.84 
Carbon dioxide 
208.00 
15-5 
225.0 
15-5 
225.00 
From this table it is evident that a moderately active individual requires 
about fifteen times as much carbon as nitrogen. 
Relative Value of the Food Principles. Proteins.-The protein of the food 
is utilized not only to supply energy but also the material necessary for the 
growth and the repair of the tissues. Owing to the protein nature of bioplasm 
this food principle is absolutely essential for the maintenance of life. Even 
with an abundance of carbohydrate and fat an animal will starve if all protein 
is withdrawn from the diet. The storage of protein does not occur except in 
the young growing animal and in adults whose tissues have been wasted by 
disease or an insufficient diet. 
The proteins vary considerably in their ability to supply the body with 
material for growth. In order to be suitable for this purpose a protein must 
contain the particular amino-acids that have a representation in the body 
proteins, and these amino-acids must be present in adequate proportion. In 
this respect the animal proteins are of greater value than those .of vegetable 
origin. Proteins that are inadequate for growth may nevertheless be sufficient 
for the maintenance of life. 244 
METABOLISM 
Numerous experiments have demonstrated that the protein portion of the 
diet should be varied in order that a variety, and an adequate proportion of 
amino-acids be insured. 
When the individual has ceased growing, the greater portion of the protein is 
utilized in the body for the energy it contains. As stated previously, the amount 
of nitrogen excreted daily on an average diet is about 15 grams. If enough 
carbohydrate is supplied in the diet to meet the energy requirements, the amount 
of protein can be reduced so that but six grams of nitrogen is excreted daily, pro- 
vided the proteins chosen are adequate for maintenance and growth. This 
corresponds to about 39.5 grams of protein. This would seem to be the portion 
of the protein utilized for the repair of the tissues. 
While at first sight a low protein diet would appear to present certain 
advantages, particularly as regards the elimination of waste by the kidneys, care- 
ful observation has shown, that individuals on a low protein diet have less power of 
resisting infectious diseases. They likewise suffer more in cold weather. When 
food is absorbed the production of heat in the body rises. This effect of food 
is called its specific dynamic action, and is due to a stimulation of the oxidative 
processes taking place in the tissues. The specific dynamic action is greatest 
for protein, hence it is that an individual on a low protein diet will suffer more 
from exposure to cold, and that people living in a cold climate eat more protein 
than those living in the tropics. 
Statistical studies made in different parts of the world show that, whenever 
possible, man instinctively choses a diet containing about 100 grams of protein. 
Carbohydrates.-As is the case with proteins the carbohydrates are essential 
to the nutrition of the body. When entirely withdrawn from the diet, carbo- 
hydrate material-dextrose-is elaborated by the body out of the proteins. A 
deficiency of carbohydrate leads, furthermore, to an imperfect oxidation of the 
fats with the consequent appearance of acetone bodies and the production of 
acidosis. 
Carbohydrate and fat are utilized to supply energy through their oxidation 
as shown by the fact that during muscular exercise there is no increase in the 
excretion of nitrogen, but a rise in the respiratory quotient. The respiratory 
quotient reveals, furthermore, that a greater proportion of carbohydrate than fat 
is oxidized by the muscles. The conclusion has, therefore, been reached that 
carbohydrate constitutes the most readily available material for the liberation 
of energy. 
Fats.-From experiments with young mice, it has been established that 
simple fats and lipoids are indispensable for the maintenance of life. As the 
tissues are capable of manufacturing fat from carbohydrate, it is believed that 
the substances lacking in a fat-free diet are the vitamins which, as stated below, 
are essential to life. 
Owing to their high calorific value fats when oxidized yield a large amount 
of energy. Fat becomes, therefore, an important article of diet when a great deal 
of muscular work is done in a cool atmosphere. Under such circumstances, fats 
may supply from 35 to 40 per cent of the calories of the diet. ESSENTIALS OF PHYSIOLOGY 
245 
Inorganic Salts.-Inorganic salts are likewise an essential part of the diet. 
Their withdrawal interferes seriously with growth. Salts of sodium, potassium, 
and calcium are necessary for the composition of the fluids and solids of the body. 
As a certain proportion of these salts is lost daily, it is necessary that they be 
replaced. Iron, found in animal and vegetable foods as a compound with 
nuclein, is also necessary for the production of hemoglobin. Finally, traces of 
iodides have been shown to be of importance in the dietary as their absence is 
often accompanied by disturbances of thyroid function. 
Vitamins.-Adequate quantities of protein, fat, carbohydrate and inorganic 
salts will not suffice to promote growth and maintain the body in health unless the 
diet contains also certain accessory food substances termed vitamins. These 
substances are imperfectly known as regards their chemical composition. They 
are found in but minute quantities in different foods, but are nevertheless of the 
greatest importance for the growth, and health of the body, and even the 
maintenance of life. 
Vitamins are of vegetable origin. They become fixed in the tissues without 
change for an undetermined period of time. They have been shown also to pass 
into the milk. Carnivora obtain their vitamins therefore indirectly, by eating 
flesh of herbivorous animals. The young receive their vitamins with the milk. 
The vitamins known at present, together with some of their properties and 
sources, are briefly discussed in the following paragraphs: 
Vitamin A (Fat-Soluble A, Antiphthalmic Vitamin).-Vitamin A is essential 
to the growth of young animals. Its absence or deficiency, in the diet of adult 
animals decreases their resistance to infection. This manifests itself by an 
infection of the eye called xerophthalmia or dry eye. There seems to be a relation- 
ship between this vitamin and the occurrence of rickets in the young. 
Vitamin B (Water-Soluble B, Aniineuritic Vitamin).-Vitamin B is not only 
essential to the growth of young animals, but also to the maintenance of life in 
the adult. The absence of this vitamin from the diet gives rise to a number of 
symptoms which eventuate in death. These symptoms resemble those of a 
human disease called beri-beri. It occurs among those who eat polished rice. 
The addition of the polishings to the diet cures the disease. 
Vitamin C (Water-Soluble C, Antiscorbutic Vitamin).-Vitamin C is essen- 
tial to metabolism and is commonly found in tissues in which active metabolism 
is taking place. Its absence from the diet results, in about twenty days, in an 
abnormal state called scurvy. The administration of vitamin C prevents and 
cures scurvy. 
Vitamin D (Antirachitic Vitamin).-This vitamin is apparently concerned 
in the metabolism of calcium and phosphorus, and thus influences the nutrition 
of bone. The occurrence of rachitis or rickets, already referred to in connec- 
tion with vitamin A, is apparenty related to the absence, or a deficiency, of 
vitamin D. 
The different vitamins are found in varying quantities in milk, butter, 
eggs, cheese, yeast, cod liver oil, leafy vegetables, roots, legumes, fruits, 
and nuts. 246 
METABOLISM 
A consideration of the facts enumerated in the preceding paragraphs shows 
that a well balanced diet must include (i) an average of about 100 grams of 
protein derived from various sources; (2) an amount of carbohydrate and fat 
varying with the energy requirements of the body; (3) enough water and 
inorganic salts to replace their loss; and (4) a choice of the articles of diet that 
will insure an adequate supply of all vitamins. In addition to these essential 
factors in the construction of a diet, it is necessary that the food be well prepared 
and appetizing in order that the processes of digestion and absorption may 
proceed normally. CHAPTER XXIX 
THE TEMPERATURE OF THE BODY AND ITS REGULATION 
The heat liberated in the tissues during the oxidation of food material 
imparts to the body a certain temperature. The body temperalure of mammals 
and birds is relatively high and can be readily detected by the sense of touch. 
These animals are therefore called warm-blooded animals. Since their tempera- 
ture is independent of variations in the external temperature, they are better 
termed constant-temper atured or homoiothermous animals. In fishes, amphib- 
ians, and reptiles, the metabolic activities of the tissues are not as great as in 
mammals and birds, so that the amount of heat liberated is relatively slight. 
Their temperature is, however, above that of the surrounding medium, but 
varies as the temperature of the medium changes. These animals are there- 
fore called cold-blooded and variable-temperatured, or poikilothermous animals. 
The average temperature of the body, in man, is 37°C. (98.4^.) as meas- 
ured in the mouth. This temperature varies to the extent of about i°F. 
during the course of the day; it is highest in the afternoon and lowest in the 
early morning. It varies slightly also after a hearty meal, increasing about 
o.5°C. and declines in starvation. Prolonged muscular exercise may tempo- 
rarily increase the temperature from i°C. to r.5°C. 
The remarkable constancy of the body temperature despite extensive 
changes in external temperature is due to the presence of a mechanism through 
which heat production and heat loss are made to balance each other. 
Heat Production.-The chemical changes that underlie the activity of 
the tissues are accomplished by the liberation of heat. Owing to their mass 
and their great activity the muscles are the organs chiefly concerned with heat 
production. The various glands of the body likewise play a part in heat 
production. The liver, being a large glandular organ in which many chemical 
processes take place, is the most important of these. This is shown by the 
fact that the blood in the hepatic vein is warmer than that of the portal vein. 
Since the amount of heat produced varies with the activity of the tissues, 
muscular exercise will materially increase the amount of heat set free. Varia- 
tions in the contraction of the muscles are, therefore, the most important means 
of controlling the amount of heat produced in the body. As a consequence of 
these variations in muscular activity, corresponding variations in the amount 
and character of the pood ingested usually occur, great increase in muscular 
activity necessitating an increased amount of carbohydrate and fat in the diet. 
Heat Loss.-The heat produced in the body is lost in corresponding amounts 
chiefly through the skin, by radiation and convection, and by the evaporation 
of perspiration (in all from 80 to 84 per cent). Heat is lost also in warming 
the food and drink to the temperature of the body (2.8 per cent); in warming the 
247 248 
THE TEMPERATURE OF THE BODY AND ITS REGULATION 
inspired air (3.8 per cent); and in the evaporation of water from the lungs 
(about 10 per cent). 
Regulation of Body Temperature.-The constant temperature of warm- 
blooded animals is the result of the controlling action of the central nerve 
system upon heat production and heat dissipation. When the spinal cord is 
injured so that the lower limbs are no longer under the control of the brain, 
they behave like the bodies of the cold blooded animals, their temperature 
rising and falling with the external temperature, often to such an extent as to 
influence the temperature of the rest of the body. 
Exposure to cold increases that form of muscular activity called tonus; 
the muscles, in time, may give the visible contractions that produce the move- 
ments of shivering. The increased muscular activity increases the amount of 
heat produced. There occurs at the same time, a constriction of the blood 
vessels of the skin, so that loss of heat by radiation and perspiration is at a 
minimum. 
On exposure to heat, the blood vessels of the skin dilate and perspiration 
takes place freely. In man these phenomena are greatly modified by clothing. 
In cold weather woolen clothing is commonly worn, as wool is a poor conductor 
of heat, but absorbs and retains moisture readily. Linen and cotton,* on the 
other hand, are better adapted for warm weather. 
The variations in the size of the cutaneous vessels and in the involuntary 
activity of the muscles are under the control of a center situated in the corpus 
striatum, probably in the caudate nucleus. Direct heating of this region 
results in a decreased production of heat in the muscles and an increase in the 
loss of heat from the skin. The converse occurs when this region is cooled. 
It is believed, therefore, that changes in the temperature of the blood constitute 
the stimulus in response to which the heat-regulating center controls the body 
temperature. It is probable, however, that aside from this mode of stimulation, 
the center is influenced by afferent nerve impulses arising by stimulation of 
the cutaneous nerves of temperature. 
Fever.-Under ordinary conditions an increased heat production is accom- 
panied by a proportionate increased heat dissipation, so that no change in the 
body temperature occurs. If, however, close-fitting, heavy clothing is worn 
in hot weather and the individual undertakes active muscular work, the inter- 
ference with heat dissipation through the skin may lead to a retention of heat 
and bring about a febrile condition. This condition is commonly called "heat 
stroke." It is more likely to occur when, in addition to a high external tem- 
perature, there is also such a high percentage of humidity in the air as to prevent 
free evaporation of the sweat. 
The usual cause of fever is an increased production of heat, the result of 
the action of toxins in the tissues. As the mechanism of heat regulation is 
at the same time disturbed, heat dissipation does not keep pace with heat 
production and the body temperature rises. Since in fever the appetite and 
the digestive functions are impaired, the production of heat is dependent upon 
the oxidation of the tissues, hence wasting occurs. CHAPTER XXX 
PHARMACODYNAMICS OF METABOLISM 
The preceding physiological discussion has shown that all physical and 
chemical stimuli which act directly on the body cells must influence their 
chemical activity and consequently affect the transformation of the matter and 
energy contained in them. 
I. Physical Stimuli, (a) Temperature.-An increase in the temperature 
causes an increase in the rate at which chemical reactions take place. Within 
certain limits the same holds true for the metabolic reactions of the living 
organism. A rise of body temperature increases and accelerates metabolism. 
Changes in body temperature and the resulting effects on body reactions 
are at times produced by hy dr other apeutic measures, i. e., the external use of 
water and its modifications: cold water, hot water, steam, and ice, in the form 
of baths, sprays, packs, douches, etc. 
A rise or a fall in body temperature may be brought about by the action of 
certain drugs. Thus, Atropine, in moderate dose inhibits perspiration and 
consequently causes a rise in temperature. Cocaine in toxic doses, produces a 
rise in temperature due to increased heat production brought about by its 
stimulating effect on the motor areas of the brain and on the reflex centers of the 
brain and cord. Aconite and V eratrum may lower body temperature by 
lessening heat production through their effect in slowing the circulation. Hyp- 
notic doses of Opium, Morphine, Codeine, etc. may produce a marked lowering 
of temperature by diminishing heat production, the result of bodily quite. 
(J) Light.-Certain light rays, especially ultra-violet and blue-violet, exert a 
direct destructive action on body enzymes and on living cytoplasm, just as they 
do on chemicals. Therapeutic application of the effects of light rays is some- 
times made in the treatment of certain skin diseases, cancer, etc. 
(c) X-rays and Radium Emanations.-X-rays and Radium emanations 
exert a destructive action on the chemistry of body cells in a manner somewhat 
similar to light rays. However, since they penetrate the soft parts of the body 
their actions are not limited to the surface, but may also affect the internal 
tissues and the blood. Certain diseases of the skin and blood, cancer, etc. are at 
times treated with these agents. 
(d) Electricity.-Nothing is known concerning the direct action of electric- 
ity on the metabolism of the body cells. 
II. Chemical Stimuli.-No attempt can be made in a textbook of this 
character to discuss all of the drugs and chemicals which affect metabolism. 
Brief mention of a few important agents will suffice. 
Water.-Water is an essential constituents of cytoplasm. The constant 
loss of water in the urine, feces, perspiration, and expired air would ultimately 
249 250 
PHARMACODYNAMICS OF METABOLISM 
result in drying and concentrating the body tissues were it not for the fact that 
the sensation of thirst leads to the replacement of the water. 
Distilled water is a violent poison to cells which are readily permeable to it. 
Semipermeable cells, though decidedly more resistant to distilled water, never- 
theless undergo some osmotic changes even when ordinary water is directly 
applied. If the semipermeability is diminished or imperfect, the osmotic 
changes produced are sufficient to cause the passage of a part of the salts out of 
the cells into the surrounding water, and the passage of a considerable excess 
of the water into the cells. Familiar examples of the deleterious action of water 
are the hemolysis or taking of blood, and the water-rigor and swelling of muscles. 
When immersed in distilled water some of the lower forms of animal life die in 
from 5 to io minutes. The drinking of distilled water by higher animals is not 
attended by toxic symptoms, since they obtain their salts mainly from food 
rather than from water. However, the intravenous injection of 100 to 150 cc. of 
distilled water per Kilo into the circulation of a rabbit or a dog will rapidly 
cause death. 
Tissue surfaces which are normally exposed to contact with water are pro- 
tected against appreciable action by being practically impermeable, as in the cases 
of the skin and the urinary bladder, or by the very rapid transfer of tissue salts 
into the water, as in the intestinal tract. However, very large quantities of water 
cause more or less swelling and irritation of the cells even in these organs. 
If an excess of water is taken, there is a temporary increase in the water con- 
tent of the body cells and fluids, a removal of some of their salts, and a con- 
sequent change in their ionic concentration. These changes result in certain 
functional phenomena which are characterized by an increase in secretion, meta- 
bolic changes, etc. However, the excess of water is rapidly eliminated in the 
excretions, especially in the urine, which are correspondingly diluted and 
increased in amount. 
If abundant amounts of water are drunk during a fast, its effects on the 
osmotic tension of the body fluids may cause an increased catabolism of proteins, 
fats, and possibly carbohydrates. 
The Absorption and Excretion of Water.-Water is practically unabsorbed 
from the stomach, where it also retards the absorption of other substances. 
Water containing Ethyl Alcohol or Carbon Dioxide is more readily absorbed 
from the stomach. Water is an excellent dilutent for irritating drugs. In the 
intestines it is rapidly absorbed, and may promote the absorption of certain 
substances in solution. Water is not absorbed in appreciable amounts by the 
skin. 
The excretion of water, is accomplished principally by the kidneys, but also 
in part by the skin, lungs and intestines. 
Glands of Internal Secretion.-A discussion of the thyroid gland, the adrenal 
glands, the pituitary body, the pancreas, the testicles and the ovaries, and their 
effects on metabolism appears in the chapter following. 
Iodine and Iodides.-Iodine and its compounds, such as the Iodides, 
influence metabolism through the thyroid glands. These drugs materially PHARMACODYNAMICS 
251 
increase the content of the active constituent of the glands-thyroxin-(an 
Iodine compound), and an increased activity of the glands consequently results. 
(See "The Thyroid" in the chapter following.) 
Quinine.-This alkaloid is a general cytoplasmic poison, and is con- 
sequently toxic to all cells and even to the unorganized ferments. Although 
relatively non-toxic to higher organisms, it is strongly toxic to cells possessing 
amoeboid and similar movement, such as amoeba, white blood cells, ciliated 
epithelium, spermatozoa, infusoria, muscle, etc. Quinine exhibits a highly 
selective action on the malarial parasites, i. e., it is under proper conditions 
specific against malarial disease. 
Quinine is said by many to reduce metabolism, more especially that 
of the proteins, resulting in a storing of proteins and consequently having a 
special value in wasting diseases and fever. Recent experimentation on man 
and animals has failed to show any alteration in the metabolism of proteins. 
Its specific effects in preventing fever in malaria are due to its destroying the 
parasite and not to direct action on the temperature controlling mechanism. 
Although at times successful in other forms of fever, Qiunine frequently fails 
to lower the temperature. 
ANTIPYRETICS 
Drugs which tend to lower the temperature in fever are called antipyretics. 
Reduction of temperature in fever may also be accomplished by the application 
of cold by such methods as the cold bath, cold pack, ice-bag, ice water rectal 
injections, etc. 
The antipyretic drugs include only those whose most pronounced action 
is to lower the temperature in fever. There are othere drugs which possess 
this power, such as Alcohol, Digitalis, Phenol, etc., but they are classified 
elsewhere because of other much more useful and important actions. The 
most important antipyretics are usually classified into three groups, viz., 
the Coal-tar or Analgesic, the Anti-malarial, and the Anti-rheumatic Anti- 
pyretics. 
(i) The official Coal-Tar or Analgesic Antipyretics are Acetanilid, Acet- 
phenetidin ("Phenacetin"), and Antipyrine. These drugs have no measurable 
effect on normal temperature. In fever they reduce the temperature by 
effecting the centers which control the tonus of the cutaneous vessels resulting 
in dilatation of the vessels of the skin, and thus promoting loss of heat by radiation 
and convection, and secondarily by favoring sweating. 
The analgesic effect of these drugs was discussed on page 103. 
(2) The Anti-malarial Antipyretics include Cinchona, its alkaloids Quinine 
Quinidine, Cinchonine and Cinchonidine, and their derivatives such as "Euquin- 
in," " Aristochin, " etc. The most important member of the group is Quinine. 
The specific effect of Quinine on the malarial organisms has been briefly 
mentioned above. This alkaloid has little, if any effect on normal temper- 
ature. Since the drug is still effective in lowering temperature after division 
of the spinal cord, it does not act in the heat-regulating center. 252 
PHARMACODYNAMICS METABOLISM 
As stated on page 251, Quinine is not infrequently unsuccessful in 
lowering the temperature in forms of fever other than malarial. The general 
view that Quinine reduces heat production by lessening the heat formed, 
largely through depression of the metabolism of proteins, is not acceptable 
because of the results of the recent investigations referred to above. Further 
research is required to determine under what conditions and in what forms 
of fever Quinine induces a fall in temperature. 
(3) The Anti-rheumatic Antipyretics include Salicylic Acid, its salts, such 
as Sodium Salicylate, and derivatives like Acetylsalicylic Acid ("Aspirin") 
and Phenyl-cinchoninic Acid A tophan" or li Cinchophen"). As with the 
preceding groups, these antipyretic drugs have practically no effect on normal 
temperature. In fever they lower temperature in a manner similar to the 
"coal-tar or analgesic antipyretics, " i. e., by dilatation of the cutaneous arterioles 
resulting in an augmentation of heat loss through increased radiation and con- 
vection of heat, and sweating. 
The analgesic effects of Salicylic Acid, its salts, and of Acetylsalicylic 
Acid, and the almost specific action in acute articular rheumatism were mentioned 
on page 103. Phenyl-cinchoninic Acid ("Atophan" or "Cinchophen") is a 
salicylic acid derivative (phenyl-quinoline-carboxylic acid) which possesses the 
antipyretic and analgesic actions of Salicylic Acid, and in addition increases 
the amount of urine and the excretion of all the elements of the urine, particu- 
larly the uric acid. The mechanism of its action probably includes an increased 
destruction of nucleo-proteins and direct stimulation of the kidneys. The drug 
has been used with more or less success in acute gouty and rheumatic conditions; 
and it is possible that its effects in these conditions are due rather to the anal- 
gesic, antipyretic, and antiseptic actions than to its effect on the excretion 
of uric acid. CHAPTER XXXI 
EXCRETION 
By excretion is understood the process whereby the waste products of 
tissue metabolism are eliminated from the body. The waste formed during 
tissue activity is discharged into the blood and is carried by this fluid to the 
various organs of excretion. These organs are the lungs, kidneys, skin, and 
the liver. The lungs excrete the carbon dioxide which is the end product of the 
metabolism of the carbon of the food. The kidneys excrete the end products 
of protein metabolism, while the liver eliminates the waste products found in the 
bile. The skin discharges, under ordinary circumstances, but small amounts 
of waste matter. 
In the process of excretion waler plays an important part in that, in all 
instances except the lungs, it constitutes the vehicle through which the waste 
is carried through the excretory organs. 
THE URINARY APPARATUS 
The urinary apparatus consists of the kidneys, whose function is to secrete 
the urine; the ureters, tubular structures through which the urine is carried to the 
bladder; and the urethra, a passageway connecting the bladder with the exterior. 
The Kidneys.-The kidneys are two bean-shaped organs situated in the 
abdominal cavity, behind the peritoneum, and extending from the eleventh 
rib to the crest of the ileum. They are about 4^ inches long, 2 inches wide, 
and inches thick. The internal border has a deep notch called the hilum. 
The kidney is invested by a membrane or capsule of white fibrous and yellow 
elastic tissue and rests in a bed of fat. 
When a longitudinal section of the kidney is made the hilum is seen to 
pass into the interior of the organ where it expands into a cavity termed the 
sinus (Fig. 134). The sinus contains the blood vessels, nerves, and the upper 
expanded portion of the ureter called the pelvis. From the pelvis a number of 
branches pass to the tips of the pyramids which they surround. The funnel- 
like extremities of the pelvis are called calyces. They receive the urine as it 
is discharged from the tubules of the kidney substance. 
The substance or parenchyma of the kidney consists of two parts: (1) an 
external or cortical part, and (2) an internal or medullary pan, consisting of from 
12 to 15 conical masses known as pyramids. The cortical part not only covers 
the bases of the pyramids but extends between them where it forms the so-called 
renal columns. 
When studied under the microscope the kidney is shown to be composed of 
innumerable tubules, blood vessels, lymphatics, and nerves, all supported by a 
connective tissue framework. 
253 254 
EXCRETION 
The Kidney Tubules.-Each tubule begins in the cortex in an invaginated 
spherical dilatation known as Bowman's Capsule, containing in its invagination 
a tuft of capillary blood vessels called the glomerulus (Fig. 135). From the 
capsule there arises, by a narrow neck, a tortuous .tubule called the first or 
proximal convoluted tubule (Fig. 136). This tubule diminishes in diameter 
and descends in a straight course toward the apex of the pyramid. The narrow 
straight tubule is called the descending limb of Henle's loop. It then bends 
upon itself to form Henle's loop, and enlarging, ascends toward the cortex 
Fig. 134.-Longitudinal section through the kidney, the pelvis of the kidney, and a number of 
renal calyces. A, branch of the renal artery; U, ureter; C, renal calyx, 1, cortex; 1', medullary rays; 
1", labyrinth, or cortex proper; 2, medulla; 2', papillary portion of medulla, or medulla proper; 2," 
border layer of the medulla; 3, 3, Transverse section through the axes of the tubules of the border 
layer; 4, fat of the renal sinus; 5, 5, arterial branches,* transversely coursing medulla rays. 
(Tyson, after Henle.) 
to form the ascending limb of Henle's loop. In the cortex, the tubule becomes 
highly contorted and is there called the second or distal convoluted tubule; 
it ends in a short junctional tubule which empties into a collecting tube. Several 
of these uniting together form an excretory tube which opens at the apex of the 
pyramid into a calyx of the ureter. 
This system of tubules is made up of a basement membrane upon which 
rests a single layer of epithelial cells. The epithelium varies in size and shape 
in different locations. In the capsule the epithelium is flat; in the convoluted 
tubules the epithelium is cuboidal, striated, and faintly granular; in the descend- 
ing limb of Henle's loop it is more or less flattened. ESSENTIALS OF PHYSIOLOGY 
255 
The Blood Vessels of the Kidney.-The artery supplying the kidney arises 
from the abdominal aorta and is called the renal artery. It enters the kidney 
at the hilum and divides within the sinus into a number of branches which pass 
into the organ between the pyramids. At the base of the pyramids these 
branches divide to form a plexus. From this plexus some branches pass toward 
the apex of the pyramid-the arteria recta. 
Others pass toward the cortex and give off 
arterioles that supply the capsules with the 
glomerular capillaries. These capillaries do 
not anastomose, but unite to form an efferent 
vessel of smaller caliber than that of the 
afferent arteriole. The efferent vessel gives 
rise to a capillary plexus which surrounds the 
convoluted tubules. Veins arise from the 
capillaries and, pursuing the same course as 
the arteries, form the renal vein which 
Fig. 135.-Scheme of the renal or Malpighian 
corpuscles. 1, interlobular artery; 2, afferent 
vessel; 3, efferent vessel; 4, outer wall; 5, inner 
wall; 6, glomerulus; 7, neck of tubule. {Stohr.) 
Fig. 136.-Diagram of three uriniferous tubules 
in relation with a collecting tubule, a. I., ascend- 
ing limb of Henle's loop; c., capsule; c. t., collect- 
ing tubule; d. c., distal convoluted tubule; d. I., 
descending limb; j., junctional tubule; p. c., proxi- 
mal convoluted tubule; p. d., papillary duct. A, 
cortex; B-D, medulla, subdivided into an inner 
zone (D) and an outer zone {B-C); the latter in- 
cludes an inner band or stripe (C), and an outer 
band (B). {Lewis and Stohr, modified from 
Huber.) 
passes out of the kidney at the hilum and empties into the inferior vena 
cava. 
The Nerves of the Kidney.-The kidneys are supplied by sympathetic 
nerve fibers. The pre-ganglionic fibers arise from the lower thoracic segments 
of the spinal cord, and pass into the small splanchnic nerves to terminate around 
the cells of the celiac and renal ganglia. From these ganglia, post-ganglionic 
fibers arise that accompany the blood vessels into the interior of the organ. 256 
EXCRETION 
These fibers are vasoconstrictor and vasodilatator in function. Secretory 
fibers have, as yet, not been successfully demonstrated. 
Composition of the Urine.-The urine is a clear yellow or amber-colored 
fluid, having an aromatic odor, and a specific gravity of from 1.016 and 1.020. 
Owing to the presence of mucus, it frothes when shaken. The normal pigment 
is termed urochrome; it is derived from bile pigments. 
The reaction of urine is usually acid to litmus and phenolphthalein. The 
acidity of the urine is due to the presence of acid salts of sulphuric and phospho- 
ric acids and other acid radicals. These acid salts are derived from the sulphur 
of proteins and the phosphorus of lecithin. The acidity is, therefore, largely 
related to the presence of meat in the diet. On a diet consisting mainly of 
vegetables and fruits the urine may become alkaline in reaction, owing to the 
preponderance of alkaline bases in such a diet. The fruit acids, as tartaric, 
citric and malic acids, are oxidized in the body to carbon dioxide which combines 
with bases to form alkaline carbonates; these carbonates pass into the urine 
and diminish its acidity, or render it alkaline. 
The quantity of urine eliminated daily varies from 1200 to 1700 cc. This 
quantity is influenced by any factor affecting the water content of the tissues. 
The ingestion of large quantities of water, or a diminution in the activity of 
the skin are accompanied by an increased excretion of urine. A small intake 
of water, excessive perspiration, or diarrhea diminish the amount of urine 
formed. The greater portion of the urine is excreted during the day; this is 
probably related to muscular activity and the more active circulation of the 
waking hours. 
Chemical Composition.-The composition of the urine varies from time to 
time in accordance with the nature of the food and the metabolism of the tissues. 
The following table gives its average composition: 
Water 1500.00 cc. 
Total solids 72.00 grams 
Urea 33.18 grams 
Uric acid (urates) 0.55 grams 
Hippuric acid (hippurates) 0.40 grams 
Creatinin, xanthin, hypoxanthin, guanin, ammonium salts, pigments, etc n . 21 grams 
Inorganic salts: sodium and potassium sulphates, phosphates and chlorides; 
magnesium and calcium phosphates 27.00 grams 
Organic salts: lactates, acetates, formates in small amounts. 
Gases: nitrogen and carbon dioxide. 
The urine contains nearly the whole of the end-products of protein meta- 
bolism. The origin of urea and uric acid has been discussed elsewhere (see 
page 240). Hippuric acid is formed within the kidneys by a synthesis of 
benzoic acid with glycin. By this means the benzoic acid found in asparagus, 
cranberries, plums, etc. is rendered innocuous. 
The urine usually contains a small amount of indican derived from the indol 
produced during the putrefaction of proteins in the intestine (see page 221). 
Delicate chemical tests have revealed the presence in normal urine of traces 
of suga? and albumin. When these substances appear in the urine in readily ESSENTIALS OF PHYSIOLOGY 
257 
detectable amounts, they must be regarded as evidence of some functional 
disturbance or of disease. As stated elsewhere, the ingestion in excess of certain 
carbohydrates will give rise to an alimentary glycosuria. This condition is of a 
temporary nature in contradistinction to the glycosuria of a well-defined case of 
diabetes. Similarly, severe muscular exercise may cause the temporary appear- 
ance of albumin in the urine. Albuminuria, on the other hand, occurs as a sign 
of disease in various forms of nephritis and of cardiac affections. 
The sodium chloride is derived from the food and varies in amount with that 
of the diet. The sulphates and phosphates, as previously mentioned, are 
derived from proteins and lecithin during their metabolism. 
The Formation of Urine.-Various theories have been presented to account 
for the formation of urine. A theory elaborated by Ludwig considers the 
process to be purely physical. In this theory, Bowman's capsule is regarded as 
a filter through which all the constituents of the urine, in a highly dilute state, 
are made to pass owing to the difference in pressure between the blood in the 
glomerulus and the interior of Bowman's capsule. To account for the normal 
concentration of urine Ludwig assumed that a portion of the water diffused 
through the epithelium lining the tubules as the dilute urine flowed past them. 
The absorbed water, he supposed, was then returned to the blood. In support 
of this theory many experiments have been made to demonstrate that the 
amount of urine excreted varies with the height of the arterial pressure. 
On the basis of certain histological features of the kidney, Bowman 
suggested that the formation of urine is the result of two different forms of 
activity. He conceived of the capsule as an apparatus for the filtration of water 
and inorganic salts only. The nitrogenous material, such as urea, uric acid, 
etc., he regarded as being excreted by the epithelium lining the tubules. The 
nitrogenous material was then washed down and dissolved by the water and 
inorganic salts filtered through the capsule. A number of ingenious experiments 
have been performed, chiefly by Heidenhain, that have lent considerable 
support to this theory. Heidenhain, however, believes that the entire process, 
including the passage of water and inorganic salts through Bowman's capsule, is 
one of secretion, influenced, however, by variations in blood pressure and 
velocity. 
According to a recent theory of Cushny based on numerous experiments, 
Bowman's capsule permits of the filtration of all the substances found in blood 
plasma, except the proteins. As this fluid flows through the tubules, the sub- 
stances useful to the. body, such as dextrose, amino-acids, chlorides, etc., are 
absorbed by the epithelium and returned to the blood. The useful material 
constitutes what Cushny calls threshold substances; this material is entirely 
absorbed unless it exceeds a certain threshold level, whereupon the excess remains 
in the urine. The remaining material, such as urea, creatinin, etc., constitutes 
the no-threshold substances; these are not absorbed, and are therefore eliminated 
no matter what their amount in the blood plasma may be. 
The Influence of Blood Pressure on the Amount of Urine Formed.-As 
suggested in a preceding paragraph, the amount of the filtrate passing through 258 
EXCRETION 
Bowman's capsule must vary directly with the difference of pressure between the 
glomerulus and the interior of the capsule. A rise in the pressure of the blood 
flowing through the glomerulus will increase this difference and, therefore, 
increase the amount of the filtrate. There is at the same time, normally, an 
increase in the velocity of the blood, so that there is a constant renewal of 
material to be filtered. 
The pressure within the glomerulus is higher than in capillaries elsewhere, 
partly because the efferent vessel of the glomerulus has a lesser caliber than the 
afferent vessel, and partly because the short renal artery springs directly from 
the aorta. The pressure of the blood in the glomerulus may be increased by: 
(i) A dilatation of the afferent vessel, provided the general blood pressure 
remains constant. The glomerulus pressure will become greater, if at the same 
time there is a constriction of the efferent vessel. 
(2) A rise in the general arterial pressure, provided there is no constriction 
of the afferent vessels of the kidneys. The rise in general blood pressure may be 
the result of an increase in the force and rate of the heart's action, or an increase 
in the contraction of the arterioles of a large vascular area. 
The converse conditions will diminish the height of the blood pressure with- 
in the glomerulus and cause a decrease in the amount of urine formed. 
The Influence of the Nerve System on Urine Formation.-The kidneys are 
supplied by vaso-constrictor and vaso-dilaiator nerves. Section of the vaso-con- 
strictor nerves causes a dilatation of the branches of the renal artery and an 
increased flow of urine. Stimulation of these nerves causes these branches to 
contract, thus bringing about a cessation of urine formation. Stimulation of the 
vaso-dilatator fibers would give rise to a dilatation of the branches of the renal 
artery and an increased formation of urine. 
The vaso-motor center for the renal vessels is probably a part of the general 
vaso-motor center situated in the medulla oblongata. Mechanical stimulation 
of the area of the medulla containing this portion of the vaso-motor center is 
followed by a notable increase in the flow of a urine free of sugar. 
Division of the spinal cord in the cervical region causes a dilatation of the 
arterioles of the entire body and a marked fall of arterial pressure. The arter- 
ial pressure is so low that, in spite of the dilatation of the renal arterioles, the 
velocity of the blood through them decreases and urine ceases to be formed. 
Micturition.-As the urine is formed, it passes into the pelvis of the ureter 
and flows along the ureter into the bladder where it accumulates. The trans- 
ference of the urine along the ureter is accomplished chiefly by rhythmical waves 
of contraction occurring at intervals of a few seconds. 
The bladder is a hollow organ capable, when fully distended, of holding 
from 600 to 800 cc. (Fig. 137). Its walls consist of four coats: viz., serous, muscle, 
areolar, and mucous. The mucous coat is lined by transitional epithelium and 
is loosely attached by areolar tissue to the underlying muscle coat, except in a 
triangular space termed the trigonum vesicae bounded by the openings of the 
ureters above and that of the urethra below. The muscle coat is generally 
described as composed of three layers of smooth muscle fibers: (1) an external ESSENTIALS OF PHYSIOLOGY 
259 
layer whose fibers are arranged longitudinally, sometimes called the detrusor 
urinae muscle; (2) a middle layer whose fibers are arranged circularly; and (3) 
an incomplete internal layer arranged more or less longitudinally. Behind 
the opening of the urethra the circularly arranged fibers are more densely packed 
and form a sphincter called the sphincter vesicae. The contraction of this 
sphincter is the most important factor for the control of the bladder. The 
wall of the urethra is, moreover, surrounded by circular muscle fibers reinforced, 
near the neck of the bladder, by voluntary muscle fibers constituting the 
sphincter urethrae muscle. 
Vertex vesicas urinariae 
Peritoneum parietale 
Vesica urinaria 
Orificium urethrae 
\ internum' 
Ductus ejaculatorius 
Symphysi 
cesium 
pubis 
Ampulla, 
ductus deferentis 
Lig. suspensor^ 
ium penis 
, Intestinum 
rectum 
V. dorsalis penis 
Pars prostatica 
' urethrae 
Corpus cavernosum 
urethrae 
Septum penis 
.Prostata 
Utriculus 
prostaticus 
Pars cavernosa 
urethrae 
■Pars analis recti 
'■Anus 
Corona glandi 
'M. sphincter ani externus 
\Glandula bulbourethralis 
, Diaphragms urogenital? 
Pars membra nacea urethrae 
Bulbus urethrae 
'■■M. sphincter ani internus 
Orificium urethrae'' 
xternum 
M. bulbacavernosus 
Tunica vaginalis 
Fig. 137.-Midsagittal section of the male pelvis. (After Sobotta and Spalteholz.) 
Testis 
The Mechanism of Urination.-In the intervals of urination the sphincter 
muscles at the neck of the bladder are in a state of tonic contraction. As 
the urine accumulates'its pressure rises and causes distention of the bladder. 
Urination usually occurs when the intravesical pressure reaches about 150 mm. 
of water; the bladder then contains about 250 cc. of urine. At that time, 
rhythmical contractions of the bladder wall, each lasting about a minute and 
gradually increasing in force, occur. 
The pressure of the urine, or the entrance of a few drops into the first 
part of the urethra, stimulates the endings of afferent nerves. The nerve 
impulses travel to the spinal cord and stimulate two sets of efferent nerves, 260 
EXCRETION 
viz., (i) motor or augmentor nerves that stimulate the muscle wall of the bladder 
(the detrusor) to contraction; and (2) inhibitor nerves that cause a relaxation 
of the sphincter vesicae muscle. As a consequence of this double action the 
urine is expelled from the bladder. 
The emptying of the bladder is aided by a voluntary contraction of the 
abdominal muscles following a deep inspiration and a closure of the glottis. 
The urethra is emptied by voluntary rhythmical contraction of the bulbo- 
cavernosus muscle. 
The afferent nerve fibers supplying the mucous membrane of the bladder 
are contained in the hypogastric and pelvic nerves. The motor or augmentor 
nerve fibers for the detrusor muscle are in the pelvic nerves or nervi erigentes. 
The same nerves contain inhibitor fibers for the sphincter muscles. These 
nerves originate in the sacral portion of the spinal cord and terminate around 
ganglia located on the sides of the bladder. From these ganglia nerve fibers 
pass to the muscles. The inhibitor nerve fibers are in the hypogastric nerves. 
These nerves originate in the inferior mesenteric ganglion and are in physio- 
logical relation to the lumbar segments of the spinal cord through the inferior 
splanchnics. Stimulation of the hypogastric nerves causes a contraction of 
the sphincter muscles and a relaxation of the detrusor muscle. The hypo- 
gastrics are therefore chiefly concerned in the accumulation of urine in the 
bladder, while the pelvic nerves or nervi erigentes are concerned in the emptying 
of the bladder. 
Through a process of education the adult has acquired the power of volun- 
tary control over the evacuation of urine. The tonic contraction of the 
sphincter vesicae may be aided by voluntary contractions of the urethral 
muscles and the reflex contraction of the bladder wall temporarily inhibited. 
As previously stated, the reflex contraction of the bladder wall and the inhibi- 
tion of the sphincter vesicae are usually assisted by voluntary contractions of 
the abdominal muscles. 
Remarks on the Hygiene of the Urinary Apparatus.-In normal individ- 
uals the activity of the kidneys is determined chiefly by changes in the amount 
of blood flowing through the organ. Changes in the blood flow through the 
kidneys may be brought about by variations in the external temperature; the 
quantity of water ingested; the quantity of certain articles-of diet such as 
protein and sugar. In cold weather the constriction of the arterioles of the 
skin is accompanied by a compensatory dilatation of those of the internal organs. 
More blood, therefore, must flow through the kidneys and more urine is formed. 
The converse condition, namely: exposure to high external temperature will 
cause a flushing of the skin, a constriction of the arterioles of internal organs, 
a diminution of blood flow through the kidneys, and a decrease in the amount 
of urine formed. 
A large intake of water, by increasing the volume of blood, will also increase 
the blood flow through the kidneys and the elimination of the excess of water 
in the urine. The ingestion of relatively large amounts of protein and of sugar, 
particularly lactose, by raising the osmotic tension of the blood causes a flow ESSENTIALS OF PHYSIOLOGY 
261 
of water from the tissues into the blood vessels. The result is the same as the 
ingestion of large quantities of water. 
On an average diet the amounts of solids eliminated does not vary greatly. 
The amount of water holding these solids in solution will, however, vary with the 
amount ingested and the amount eliminated by the skin. A sufficient amount 
of water should be drunk to keep the volume of the urine at its average level, 
particularly since certain substances eliminated in the urine are not very 
soluble. 
An increased frequency of urination may be the result of an increased 
sensitiveness of the bladder due to an inflammatory condition of its mucous mem- 
brane or the presence of an irritating substance in the urine, as when highly 
spiced foods have been eaten freely. Excitement may also lead to increased 
frequency of urination owing to the rapidity with which the urine is formed and 
the consequent rapid distention of the bladder. Under such conditions the 
critical rise of intravesical pressure occurs before the average quantity of urine 
has accumulated; hence the frequency with which the urine must be voided. 
When urine ceases to be formed, as may occur in acute inflammation or 
congestion of the kidneys, the condition is called suppression. When the urine 
is formed as usual but cannot be expelled, the condition is called retention. 
Retention of the urine is frequently due to the mechanical obstruction of an 
enlarged prostate or a stricture of the urethra. 
THE SKIN 
The skin forms the external covering of the body and is continuous with 
the mucous membrane of various canals that open on its surface. Its area 
varies with the height and weight of the individual from 1.17 to 1.35 square 
meters. The skin fulfills several important functions: viz., (1) it serves to 
protect the underlying parts from mechanical injury and from infection by micro- 
organisms; (2) it serves as a sense organ for the reception of stimuli arising in the 
external world; (3) it is an excretory organ; and (4) it is the chief organ concerned 
in the regulation of body temperature. 
Structure of the Skin.-The skin consists of two layers: a superficial layer, 
the epidermis or cuticle; and a deep layer, the corium or cutis ver a (Fig. 138). 
The epidermis or cuticle is the non-vascular layer and is made up of strati- 
fied epithelium. It is subdivided into two portions: the superficial portion, 
stratum corneum, or ]}orny layer, which separates after blistering from the deep, 
soft portion or stratum mucosum called, also the Malpighian layer. The 
Malpighian layer contains pigment granules which give a more or less dark 
color to the skin. 
The corium or cutis vera consists of areolar connective tissue and elastic 
fibers. It is subdivided into two layers: the superficial layer or stratum pap- 
illare, the surface of which extends in finger-like projections, termed papillae, 
under the epidermis; and the stratum reticulare which binds the skin to the 
underlying structures. The reticulate layer supports blood vessels, nerves, 262 
EXCRETION 
lymphatics, hair follicles, and sweat glands. The papillae contain capillary 
loops and nerve terminals. 
Appendages of the Skin.-The appendages of the skin are the sudoriferous 
or sweat glands, the sebaceous glands, the nails, and the hair. 
The appendage of greatest physiological significance consists of the sweat 
glands, since they play an important part in the regulation of body temperature 
and may, on occasion, eliminate appreciable quantities of waste material. 
The Sweat Glands.-The sudoriferous or sweat glands are tubular structures, 
the deeper or secretory part of which is coiled in a little ball in the subcutaneous 
tissue or deeper part of the corium. The ducts pass through the corium and epi- 
Fig. 138.-Section perpendicularly through the healthy skin, a, epidermis or scarfskin; b, 
rete mucosum, or rete malpighii; c, papillary layer; d, derma, corium, or true skin; e, panniculus 
adiposus, or fatty tissue;/, g, h, sweat-gland and duct; i, k, hair, with its follicle and papilla; I, seba- 
ceous gland. 
dermis to open on the surface by a funnel-shaped orifice or pore. Each sweat 
gland is surrounded by a capillary network and is supplied by sympathetic 
nerves. 
The Perspiration.-The perspiration or sweat is a clear colorless fluid, 
having a specific gravity varying from 1.003 t° i-oo6. When first formed it is 
acid in reaction, but after profuse sweating may become neutral or alkaline to 
litmus. It has a saline taste owing to the presence of sodium chloride which is 
found to the extent of 0.3 to 0.5 per cent. Aside from sodium chloride it con- 
tains phosphates, small quantities of urea, certain volatile organic acids such as 
acetic, propionic, butyric and caproic acids, and carbon dioxide. 
The amount of perspiration varies considerably with the external tempera- 
ture, but has been estimated at from 700 to 1000 cc. A close relationship exists ESSENTIALS OF PHYSIOLOGY 
263 
between the activity of the skin and that of the kidneys. Free perspiration is 
usually accompanied by diminution of the amount of urine. In certain 
inflammatory conditions of the kidneys when little or no urine is formed the per- 
centage of urea excreted by the sweat rises. In such cases enough urea may be 
excreted by the sweat that upon evaporation crystals of urea may be seen upon 
the skin. 
The Sweat Nerves.-The sweat nerves are a part of the autonomic nerve 
system. The preganglionic fibers arise from the spinal cord between the second 
thoracic and the third or fourth lumbar spinal segments. These fibers terminate 
around the cells of the sympathetic ganglia from which postganglionic fibers 
arise that pass into the spinal nerves and are distributed to the sweat 
glands throughout the body. 
It is probable that a general center, controlling the activity of the sweat 
glands through the intermediation of the sweat nerves just mentioned, is located 
in the medulla oblongata. The general sweat center of the medulla and the local 
sweat centers of the spinal cord may be stimulated reflexly, by a rise of body 
temperature, and a rise in the percentage of carbon dioxide in the blood. The 
general sweat center may also be stimulated as a concomitant of certain emo- 
tional disturbances. 
The Sebaceous Glands.-The sebaceous glands are simple and compound 
alveolar glands located in all situations where hair is found. There are from 
one to four glands associated with each hair, and their ducts open into the 
upper part of the hair follicle. They consist of polyhedral cells resting on a 
basement membrane. These cells contain drops of an oily material called 
sebum. This oily material is liberated by the breaking down of the super- 
ficial cells, and is discharged into the hair follicle. The emptying of the 
sebaceous glands is aided by the contraction of strands of smooth muscle 
fibers termed arrectores pilorum muscles. These muscles are found in the true 
skin on the side toward which the hair leans; their contraction makes the hair 
stand erect and at the same time compresses the sebaceous glands. The 
puckered condition of the skin, called goose-skin, is the result of their contraction. 
The mammary glands are modified and highly developed sebaceous glands. 
The Hairs.-Hairs of various lengths and thicknesses are found on various 
parts of the body. A hair consists of a root and a shaft. The root is embedded 
in a tubular depression of the skin, called the hair follicle. The follicle is made 
up of a sheath of connective tissue and two root sheaths composed of epidermic 
cells. The bottom of the hair follicle is formed by a conical projection of the 
corium-the papilla--which contains blood vessels and nerves, and is capped 
by the bulbous end of the hair root. 
The shaft of the hair consists from without inwards of three layers: the 
cuticle, cortex, and medulla. The cuticle is composed of a layer of imbricated 
scales. The cortex is made up of longitudinally arranged fusiform cells contain- 
ing pigment and-in white hair-air spaces. The medulla forms the core of 
the hair and consists of polyhedral cells containing pigment, air spaces, and fat 
granules. 264 
EXCRETION 
Straight hairs have an oval outline while curly hairs are flat on cross section. 
The Nails.-The nails are highly developed epidermal structures and con- 
sist of a root embedded in the skin, and a body or exposed part resting on the 
corium. The portion of the corium under the body is called the nail-bed, 
while that under the root is termed the matrix. The corium under the nail 
is very vascular and highly sensitive, and gives the pink, color.to the nail. Near 
the root, however, there is a small semilunar area less vascular than the rest 
of the body, and termed the lunula. 
The nail is generated at the matrix, and destruction of this structure is 
followed by the loss of the nail. CHAPTER XXXII 
PHARMACODYNAMICS OF EXCRETION 
It will only be necessary to discuss the pharmacodynamics of the renal 
function and of the secretion of sweat, since that of the lungs and the liver as 
organs of excretion has already been mentioned in preceding chapters. 
DIURETICS 
A diuretic is a remedy which tends to increase the flow of urine. 
Diuresis is an increase in the quantity of urine. One of the first conditions 
necessary for the formation and excretion of urine is the presence of available 
water in the blood. Since the blood tenaciously retains its normal water 
content, it is therefore necessary that there be a definite, though slight, excess 
of water in the blood to be drawn upon, i. e., a temporary hydremia, in order 
that diuresis may take place. 
From the physiological discussion of the urinary apparatus, the urine, and 
the formation of urine, it is evident that diuresis may be brought about by 
(i) changes in the general circulation; (2) stimulation of the kidney cells; (3) 
salt action. 
(1) Diuretics Which Act by Changes in the General Circulation.-The most 
important members of this group are Digitalis and its allies, Strophanthus, 
and Squill. These drugs act as diuretics only in cases of failing circulation 
which are attended by an accumulation of fluid in the tissue spaces and serous 
cavities of the body, i. e., edema and dropsy. 
Since the members of this group produce little diuresis in normal animals, 
in cardiac diseases without edema or dropsy, and in purely nephritic edemas, the 
diuretic effect cannot be due to any direct action on the kidney. It must 
therefore be due mainly to the improvement in the circulation effected by these 
drugs (see pages 155, 156). The accumulated tissue fluid passes into the blood 
creating a pronounced condition of hydremia, which together with the increase 
in the blood flow through the kidney results in diuresis. The reported dilatator 
effect of Digitalis on the renal vessels has been mentioned on page 160. In 
normal individuals and in cardiac conditions unattended by dropsy or edema 
the Digitalis bodies fail to produce a diuresis because the kidney circulation is 
adequate for the secretion of all the available body fluid; while in nephritis 
they fail because the anuria is not due to defective circulation. 
(2) Diuretics Which Act by Stimulation of the Kidney Cells.-The drugs 
in this group may be divided into two subgroups as follows: 
(a) Nonirritant Stimulant Diuretics.-Caffeine, Theophylline and Theo- 
bromine are the principal members of this subgroup. Experimentation has 
265 266 
PHARMACODYNAMICS OF EXCRETION 
shown that Caffeine is strongly diuretic, producing diuresis in the isolated 
kidney as well as in the intact animal. Neither do changes in the blood pressure 
in the intact animal affect the diuretic action of the drug. It is evident there- 
fore that Caffeine diuresis is not due to action on the general circulation. 
The diuretic action of Caffeine is probably to an alteration in the per- 
meability of the glomerular capsule which permits more rapid filtration 
through it. The rapid flow of this fluid through the tubule reduces reabsorp- 
tion, so that more of the glomerular filtrate reaches the ureter than usual. 
Theophylline (or Theocine), Theobromine, and Theobromine Sodio-salicylate 
("Diuretin") are more powerful and prompt diuretics than Caffeine, and 
do not possess the marked central effects of Caffeine (pages 92, 93). 
(b) Irritant Stimulant Diuretics.-Only a few of the numerous members of 
this subgroup need be mentioned: Oils of Turpentine, Juniper and Sandalwood, 
Balsam of Copaiba, Cubeb, Buchu, Scoparius ("Broom"), Asparagus, and 
Triticum, and absorbable metallic salts, especially Calomel in large dosage. 
Alcohol, Hexamethylenamine, and the Nitrates are mildly irritant. In over- 
dosage these drugs may produce inflammation of the cells of the kidney 
tubules. Because of their irritating properties they are contraindicated in kidney 
disease. 
(3) Diuretics Which Act by Salt Action.-Water, salts, sugars, urea, etc. 
produce diuresis: (1) by lessening the viscidity of the blood, thereby increasing 
its filtrability and raising the glomerular pressure; (2) by shrinking the kidney 
cells; (3) by decreasing or preventing tubular absorption; and (4) possibly by 
slightly stimulating the activity of the kidney cells. 
Water.-Drinking water is a hypotonic solution and is practically unab- 
sorbed by the stomach. However, it abstracts salts from the mucus, food, and 
superficial cells of the alimentary tract, or takes up the Sodium Chloride formed 
by the neutralization in the duodenum of the Hydrochloric Acid of the gastric 
juice. In this way the water becomes a saline solution and is absorbed instead 
of passing on into the rectum. The drinking of a large quantity of water does 
not ordinarily result in the elimination of the excess of water in the feces. 
Instead, for the reason just mentioned, the water is absorbed and produces a 
diuresis. Waier in large quaniities is diuretic, and as a consequence of its own 
elimination, assists in the removal of certain soluble substances, particularly 
urea, sulphates, and phosphates. 
Carbonated water, lemonade and infusions (teas) are usually more palatable, 
and, because of the presence of the added substances, enhance the diuretic 
action of the water. 
Milk is another efficient diuretic, its action depending largely upon its water 
content, and partly upon its sugar (lactose). 
Inorganic Salts, such as Sodium Bicarbonate, Sodium and Potassium Iodides 
and Nitrates, are also effective diuretics. Organic Salts such as Sodium and 
Potassium Citrates and Acetates, which are oxidized to bicarbonates in the body, 
are quite effective and are possibly the most commonly used agents in this 
group. PHARMACODYNAMICS 
267 
Therapeutic applications of diuretics include: (1) the removal of dropsy and 
edema i. e., the removal of liquid from the body; (2) the promotion of the elimi- 
nation of toxins, whether of metabolic or bacterial origin; and (3) the dilution of 
the urine so as to render it less irritating in the urinary passages, to dilute 
irritating poisons which are eliminated in the urine, or to prevent the formation of 
urinary calculi ("stones"). 
DIAPHORETICS 
Remedies which induce profuse sweating (diaphoresis) are termed diaphor- 
etics, sudorifics or hydrotics. Diaphoresis may be produced by methods of 
raising and maintaining the rise of body heat, or by drugs. 
(1) Methods of Raising and Maintaining the rise of Body Heat, 
include: 
(a) Increasing heat production by exercise. 
(b) Inhibiting or preventing heat loss by means of extra bed clothes, blankets, 
or heavy sweaters. 
(c) The use of artificial heat, either internally by means of hot drinks, or 
externally by means of hot baths, vapor baths, hot water bottles, etc. 
Water, in addition to being diuretic when taken internally in large quantity, 
is also diaphoretic, especially if taken in the form of large drinks of hot lemonade, 
etc. Cold Water is primarily diuretic, but if large drinks of it are taken along 
with such measures as exercise, hot baths, etc., a copious diaphoresis results. 
The diaphoresis obtained by these methods is the result of reflex and direct 
stimulation of the sweat centers. 
(2) Drugs frequently used to induce diaphoresis include: (a) Drugs which 
peripherally stimulate secretory structures, such as Pilocarpine which has been 
discussed on page in. 
(b) Drugs which stimulate the sweat centers, such as Camphor and Ammonium 
Acetate. 
(c) Drugs which dilate the cutaneous arterioles such as counterirritants like 
Mustard ("mustard foot-bath") and Alcohol (page 27); and the Salicylates 
and the Coal-tar Antipyretics (page 251). 
Diaphoresis is employed therapeutically principally to remove water from the 
body, as in edema and dropsy; to overcome chill and cold by reestablishing normal 
cutaneous circulation and thereby relieving internal congestion; to assist the 
kidneys in the removal of toxins by promoting their elimination in the sweat, 
thus relieving kidneys which are possibly inflamed or overtaxed; and to lessen 
obesity as by exercise in heavy woolen clothing, hot baths (Turkish), and restric- 
tion of liquids in the diet. 
ANHYDROTICS 
Remedies which tend to reduce or suppress sweating are called anhydrotics. 
For local sweating of the hands, feet, etc., Alcohol, Spirit of Camphor, and 
astringent solutions, such as a solution of Alum or Aluminium Chloride, are 
commonly used. Boric Acid and Salicylic Acid, separately or combined, in the 
form of a dusting powder are used also. 268 
PHARMACODYNAMICS OF EXCRETION 
The principal use of general anhydrotics is in the night sweats of tuberculosis. 
Atropine is the most powerful anhydrotic. Its mechanism of action has been 
discussed on page no. However, the drying effects on the saliva and mucus and 
the dilatation of the pupil produced by the drug limit its usefulness. 
Agaricin or Agaric Acid (obtained from the fungus, Polyporous albus) is 
anhydrotic probably because it strongly depresses the myoneural junctions of the 
secretory nerve endings of the sweat glands. Although the drug has not the 
undesirable side-actions of Atropine, its use is limited because the effects pro- 
duced are not constant and prompt. CHAPTER XXXIII 
THE INTERNAL SECRETIONS 
The glandular organs so far discussed, all possess a duct through which 
the material elaborated by the gland cells is conveyed to the surface of a mucous 
membrane or the skin. The glands whose secretions are poured on the internal 
or external surfaces of the body, are called glands of external secretion. Of 
such nature are the glands lining or communicating with the alimentary canal, 
and the glands of the skin. 
There are, in various situations, other glandular organs possessing no ducts, 
whose secretions pass either directly or indirectly into the blood stream to be 
distributed throughout the body. The secretions elaborated by these organs, 
being poured into the true interior of the body, are called internal secretions. 
A number, at least, of the internal secretions have a drug-like action: 
for this reason it has been suggested that they be called autacoids. Some 
autacoids have a stimulating action; these are termed hormones. Other 
autacoids have an inhibitory action and are called chalones. The internal 
secretions are, furthermore, classified into a group influencing the processes 
of growth: these are designated as morphogenetic autacoids. 
The organs engaged in the formation of internal secretions are termed 
ductless glands, glands of internal secretion, or endocrine glands. Some of these 
organs have no other function, while others, besides elaborating an internal 
secretion, produce also an external secretion. 
The endocrine glands are the thyroid, the para-thyroids, the adrenals, the 
pituitary body or hypophysis cerebri, the thymus, the pancreas, the testicles, and 
the ovaries. 
THE THYROID 
The thyroid gland consists of two lobes, one on each side of the upper 
part of the trachea. These lobes are united by a narrow band of thyroid tissue 
termed the isthmus (Fig. 139). A microscopic examination of the organ shows 
that it is composed of closed sacs, or vesicles, of various sizes. Each vesicle 
consists of a single layer of more or less cubical cells and is filled with a clear, 
viscid fluid called colloid substance (Fig. 140). The vesicles are held by connec- 
tive tissue which likewise gives support to numerous blood and lymphatic 
vessels and to nerves. The lymph vessels have occasionally been found to 
contain colloid material. 
The Effect of Absence, or Disease of the Thyroid.-The importance of the 
thyroid is best understood by a reference to the effects that accompany (1) its 
congenital absence or atrophy in early life; (2) its atrophy in adult life; and 
(3) its hypertrophy with excessive activity. 
269 THE INTERNAL SECRETIONS 
270 
When the thyroid gland is absent at birth, or when it atrophies in early 
youth, a condition supervenes to which the name cretinism is given (Fig. 141). 
Fig. 139.-View of thyroid body. 1, thyroid 
isthmus; 2, median portion of crico-thyroid 
membrane; 3, crico-thyroid muscle; 4, lateral 
lobe of thyroid body. {After Morris.) 
Fig. 140.-A lobule from a thin section of the thyroid 
gland of adult man. X 250. (Stohr.) 
Fig. 141.-Cretin before (A) and after (B) treatment with sheep's thyroid. (Nicholson.) 
The growth of the skeleton is greatly delayed, particularly as regards the 
length of the long bones. The skin appears swollen and yellow in color, the 
abdomen is enlarged, and the root of the nose depressed. There is also a lack ESSENTIALS OF PHYSIOLOGY 
271 
of development of the muscular and central nerve systems. The arrest of physi- 
cal and mental development results in the formation of a dwarf of low mental 
capacity, idiocy being, in fact, common in this condition. 
When the thyroid gland atrophies or undergoes degeneration after adult 
development has been reached, the disease is known as myxedema. In this 
case, the individual increases markedly in weight, owing to the deposition 
of fat in the subcutaneous tissues. The skin becomes thick and dry and 
the hair falls out. There is a decline in the sexual function, and various 
forms of mental disturbances occur. There is a considerable reduction in the 
amount of oxygen absorbed and of carbon dioxide exhaled-an indication of a 
Fig. 142.-Exophthalmic goiter. The patient shows a goiter of moderate size; great exoph- 
thalmos, smooth forehead, and abnormal expression. (From MacCallum, Text-book of Path- 
ology, W. B. Saunders Co., Publishers.) 
decrease in the rate of the oxidative processes of the tissues. The deposition 
of fat is doubtless related to this decline in the rate of metabolism. 
The same phenomena occur following the surgical removal of the thyroid 
alone. In this case the condition is called cachexia strumipriva or operative 
myxedema. 
The absence or deficiency of thyroid function exhibited in cretinism and 
myxedema may be termed hypothyroidism. 
The Effects of Hyperactivity of the Thyroid.-In excessive activity of the 
thyroid gland phenomena occur that are opposite to those just described. 
There is marked nervous excitability, increased frequency of the heart's action, 
tremor of the limbs, protrusion of the eyeballs, flushing of the skin, increased 
sweating, and wasting of the body. There is usually an enlargement of the 
thyroid gland with an increased vascular supply. The consumption of oxygen 
and excretion of carbon dioxide and nitrogen are greatly increased. 272 
THE INTERNAL SECRETIONS 
Since similar phenomena follow the prolonged administration of the 
dried powdered gland or of its active principles, the condition may be termed 
hyperthyroidism. The name of exophthalmic goiter is also given to this affec- 
tion because the most evident and striking signs of the disease are, usually, 
the protruding eyes (exophthalmos) and the enlargement of the thyroid (goiter) 
(Fig. 142). 
The Hormone of the Thyroid.-The active substance elaborated by the 
thyroid gland has recently been isolated in a pure crystalline form. It is an 
indol-compound containing about 60 per cent of iodine, and is called thyroxin. 
This substance is probably combined with the protein of the colloid material 
to form iodo-thyro-globulin. 
THE PARATHYROIDS 
The parathyroid glands are small bodies of an ovoid shape, 5 to 7 mm. in 
length (or an average of in.). There are usually four parathyroids situated 
Fig. 143.-Section of a human parathyroid gland. (Huber.) 
on the posterior aspect of the thyroid gland and more or less embedded in 
its substance. 
These small bodies consist of masses of epithelial cells containing granules 
(Fig. 143). Numerous sinus-like capillaries are in direct relation with the 
cells. Many nerve fibers pass to the blood vessels and the epithelial cells. 
The Effects of Removal of the Parathyroids (Parathyroidectomy).-The 
removal of all parathyroids is usually fatal, especially in carnivora. For a 
day or two after the operation the animal refuses food and loses weight. Fibril- 
lary contractions of the muscles and tremors occur which later pass into muscular 
spasms and clonic contractions. The frequency of the heart increases, and 
there is profuse salivation and diarrhea. In dogs there occurs, in some cases, 
a spasm of the adductor muscles of the larynx with the result that the respira- 
tions are noisy and high pitched (laryngismus stridulus). These symptoms 
occur more readily and with greater intensity on a meat diet than on one of 
vegetable or milk. ESSENTIALS OF PHYSIOLOGY 
273 
Similar phenomena occur in man following the surgical removal of the 
parathyroids or their destruction by disease. The condition is called tetany. 
The tonic spasm of the flexor muscles gives to the hands and feet a character- 
istic attitude. 
The cause of the symptoms of tetany has been ascribed to an intoxication 
by guanidine (a derivative of the amino-acid arginine, and of creatine). The 
injection of this substance into normal animals reproduces closely the symptoms 
that follow parathyroidectomy. It would appear from these experiments 
that the parathyroids are concerned in controlling the metabolism of guanidine. 
There is also a great diminution in the amount of calcium in the blood of chil- 
dren suffering from tetany. 
The true function of the parathyroids cannot be said to have been fully 
determined. 
THE ADRENAL GLANDS 
The adrenal glands, called also suprarenal glands and suprarenal bodies 
or capsules, are two pyramidal-shaped structures, a right and a left, situated 
each upon the upper pole of the corresponding kidneys. Their greatest 
diameter is about 5 cm. (about 2 in.). 
A microscopic examination of the adrenal shows that it is composed of 
two parts, an external part termed the cortex, enclosing the central part known 
as the medulla (Fig. 144). 
The cortex consists of epithelial cells arranged in solid columns and is 
subdivided into three zones which, from without inward, are: the zona glomeru- 
losa, zona fasciculata, and zona reticularis. Between the columns of cells are 
found large sinus-like capillaries. The cells contain many lipoid granules. 
The medulla consists of polygonal cells forming a meshwork around large 
blood sinuses. The blood flows through the capillaries of the cortex into the 
sinuses of the medulla. The cells of the medulla are granular and pigmented, 
and contain a material which stains brown with salts of chromic acid; for this 
reason this material is called chromaffin material. 
The adrenal is richly supplied with nerve fibers derived from the semilunar 
ganglia and contains some nerve cells in the medulla. 
The cortex and medulla have different embryonic origins, the cortex being 
developed from the genital ridge, while the medulla is derived from the primi- 
tive sympathetic system. 
The Effects of Removal of the Adrenals.-The removal of the adrenals in 
mammals results invariably in the death of the animal within a few days. The 
first symptoms develop within 24 or 48 hours following the operation. These 
symptoms consist of muscular weakness, which becomes rapidly worse; of a 
feeble heart's action, dyspnea and a fall of body temperature. The blood 
pressure declines to a very low level, and the animal dies in a few days after 
a period of coma or following convulsions. 
The Effects of Disease of the Adrenals in Man.-A destruction of the 
adrenals, usually due to tuberculosis, occurs occasionally in man. The phenom- 274 
THE INTERNAL SECRETIONS 
ena that follow resemble closely those due to the removal of these organs in 
animals. There is great muscular weakness, a weak heart's action, a low blood 
Capsule 
Zona glomerulosa 
Zona fasciculata 
Zona reticularis 
Medulla 
Fig. 144.-Section through cortex and medulla of the suprarenal body of adult man. X 200. 
{Schaper.') 
pressure, subnormal temperature, a bronzing of the skin and mucous membranes, 
and gastro-intestinal disturbances. This disease is known as Addison's 
disease; it is invariably fatal. ESSENTIALS OF PHYSIOLOGY 
275 
Experiments and postmortem studies indicate that, of the two parts of 
the adrenals, the cortex is the part essential to life. 
Aside from this observation, little is known of the function of the cortex. 
Clinical studies have shown, however, that a hypertrophy of the cortex is 
accompanied by sexual precocity. Children with this abnormal growth of 
the cortex acquire the physical appearance of mature individuals. 
The Internal Secretion of the Medulla.-Aqueous extracts prepared from 
the adrenal contain an active principle, which has been isolated in a chemically 
pure state, termed epinephrine or adrenalin. This substance is produced 
in the cells of the medulla only. It is the material which stains brown with a 
chromate solution. 
The injection of a weak solution of epinephrine into a vein causes a notable 
rise in arterial pressure and a slowing of the heart beat. If the vagus nerves 
are cut before the solution is injected, the frequency and force of the heart 
beats are increased so that the blood pressure rises to a great height. The 
marked rise of blood pressure is due chiefly to the constriction of the arterioles of 
the b ody. The general action of epinephrine is similar to the effects of stimulation 
of all parts of the sympathetic nerve system. The seat of action of epinephrine 
is upon the myoneural junction or receptive substance lying between the nerve 
ending and the muscle substance proper. Since its action is one of stimulation, 
its effects will vary in accordance with the action of the sympathetic nerves 
distributed to the organ involved. Thus, epinephrine will cause a constriction 
of the arterioles; a dilatation of the bronchioles; an inhibition of the intestine. 
The injection of epinephrine also gives rise to a glycosuria owing to the rapid 
transformation of the glycogen of the liver into dextrose. 
The secretion of epinephrine is under the control of the central nerve system 
through the splanchnic nerves. Experiments performed by Cannon would 
indicate that such emotional disturbances as fright and anger lead to an out- 
pouring of epinephrine into the blood with the apparent object of energizing 
the individual to meet the emergency. While his results have been contro- 
verted, a new series of experiments have reaffirmed and strengthened them. 
THE PITUITARY BODY 
The pituitary body or hypophysis cerebri is a small organ situated under the 
base of the brain, in a bony depression of the cranial floor. Its greatest dia- 
meter is about 14 mm.'(about a half inch), and it weighs about 0.5 gm. (about 
7^ gr.). It consists of two lobes derived from different embryonic structures 
(Fig. 145). The anterior lobe is developed from an upward growth of the epi- 
thelial lining of the primitive mouth; the posterior lobe, from a downward growth 
from the floor of the third ventricle of the brain. The cavity of the growth 
derived from the primitive mouth persists as a cleft separating the anterior 
from the posterior lobes. The epithelium of the portion derived from the primi- 
tive mouth becomes differentiated into two parts, viz., a pars anterior-the ante- 276 
THE INTERNAL SECRETIONS 
rior lobe proper, and a pars intermedia, situated posterior to the cleft and covering 
the tissue derived from the floor of the third ventricle termed pars nervosa. 
The pars anterior is composed of solid rows of cells between which numerous 
sinus-like capillaries are found. Some of the cells contain oxyphil, others baso- 
phil granules. The pars intermedia has the same general structure but the 
granules of the cells are finer and some of the cells undergo a hyaline or colloid 
change. The pars nervosa consists of neuroglia tissue. Degenerated cells and 
colloid material from the pars intermedia are found between the cells and fibers 
of the pars nervosa and may be traced along the stalk of the organ to the cavity 
of the third ventricle. This hyaline or colloid material constitutes the secre- 
tion of the pars intermedia and its discharge takes place, apparently, into the 
Fig. 145.-Median sagittal section through pituitary of monkey; semidiagrammatic. a, optic 
chiasma; b, third ventricle; c, g, pars intermedia; d, epithelium of pars intermedia extending round 
neck of pars nervosa; e, pars glandularis seu epithelialis; f, intraglandular cleft, lying between pars 
glandularis (e) and pars intermedia (g); h, pars nervosa. {Herring.) 
cerebro-spinal fluid of the third ventricle from which it gains the general 
circulation. 
Function of the Anterior Lobe.-1Complete removal of the anterior lobe alone 
is followed, within a few days, by the death of the animal. This is preceded 
by a gradually oncoming weakness, muscular tremors, a low frequency of 
respiration and of the heart's action, a subnormal temperature, and finally 
coma just before death. The removal of the posterior lobe does not result 
fatally, so that of the entire pituitary body the anterior lobe is the part essential 
to life. 
When only a portion of the anterior lobe of the pituitary body is removed 
from young animals, their growth no longer proceeds normally. The epiphyses 
do not become ossified; the animal remains small but increases in weight owing ESSENTIALS OF PHYSIOLOGY 
277 
to the accumulation of fat. The sexual organs remain infantile and the mental- 
ity is sluggish and dull. A material named tethelin has recently been isolated 
from the anterior lobe, and is capable of stimulating growth in young animals. 
The condition of hypopituitarism superinduced by the removal of a part of 
the anterior lobe occurs in man as the result of destructive disease of this lobe. 
If the affection occurs in early youth, the same phenomena occur as already 
described, viz., the individual fails to grow, becomes obese, and the sexual 
organs retain their infantile appearance (Fig. 146). The mentality of the indi- 
vidual, likewise suffers in its development, and may 
even become abnormal. 
When, however, there is an excessive growth and 
activity of the anterior lobe, a condition occurs that is 
known as hyperpituitarism. If the disease occurs in 
youth, before the epiphyses have become ossified, the 
bones grow to excessive length and the individual be- 
comes a giant (Fig. 147). When the affection does not 
begin until after the epiphyses are entirely ossified, the 
excessive development of the bones becomes most evi- 
dent in certain locations. Thus, the lower jaw and the 
supraorbital ridges; the bones of the hands and of the 
feet become greatly enlarged. There is, likewise, a 
thickening and dryness of the skin and an increase of 
the hairs over the body. The sexual power declines 
early in the disease. This affection is known as acro- 
megaly (Fig. 148). 
The function of the anterior lobe would therefore 
appear to be the production of one or more autacoids 
which regulate growth and sexual development. 
Functions of the Posterior Lobe (Inclusive of Pars 
Intermedia}.-The posterior lobe, as already stated, is 
not essential to life, but its removal is followed by an 
increased tolerance for sugar. The posterior lobe is, therefore, concerned with 
the metabolism of carbohydrate. This is further shown by the fact that an 
aqueous extract of this lobe when injected into the circulation causes glycosuria 
and polyuria. This extract causes also a constriction of all the arterioles of the 
body, except those of the kidney, and a rise of blood pressure. The polyuria 
must, therefore, be due to the increased blood flow through the kidney. The 
extract of the posterior lobe acts on other smooth muscle, particularly on that 
of the uterus during and after childbirth, that of the bladder, intestine, bron- 
chioles, and of the mammary gland. 
The hormone contained in the extract has been given the name pituitrin. 
This substance differs in its action from adrenalin in that it acts directly on the 
smooth muscle fibers. This material is elaborated in the pars intermedia and is 
discharged into the cerebro-spinal fluid as previously explained. The secretory 
activity of the pars intermedia is, apparently, under the control of the nerve 
Fig. 146.-Case of hypopi- 
tuitarism in a man, age 47. 
Note the adiposity; the fem- 
inine configuration and the 
infantile genitalia. (Lisser, 
courtesy of Endocrinology.) 278 
THE INTERNAL SECRETIONS 
Fig. 147.-Giant, 8 feet 4 inches high, weighing 385 pounds. Note the acromegalic features. (Cour- 
tesy of The New York Times.) ESSENTIALS OF PHYSIOLOGY 
279 
system, as stimulation of the superior cervical ganglion is often followed by a 
glycosuria which, however, does not take place if the posterior lobe has been 
removed. 
Fig. 148.-Acromegaly. This man was an acromegalic giant aged thirty-five, with blindness and 
large tumor of the hypophysis. (Cushing.) 
The thymus is a glandular organ located in the upper and anterior part of 
the thoracic cavity just behind the sternum. It increases in weight from birth 
until the age of puberty, after which it undergoes involution. Remains of it, 
however, are found even in advanced years. The organ consists of a cortical 
part containing numerous lymphocytes, and of a medullary part composed of a 
reticulum supporting lymphocytes and concentrically arranged epithelial bodies 
known as corpuscles of Hassall. 
The function of the thymus is obscure. It has been supposed to be 
concerned with the regulation of the growth of the bony skeleton. The experi- 
ments on which this belief rested have, however, been shown to be undepend- 
able. A relationship does exist, however, between the thymus and the testicles. 
The removal of the thymus is followed by a rapid development of the testicles, 
while castration delays the involution of the thymus. 
In common with other lymphadenoid organs it supplies the blood with 
lymphocytes. 
THE THYMUS 
THE PANCREAS 
The pancreas has a double function. It produces an external secretion of 
much importance in digestion, and elaborates an internal secretion essential in the 280 
THE INTERNAL SECRETIONS 
metabolism of carbohydrate. The latter function is carried out through the 
activity of the Islands of Langerhans and has been discussed on page 238. 
THE TESTICLES AND OVARIES 
The testicles and ovaries are primarily engaged in producing those cellular 
elements, the union of which results in the production of a new being. Aside 
from this function, the glands of generation produce internal secretions that are 
essential for the development of those secondary sexual characteristics that dis- 
tinguish one sex from the other. 
The internal secretion of the testicles is the product of the activity of masses 
of epithelial cells found between the seminiferous tubules and termed the 
interstitial cells of Leydig. The removal of the testicles in man, in early life, 
is followed by a failure of the development of certain features characteristic 
of the mature individual. The larynx remains small and undeveloped so that 
the change of voice occurring at puberty does not take place; hair does not grow 
on the face; the bones remain slender and may grow to an abnormal length 
owing to a delay in the ossification of the epiphyses; there is a-considerable 
amount of fat under the skin and the general appearance of the body approaches 
that of the female. The accessory genital glands, such as the prostate, fail to 
develop, and sexual desire is absent. 
That these effects of castration are due to the loss of the internal secretion 
of the interstitial cells is shown by the fact that the destruction of the semini- 
ferous tubules is not accompained by such changes. The destruction of the 
seminiferous tubules may be accomplished by removing the testicles and trans- 
planting them in some other part of the body, or simply by tying the vas deferens 
(as the duct of the testicle is called). 
The ovaries contain cellular elements analogous to those found in the tes- 
ticles. These cells are found in the stroma of the organ and are, likewise, 
called interstitial cells. The removal of the ovaries in a young female leads to a 
failure of development of the internal and external genital organs. Menstrua- 
tion does not occur; the mammary glands do not develop; the voice is deeper 
than in the average female; and hair may grow on the face. 
Following the discharge of an ovum, a yellowish structure gradually 
develops in the cavity of the follicle in which the ovum formed. To this struc- 
ture the name corpus luteum is given. In the absence of conception, the corpus 
luteum gradually disappears. If, however, impregnation has occurred, the cor- 
pus luteum remains throughout pregnancy. The presence of the corpus luteum 
appears to be necessary for the implantation of the developing embryo in the 
uterine membrane since its removal is followed by the discharge of the embryo. 
The corpus luteum may also be concerned in the development of the mammary 
glands during pregnancy. CHAPTER XXXIV 
PHARMACODYNAMICS OF THE INTERNAL SECRETIONS 
The pharmacodynamics of the internal secretions has been covered in 
sufficient detail in the physiological discussion of the glands of internal secre- 
tion. Several common therapeutic uses of the more important ones follow. 
Thyroid Gland.-Although the use of thyroid preparations is usually success- 
ful in treating the symptoms of hypothyroidism, such as cretinism and myxedema, 
the results are temporary, persisting only as long as the drug is administered, 
and are frequently incomplete. 
Obesity has also been treated with preparations of the thyroid glands, but 
the results are not permanent and overdosage results in dangerous effects. 
Only small doses, under the close supervision of a physician, should be used, and 
the protein of the diet should be increased since the drug increases metabolism 
especially that of protein. 
Very small doses are often used in the treatment of certain forms of goiter. 
The iodides, which are elaborated into thyroxin, the active constituent of the 
thyroid gland, are also effective in this condition. They may be employed as a 
preventative of simple goiter in children (which is probably a reaction of deficient 
Iodine in the diet) by administrating Sodium Iodide twice a year; 
Adrenal Glands.-Beside the employment of preparations of the adrenal 
glands and its active constituent Epinephrine for the local effects (page 112), as 
an emergency circulatory stimulant (page 156), and as an antiasthmatic (page 
183), these drugs have also been employed in Addison's Disease but without 
success (page 274). 
Pituitary Body.-The therapeutic employment of Pituitary Body prepara- 
tions other than their uses in shock and collapse, in uterine inertia and in 
tympanites or intestinal paralysis (page 44), is still in the experimental stage. 
Ovarian extracts and Corpus luteum have been used with more or less incon- 
stant benefit to relieve the symptoms which follow natural or artificial meno- 
pause. 
281 CHAPTER XXXV 
THE SENSE ORGANS 
The consciousness possessed by the individual of himself and his surround- 
ings is obtained through the effect of various stimuli acting on the sense organs. 
Nerve impulses generated in the terminals of afferent nerves distributed to the 
sense organs are conveyed to the cerebral cortex where the characteristic 
sensations arise. 
The sensations of well-being, hunger, thirst, etc. are dependent on stimuli 
arising in the viscera. The sensation of the extent and direction of the move- 
ments of the limbs, are the result of stimuli arising in the muscles and joints; 
while those on which a knowledge of the position of the body depends, are due to 
stimuli aroused in the semicircular canals and the vestibular structures of the 
internal ear. The sensations evoked through these various mechanisms barely 
enter into consciousness and lack sharpness of definition. 
The sensations caused by stimulation of the surface of the body produce, 
however, a well-defined reaction in consciousness, so that the quality and the 
intensity of the stimulus can usually be recognized. These are the sensations of 
touch, temperature, and pain; taste; smell; light and color; sound and its various 
qualities. 
The essential parts of the mechanism necessary for the production of a 
sensation are: (i) a specialized end-organ; (2) an afferent nerve path; (3) 
specialized sensor nerve cells in the cortex of the brain. For each sense there 
is an end-organ especially adapted to receive the kind of stimulus for that sense. 
These end-organs can, nevertheless, react through other forms of stimulation, 
but the reaction in consciousness is indefinite. The customary stimulus for 
any particular sense, is called the adequate stimulus. Thus, the adequate 
stimulus for the retina, is the light wave; the adequate stimulus for the organ of 
Corti or the internal ear, is the sound wave. As the nerve impulses transmitted 
by the afferent pathway do not seem to differ in their nature it must be supposed 
that the difference in sensation is related to a difference in the organization of 
the sensor cells of the cerebral cortex. 
Classification of Sense Organs.-The sense organs may be classified in 
accordance with the kind of sensation to which they give rise, as follows: 
Structure 
Kind of Sensation 
Skin. 
Touch 
Pain 
Heat 
Cold 
Feeling 
Tongue. 
Acid 
Sweet 
Bitter 
Saline 
Taste 
282 ESSENTIALS OF PHYSIOLOGY 
283 
Structure 
Kind of Sensation 
Spicy 
Flowery 
Fruity 
Resinous 
Burnt 
Foul 
Nose. 
Smell 
Light 
Color 
Shape 
Distance 
Eye. 
Sight 
Ear (cochlea). 
Tone 
Harmony 
Ear 
Hearing 
semicircular canals 
utricle and saccule 
Dynamic sense 
Static sense 
Muscles and joints Sense of relative position 
CUTANEOUS SENSATIONS 
Stimulation of the skin gives rise to sensations of touch or light pressure, 
pain, heat and cold in accordance with the character of the stimulus. These 
Fig. 149.-Free nerve endings in epithelium 
(Morris' Anatomy, after Retzius.) 
Fig. 150.-Tactile cells in the epithelium of the 
groin of a guinea pig. a, tactile cell; c, epithelial 
cell; m, tactile meniscus, at the end of a nerve 
fibril; n, nerve fiber. Highly magnified. (Ranvier.) 
different sensations are not the result of a stimulation of the same kind of nerve 
terminals. For every kind of sensation there is a specialized nerve ending 
distributed to definite areas of the skin. Accordingly, the stimulation of minute 
areas of the skin will arouse but one form of sensation, such as pain, or touch, 
or heat, or cold. 
The Peripheral or,End-organs in the Skin.-This term is given to specialized 
organs found in the skin, and in other sense organs, whose structure is particu- 
larly adapted to respond to specific stimulation. These end-organs contain 
the endings of afferent nerve fibers and exhibit different forms. The chief 
of these end-organs of the skin are as follows: 
(i) Free Nerve Endings or End-fibrils.-These are varicose, naked fibrils 
forming a net-work between the epithelial cells of the epidermis and those of 
the anterior layer of the cornea (Fig. 149). 284 
THE SENSE ORGANS 
(2) Tactile Cells of Merkel.-These are modified epithelial cells of an oval 
shape, found in the deeper layers of the epidermis and in the root sheaths of 
hairs (Fig. 150). 
(3) The Tactile Corpuscles of Meissner.-These end-organs consist of more 
or less elliptical bodies made up of a connective tissue sheath enclosing many 
flat epithelial cells among which a complicated net- 
work of nerve fibrils is found. These end-organs are 
most numerous iii the papillae of the derma of the 
finger tips, and the palm of the hand (see Fig. 38). 
(4) End-bulbs of Krause.-These are speroidal 
structures consisting of a connective tissue capsule 
enclosing a net-work of varicose nerve endings. They 
are found in the conjunctiva, in the connective tissue 
of the skin of the lips, of the glans penis and clitoris 
(see Fig. 39). 
(5) The End-organs of Ruffini.-These organs 
resemble the tactile corpuscles, but have a connec- 
tive tissue sheath in the interior of which the nerve 
fiber branches out and becomes embedded in a gran- 
ular material. They are found in the deeper por- 
tions of the true skin, near the subcutaneous tissue, 
and are particularly numerous in the skin of the finger 
tips (Fig. 151). 
(6) The Lamellar Corpuscles of Pacini or Vater.- 
These end-organs are oval structures consisting of a 
lamellated connective tissue coat and a granular core, 
into which the nerve fiber penetrates and breaks up 
into a number of branches ending near the end of the 
corpuscle, in a disk-like expansion. These corpuscles 
are the largest of the end-organs; they are found in 
the subcutaneous tissue of the finger tips, genital 
organs, mesentery, and other serous membranes (see 
Fig- 40). 
These various end-organs react in a specific 
manner to adequate stimuli. As the end-organs have 
a discrete distribution, various areas of the skin will 
respond to one form of stimulation only. A correla- 
tion of the type of response with the kind of end-organs 
found in the area stimulated has enabled physiologists to determine with a cer- 
tain degree of probability the kind of sensation subserved by some of the end- 
organs. The free nerve endings would seem to be related to the sense of pain 
since the lightest touch of the cornea causes pain. The tactile corpuscles of 
Meissner, being most abundant in those areas of the skin having the greatest 
delicacy of touch (like the skin of the finger tips), are doubtless concerned 
in the reception of the stimulus of light pressure. Similarly, the position 
Fig. i5i.-Ruffini's end-or- 
gan. A single nerve fiber breaks 
up to form the tangle of nerve 
fibrils within the organ. gH, 
medullary sheath; il, terminal 
fibrils of the axis cylinder; L, 
connective tissue capsule. {Jor- 
dan and Ferguson, after Ruffini.) ESSENTIALS OF PHYSIOLOGY 
285 
of the end-organs of Ruffini and of the lamellar corpuscles of Pacini in the deeper 
layer of the skin or in the subcutaneous tissue indicates that these organs are 
related to the reception of the stimulus of deep pressure. 
THE SENSE OF TASTE 
The sense of taste is the sense by which the savor of substances are ascertained 
when applied to taste organs found mainly in the tongue. 
The end-organ subserving the sense of taste is called the taste-bud. This 
structure contains the nerve endings of the gustatory nerves, the adequate 
stimulus for which is matter in a state of solution. The gustatory nerves are, 
partly, the chorda tympani branch of the facial nerve, and partly, the glosso- 
pharyngeal nerve. The afferent fibers of these nerves pass into the medulla 
Taste pore. 
Supporting cell 
Taste cell 
Supporting 
cells. 
Tunica 
propria. 
Taste cells. 
Stratified 
epithelium. 
Taste fibre 
Fig. 152.-From a vertical section of a human 
foliate papilla. X 330. {From Lewis and Stohr's 
Histology.) 
Fig. 153.-Diagram illustrating the struc- 
ture of the taste-buds. (From Morris' Human 
Anatomy.) 
where they terminate around the cells of the nucleus solitarius. From these 
cells, fibers arise that cross the median line and ascend to the optic thalamus, 
from which other fibers pass to the cortex of the brain where the sensation of 
taste is evoked. 
While the taste area is more or less widely distributed in the mouth cavity 
it is located chiefly in the tongue. 
The Tongue.-The tongue is essentially a muscular organ covered by the 
mucous membrane that lines the interior of the mouth. The upper surface, 
or dorsum, of the tongue contains numerous papillae supplied with blood 
vessels and nerves (Fig. 152). The papillae occur in three varieties, viz., 
the filiform or conical, the fungiform, and the circumvallate. 
The filiform papillae are slender conical or tuft-like projections found in 
all parts of the dorsum of the tongue, except near the root. They constitute 
the most numerous of the papillae. 
The fungiform papillae are more or less rounded structures found in all 
parts of the tongue, but chiefly near the margin and tip. They are easily 
recognized by their bright red color. 286 
THE SENSE ORGANS 
The circumvallate papillae are a group of eight or twelve elevations arranged 
at the base of the tongue in the form of a V. They consist of a central part 
surrounded by a deep trench and wall, or circumvallation. 
The End-organ of Gustation or Taste-bud.-These organs are ellipsoidal or 
spheroidal structures consisting of epithelioid cells acting as support to neuro- 
epithelium in which the terminals of the gustatory nerve fibers end (Fig. 153). 
The apex of the taste-bud ends near the surface into a narrow funnel-shaped 
opening, called the tasie-pore. The interior of the taste pore contains hair-like 
filaments springing from neuro-epithelial cells. 
Taste-buds are found abundantly in the walls of the circumvallate papillae, 
and in lesser numbers, in the fungiform papillae. They occur elsewhere in 
the epithelium of the base of the tongue, the soft palate, uvula, epiglottis, etc. 
Kinds of Taste Sensations.-The varieties of sensations aroused by soluble 
substances in contact with the sense organs are a mixture of heat, cold, touch, 
and odor. Many so-called taste sensations are wholly dependent upon the 
sense of smell. By closing the nostrils and using weak solutions having the 
temperature of the mouth, four chief varieties of taste sensations have been 
ascertained, viz., acid, sweet, bitter, and saline. Two other sensations have been 
suggested in addition to those just mentioned. These are the alkaline and the 
metallic tastes. 
These elementary taste sensations are subserved by different nerve termi- 
nals as shown by the unequal sensitiveness of various areas of the tongue to 
different substances. The tip and sides of the tongue are more sensitive to 
sweet and sour substances, while the back of the tongue is more responsive 
to bitter substances. 
The Conditions Necessary for the Stimulation of the Nerves of Taste are, 
chiefly, that the substance should be in solution and that it possess a certain 
chemical constitution. The acid taste is dependent on the presence of hydrogen 
ions, and the alkaline taste on hydroxyl ions. Alcohols and sugars usually 
have sweet tastes, while their metallic derivatives are bitter. 
THE SENSE OF SMELL 
The sense of smell is the sense through which certain properties or qualities 
of substances stimulating the endings of the olfactory nerves, are perceived. 
The structures concerned in the sense of smell consist of the olfactory 
portion of the nasal cavities, the olfactory nerves, the olfactory tracts, and the 
gray matter of the hippocampal and uncinate convolutions of the cerebrum. 
The adequate stimulus is matter in the gaseous or vaporous state. 
The Nasal Fossae.-The nasal fossae are separated from each other by a 
more or less smooth vertical septum. The external wall of each fossa has four 
recesses formed by the three overhanging turbinate bones (Fig. 154). The 
fossae are lined by a mucous membrane. The upper recess is called the olfac- 
tory'cleft or sulcus and is alone concerned with smell. The three lower recesses- 
superior, middle, and inferior meatus-are a respiratory passageway. 287 
ESSENTIALS OF PHYSIOLOGY 
Superior nasal meatus 
Superior nasal concha 
Supreme nasal meatus 
Supreme nasal concha 
Middle nasal concha 
Sphenoidal sinus 
Sphenoethmoidal recess 
Agger nasi 
* 
Carina nasi ' 
Atrium of middle meatus 
Posterior nasal 
sulcus 
Limen vestibuli - 
Vestibule- 
Apical recess " 
Pharyngeal tonsil 
Pharynrgeal recess 
Pharyngeal ostium 
of auditive tube 
Sal pingopalatine 
plica 
Sal pinogopharyn - 
geal plica 
Middle nasal meatus 
Inferior nasal concha 
J 
Inferior nasal meatus 
Fig. 154.-Lateral wall of the right nasal fossa and the nasal pharynx. (From Morris' Human 
Anatomy.) 
Fig. 155.-Diagram of the central course of the olfactory fibers; I, olfactory bulb; II, olfactory 
tract; III, cortex of the hippocampal lobe (gyrus uncinatus); IV, anterior commissure, olfactory por- 
tion; A, olfactory epithelial cells of nose (their fibers, olfactory nerve fibers, terminate in the 
glomeruli of the bulb); B, glomeruli of olfactory bulb where the olfactory fibers come in contact with 
the dendrites of the mitral cells; C, mitral and brush cells; 1,2,3, axons from the mitral cells constitut- 
ing the fibers of the olfactory tract. Fibers 3, which enter the commissure, arise, according to some 
observers, from cells in the olfactory lobe near the base of the tract. (From Howell' Text-book of 
Physiology, W. B. Saunders Co., Publishers'). 288 
THE SENSE ORGANS 
The End-organ of Smell.-The mucous membrane lining the olfactory 
cleft differs in appearance from that lining the respiratory recesses. It is 
thicker and yellow in appearance, and consists of a layer of columnar cells 
supporting bipolar nerve cells which end at the surface of the membrane in 
hair-like processes. Each nerve cell sends an axon to the olfactory bulb (Fig. 
155). The mucous membrane is kept moist by the secretion of small alveolar 
glands known as Bowman's glands. 
Kinds of Olfactory Sensations.-Various classifications of odors have been 
suggested, but none has found general acceptance. The classification sug- 
gested by Henning gives six fundamental classes as follows: 
(1) Spicy odors, as anise and cloves. 
(2) Flowery odors, as geranium and heliotrope. 
(3) Fruity odors, as bergamot and acetic ether. 
(4) Resinous or balsamic odors, as turpentine and eucalyptus oil. 
(5) Burnt odors, as tar and pyridin. 
(6) Foul odors, as hydrogen sulphide and mercaptan. 
The Stimulation of the Olfactory End-organ.-In quiet respiration the 
movement of the air takes place below the superior turbinate bone. The 
odorous particles carried by the air must, therefore, reach the olfactory region 
by diffusion. By sniffing, however, the air may be drawn toward the olfactory 
area and the acuteness of smell raised. 
In order that a substance may be capable of stimulating the olfactory cells 
it must be in the gaseous or the vaporous state or in a condition of extremely 
fine subdivision. Moreover, the substance must be soluble in water inasmuch 
as the hair-processes of the olfactory cells are submerged in the watery mucus 
covering the membrane. 
The sense of smell is not well developed in man, although certain substances 
may be detected by man even when present in a state of high dilution. Thus 
musk can be perceived when in a dilution of 1 in 8,000,000 parts of air, and 
mercaptan in dilutions of 1 in 25 billion parts of air. CHAPTER XXXVI 
THE SENSE OF SIGHT 
The sense of sight is the sense by which light and color are perceived. 
The structures necessary for the visual sense include the eyeball, the optic 
nerve, the optic tracts, the optic radiation, and the nerve cells in the gray 
matter of the cuneus in the occipital lobe of the cerebrum. 
The adequate stimulus is that form of energy consisting of electro-mag- 
netic waves traveling through the ether. 
Visual axis 
Optic axis 
Suspensory liy. 
.Iris 
hqueows humor 
ciliary process 
Ciliary musclr' 
Equatorial 
\ diameter 
Vitreous 
humor 
Helma 
Sclera.- 
''Chorioid 
Optic nerve. 
' iliac ala lute a 
Fig. 156.-The right eye viewed in horizontal section. (Brubaker after Toldt.) 
The Eye-ball.-The eye-ball is located in the anterior portion of the 
orbital cavity where'it is held by a fibrous membrane, known as the capsule 
of Tenon. The eye-ball can be turned in any direction by the contraction 
of the six muscles attached to its outer coat. The eye-ball is spheroidal 
in shape, being a trifle longer in its antero-posterior than in its transverse 
diameter. It consists of three coats enclosing the refracting media. The coats, 
from without inward, are the sclera and cornea, the chorioid and iris, and the 
retina. The refracting media are the aqueous humor, the crystalline lens, 
and the vitreous humor (see Fig. 156). 
289 THE SENSE OF SIGHT 
290 
The sclera is the thick, white membrane covering the posterior five-sixths 
of the eye-ball. It is made up of dense fibrous tissue and is pierced, posteriorly 
and a little toward the nasal side, by the optic nerve. The cornea is the trans- 
parent membrane forming the anterior one-sixth of the outer coat. The curva- 
ture of the cornea is greater than that of the sclera; it is slightly greater also in 
the vertical than in the horizontal meridian. The cornea consists of thin parallel 
layers of transparent fibrous tissue and is permeated by spaces filled with lymph. 
Both the anterior and the posterior surfaces are covered by epithelium resting 
on an elastic membrane. At the junction of the sclera with the cornea there is a 
vein forming a complete circle and termed the canal of Schlemm. Near the pos- 
terior margin of the cornea, the posterior elastic lamina divides into a network, 
the spaces of which are called the spaces of Fontana. These spaces are filled 
with the aqueous humor and are in communication with the canal of Schlemm; 
hence the angle between the cornea and the iris is known as the filtration angle. 
The middle coat of the eye-ball consists of the chorioid, ciliary body, and 
iris. This coat consists of fibrous connective tissue supporting numerous blood 
vessels. It is, therefore, the vascular coat of the eye, and plays an important 
part in its nutrition and in the maintenance of a uniform temperature. At its 
anterior end the chorioid coat is continued into a relatively thick structure 
termed the ciliary body. This body consists of about seventy ciliary processes 
and of a muscle known as the ciliary muscle. This muscle is composed of smooth 
muscle fibers, the majority of which arise from the edge of the sclera near the 
cornea, and run a radial course to be attached to the ciliary processes and the 
most anterior part of the chorioid. Some of the fibers pursue a circular 
course at the anterior and inner part of the ciliary body. 
The iris is the disc-shaped, colored membrane seen in the anterior part of 
the eye behind the cornea. Somewhat to the nasal side of the center of the iris, 
there is a circular aperture known as the pupil. The iris is attached to the 
anterior part of the ciliary body near the corneo-scleral junction. It is made up 
of connective tissue supporting blood vessles and smooth muscle fibers. Some 
of the muscle fibers form a complete circle near the edge of the pupil; these 
constitute the sphincter pupillae muscle. Other muscle fibers are arranged 
radially and are situated near the posterior surface of the iris; they constitute 
the dilatator pupillae muscle. The anterior surface of the iris is covered by 
epithelial cells continuous with those lining the posterior surface of the cornea. 
The posterior surface of the iris is covered by pigment cells. In blue eyes these 
are the only pigment cells found in the iris, but in brown and black eyes pigment 
cells are found also among the connective tissue fibers within the iris. 
The Retina.-The internal coat of the eye is termed the retina. This coat 
does not line the entire interior of the eye-ball, but ends just behind the ciliary 
processes in an indented margin termed the ora serrata. When examined under 
the microscope the retina is seen to consist of cellular elements so arranged as to 
give it the appearance of a number of layers as follows: 
(i) The layer of pigment cells. 
(2) The layer of rods and cones. ESSENTIALS OF PHYSIOLOGY 
291 
(3) The external limiting membrane. 
(4) The outer nuclear layer. 
(5) The outer molecular layer. 
(6) The inner nuclear layer. 
(7) The inner molecular layer. 
(8) The layer of ganglion cells. 
(9) The layer of nerve fibers. 
(10) The internal limiting membrane. 
A careful analysis of the elements entering into a formation of the retina 
shows, however, that it consists essentially of a layer of pigment cells, a layer of 
visual cells-the rods and cones-and their 
processes, a layer of bipolar cells and their 
processes, a layer of ganglion cells from 
which arise the nerve fibers that pass out 
of the eye-ball as the optic nerve. These 
various elements are supported by neur- 
oglia cells termed fibers of Muller. These 
essential elements of the retina are repre- 
sented in Fig. 157. 
At the posterior pole of the eye there 
is in the retina, a small oval yellowish spot 
known as the macula lutea in the center of 
which there is a depression called the/ouea 
centralis. In the fovea there are no rods, 
cones only being present. The other ele- 
ments of the retina are absent. The fibers 
arising from the ganglion cells converge to 
a point on the nasal side of the posterior 
pole where they form a white disc, the 
optic disc, which therefore represents the 
point of exit of the optic nerve. This 
nerve, on its way out of the eye-ball, passes through an opening in the chorioid 
and through perforations in the sclera. 
The retina is supplied with blood by an artery that gains entrance into the 
eye-ball by passing through the optic nerve. In the optic disc it divides into two 
chief branches which again subdivide a number of times. The veins arising 
from capillaries follow the same general course as the arteries. These blood 
vessels remain in the anterior layers of the retina. 
The Refracting Media.-The interior of the eye-ball contains the refracting 
media, viz., the aqueous humor, the lens, and the vitreous humor. The 
aqueous humor is a watery fluid secreted by gland-like structures in the ciliary 
processes. This fluid gains the space between the cornea and the iris by passing 
through the pupil. Its accumulation is prevented by a constant drainage 
through the spaces of Fontana and the canal of Schlemm. The hardness or 
Fig. 157.-Diagram of the human retina, 
showing the relationships to each other of the 
retinal neurons, and their disposition in the dif- 
ferent layers. (From Fox's Ophthalmology.) 292 
THE SENSE OF SIGHT 
tension of the eye-ball is due, chiefly, to the presence of this fluid under a pres- 
sure of about 25 mm. Hg. 
The crystalline lens is a biconvex, transparent structure located just 
behind the iris opposite the pupil. It consists of transparent fibrous laminae 
enclosed in a transparent capsule. The core of the lens is denser than the peri- 
phery. The convexity of the posterior surface is greater than that of the 
anterior. The lens rests in a concavity in the anterior part of the vitreous 
humor, and is held in position by the suspensory ligament. This ligament is 
formed by fibers arising from the ciliary processes attached mainly to the front, 
but also to the back of the lens near the equator. 
The vitreous humor fills the interior of the eyeball not occupied by the 
aqueous humor and the lens. It consists of a transparent, jelly-like material 
enclosed in a transparent membrane termed the hyaloid membrane. 
Formation of an Image on the Retina.-Owing to the action of the 
curved surfaces of the various refracting media, images of external objects 
are formed on the retina in the same 
manner that images are formed on the 
ground glass plate of a photographic 
camera. That this is the case can be 
demonstrated with the excised eye of an 
albino rabbit. If such an eye be placed 
in a blackened tube and the cornea tur- 
ned toward an electric lamp, an image of 
the lamp will appear at the back of the 
eye. This image will be inverted and its sides reversed; it will likewise be con- 
sderably smaller than the object and will vary in size inversely as the distance 
from the object. The image seen through the back of the eye-ball, is normally 
formed on the free ends of the rods and cones of the retina. 
Action of the Refracting Media.-In the photographic camera the refracting 
apparatus consists, usually, of a single biconvex glass lens. Parallel rays of 
light passing into the lens are bent toward each other, or converged, not only 
at the anterior surface where they penetrate into the denser medium of the glass, 
but also at the posterior surface where they pass from the dense medium of the 
glass into the less dense medium of the air. The rays of light ultimately con- 
verge to a single point which is known as the principal focus of the lens. Images 
are made up of innumerable such focal points. When the rays of light are diver- 
gent they are brought to a focus some distance behind the principal focus pro- 
vided the lens has a sufficient refracting power, either because of the degree of 
its convexity, or because of the nature of its material. The formation of an 
image from an object is illustrated in Fig. 158. 
In this figure a pencil of light is represented passing from the tip of the 
arrow into the eye. The limiting rays of this pencil of light undergo refraction 
and are brought to a focus on the retina; the axial ray passes through the 
optical center, or nodal point, of the lens and is continued without change of 
direction. Another similar pencil of light is represented as passing from the 
Fig. 158-Refraction of homocentric raysand 
the formation of an image. (Brubaker.) ESSENTIALS OF PHYSIOLOGY 
293 
butt end of the arrow, and its rays take a course similar to those of the tip. 
The image formed on the retina is, therefore inverted. Between the tip and the 
butt end of the arrow innumerable pencils of light are sent forth into the eye, and 
are brought to a focus upon the retina where they form the image of the rest of 
the arrow. 
In a camera provided with a single biconvex lens, there are but two points at 
which the rays of light undergo refraction. In the eye, however, the refracting 
apparatus is more complex and rays of light are refracted at several points. 
These points are the anterior surface of the cornea, the anterior surface of the 
lens, and the posterior surface of the lens. Owing to the complexity of such a 
system the calculation of the paths of the rays of light presents certain diffi- 
culties. It has been shown, however, that the refracting apparatus of the eye 
can be mathematically simplified so that there will be but one point at which 
refraction can be imagined to take place. This simplified eye is termed the 
-Epi&eluMC 
-J3owrums3femining 
- Cornen proper 
-ZJescemeZ 'Menbrsme 
- SpenderZridtJi 
. SanaZ ScAZertTp^ 
CUiaryJfit^ia 
Sclera, 
(Zltaru 
Fig. 159.-The left half represents the eye in a state of rest. The right half in state of accommoda- 
tion. (Brubaker.') 
reduced or schematic eye. This hypothetical eye has a uniform medium having a 
refractive index of 1.33, and a refracting surface 2.1 mm. back of the anterior 
surface of the cornea, with a radius of curvature of 5 mm. The nodal point is 
7.1 mm. from the anterior surface of the cornea and the principal focal distance 
is 15.5 mm. from the nodal point; this corresponds to the position of the retina. 
Accommodation.--The refracting apparatus of the normal or emmetropic 
eye is of such nature that, with the eye at rest, parallel rays of light are brought 
to a focus on the retina. Parallel rays of light issue from objects situated at an 
infinite distance. Objects near the eye give off divergent rays. It is not 
possible, therefore, to see distinctly at one and the same time, objects situated 
far away and objects close to the eye. To see objects near at hand the eye 
must be adjusted so that the divergent rays given off by the near object will be 
brought to a focus on the retina. This adjustment of the eye for vision at 
different distances is termed accommodation. 
Mechanism of Accommodation.-The increased refractive power necessary to 
see objects near at hand is obtained by an increase in the convexity of the lens. 
The lens is elastic and is surrounded by a capsule connected with the ciliary 
processes by the suspensory ligament. The suspensory ligament is kept taut and 
the lens is thereby kept relatively flattened by the intra-ocular pressure. This 
is the condition that obtains when the eye is at rest and is, therefore, adjusted 
for distant vision. During accommodation the ciliary muscle contracts and 
thus causes a relaxation of the suspensory ligament. As a result, the lens by 294 
THE SENSE OF SIGHT 
virtue of its elasticity bulges forward and slightly backward, increasing its con- 
vexity and, therefore, its refractive power (Fig. 159). 
At the same time that this change occurs there is a contraction of the pupil 
brought about by the contraction of the sphincter pupillae and a convergence 
of the eyes caused by the contraction of the internal recti muscles. These two 
movements are always associated with accommodation. 
Range of Accommodation.-In the normal eye the farthest point that can be 
seen distinctly without accommodation is situated at infinity. It is called the 
punctum remotum. For practical purposes a point not nearer than 6 meters 
(about 20 feet) is regarded as the far point. To see objects closer than this 
distance accommodation must come into play. There comes a time when an 
object brought gradually closer to the eye becomes indistinct. The nearest 
point at which an object can be seen distinctly by the eye is called the near point 
or punctum proximum. 
As the elasticity of the lens diminishes with age the near point gradually 
recedes from the eye. Consequently the range of accommodation is not as great 
in old age as in youth. 
The force of accommodation, representing the energy spent by the ciliary 
muscle, may be expressed in terms of a lens of such refractive power that when 
placed in front of the crystalline lens in a state of rest, would bring the diverging 
rays coming from the near point to a focus on the retina. The unit of measure- 
ment of the refractive power of lenses is the diopter.1 The following table 
shows the range of accommodation at different ages: 
Age 
Range of accommodation in 
diopters 
Near point, cm. 
IO 
14 
7 
20 
10 
10 
30 
7 
14 
40 
4-5 
22 
50 
2-5 
40 
60 
1 
100 
70 
0.25 
400 
The table shows that at about the age of 45 the near point has so far 
receded that objects can no longer be seen distinctly at the usual reading 
distance. Hence, it is necessary, at about that age, to aid the mechanism of 
accommodation when doing near work by the use of convex lenses of such refrac- 
tive power that the near point will be brought about 25 cm. (about 10 inches) 
from the eye. The vision of old age is called presbyopia. 
1 A diopter is the amount of refractive power possessed by a flint glass lens capable of focusing 
parallel rays of light at a distance of i meter or 100 cm. The refractive power of lenses is obtained 
by dividing 100 cm. by the focal distance in centimeters. Thus, a lens having a focal distance of 
50 cm. would have a refractive power of two diopters (abbreviated 2D). ESSENTIALS OF PHYSIOLOGY 
295 
Functions of the Iris.-Ordinary observation shows that the size of the 
pupil varies with the intensity of the light, being large in dim and small in 
bright light. The iris, therefore, serves to regulate the amount of light entering 
the eye, and so determines the intensity of stimulation of the retina. As 
previously stated, the pupil decreases in size during accommodation. This 
serves the purpose of causing a sharper definition of the image of the object 
looked at. The interposition of the iris in front of the lens likewise corrects 
in great part the spherical aberration common with simple lenses. 
The variations in the size of the pupils with varying intensities of light are 
brought about by the reflex action of the sphincter and dilatator pupillae muscles 
(see Fig. 160). The afferent fibers of the reflex arc arise in the retina and pass 
Sup.Corp. Quad 
,Cil iary. M. 
Ciliary G. 
Nue.JH 
xCire. M 
^ad. M 
SupACerv. G. 
Fig. 160.-Diagrammatic representation of the nerves of the intrinsic muscles of the eye. Sup. 
Corp. Quad., superior corpora quadrigemina; Nuc. Ill, nucleus of the third cranial nerve; Sup. 
Cerv. G., superior cervical ganglion; Circ. M., circular muscles of the iris; Rad. M., radial muscles of the 
iris; Ciliary G., ciliary ganglion. (C. W. Greene.) 
into the optic nerve. Owing to the partial decussation of the optic nerves 
stimulation of the retina of one eye leads to the contraction of the pupils of 
both eyes. The fibers of the optic nerve connect with nerve cells in the superior 
colliculus. From these cells fibers pass to the nuclei of both oculo-motor 
nerves (third cranial nerve). The oculo-motor nerve sends fibers to a sympathe- 
tic ganglion located in the orbital cavity and called the ciliary or ophthalmic 
ganglion. From this ganglion post-ganglionic fibers pass to the sphincter 
pupillae muscle. These nerve paths constitute the reflex arc through which 
the contraction of the pupil takes place when the retina is stimulated by the 
proper intensity of light. 
The dilatator pupillae muscle is supplied by sympathetic fibers arising 
from the first and second segments of the spinal cord. These preganglionic 
fibers ascend in the cervical sympathetic nerve to the superior cervical ganglion 
from which postganglionic fibers pass to the eye in company with the internal 
carotid artery and the ophthalmic division of the fifth cranial nerve. The 296 
THE SENSE OF SIGHT 
center regulating the activity of these fibers is located in the medulla. This 
center is in a state of tonic activity so that when the sphincter pupillae muscle 
relaxes the dilatation of the pupil is accomplished by the unopposed action of 
the dilatator pupillae muscle. 
REFRACTION IN ABNORMAL EYES 
(Errors of Refraction, or Ametropia) 
Hypermetropia.-When the antero-posterior diameter of the eye is shorter 
than normal, parallel rays of light entering the eye strike the retina before they 
Fig. 161.-Hypermetropia. Parallel rays focused 
behind the retina. (Brubaker.) 
Fig. 162.-Correction of hypermetropia by a 
convex lens. (Brubaker.) 
can be brought to a focus (Fig. 161). In order that distant objects may be seen 
distinctly it is necessary for such an eye to increase its refractive power by the 
usual mechanism of accommodation. Owing to this circumstance, the entire 
Fig. 163.-Myopia. Parallel rays focus a't F, 
cross and form diffusion-circles; divergent rays 
from A focus on the retina. (Brubaker.) 
Fig. 164.-Correction of myopia by a concave 
lens. (Brubaker.) 
power of accommodation will have been used up long before an object can be 
brought close to the eye. The near point will, therefore, be much farther from 
the eye than under normal conditions. This condition is, therefore, called 
far-sightedness or hypermetropia. Slight degrees of 
hypermetropia can be overcome by accommodation, 
although the constant contraction of the ciliary 
muscle may lead to various symptoms charac- 
teristic of eye-strain. This error of refraction can 
readily be corrected by the use of convex lenses (Fig. 
162). 
Myopia.-When the antero-posterior diameter of the eye is longer than 
normal, parallel rays of light after passing into the eye are brought to a focus 
before they reach the retina, after which they diverge and cause a blurred and 
indistinct image (Fig. 163). Divergent rays only can be brought to a focus 
upon the retina. For this reason the far point is always at a definite distance 
from the eye, and the near point is much nearer the eye than the normal. This 
condition is, therefore, called near-sightedness or myopia. Parallel rays of 
Fig. 165.-(Thorington.) ESSENTIALS OF PHYSIOLOGY 
297 
light may be caused to be brought to a focus on the retina in myopia, by placing 
concave lenses before the eyes (Fig. 164). In this way, a myopic individual 
is enabled to see distant objects. 
Astigmatism.-Ordinary astigmatism is due to an unequal degree of 
curvature of the various meridians of the cornea. As a consequence, the rays 
of light passing through the meridian of greatest curvature are brought to a 
focus before those that enter the meridian of least curvature. No single focus 
can therefore be formed and the image of the object looked at is more or less 
indistinct and distorted. In the usual form of astigmatisn the vertical meridian 
of the cornea is the one of greatest and the horizontal meridian of least con- 
vexity (Fig. 165). 
This defect is corrected by wearing cylindrical lenses. 
Functions of the Retina.--The layer of rods and cones is the part of the 
retina that responds to the stimulating action of the light rays. The manner 
Fig. 166.-Diagram for observing the situation of the blind spot. (Helmholtz.) 
in which these elements respond, to give rise to the nerve impulses that are 
transmitted to the brain, is unknown. The other elements of the retina are 
insensitive to light as is evident from the fact that in the fovea cones only are 
present and that stimulation of the optic disc fails to excite any sensation. 
The optic disc is therefore known as the blind spot (Fig. 166). 
The rods and cones, it is believed, fulfill different functions. The cones 
are more numerous in the central part of the retina, and the rods occur in 
greater number in the peripheral portion. The rods, furthermore, contain a 
pigment known as visual purple or rhodopsin which is bleached when the 
retina is exposed to light, and is regenerated from the pigment layer when 
the eye is placed in the dark. Since the most acute vision is obtained when 
the rays of light strike the fovea, and it is precisely this part of the retina 
that is used in bright daylight, it is generally believed that the cones are alone 
used for daylight vision. The cones, it is further believed, are alone concerned 
with color vision. The peripheral portion of the retina in which the rods 
predominate greatly, is relatively color-blind. 
The rods are, apparently, concerned with vision under conditions of feeble 
illumination, as in twilight. The activity of the rods is, however, dependent 
on the presence of visual purple. Since the regeneration of visual purple 
requires time, the eye cannot immediately distinguish objects when passing 
from bright daylight into a dimly lighted place. Once objects become visible 
the eye is said to be "dark-adapted." 
Accessory Structures of the Eye.-The eye-ball is protected by two move- 
able curtains, known as the eyelids, and the lachrymal apparatus (see Fig. 167). 298 
THE SENSE OF SIGHT 
The eyelids are folds of skin enclosing the muscle fibers of the orbicularis 
oculi and glands supported by connective tissue. The skin forming the internal 
lining of the eyelids is greatly modified and is termed the conjunctiva. The 
conjunctiva is reflected over the front of the eye-ball to which it adheres closely. 
The margin of each lid is strengthened by a condensation of fibrous tissue 
known as the tarsus. At the line of junction of the skin with the conjunctiva 
there are short, curved hairs-the eyelashes. The glands found in the eyelids 
are inodifications of sebaceous glands known as Meibomian glands. They are 
located near*the conjunctiva and their ducts open along the free border of the 
lids. Their secretion is oily in character and serves to prevent the tears from 
running over the lids and down the cheek. 
The lachrymal apparatus includes the lachrymal gland, lachrymal ducts, 
lachrymal and naso-lachrymal duct. The lachrymal gland is a flat, oval 
Palpebra superior 
Inferior lacrimal gland 
Excretory ducts, 
Superior lacrimal gland 
Tendon of superior oblique 
| Superior lacrimal duct 
Lacus lacrimalis 
Medial palpebral commissure 
- Fornix of lacrimal sac 
~ Junction of lacrimal ducts 
- Inferior lacrimal duct 
- Nasolacrimal duct 
Lacrimal papilla and punctum 
Inferior oblique 
Palpebra inferior 
Fig. 167.-Dissection of the eye to show the lacrimal apparatus, anterior view. (From Morris' 
Human Anatomy.) 
structure located at the upper and outer part of the orbital cavity. It is a 
compound racemose gland resembling a serous salivary gland in structure. 
From 6 to 14 ducts lead the secretion-the tears-to the outer corner of the 
upper eyelid. The secretion is spread over the cornea by the movements 
of winking and keeps it moist and clean. The secretion is drained by two 
lachrymal ducts whose orifices-the puncta lacrymalia-may be seen at the 
apices of two papillae at the inner corner of the lids. These ducts open into 
the lachrymal sac which is continuous with a duct known as the naso-lachrymal 
duct. This duct opens in the inferior meatus of the nose. 
The lachrymal glands are supplied with secretory fibers by the fifth 
nerve and the cervical sympathetic. The secretion may be excited reflexly 
by the stimulation of the conjunctiva, the cornea, etc., and by emotional 
disturbances. 
Hygiene of the Eyes.-The use of the eyes for close vision necessitates the 
effort of accommodation. If the eye is used excessively the ciliary muscle will, 
like any other muscle, suffer from fatigue and various symptoms will make ESSENTIALS OF PHYSIOLOGY 
299 
their appearance indicating that the eyes have been overtaxed. These symp- 
toms may consists of pain in the eye, headaches of the frontal or occipital type, 
lachrymation, photophobia (undue sensitiveness to light), etc. The general 
state of nutrition of the body influences to a marked degree the ability to use 
the eyes for close application. General fatigue, being accompanied by the 
accumulation of fatigue products in the circulating blood, reduces the power 
of accommodation. It is, therefore, unwise to attempt to use the eye for close 
work when tired. 
These remarks apply with even greater force in cases of hypermetropia since, 
in this condition, the accommodation must be used even for distant vision. In 
astigmatism of slight extent, the eye attempts to correct the defect probably 
by an unequal contraction of the various parts of the ciliary muscle. Eye- 
strain may, therefore, occur not only in hypermetropia but in astigmatism as well. 
. A common cause of myopia is the use of the eyes for near-vision at a time 
when the coats of the eye-ball have been weakened by disease. This is more 
likely to occur in young children following one of the infectious diseases of 
childhood. The effort at convergence necessary for near-vision raises the intra- 
ocular pressure and the weakened eye-ball stretches. It is obvious, therefore, 
that a child recovering from an infectious disease should not be permitted to 
use the eyes for near work until fully recovered. Aside from this cause, the 
prolonged use of the eyes in a badly lighted room, or at too near a distance-- 
as in case of a faulty desk-may be contributing factors in the development of 
myopia. 
As these various optical defects influence the general health of the body, 
it is necessary that they be corrected by a competent ophthalmologist. The 
correction of presbyopia should not be left to the individual as is too often the 
case, but should likewise be entrusted to an expert. CHAPTER XXXVII 
PHARMACODYNAMICS OF THE EYE 
Mydriatics.-Drugs which cause a dilatation of the pupil are termed 
mydriatics. The more important mydriatics are Atropine, Homatropine, 
Cocaine, and Epinephrine. 
Atropine.-Atropine produces four principal effects on the eye, viz., (i) it 
dilates the pupil (mydriatic); (2) paralyzes accommodation (cycloplegic); (3) 
increases intraocular tension; and (4) lessens pain (anodyne). 
(1) Dilatation of the Pupil by Atropine.-As stated in the physiological dis- 
cussion of the function of the iris (page 295) variations in the size of the pupil are 
brought about by the action of two sets of muscles, viz., the circular or sphincter 
pupillae muscle, supplied by the oculomotor or third cranial nerve, and the 
radial or dilatator pupillae muscle, supplied by sympathetic fibers arising from the 
superior cervical ganglion. 
If a weak solution (1 per cent) of Atropine Sulphate is dropped into one eye, 
dilatation of the pupil takes place in about fifteen minutes. The other eye is not 
affected. Experiments have shown that Atropine dilates the pupil by strongly 
depressing or paralyzing the myoneural junctions of the endings of the oculo-motor 
or third cranial nerve, thereby permitting the unopposed action of the radial or 
dilatator pupillae muscle. Maximum dilatation requires about two hours, and 
recovery takes place so gradually that the pupil is not completely restored to 
normal for a week or two. 
(2) Paralysis of Accommodation of Atropine.-By depressing the myoneural 
junctions in the ciliary muscle Atropine paralyzes accommodation {cycloplegic}, 
so that near objects are indistinct. In fitting glasses this is essential in that 
it permits the accurate determination of the refraction, and, by dilatation of 
the pupils facilitates ophthalmoscopic examinations of the lens, etc. 
(3) The Effect of Atropine on Intra-ocular Tension.-As stated on page 291, 
the tension of the normal eye-ball is chiefly dependent upon two factors, viz.; 
(1) The amount of the aqueous humor, and (2) the ready escape of this intra- 
ocular fluid through the spaces of Fontana into the canal of Schlemm. The 
intra-ocular tension may therefore be raised {a) by an increase in the secretion of 
aqueous humor, or (b} by dilatation of the pupil which results in shutting off 
the spaces of Fontana, because of the relaxed ciliary muscles, and thus inter- 
feres with the escape of the intra-ocular secretion. Atropine increases the intra- 
ocular tension by dilatation of the pupil. It is for this reason that Atropine is 
avoided in the eye disease known as glaucoma, a condition in which the intra- 
ocular tension is abnormally high. 
(4) The Anodyne Effect of Atropine on the Eye.-Because of the moderate 
depression produced by Atropine on the sensory nerve endings (page in) there 
is some relief from the pains of inflammation of the iris, cornea, etc. 
300 PHARMACODYNAMICS 
301 
Atropine is one of the drugs most used in ophthalmology. The actions 
described are produced not only by local application but also when given by 
mouth or by the hypodermic method. 
Homatropine.-Homatropine is an artificial alkaloid chemically related to 
Atropine. Homatropine Hydrobromide is the salt usually employed. It 
possesses the same qualitative effects as Atropine, but is weaker and the 
cycloplegic effect is of much shorter duration, restoration of accommodation 
taking place in about 24 hours and complete restoration of the pupil in from 48 
to 72 hours. Homatropine is consequently preferred to Atropine for fitting 
glasses and for ophthalmoscopic examinations, while Atropine is preferred in 
cases such as inflammatory eye conditions, where prolonged mydriasis is 
desired. 
Cocaine.-When a minim or two of a 2 to 4 per cent aqueous solution of 
Cocaine Hydrochloride is dropped into the eye there is immediate though 
transient irritation (since the drug is a general cytoplasmic poison), with result- 
ing reflex contraction of the pupil. Anesthesia of the cornea and conjunctiva, 
with blanching and absence of the winking reflex rapidly follow. Very soon 
the pupil dilates and remains so for from one to two hours. The dilatation is 
produced also by injection into an excised eye. Cocaine mydriasis, how- 
ever, differs from that of Atropine in that, with Atropine the dilatation is 
greater, the light reflex is lost, and the intra-ocular tension is always increased. 
These differences indicate a different mode of action. Experimentation has 
shown that Cocaine mydriasis is a peripheral action and is probably due to the 
fact that Cocaine acts directly on the muscle fibers of the iris and weakens the 
circular muscle. 
The majority of the Cocaine substitutes do not produce mydriasis. 
Since accommodation is paralyzed only by concentrations of Cocaine 
sufficiently high to probably produce cloudiness and even ulcers of the cornea, 
this drug is not available by itself for fitting glasses. 
Epinephrine.-If a solution of Epinephrine sufficiently strong to penetrate 
into the eye is employed locally, the pupil is dilated. The effect is due to stimu- 
lation of the sympathetic nerve endings in the fibers of the radial or dilatator 
pupillae muscle, and, since the drug is effective after degeneration of these end- 
ings the action must be on the myoneural junctions. 
Ordinarily a 1:1000 solution does not dilate the pupil, but simply produces 
the characteristic local vaso-constrictor effects on the conjunctival vessels. 
This action is frequently made use of to lessen conjunctival swelling and thus 
favor the finding and removal of foreign bodies. 
Myotids.-Drugs which cause a constriction of the pupil are termed 
myotics. Physostigmine and Pilocarpine are the more important members 
of this group. 
Physostigmine.-As already stated on page 112 Physostigmine or ' 'Eserine" 
is used to contract the pupil after drugs of the Atropine group. Physostigmine 
acts by stimulating the myoneural junctions of the oculo-motor or third cranial 
nerve. The pupil regains its normal size in from two to four days. 302 
PHARMACODYNAMICS OF THE EYE 
Physostigmine, by stimulating the myoneural junctions of the third nerve 
in the ciliary muscle, causes the sight to be fixed in accommodation for near 
objects. 
Another effect of Physostigmine on the eye is a decrease in the intra-ocular 
tension resulting from the increased escape of the intraocular fluid through the 
spaces of Fontana which are widened by the contraction of the pupil. This 
effect is aided by the contraction of the vessels of the eye-ball produced by 
Physostigmine resulting in diminished secretion. Accommodation is restored to 
normal more rapidly than the pupil. 
Physostigmine is therefore antagonistic to Atropine in its effects on the 
eye, and is consequently used to counteract the effect of Atropine. The drug is 
much more powerful in this respect than Pilocarpine. It is also employed to 
lower the intra-ocular tension in glaucoma. 
Pilocarpine.-By stimulation of the myoneural junctions of the oculomotor 
or third nerve endings (see page in) Pilocarpine contracts the pupil. The 
contraction lasts but three or four hours. 
It also stimulates the myoneural junctions of the third nerve 'in the ciliary 
muscle causing it to contract and consequently making the lens bulge and thus 
fixing accommodation for short distances. 
Intra-ocular tension is decreased, coincident with the contraction of the 
pupil, and results from the increased escape of fluid which follows the widening 
of the spaces of Fontana when the pupil contracts. 
All these actions are weaker and less prolonged than those produced by 
Physostigmine. It has been used in the eye as an antagonist to Atropine and 
in treating glaucoma, but, as already stated, Physostigmine is preferred. CHAPTER XXXVIII 
THE SENSE OF HEARING 
The sense of hearing is the sense by which atmospheric vibrations are 
perceived as sounds. The structures concerned in the sense of hearing are the 
ear, the auditory nerve, the auditory tract (or lateral fillet), the auditory radiation, 
and nerve cells in the cortex of the temporal lobe. 
The adequate stimulus is the mechanical action of atmospheric vibrations 
of certain frequencies and sufficient intensity upon the receptive organ (organ 
of Corti) of the ear. 
Tympanic membrane 
Semicircular Glands in os- 
canals (ducts) secus meatus 
Cochlea 
Cavity of tympanum 
, Cartilage 
.Auricle 
Cartilaginous 
> meatus 
.Osseous 
meatus 
Cartilage of 
external 
meatus 
.Parotid gland 
Styloid process 
Internal 
"carotid artery 
Cartilaginous tuba auditiva 
Osseous tuba auditiva 
Fig. 168.-Vertical section of the middle and external ear. (From Morris' Human Anatomy.) 
The Ear.-The organ of hearing is customarily divided into three parts, 
termed the external, the middle and the internal ear (see Fig. 168). 
The External Ear.-The external ear consists of the auricle or pinna and the 
external auditory canal. The auricle is a cartilaginous structure covered with 
skin and attached by fibrous tissue to the auditory canal. The deep concavity 
near the center is known as the concha. The external auditory canal passes from 
the concha inwards, forwards, and slightly upwards, and then turns downwards 
to its end. It is about 24 mm. long (about 1 in.), and consists partly of carti- 
303 304 
THE SENSE OF HEARING 
lage and partly of bone lined by skin. The skin covering the cartilaginous 
part contains fine hairs and modified sweat glands termed ceruminous glands 
which secrete the ear-wax or cerumen. The inner extremity of the canal is 
closed by the tympanic membrane. 
The Middle Ear.-The middle ear or tympanum is a narrow cavity located 
within the temporal bone. This cavity is lined by mucous membran and com- 
municates posteriorly with spaces found in the mastoid process, and anteriorly 
with the pharynx through the Eustachian tube. The middle ear is separated 
from the external ear by the tympanic membrane (Fig. 169). 
The tympanic membrane is a thin, elliptical membrane placed obliquely at 
the end of the external auditory canal. Although exceedingly thin, it is com- 
Superior malleolar ligament Incus 
Head of malleus 
■Posterior ligament of incus 
Posterior portion of 
epitympanic recess 
Chorda tympani nerve 
-Base of stapes 
Tendon of tensor tympani 
Manubrium of malleus 
•Lenticular process of incus 
Tensor tympani muscle 
.Posterior portion of 
membrana tympani 
Tuba auditiva 
Fig. 169.-Medial'surface of right membrana tympani. (From Morris' Human Anatomy.) 
posed of a layer of fibrous tissue covered externally by skin and internally by 
mucous membrane. It is funnel-shaped and has slightly convex sides. 
The Auditory Ossicles.-An articulated chain of bones stretches from the 
tympanic membrane to the medial wall of the middle ear. These small bones, 
or ossicles, are known as the malleus, incus, and stapes. The handle of the mal- 
leus is attached to the connective tissue layer of the tympanic membrane along 
its entire length. The incus articulates with the head of the malleus. The 
stapes articulates by its head with the long process of the incus and by its oval 
base with the edges of an oval opening-the fenestra ovalis-in the wall separat- 
ing the middle from the internal ear. These bones are held suspended by vari- 
ous ligaments. Two of these bones, viz., the malleus and the stapes, are acted 
upon by muscles. 
The Tensor Tympani Muscle.--This muscle is located just above the Eusta- 
chian tube and sends its tendon over a tiny bony process acting as pulley, across 
the tympanic cavity to be inserted into the handle of the malleus. ESSENTIALS OF PHYSIOLOGY 
305 
The Stapedius Muscle.-The stapedius muscle is a small muscle situated in 
the interior of a pyramid of bone springing from the posterior wall of the middle 
ear. Its tendon is inserted in the neck of the stapes. 
The Eustachian Tube.-The middle ear communicates with the naso- 
pharynx through a tubular structure known as the Eustachian tube. The 
walls of this tube are partly bone and partly cartilage, and are lined by mucous 
membrane covered with ciliated epithelium. 
Superior semicircular canal - 
'Ampulla 
"Ampulla 
Posterior semicircular canal- 
Lateral semicircular canal- 
Vestibule and fenestra ovalis* 
Second turn of cochlea 
Cupula of cochlea 
Fenestra cochlearis 
Ampulla 
Commencement of first turn of the cochlea 
Fig. 170.-The osseous labyrinth of the right side. (Modified from Soemmerring. Enlarged.) 
The Internal Ear.-The internal ear or labyrinth is situated within the pet- 
rous portion of the temporal bone, and consists of an osseous portion giving 
lodgment to the membranous part. 
The osseous labyrinth includes the following parts, viz., the cochlea, vestibule, 
and semicircular canals (Fig. 170). The membranous labyrinth consists of the 
membranous cochlea, the utricle, the saccule, and the membranous semicircular 
canals; the utricle and saccule are located within the vestibule. 
Scala vestibuli- 
-Lamina spiralis 
Scala tympani- 
Modiolus 
Fig. 171.-Interior of the osseous cochlea. (From Morris' Human Anatomy.) 
The Osseous Labyrinth.-The cochlea is a conical structure consisting of a 
tube winding spirally two and a half times around a central pillar known as the 
modiolus (Fig. 171). A flat shelf of bone, partially subdividing the tubular 
cavity, springs from the modiolus and winds spirally to its apex. It is known as 
the lamina spiralis ossea. The membranous cochlea is attached to the edge of 
the spiral lamina, so that the spaces above and below the spiral lamina are 
entirely separated from each other. The upper space opens in the vestibule 
and is, therefore, called the scala vestibuli; the lower space opens into the tym- 
panum through a round opening-the foramen rotundum-and is consequently 
named the scala tympani. In the living condition the foramen rotundum is 306 
THE SENSE OF HEARING 
closed by a membrane. The two scalae communicate with each other at the 
apex of the cochlea by an aperture named the helicotrema. The modiolus is 
pierced by a number of passageways for the auditory nerve fibers. These 
passageways ultimately end in a spiral canal near the attached edge of the spiral 
lamina. This spiral canal contains the ganglion cells from which the auditory 
nerve arises. Numerous small canals transmit the nerve fibers to the free edge 
of the spiral lamina. 
The vestibule forms the central part of the osseous labyrinth. It is an 
ovoid space separated from the middle ear by a bony partition having near its 
center an oval opening-the fenestra ovalis-which is closed by the base of the 
stapes and its annular ligament. The inner wall is perforated by twelve to 
Superior and lateral membranous ampullaa 
Superior semicircular 
/ duct 
Cupular cecum 
Saccule 
Posterior semicircular 
> duct 
Cochlear duct 
Ductus reuniens 
Vestibular cecum 
Utricle, 
1 Lateral semicircular duct 
Posterior membranous ampulla 
Ductus endolymphaticus 
Fig. 172.-Diagram of the left membranous labyrinth. (Deaver.) 
fifteen small openings that serve to transmit the nerve fibers of the vestibular 
portion of the acoustic nerve. 
The osseous semicircular canals are three in number and are found above 
and behind the vestibule. From their respective positions they are named the 
superior vertical, the posterior vertical, and the horizontal.. These canals lie at 
right angles to each other. As the two vertical canals fuse by one of their extrem- 
ities, there are but five openings into the vestibule. One end of each canal is 
dilated and called the osseous ampulla. 
The two vertical canals make an angle of 450 with the medial plane of the 
body. If the position of the semicircular canals on the two sides of the median 
plane of the body be compared with each other, it will be seen that the horizontal 
canals lie on the same plane, and that the superior vertical canal on one side 
lies on a plane parallel to that of the posterior vertical canal of the opposite side. 
It will be obvious also that the two superior vertical, as well as the two posterior 
vertical canals lie in planes at right angles to each other. 
The Membranous Labyrinth.-The membranous part of the labyrinth 
occupies but a part of the space of the bony labyrinth. It is filled with a fluid ESSENTIALS OF PHYSIOLOGY 
307 
called endolymph, and is likewise surrounded by a fluid contained in the space 
between the bony and the membranous part known as perilymph. 
The vestibule contains two membranous structures, the utricle and saccule 
(see Fig. 172). The utricle communicates, on the one hand, with the membra- 
nous semicircular canals, and on the other hand, with the saccule by means of a 
small duct-the ductus utriculosaccularis. This duct communicates with 
another duct-the ductus endolymphaticus-which ends in a dilated, blind 
extremity under the dura mater which it reaches through an aqueduct in the 
petrous portion of the temporal bone. The saccule is smaller than the utricle, 
is of an oval shape, and is joined to the membranous cochlea by a short duct- 
the ductus reunions. 
Membrana tectoria. 
Capillaries of the stria. 
Hair cells. 
Hensen's 
cells. 
Claudius's 
cells. 
Labium vestibulare 
Sulcusspiralis. 
Inner 
Outer 
Nerve bundle. 
Labium 
tympanicum. 
Inner Outer 
Deitef's 
cells. 
Membrana 
basilaris. 
Connective 
tissue. 
Fig. 173.-Section through the organ of Corti. X 240. x, intercellular "tunnel" traversed by 
nerve fibers. (Lewis and Stohr.) 
Pillar cells. 
The membranous semicircular canals spring from the utricle. Their 
diameter is only about one-fourth that of the bony canals, expect at the ampul- 
lary end where they nearly fill the corresponding parts of the osseous canals. 
The End-organs of the Utricle, Saccule and Semicircular Canals.-The 
walls of these structures consist of connective tissue lined internally by epithe- 
lium. In the utricle and saccule there are localized thickenings of the epithelium 
known as maculae acusticae. The epithelium assumes a columnar shape and 
is provided with hair-like processes projecting into the endolymph. Among 
these processes are found crystals of calcium carbonate held by a gelatinous 
material. These crystals are termed otoliths. 
Similar structures are found in the ampullae of the semicircular canals 
where they are termed cristae ampullaris. The cristae are covered with hair 
cells whose processes float in the endolymph. They do not, however, contain 
any otoliths. 308 
THE SENSE OF HEARING 
The base of the hair cells receives the terminals of the vestibular division 
of the auditory nerve. 
The membranous cochlea is a triangular tube closed at both ends. The 
base of the tube is attached to the outer wall of the bony cochlea, while the 
apex is attached to the edge of the spiral lamina. The interior of the mem- 
branous cochlea forms what is known as the scala media. The wall of the tube 
below the scala vestibuli is called the membrane of Reissner. The portion of the 
membranous cochlea stretching from the edge of the spiral lamina to the bony 
wall is termed the basilar membrane, and gives support to a highly specialized 
end-organ known as the organ of Corti. 
The organ of Corti, as seen on cross-section, consists of various types of 
epithelial cells bearing a definite relation to each other (see Fig. 173). Two 
rows of cells known as rods of Corti rest on the basilar membrane and are 
inclined toward each other to leave a space known as the tunnel of Corti. Internal 
to the rods of Corti there is a single row of hair cells; while external to the outer 
rods three or four rows of similar cells occur. The outer hair cells are supported 
by Deiter's supporting cells. These cells rapidly decrease in size, to give place 
to two other types of supporting cells. Springing from the apex near the lower 
edge of the membrane of Reissner a thin membrane spreads over the organ of 
Corti-the membrana tectoria. In the lining condition this membrane is 
probably attached to the cells of Dei ter. 
The terminals of the auditory nerve are distributed to the base of the 
hair cells. 
THE PHYSIOLOGY OF THE AUDITORY APPARATUS 
The general function of the auditory apparatus is the reception of those 
atmospheric vibrations capable of exciting the hair cells of the organ of Corti. 
The effects they produce on the hair cells result in the production of nerve 
impulses which on reaching the cortex of the temporal lobe evoke in conscious- 
ness the sensation of sound. 
Characteristics of Sounds.--The physical basis of sounds are the vibrations 
imparted to the atmosphere by elastic bodies, such as strings, plates, mem- 
branes, rods, etc. These vibrations consist of alternate condensations and rare- 
factions of the air traveling in all directions, in a wave-like manner. When 
these waves follow each other rhythmically the sensation aroused is a musical 
sound; when the waves are arhythmic, or of exceedingly short duration, the 
sensation is that of a noise. 
Musical sounds are characterized by loudness or intensity, pitch and quality 
or timbre. The loudness or intensity of a sound depends on the amplitude or 
force of the vibrations. 
The pitch of a sound is determined by the number of vibrations taking 
place per second. The greater the frequency of the vibrations the higher the 
pitch. The lowest rate of vibration capable of stimulating the auditory appa- 
ratus varies in different individuals from 16 to 20; the highest rate lies between 
35,000 and 40,000 per second. ESSENTIALS OF PHYSIOLOGY 
309 
The quality, or timbre of a sound depends on the form of the vibratory wave. 
Most vibrating bodies vibrate not only as a whole but also in sections bearing 
a definitie ratio to the whole. Thus the halves, thirds, fourths, etc. vibrate 
simultaneously with the whole. These secondary vibrations give rise to what 
is known as overtones or harmonics. The overtones blend with the fundamental 
tone and produce a compound vibration varying in form with the type of the 
sounding body. For this reason various musical instruments, as the violin, 
piano, flute, etc. produce sounds of such different qualities that there is no 
difficulty in recognizing one from the other. 
The Functions of the External Ear.-The auricle or pinna serves to collect 
sound waves and reflect them into the external auditory canal. The auricle 
of man being relatively small and immovable is virtually functionless. The 
sound waves on entering the external auditory canal undergo a series of reflec- 
tions before they strike the tympanic membrane. 
The hair and ear-wax protect the tympanic membrane by preventing 
insects and foreign bodies from finding easy access into the external auditory 
canal. 
The Function of the Middle Ear.-The tympanic membrane is set into 
vibration by the sound waves directed against it by the external auditory canal. 
The structure and form of the membrane adapt it to a wide range of vibrations; 
it also magnifies the size of the vibrations. As the handle of the malleus is 
inserted in the membrane, the chain of ossicles acts as a damper, so that when 
the sound vibrations acting on the membrane have ceased, the membrane 
does not continue vibrating. 
The function of the tensor tympani muscle, it is generally believed, is to 
regulate the tension of the tympanic membrane so as to adjust it for vibrations 
of various frequencies. This function may be looked upon as one of 
accommodation. 
There is more uncertainty concerning the function of the stapedius muscle. 
It may serve to decrease the force with which the stapes moves against the 
fenestra ovalis; or it may act through the chain of ossicles to cause a relaxation 
of the tympanic membrane. The stapedius muscle is supplied by a branch of 
the facial nerve; when this nerve is paralyzed, loud sounds give rise to a painful 
sensation. 
In order that the tympanic membrane may vibrate freely, it is necessary 
that the pressure of the air remain the same on each side. This equalization of 
pressure takes place through the Eustachian tube. That this is a matter of 
importance for normal hearing is shown by what happens when the Eustachian 
tube is closed by the swelling of its mucous membrane from "colds in the head. " 
The acuteness of hearing is considerably decreased and the sounds appear 
muffled and distant. 
The vibrations of the tympanic membrane are transmitted by the chain of 
ossicles to the fenestra ovalis where they cause corresponding vibrations in the 
perilymph. The ossicles act as levers that serve to decrease the amplitude of 
the vibrations and at the same time increase their force. This action is aided, THE SENSE OF HEARING 
310 
further, by the relative size of the tympanic membrane and that of the fenestra 
ovalis. It has been estimated that the pressure of a sound wave acting on the 
tympanic membrane is increased .30 times by the time it reaches the fenestra 
ovalis. 
The Function of the Cochlea.-The waves of pressure in the perilymph are 
transmitted throughout the scala vestibuli and the scala tympani. The mem- 
brane of the fenestra rotunda follows the waves of pressure and acts as an 
equalizing mechanism to permit of free motion of the foot of the stapes. The 
pressure waves set up in the perilymph act through the membrane of Reissner 
and the basilar membrane upon the endolymph of the scala media, and thus upon 
the organ of Corti. 
Various theories have been offered of the manner in which the hair cells of 
the organ of Corti are stimulated. Most theories assume that some parts of the 
organ of Corti act as a series of resonators capable of vibrating in sympathy 
with sound waves of the same vibratory frequency. The phenomenon ot 
sympathetic resonance can be demonstrated readily by lifting the dampers of the 
strings of a piano and singing a given note; the strings of the piano whose fre- 
quency of vibrations corresponds with the note sung will be observed to vibrate. 
Helmholtz suggested that the fibers of the basilar membrane, of which there are 
about 24,000 act as resonators adapted to sounds of different pitch, as they 
gradually increase in length from the base to the apex of the cochlea. In this 
view, the vibrations of the basilar membrane are in some way transmitted to 
the hair cells and the tectorial membrane acts as a damper. According to 
Wrightson, the vibrations transmitted to the perilymph act on the basilar mem- 
brane so as to cause a lateral movement of the hairs of the hair cells, the tectorial 
membrane acting as a pivot for the ends of the hairs. In any event, nerve 
impulses are aroused in the terminals of the nerve fibers ending at the base of the 
hair cells. The nerve impulses are transmitted by the acoustic nerve to the med- 
ulla and ultimately reach the cerebral cortex of the temporal lobe where the 
sensation of sound is evoked. 
THE LABYRINTHINE SENSATIONS 
The Static Sense.-The sensations through which one becomes aware of the 
position of the body when at rest are mediated, in part at least, by the utricle and 
saccule. A change of position of the head causes a shifting of the weight of 
the otoliths on the hairs of the maculae acusticae. The nerve endings at the base 
of the hair cells are, therefore, variously stimulated as the head changes position. 
To a certain extent the otolithic organs are stimulated also when movements 
take place in one plane forwards or backwards. Owing to the central con- 
nections made by the fibers of the vestibular nerve supplied to these organs, 
adaptive movements take place reflexly with the apparent purpose of main- 
taining the equilibrium of the body. 
The Dynamic Sense.-The sensations arising when the body is rotated 
around various axes are subserved by the semicircular canals. Aside from this 
function, various reflexes necessary for the maintenance of muscle tone and ESSENTIALS OF PHYSIOLOGY 
311 
equilibrium take place through the activity of the fibers of the vestibular nerve 
distributed to the cristae ampullaris of the semicircular canals. The destruc- 
tion of the canals of one side in a pigeon is followed by a serious disturbance of 
equilibrium. Any attempt to move leads to inco-ordinate movements and a fall 
toward the side of the injury. In the course of time the animal learns to move 
about, but suffers from loss of tone in the muscles of the opposite side of the 
body. 
The stimulus acting normally on the cristae acusticae is the pressure of the 
endolymph upon the hairs of the hair cells when the body is rotated in the plane 
in which the canal lies and in the direction of the ampulla. CHAPTER XXXIX 
VOICE AND SPEECH 
Vocal sounds are produced by the vibrations of two elastic membranes-the 
vocal bands or cords-situated in the larynx. These sounds are modified by 
the resonating changes formed by the chest, the upper respiratory passages, 
the mouth, and the accessory sinuses of the nose. 
Articulate speech consists of vocal sounds modified by the action of the 
muscles of the palatal region, the tongue, the lips, and the lower jaw. 
Fig. 174. 
Fig. 175. 
Fig. 174.-Laryngeal cartilages and ligaments, anterior surface, i, hyoid bone; 2, 2, 3, 3, 
greater and lesser cornua; 4, Thyroid cartilage; 5, thyro-hyoid membrane; 6, thyro-hyoid ligaments; 
7, cartilaginous nodule; 8, cricoid cartilage; 9, the crico-thyroid membrane; 10, the crico-thyroid liga- 
ments; 11, trachea. {SappeyC) 
Fig. 175.-Laryngeal cartilages and ligaments, posterior surface. 1, 1, thyroid cartilage; 2, 
cricoid cartilage; 3, 3, arytenoid cartilages; 4, 4, crico-arytenoid articulations; 5, 5, crico-thyroid articu- 
lations; 6, union of the cricoid cartilage and of the trachea; 7, epiglottis; 8, ligament uniting it to the 
reentering angle of the thyroid cartilage. (Sappey.) 
The Larynx.-The larynx is situated at the upper end of the trachea and 
consists of a framework of cartilages articulating with each other. A number 
of muscles are attached to the various cartilages and determine the movements 
necessary for the functions of the larynx. The larynx is invested externally 
by fibrous tissue and is lined internally by mucous membrane continuous with 
that of the trachea below and of the pharynx above. 
The Laryngeal Cartilages.-The chief cartilages are the cricoid, thyroid, 
two arytenoids, and the epiglottis (see Figs. 174 and 175). The cricoid cartilage 
312 ESSENTIALS OF PHYSIOLOGY 
313 
is shaped like a signet ring the broad part directed backward, and rests upon the 
first ring of the trachea. The thyroid cartilage consists of two quadrilateral 
plates united anteriorly at an acute angle. The upper border of the thyroid 
has a deep notch at the center. The tip of the posterior inferior angle of each 
plate of the thyroid cartilage, articulates with the side of the cricoid and permits 
of an upward and downward movement of these 
cartilages. The arytenoid cartilages are more or 
less pyramidal in shape and are attached by their 
anterior angle to the vocal bands. The external 
angle receives the insertion of muscles. The infer- 
ior surface of the arytenoids is concave and articu- 
lates with the cricoid. This articulation permits 
of a rotation and of lateral and medial movements 
of the arytenoid cartilages. The epiglottis is a leaf- 
shaped, elastic cartilage placed vertically and 
attached to the thyroid cartilage at the median 
notch. It is bound by membranes and ligaments 
to the thyroid and arytenoid cartilages, and to the 
base of the tongue. Two small nodules of elastic 
cartilage are found on each side in a fold of mem- 
brane uniting the arytenoids and the epiglottis. 
They are the cornicula laryngis and the cuneiform 
cartilages. They are of no functional significance. 
The vocal bands, vocal folds or cords, consist of 
a ligament of yellow elastic fibers covered by a thin 
mucous membrane forming a sharp free edge (Fig. 
176). The vocal bands stretch from the angle 
between the two plates of thyroid cartilage in 
front and the vocal process of the arytenoid carti- 
lage behind. The epithelium covering the mucous 
membrane of the larynx is ciliated except over 
the vocal bands where it is of a stratified, squam- 
ous variety. The vocal bands vary in length in 
the male from 20 to 25 mm., and in the female 
from 15 to 20 mm. The space between the vocal 
bands is called the rima glottidis or glottis. 
The Intrinsic Muscles of the Larynx- The 
muscles directly concerned in the movements of 
the laryngeal cartilages are: (1) Two posterior crico-arytenoid muscles arising 
from the signet part of the cricoid cartilage and inserted into the external angle 
of the arytenoid cartilage. The contraction of these muscles causes a widening 
of the glottis, such as is necessary for free breathing (see Figs. 177 and 178). 
(2) Two lateral crico-arytenoid muscles arising from the side of the cricoid 
cartilage and inserted into the external process of the arytenoid cartilage. 
Their contraction approximates and stretches the vocal bands. 
Fig. 176.-Longitudinal section 
of the human larynx, showing the 
vocal bands. I, ventricle of the 
larynx; 2, superior vocal cord; 3, 
inferior vocal cord; 4, arytenoid 
cartilage; 5, section of the arytenoid 
muscle; 6, 6, inferior portion of the 
cavity of the larynx; 7, section of 
the posterior portion of the cricoid 
cartilage; 8, section of the anterior 
portion of the cricoid cartilage; 9, 
superior border of the cricoid carti- 
lage; io, section of the thyroid car- 
tilage ; 11, 11, superior portion of the 
cavity of the larynx; 12, 13, aryte- 
noid gland; 14, 16, epiglottis; 15, 
17, adipose tissue; 18, section of 
the hyoid bone; 19, 19, 20, trachea. 
(Sappey.) 314 
VOICE AND SPEECH 
(3) Two thyro-arytenoid muscles-thin muscles the inner part of which 
lie in the vocal bands. They have the same origin and insertion as the vocal 
bands, and when they contract they relax, the vocal bands. 
(4) Two crico-thyroid muscles arising from the lower border and lateral 
surface of the cricoid cartilage and inserted into the lower border and medial 
surface of the thyroid cartilage. Their action is to make the vocal bands 
tense. 
(5) Two sets of muscles, the arytenoids and the aryepiglottis muscles act 
as sphincters for the upper opening of the larynx. 
Fig. 177. 
Fig. 178. 
Fig. 177.--Posterior view of the muscles of the larynx, I, posterior crico-arytenoid muscle; 2, 
3, 4, different fasciculi of the arytenoid muscle; 5, aryteno-epiglottidean muscle. (Sappey.) 
Fig. 178.-Lateral view of the muscles of the larynx. 1, body of the hyoid bone; 2, vertical 
section of the thyroid cartilage; 3, horizontal section of the thyroid cartilage turned downward to 
show the deep attachment of the crico-thyroid muscle; 4, facet of articulation of the small cornu of 
the thyroid cartilage with the cricoid cartilage; 5, facet on the cricoid cartilage; 6, superior attachment 
of the crico-thyroid muscle; 7, posterior crico-arytenoid muscle; 8, 10, arytenoid muscle; 9, thyro- 
arytenoid muscle; 11, aryteno-epiglottidean muscle; 12, middle thyro-hyoid ligament; 13, lateral 
thyro-hyoid ligament. (Sappey.) 
The nerves endowing the mucous membrane of the larynx with sensibility 
and supplying the muscles are branches of the vagus. The sensor fibers are 
supplied by the superior laryngeal; the same nerve innervates the crico-thyroid 
muscles. All other muscles of the larynx are innervated by the inferior laryn- 
geal nerve. 
The Mechanism of Voice Production.-The conditions necessary for the 
production of vocal sounds are: (1) an expiratory blast produced by the con- 
traction of the muscles of the thorax and abdomen concerned in forced expira- 
tion; (2) an approximation of the vocal bands; (3) a tension of these bands. 
The resistance offered to the passage of the air by the narrow space between the 
bands causes the pressure of the expired air to rise rapidly and the vocal bands 
are set into vibration. The pressure to which the air rises for the production ESSENTIALS OF PHYSIOLOGY 
315 
of sounds of moderate loudness and pitch varies between 140 and 240 mm. 
of water, and for loud sounds to about 940 mm. of water. 
The loudness of the sound depends on the pressure of the air; hence, on 
the extent of the expiratory effort. The pitch is dependent partly on the length 
and partly on the tension of the vocal bands. The pitch is also influenced 
by the force of the air current so that when a note is sung crescendo the rising 
volume of the sound must be produced by a corresponding relaxation of the 
vocal bands. The quality or timbre of the voice is determined by the resonating 
properties of the air in the chest, and that in the mouth, pharynx, and the acces- 
sory sinuses of the nose. The chest cavity resonates with the notes of low pitch, 
while the cavities of the head resonate with those of higher pitch. 
The range of vocal sounds seldom exceeds one and three-quarters to two 
octaves in any one individual. 
The Mechanism of Articulate Speech.-Speech consists of a modification 
of laryngeal sounds occasioned by changes in the shape of the mouth and 
pharynx and movements of the lips and teeth. 
Vowel sounds are continuous laryngeal tones modified by changes in the 
capacity and shape of the mouth. Consonant sounds are produced by more or 
less complete interruptions of vowel sounds in various situations. Accordingly 
the consonant sounds have been classified as labials (p, b, m), labio-dentals (f, 
v), linguo-dentals (s, z), anterior linguo-palatals (t, d, 1, n, r, sh, zh), and poste- 
rior linguo-palatals (k, g, h, y). These names indicate the locations in which 
the sounds are produced and the various positions in which the blasts of 
air are interrupted. 
No vibration of the vocal bands takes place in whispering; the glottis is 
open, and words are produced during expiration by the same mechanism 
employed in usual speech. CHAPTER XL 
HYGIENE OF THE REPRODUCTIVE ORGANS 
The subject matter presented below is taken from Pamphlet No. 6, Divi- 
sion of Venereal Disease, of the United States Public Health Service. This 
matter is of special interest to dentists and pharmacists since they are often 
consulted by patients suffering from venereal disease. The treatment of these 
affections requires special knowledge and great skill. Considering the serious 
consequences of inadequate treatment, competent physicians only should 
undertake the treatment of venereal disease. 
CONTINENCE 
Ignorant gossip has said that the reproductive organs, like the muscles, 
are developed through exercise and become weak through disuse. Mere 
knowledge of the action of the internal sex glands is sufficient to nail this lie. 
A part of the secretions of the sex glands is reabsorbed into the blood, especially 
during young manhood, with great gain to muscular strength and nervous 
energy. That continence is practicable and healthful is shown by the experi- 
ence of athletes and members of exploring expeditions. A statement recently 
signed by 360 of the foremost medical men in the United States declares that 
there is no evidence that abstinence from sex activity is "inconsistent with the 
highest physical, mental and moral efficiency." The American Medical 
Association in its convention June 7, 1917, adopted a similar statement. 
In the matter of the "sex necessity" the most distinguished specialists 
and scientists point to an absolutely opposite course from the "know-it-all" 
ignorant gossip of the uninformed. Straight living is a sign of strength; it 
is common sense based upon the experience and suffering of past generations 
throughout history. 
If a man uses his reason, stops and thinks, he knows that he must either 
indulge his sex appetite or control it. For an unmarried man indulgence 
means self-abuse or prostitution, both of which endanger his health and rob 
him of self-respect. The reasonable, wise man finds the only way open to him 
is self-control. Increasing thousands of young men of the finest type of 
America's life are proving continence practicable for unmarried men. 
The main facts of prevention for men then relate to the means and methods 
of attaining self-control. 
CONTROL OF THE SEX IMPULSE 
Fitness, physical and mental, is the key to the proper use and control of 
the sex impulse. Vigorous recreation, hard work, wholesome companionships 
are the preventives of extreme temptations to use the reproductive organs 
316 ESSENTIALS OF PHYSIOLOGY 
317 
in a dangerous manner. Especially necessary in the fight for self-control is 
the avoidance of alcoholic liquor which breaks down the higher centers of mental 
control. Sound, healthy sex control may usually be attained by following these 
suggestions: 
(i) There should be an abundance of outdoor sports, gymnasium work, 
where possible, and swimming, walks in the country and similar physical activi- 
ties including fresh air and exercise vigorous enough to throw off waste products 
through free perspiration. A cold shower or sponge bath, followed by a brisk 
rub-down with a coarse towel, is helpful and necessary as an accompaniment of 
exercise. Wise choice of nourishing food and plenty of water help in the impor- 
tant matter of removing of wastes by regular bowel movements. Sufficient 
sleep and abundant fresh air, night and day, are essential. The bodily resis- 
tance thus developed will not only go far towards controlling the sex impulse 
but will help to avoid tuberculosis, grip, colds, diphtheria and minor ailments. 
(2) The second means of self-control is mental. Wholesome occupation, 
whether it be one's principal daily work or a favorite hobby, should be entered 
into with the whole mind. This leaves little time for smut and vice. Many 
young men, who avoid the grosser bodily and mental wrecks of venereal disease, 
waste the hours at the tip top of mental energy on imaginations of sex indul- 
gence and on useless worries over escapades and tempting sex situations with 
girls. These energies when redirected have produced some of the greatest 
works of inventive and artistic skill. 
(3) A third powerful help to self-control is friendly associations, especially 
with women of high character, women who respect themselves and their work. 
In wholesome associations with such women, in games, music, dances, picnics 
or constructive enterprise a man's sex desires are transformed. The way of 
the man who shuns women is much more difficult than that of the man who 
realizes that it is not good for man to be alone, and who plans to meet the need 
for woman's companionship. 
The problems of sex direction must be solved by man and woman working 
together. This comradeship makes it clearer that it is a social crime and 
mockery to have anything but a single standard of honor for men and women. 
To go through the forms of courtesy and chivalry in public while in secret to 
degrade particular women in thought, speech or act is a relic of an age which is 
passing. 
(4) These redirections of the thoughts and actions will not do away with 
the necessity of the exercise of strong will power. In present day surroundings 
temptations are constantly lurking for the unwary and most men face in their 
early manhood a mighty personal struggle. Knowledge will do much but 
determination is necessary for sound sex life. Those who give up by saying 
"human nature is human nature and nothing can curb it" are ignorant of 
the struggle of man throughout the ages in almost every line to curb "human 
nature" by self-control. The impulse is normal and natural. It can be 
accepted as a motive for marriage with a clean, decent woman, or as a weak 
excuse for intercourse with a prostitute. Fire is a great blessing to mankind. 318 
HYGIENE OF THE REPRODUCTIVE ORGANS 
By means of it, machinery is made to perform gigantic tasks. It warms our 
houses and cooks our food. The warmth and glow of a campfire is a source 
of great pleasure to campers. When fire is controlled it is a valuable aid to 
man, but when it gets beyond control it causes ruin. 
So sex energy must be controlled and directed. The man needs the full 
power of his will to keep his sex desires from leading him into practices that 
weaken and destroy himself and others. So controlled, sex means manliness, 
womanliness, courtship, love, marriage, home, father, mother, family life, 
education, filial love, brotherhood. 
VENEREAL DISEASES 
Venereal diseases are germ diseases passed from men to women and women 
to men usually through the sex organs. They are chiefly gonorrhea (or clap) 
and syphilis (pox or lues).1 Gonorrhea is also called a dose, gleet (an old case) 
or chordee (painful erections). These are two of the worst diseases now preva- 
lent. Every prostitute has them sooner or later, because she catches them 
from one or more of the hundreds of men she sells herself to. Most professional 
prostitutes (about 90 per cent) have one or both diseases. 
Any girl who will do business on the quiet and who may not charge any- 
thing (charity girl) may also have caught the disease from the first man who had 
her. The man who first ruins a girl is likely to be the carrier of disease as well 
as shame. The girl herself may not even know she is diseased or she may lie 
about herself. Any man who joins his body with the body of a prostitute or loose 
girl of any kind runs the risk of catching one of these diseases. 
Some people clung for a long time to the idea that if women were examined 
by doctors and men were allowed to use only those women thus examined it 
would be safe. This method will not work. It has proved useless as well 
as unjust and it encourages the business of the pimps, the madames, quack 
doctors and irregular intercourse itself. It is very hard to be sure that a woman 
is not diseased; it is easy for her to hide it; she may get the germs again from 
another man five minutes after she gets a clean bill of health from a doctor. 
Isolating all the diseased women and treating them until cured will help, but, 
so long as prostitution continues, diseased men will spread the disease. 
There is no certain preventive against venereal diseases except to use 
common sense and keep away from prostitutes. The many antiseptic washes, 
lotions, and injections that are used to prevent the development of these 
diseases after exposure are not entirely reliable because the skin and mucous 
membranes into which the germs have quickly penetrated may act as a wall, 
preventing the antiseptic from reaching them. 
GONORRHEA 
The persistence of this disease in the deeper parts long after it is outwardly 
cured, leads to the unsuspected communication of the disease to women with 
1 Small pox is called "small" because syphilitic sores are so much worse. Syphilis is also called 
lues, hard chancre, "siff," "old rale," "blood poison." ESSENTIALS OF PHYSIOLOGY 
319 
whom the individual may cohabit. Among these women may be his bride, who 
thereupon enters upon a period of ill-health that may ultimately compel the 
mutilation of her internal sexual organs by a surgical operation or cause the loss 
of her life. Much of the surgery of these organs performed upon women has 
been rendered necessary by gonorrhea contracted from the husband. Some- 
times the germs of the disease get into the baby's eyes at the time of birth and a 
few hours later cause permanent blindness. Such blindness may be prevented 
by the use of a solution which any doctor can administer directly after birth. 
The infection of innocent women, however, can not be so easily prevented. 
If a man who has had gonorrhea plans to marry, he should see a reliable 
physician and obtain a thorough examination to be sure there is no danger of 
infecting his future wife. Some states very wisely require an examination before 
they will issue a marriage license. If the man who has had the disease seems 
unwilling to have an examination for his own satisfaction, the woman whom he 
wishes to marry or, if necessary, her father, her mother, or her brother should 
demand it. 
Gonorrhea is a disease caused by germs (gonococci) getting into the urinary canal (in 
the penis) and attacking the inside of the sex organs. Very often these germswill be carried 
by the blood and attack other distant parts of the body (joints, heart, etc.). This disease 
is hardly ever contracted except as the result of sex intercourse with loose women. The first 
sign is usually a burning pain in the penis when making water. This happens usually three 
to fourteen days after being with a woman who has the disease. The urine at this time may 
show small fine flakes in it. After a day or two more a thick yellowish matter comes from 
the mouth of the penis. This is pus. It contains thousands of gonorrhea germs to every drop 
and is very dangerous. A small drop getting into the eye may easily cause blindness in a few 
days. 
If proper treatment is used by a doctor at this time and his advice is followed, the 
disease may be kept from spreading into the blood and prevented from doing damage to 
other organs of the body. 
When good advice and treatment are not taken, however, gonorrhea may become one of 
the most dreadful diseases afflicting mankind-and one of the hardest to cure. It sometimes 
results in complete loss of sex power or even sterility (inability to have children). Some- 
times, when treated wrongly or left too long without treatment, gonorrhea is absolutely 
incurable. 
Self treatment or quack treatment or quick cures are all dangerous. 
Some of the effects of this disease are: A painful kind of rheumatism, sometimes per- 
manently stiffening the joints; disease and blocking of the glands and organs making and 
storing the seminal fluid (the male seed); disease of the testicles, causing sterility; bladder 
disease; abscess of the kidney. Another serious result of gonorrhea is stricture. This 
is a scar in the urinary canal (inside of the penis). Like the scar of a burn it gradually pulls 
together (contracts) and finally may close down altogether so that the man cannot pass his 
urine. Then it can only be cured by a surgical operation. 
Gonorrhea can best be prevented by avoiding prostitutes. 
Practically all prostitutes have gonorrhea. 
Can Gonorrhea Be Cured?-To treat a new case of gonorrhea properly takes about four 
weeks. It sometimes takes much longer to bring about a real cure. When the discharge 
coming from the penis stops, the disease is not necessarily cured. Often, when this is the 
case, there will be a small drop at the end of the penis on getting up in the morning. The 
doctor, by careful examination, can find other sure evidence. Such cases are as dangerous 
as those having much pus. 320 
HYGIENE OF THE REPRODUCTIVE ORGANS 
Any man who thinks he, perhaps, has this disease should put himself under the care of a 
good physician at once and make sure. If he has it, he should keep going for treatment 
until pronounced really cured by the doctor. 
Gonorrhea is immeasurably worse than a bad cold. 
SYPHILIS 
A man, having syphilis, may transmit it to his wife, and she may 
transmit it to the body of the child before birth, so that the child will be born 
dead, or so that, if it is born, it will be crippled in mind and body. Syphilis is 
transmitted to the offspring in full virulence and its inherited effects are appalling. 
If a man has ever had syphilis, he should of course obtain a thorough 
medical examination before marrying. If there are any signs of the disease 
remaining, he should refrain from entering the marriage relation. 
The disaster to the individual wrought by syphilis is shown in the attitude 
of the leading insurance companies toward those so infected-a purely business 
proposition without sentimental considerations. They refuse to insure the life 
of a syphilitic person for four or five years after the disease was contracted, and 
then only upon special terms, for their records prove that syphilis shortens life, 
and that the death rate for those who have had syphilis is double the rate for 
those who have never contracted it. 
Syphilis is a contagious, slow-acting (or chronic) disease caused by germs which, with 
their poison, are carried by the blood through the whole body, reaching every organ. 
Syphilis, like gonorrhea, is usually caught from loose women or whores, but it is also 
transmitted by kissing and sometimes by touching things which have been used by syphilitic 
people, such as clothing, cups, pipes, towels, beds, etc. 
The germ causing syphilis can get into the blood through the tender lining of the penis, 
the lips, or the eye, or through a break in the skin. This break in the skin may be so small 
that it can not be seen with the naked eye. 
The Course of the Disease.-After the germs get under the skin, it then takes two to 
eight weeks before they make enough poison to cause the first sign to appear. This is a small 
red spot, or pimple, or an ulcer, known as a chancre, or hard sore. This is the best time for 
treatment if one wants to be cured. 
Sometimes a chancre is so small and so slightly inflamed that a man does not pay any 
attention to it. Any small pimple or sore spot on the sex organs should be most carefully 
watched by a doctor. It may be a chancre. 
If not stopped, the syphilis germs and their poison are now carried to other parts of the 
body. In six weeks to three months the disease has developed far enough to cause the 
symptoms of the second stage. These signs are of great variety. They may be very severe. 
They may be so light as not to be noticed. It takes an experienced doctor to recognize them. 
They may be found in any part of the body. Some of the signs of the second stage are: 
Headache, bone-pains, fever, sores in the mouth and throat, skin rashes, swelling of the 
glands, sore throat, rapid loss of hair, etc. These signs may all appear at once, but if only 
one or two of them show, this does not necessarily mean that it is a light case. 
Steady treatment at this time is absolutely necessary. Otherwise it may be too late. 
The third stage comes on very, very slowly. It takes from one to twenty years to show 
itself. If early, proper, thorough treatment were always taken during the first and second 
stages, the frightful effects of the third stage, which destroy brain, nerves, blood vessels, 
bones, liver, arteries, and other parts of the body, would never exist. Locomotor ataxia, 
certain kinds of paralysis, paresis (brain softening), some forms of insanity, deformities of ESSENTIALS OF PHYSIOLOGY 
321 
bones and joints, are all different forms of the third stage of syphilis, but they do not happen 
in well-treated and early-treated cases. 
Nor do they happen to men who have sense enough to leave prostitutes alone, unless in 
rare instances through accidental infection. 
Syphilis in its first stage is highly contagious. In its second stage it is also catching. 
Mouth sores come in the second stage. If a man with these sores kisses another person, he 
may give the disease to that person. In general proper treatment during this stage makes a 
man less of a danger to other people. In its third stage it is very slightly catching, but 
causes the most damage to the man who has it. 
If a person has syphilis it shows in the blood. The signs and symptoms and the Wasser- 
mann blood test leave no doubt. 
Syphilis may show itself at different times for a year or more, and, without much treat- 
ment, it may seem to be cured after each attack. But it is still in the body. 
After a month of treatment a man may be well so far as he can tell. But he is not cured. 
Not only is he still full of the disease but he can give it to others. He must not have sex 
intercourse, even though married, until his doctor is sure that he will not give disease to his 
wife. He must avoid kissing and should use only his own brushes, pipes, razors, towels, etc., 
and not let others use them without scalding. He must protect other people until the doctor 
says he is no longer a source of danger to his family and comrades. 
Can Syphilis Be Cured?-The answer is yes, if treated soon enough. But not in a week or 
a month. A patient must be under a doctor's care for a period of one to three years before a 
cure is certain. The blood test and others must be used to be certain that a man is cured. 
CHANCROID (SOFT CHANCRE) 
Soft chancre is a filthy sore on or near the sex organs, caught from an especially dirty 
woman. It is not so dangerous as syphilis or gonorrhea, and does not get into the blood; 
but an old case may get into the groin (buboes or "blue balls"). This is hard to cure and 
puts a man on the sick list. It may also eat in until the affected parts have to be cut away. 
What is more important, soft chancre looks so much like hard chancre (syphilis) that you 
can't take chances. It may hide a syphilitic chancre. If you have any sore, see your physician. 
OTHER "SEX" COMPLAINTS 
Varicocele, hydrocele, pediculosis (crabs), and spermatorrhea are all less dangerous than 
the venereal diseases. They are not germ diseases and can usually be cured by following 
simple advice from your physician. 
CAUTION 
It should be remembered that blindness, invalidism, paralysis and insanity 
are often due to other causes than syphilis and gonorrhea. One should be care- 
ful, therefore, to make no false accusations regarding any one who may suffer 
from these afflictions. 
QUACKS 
For years "quack" doctors and "medical" institutes have made capital out 
of the ignorance of men concerning facts about their reproductive organs. In 
many cities these unscrupulous men advertise to cure "lost manhood, " "nervous 
debility," "pimples," and other things which have nothing to do with sexual 
health. They try to frighten people into paying large sums for the cure of 
"diseases" that do not exist, and scare boys into thinking the normal experi- 
ences of growing manhood are indications of sexual disorders. They are more 322 
HYGIENE OF THE REPRODUCTIVE ORGANS 
interested in a patient's money than his health. A good doctor never advertises; 
he waits until a man comes to him. 
Men suffering from any sex disease should beware of these same 11 medical 
institutes" and advertising quacks. Patent medicines and "favorite pre- 
scriptions" are dangerous. Every case needs individual attention and the care 
of an absolutely reliable physician. 
If a man has no money he can secure free treatment in almost every state 
and city at a dispensary. In many states the Boards of Health have established 
public clinics where scientific treatment and advice are freely given for venereal 
disease. 
SEX IN LIFE 
Sex links the man who marries to the past and to the future in a great chain 
of human beings. A man by one false step may infect the racial stock, wreck 
the hopes of fathers and mothers reaching back for hundreds of years and blight 
the lives of generations to come. The spark of life is a sacred trust to be received 
reverently and transmitted undimmed to future generations. INDEX 
Abducent nerve, 90 
Aberration, spheric, 295 
Absorbents, 24 
Absorption, 232 
of drugs, 234 
by epithelium of villi, 233 
of foods, 233 
of fat, 234 
of protein, 234 
of sugar, 233 
of water and inorganic salts, 233 
in stomach, 206 
Acacia, action on epithelial tissue, 24 
on respiration, 182 
as a constituent of Bayliss' solution, 125 
Accommodation of the eye, 293 
contraction of sphincter pupillae in, 294 
convergence of eyes during, 294 
force of, 294 
mechanism of, 293 
range, 294 
Acetanilid, action on central nerve system, 103 
on excretion, 267 
on metabolism, 251 
Acetphenetidin, action on central nerve system, 
103 
on excretion, 267 
on metabolism, 251 
Acetates, action on blood, 127 
on excretion, 266 
Acetylsalicylic acid, action on central nerve 
system, 103 
on excretion, 267 
on metabolism, 252 
Acidosis, 238 
Acids, acetic, 127, 266 
acetylsalicylic, 103, 252, 267 
agaric, 268 
amino-, 185, 240 
boric, 29, 267 
caustic, 26 
chemical antidotes for, 26 
chrysophanic, 227 
citric, 125, 127, 266 
crotonic, 228 
diethylbarbituric, 101 
filicic, 231 
glacial acetic, 26 
hydrochloric, 26 
hydrocyanic, 92 
nitric, 26 
Acids, phenylcinchoninic, 252 
salicylic, 29, 103, 226, 252, 267 
sarcolactic, 36 
sialogogue action of, 223 
sulphuric, 26 
tannic, 25, 229, 230 
trichloracetic, 26 
uric, 240 
vegetable, 185 
Aconite, action on circulation, 157 
on metabolism, 249 
Aconitine, see aconite. 
Acoustic or auditory area, 87 
nerve, 90 
Acromegaly, 277 
Action currents of muscles, 35 
Actions of drugs, 11 
direct, 13 
direct local, 12 
general, 12 
intensity of, 12 
local, 12 
primary, 13 
reflex, 63 
remote, 12 
remote local, 13 
salt-action, 13 
systemic, 12 
Activator, definition of, 189 
Addison's disease, 274, 281 
Adrenal bodies or glands, 273 
embryologic development, 273 
effects of disease, .273 
internal secretion, 275 
of injection of extracts, 275 
removal of, 273 
Adrenal cortex, 273 
Adrenalin, 275 
action on sympathetic division, 112 
on circulation, 156, 159, 275 
on digestive apparatus, 275 
on eye, 301 
on internal secretion, 281 
on metabolism, 250 
on respiration, 183, 275 
influence of nerve system on production of, 
275 
seat of action, 275 
Agar-agar, action on epithelial tissue, 24 
on digestive apparatus, 227 
Agaricin, 268 
system, 103 
323 INDEX 
324 
Air cells, 162 
Air passages, 161 
Alcohol, ethyl ("grain"), 26, 27, 29, 43, 99, 159, 
180, 266, 267 
methyl ("wood"), 99 
Alcohol (ethyl) action on central nerve system, 
99 
on circulation, 159 
on epithelial tissue, 26, 27, 29 
on excretion, 266, 267 
on fatigue, 43 
on respiration, 180 
on skeletal muscle tissue, 43 
poisoning by, 99 
Alcohol^ wood, action on central nerve system, 
99 
Alcoholism, 99 
Alimentary canal or tract, 188 
Alkalies, caustic, 26 
chemical antidotes for, 26 
Alkalinizers, local, 127 
systemic, 126 
All-or-none law of skeletal muscle, 35 
Aloes, 227, 228 
Alterative, 183 
Alum, action on digestive apparatus, 226, 230 
on blood, 25, 128 
on epithelial tissue, 25, 26 
on excretion, 267 
burnt, 26 
Aluminium acetate, 29 
chloride, action on excretion, 267 
Alveolar air, 171 
composition of, 171 
Alypine, 115 
Ametropia, 296 
Amino-acids, 185, 240 
Amitosis, 9 
Ammonia, 156, 159, 181 
action on circulation, 156, 159 
on digestive apparatus, 224 
on epithelial tissue, 27 
on excretion, 267 
on respiration, 181, 182 
aromatic spirit of, 156, 159, 181, 224 
water, 27, 156 
Ammoniated mercury ointment, 30 
Ammonium acetate, action on excretion, 267 
carbonate, 156, 182 
chloride, 182 
hydroxide, 27, 156 
Amoeba, 2 
Amorphous filicic acid, 231 
Amphiarthroses, 22 
Amylase, 189, 211, 212 
Amylopsin, 211, 212 
Anabolism, 7, 237 
Analgesia, 103, 104 
spinal, 114 
Analgesics, 103 
antipyretic, 251 
local, 104 
Anaphylaxis, 128 
Anatomy, 4 
Anemia, 124 
Anesthesia, 76, 95 
general, 95 
stages of, 97 
infiltration, 114 
local, 114 
peri- or intraneural, 114 
regional, 115 
scopolamine-morphine, 103 
spinal, 114 
subcutaneous, 114 
terminal, 114 
Anesthetics, 95 
general, 95 
local, 114 
Anhydrotics, 267 
Animal body, structure of, 9 
heat, 247 
machine for doing work, 241 
Anise, 224 
Anodynes, 103 
local, 104 
Antacids, 225 
local, 127, 225, 226 
systemic, 126 
Antemetics, 226 
Anthelmintics, 229 
Anthemis, 224 
Antiasthmatics, 183 
Antibodies, 127 
Antidiarrheics, 228 
Anti-dromic vasodilatator nerves, 148 
Antihysterics, 104 
Antiluetics, 30 
Antimony and potassium tartrate, action on 
epithelial tissue, 27 
on respiration, 182 
Anti-peristalsis, 221 
Antipyretics, 251 
analgesic or coal-tar, 251, 267 
antimalarial, 251 
antirheumatic, 252 
Antipyrine, action on central nerve system, 103 
on excretion, 267 
on metabolism, 251 
Antiseptics,. 27 
intestinal, 29 
mucous membrane, 29 
skin, 29 
urinary, 29 
Antisialogogues, 223 
Antispasmodics, 104 
Antisyphilitics, 30 
Antithrombin, 123 INDEX 
325 
Antitoxic serums, 127 
Antitoxins, 127 
diphtheria, 128 
tetanus, 128 
Antizymotics, 28 
Aperients, 227 
Aphasia, 88 
Apomorphine, action on digestive, apparatus, 226 
on respiration, 182 
Apparatus, 4 
Appetite juice, 203, 223 
Arachnoid, 55 
Arborization, 47 
Argyrol, 29 
Aristochin, 251 
Aromatics, 224 
sialogogue action of, 223 
Arrectores pilorum muscles, 263 
Arsenic, 26, 30, 126 
action on blood, 126 
trioxide, 26 
Arsenobenzol, 30 
Arsphenamine, 30 
Arterial circulation, 144 
pressure, 144 
Arteries, functions of, 144 
structure and properties of, 142 
Arteriole, 143 
Articulate speech, 312 
mechanism of, 314 
Articulations, 22 
Artificial respiration, 178 
Asafetida, 104 
Ascaricides, 230 
Asepsis, 28 
Asparagus, 266 
Asphyxia, 178 
Aspidium, 231 
Aspirin, see acetylsalicylic acid. 
Assimilation, 7, 237 
Association centers of cerebrum, 88 
Asthenia, 79 
Astigmatism, 297 
Astringents, 25, 228, 267 
metallic, 25 
vegetable, 25, 229 
As-Vs interval, 136 
Asynergia, 79 
Ataxia, 79 
Atonia, 79 
Atophan, 252 
Atropine, action on eye, 300 
on central nerve system, 102, 104 
on circulation, 159 
on digestive apparatus, 223, 226 
on excretion, 268 
on metabolism, 249 
on parasympathetic division, no 
on respiration, 181, 183 
Atropine, action on salivary glands, 223 
poisoning by, in 
Auditory apparatus, 303 
physiology of, 308 
Auriculo-ventricular bundle, 135 
Autacoids, 269 
morphogenetic, 269 
Autonomic nerve system, 105 
parasympathetic division, 106 
pharmacodynamics of, 110 
sympathetic division, 106 
pharmacodynamics of, 112 
Autonomic nerve system, anatomic relation of 
central nerve, 58 
autonomic or sympathetic ganglia, 106 
functions of autonomic nerve system, 106 
pharmacodynamics of autonomic nerve 
system, 109 
relation of ganglia, to peripheral structures, 
106 
system to sympathetic ganglia, 105 
Axon, 47 
Hillock, 47 
reflex, 148 
Axoplasm, 47 
Bacilli, 28 
Bacteria, 28 
Bacteriology, 28 
Balsam of copaiba, 29, 266 
Peru, 183 
Tolu, 183 
Basal ganglia, 82 
metabolism, 242 
Belladonna, see atropine. 
Benzoates, 183 
Betanaphthol, 29 
Bichloride of mercuy, see mercuric chloride. 
Bile, 215 
acids, 216 
composition of, 216 
elaboration of, 217 
functions of, 217 
mode of secretion, 217 
pharmacodynamics of, 228 
pigments, 216 
salts, 216 • 
storage and discharge of, 217 
influence of nervous system on, 217 
total quantity of, 217 
Bilirubin, 216 
Biliverdin, 216 
Bioplasm, 2 
conductivity, 9 
irritability, 9 
movement, 9 
physiological properties, 9 
Bismuth subcarbonate, 226, 229 
subgallate, 229 326 
INDEX 
Bismuth subnitrate, 226, 229 
Bitter orange peel, 224 
Bitters, 223 
aromatic, 224 
astringent, 224 
sialogogue action of, 223 
simple, 224 
Black wash, 30 
Bladder, 259 
Blaud's pills, 125 
Bleeder, 123 
Blood, 116 
changes in, during respiration, 172 
chemical reaction of, 117 
chemistry of, 122 
coagulation of, 122 
composition of, 116 
corpuscles, 11.7, 119, 121 
crenation of, 13 
general composition of, 116 
hemolysis of, 13 
laking of, 13 
pharmacodynamics of, 125 
physical composition, 116 
plasma, 121 
composition of, 121 
platelets, 121 
pressure, 146 
arterial, 144, 146 
capillary, 145, 146 
causes of, 144 
pulse, 146 
venous, 146 
properties, 116 
quantity of, 123 
reaction, 117 
serum, 122 
specific gravity, 117 
temperature, 117 
velocity of, in arteries, 146 
in capillaries, 146 
in veins, 146 
viscosity, 117 
Bone, 17 
composition of, 18 
corpuscle, 18 
histology of, 18 
hygiene of, 23 
Bones of skeleton, 20, 21 
Boric acid, action on epithelial tissue, 29 
on excretion, 267 
Brain, 72 
parts of, 73 
Bromides, action on central nerve system, 
100 
on digestive, apparatus, 223, 226 
on respiration, 182 
poisoning by, 100 
Bromism, 100 
Bronchial innervation, 164 
Bronchioles, 162 
Bronchoconstrictors, 164 
Bronchodilatators, 164 
Broom, 266 
Brown-Sequard symptom complex, 69 
Buchu, 266 
Burdach, fasciculus of, 67 
Burnt alum, see alum. 
Cachexia strumipriva, 271 
Caffeine, action on cardiac muscle, 45 
on central nerve system, 92 
on circulation, 157, 159, 160 
on excretion, 265 
on respiration, 181 
on skeletal, voluntary or striated muscle, 
43 
effect on fatigue, 43 
Calabar bean, see physostigmine. 
Calamus, 224 
carbonate, 24, 225, 229 
Calcium oxide, 26 
hydroxide solution, 225, 230 
salts of the body, 122 
Calomel, 29 
action on digestive, apparatus, 227, 228, 
229, 230 
on excretion, 266 
Calorie, 241 
definition, 241 
Calorimeter, 241 
Calumba, 224 
Camphor, action on circulation, 159 
on digestive apparatus, 229 
on epithelial tissue, 27, 29 
on excretion, 267 
spirit of, 183, 267 
Cantharides, 27 
Capillary blood vessels, 143 
functions of, 145 
variations in caliber, 145 
drugs producing, 158 
Capsicum, action on epithelial tissue, 27 
on digestive apparatus, 224 
Capsule, internal, 82 
functions of, 82 
Carbohydrate metabolism, 237 
oxidation of, 242 
release of sugar, 237 
storage of sugar, 237 
influence of nerve system on, 238 
Carbohydrates, 244 
assimilation limit of, 239 
Carbon dioxide, action on respiration, 176, 
180 
Carbon equilibrium, 243 
Carbon monoxide, 118 
hemoglobin, 118 INDEX 
327 
Cardamom, 224 
Cardiac cycle, 133 
action of valves during, 133 
movement of the blood during, 133 
Cardiac depressants, 157 
Cardiac muscle, 42, 133 
pharmacodynamics of, 43, 44, 45, 155, 156, 
i57,158 
Cardiac nerves, 137 
Cardio-accelerator center, 141 
Cardio-inhibitor center, 140 
Carminatives, 224 
Cartilage, hyaline, 17 
white fibro-, 17 
yellow fibro-, 17 
Cascara, 227, 228 
Caseinogen, 204 
Castor oil, 227, 228, 230 
Castration, effects of, 280 
Catabolism, 237 
Catalysis, 189 
Catechu, 25, 229 
Cathartics, 226 
acting by special affinity, 228 
classification of, 227 
localization of action of, 228 
rapidity of action of, 228 
Caudate nucleus, 82 
Caustic acids, 26 
antidotes for, 26 
Caustic alkalies, 26 
antidotes for, 26 
Caustic metallic salts, 26 
Caustics, 26 
Cells, the life of, 7 
chemical composition, 7 
manifestations of life by, 7 
pharmacodynamics of, 11 
physiological properties of, 9 
reproduction of, 8 
structure of, 6 
Cellulose, 187, 221 
Centers, 77 
articulation, 77 
cardiac, 77 
deglutition, 77 
mastication, 77 
nerve, 49 
respiratory, 77 
salivary, 77 
vasomotor, 77, 147 
Central nerve system, 55 
pharmacodynamics of, 92 
Centroso me, 7 
Cerebellar tracts, 77 
Cerebellum, 77 
functions of, 79 
results of experimental lesions, 79 
Cerebro-spinal fluid, 55 
system, 55 
Cerebrum, 72, 80 
association areas of, 88 
convolutions of, 81 
fissures of, 81 
functions of, 84 
lobes of, 81 
localization of function in, 85 
motor area of the brain, 85 
sensor areas of the brain, 86 
auditory, 86 
cutaneous, 86 
gustatory, 88 
muscle sense, 86 
olfactory, 88 
visual, 86 
speech area, 88 
structure of, 82 
Cerium oxalate, 226, 228 
Cevadine, action on circulation, 158 
on skeletal, voluntary or striated muscle, 
43 
Chalk, 24 
prepared, 225, 229 
Chalones, 269 
Chamomile, 224 
Chancre, 320 
Chancroid, 321 
Charcoal, 24 
Chemical control of respiration, 176 
Chloral alcoholate, 101 
hydrate, action on central nerve system, 
100 
on circulative, apparatus, 226 
on respiration, 182 
poisoning, 101 
Chloretone, 101 
Chlorides of mercury, see mercury. 
Chloroform, action on central nerve system, 96, 98 
on circulation, 159 
on epithelial tissue, 27 
on respiration, 183 
anesthesia, 98 
liniment, 183 
Cholagogues, 216, 228 
Cholesterol, 216 
Chorda tympani nerve, 195 
Chorioid, 289, 290 
Chromaffin, 273 
Chromatin, 6 
Chyle, 234 
Chyme, 209 
Ciliary ganglion, 295 
muscle, 290 
function of, 293 
Cimicifuga, 224 
Cinchona, action on digestive apparatus, 224 
on metabolism, 251 
structure of, 77 328 
INDEX 
Cinchona, compound tincture of, 224 
red, 224 
Cinchonidine, 251 
Cinchonine, 251 
Cinchophen, 252 
Circulation of blood, 129 
hygiene of, 149 
pharmacodynamics of circulation, 155 
pulmonic, 142 
systemic, 142 
vascular apparatus, 129, 142 
Circulatory stimulants, 155 
Cisterna chyli, 152 
Citrates, action on blood, 127 
on excretion, 266 
Clarke's vesicular column, 59 
Classification of antacids, 126 
of antipyretics, 251 
of cathartics, 227 
of counterirritants, 27 
of diuretics, 265 
of drugs affecting the calibre of vessels, 158 
of emetics, 225 
of expectorants, 182 
of food principles, 184 
of hypnotics, 100 
of joints, 22 
of narcotics, 95 
of nerve fibers, 48 
of nerves, 53 
of protectives, 24 
of sense organs, 282 
of stimuli, 9 
of tracts of spinal cord, 66 
Closure of posterior nares, 199 
Coal-tar anti-pyretics, 251, 267 
Coagulation of blood, 122 
Cocaine, action on central nerve system, 104 
on circulation, 159 
on digestive apparatus, 226 
on epithelial tissue, 26 
on the eye, 301 
on metabolism, 249 
on sympathetic division, 114 
Cocci, 28 
Cochlea, 305 
functions of, 310 
Cocoa butter, action on digestive apparatus, 227 
on epithelial tissue, 24 
suppositories, 24, 227 
Codeine, action on central nerve system, 102, 103 
on digestive apparatus, 226 
on metabolism, 249 
on respiration, 182, 183 
Coffee, 92 
Cold, 226, 251 
cream, 24 
icerbag, 251 
Collaterals, 47 
Colloid substances, 269 
Colocynth, 228 
Colocynthin, 228 
Complemental air, 168 
Compound cathartic pills, 228 
Compound effervescent powder, 227 
Condiments, 185, 224 
Conductivity, 9 
of muscle, 33 
of nerve, 52 
Condurango, 224 
Connective tissues, 15 
Convolutions of cerebrum, 81 
Coordination, mechanism of, 65, 79, 310 
Copaiba, 29 
Copper sulphate, action on digestive apparatus, 
226 
on epithelial tissue, 25, 26 
Cornea, 289 
Corpora striatum, 82 
Corpus luteum, 280 
action on internal secretion, 280 
Corpuscles of Hassall, 279 
Corrosive acids, 26 
alkalies, 26 
Corrosives, 26 
Cottonseed oil, 24 
Counterirritants, 27,104, 183, 226, 267 
Counterirritation, 27,104,183, 226, 267 
action on central nerve system, 104 
on digestive apparatus, 226 
on excretion, 267 
on respiration, 183 
Cranial nerves, 88 
origin of, 88 
Cranium, 20 
Cream of tartar, 127, 227 
Creatinin, 256 
Crenation, 13 
Creosote, 182 
Cresol, 29 
Cretinism, 270 
Cristae ampullaris, 307 
Croton oil, 27, 228 
Crystalline lens, 292 
Cubeb, 29, 182, 266 
Cusso, 231 
Cutaneous sensations, 283 
Cycloplegic, 300 
Cytoplasm, 6 
Defecation, 221 
nerve mechanism of, 220 
Degeneration, Wallerian, 52 
Deglutition, 197 
act of, 198 
nerve mechanism of, 199 
Delirium tremens, 99 
Demulcents, 24 INDEX 
329 
Dendrites, 47 
Dendrons, 47 
Depression, 11 
Depressor nerve, 148 
fibers, 148 
Detrusor urinae muscle, 259 
Dextrin, 196 
Dextrose, 185, 218, 237 
Diabetes, 238 
Diabetic center, 238 
Diapedesis of leucocytes, 121 
Diaphragm, 165 
Diaphoretics, 267 
Diarthroses, 22 
Diastase, 225 
Diet, 241 
Diethylbarituric acid, 101 
Digestion, 188 
hygiene of, 222 
pharmacodynamics of, 223 
Digestive apparatus, 188 
ferments, 188, 224 
fluids, 188 
Digitalein, 44 
Digitalin, 44 
Digitalis, action on cardiac muscle tissue, 45, 155 
on the circulation, 155, 159, 160 
on the digestive apparatus, 226 
on excretion, 265 
on involuntary or smooth muscle tissue, 
44 
Digitonin, 44 
Digitoxin, 44 
Dilatator pupillae muscle, 290, 295 
Dionine, action on central nerve system, 102 
on eye, 102 
on respiration, 182 
Diopter, 294 
Direct or dorsal spino-cerebellar tract, 67 
Direct local action, 13 
Disinfectants, 27 
Disinfection, 28 
of mucous membranes, 28 
of the skin, 28 
Dissimilation, 7, 237 
Diuretics, 265 
acting by changes in general circulation, 265 
by salt-action, 266 
by stimulation of kidney cells, 265 
irritating stimulant, 266 
non-irritating stimulant, 265 
therapeutic applications of, 267 
Diuretin, 226 
Drastics, 127, 228 
Dropsy, 149 
Drugs, definition of, 5 
absorption of, 234 
centrally acting vasoconstrictor drugs, 158 
vasodilatator drugs, 159 
Drugs, excretion of, in saliva, 223 
peripherally acting vasoconstrictor drugs, 
159 
vasodilatator drugs, 160 
which affect the calibre of vessels, 158 
Drunkenness, 99 
Ductless glands, 269 
Dura mater, 55 
Dusting powders, 24 
Dynamic sense, 310 
Ear, 303 
internal ear, 305 
middle ear, 304 
Ear bones, 304 
function of, 304 
Edema, 149 
Egg white, 24 
Elaterium, 228 
Electricity, 249 
Emetics, 225 
central, 225 
local or reflex, 226 
Emmetropia, 293 
Emodin, 227 
Emollients, 24 
Encephalic nerves, 88 
Encephalon, 72 
Endocardium, 132 
Endocrine glands, 269 
Endoneurium, 51 
Enemas, 227 
Enterokinase, 212 
Enzymes, 188 
reversibility of action of, 189 
specific action of, 189 
Epidermis, 261 
Epiglottis, 161 
Epinephrine, 275 
action on epithelial tissue, 26 
on circulation, 156, 159 
on eye, 301 
on internal secretion, 281 
on metabolism, 250 
on respiration, 183, 275 
on sympathetic division, 112 
Epineurium, 51 
Epispastics, 27 
Epithelial tissues, 14 
functions of, 15 
pharmacodynamics of, 24 
Erepsin, 212 
Ergamine, 44 
Ergot, 44, 113, 159 
Ergtoxin, action on circulation, 159 
on involuntary or smooth muscle, 44. 
on sympathetic division, 113 
Errors of refraction, 296 
Erythroblasts, 118 INDEX 
330 
Erythrocytes, 117 
Erythrol tetranitrate, 160 
Escharotics, 26 
Eserine, see physostigmine. 
Esophagus, 188 
Ether, action on central nerve system, 96 
on circulation, 159 
on digestive apparatus, 224 
on respiration, 180 
anesthesia, 96 
compound spirit of, 159, 180, 224 
Ethyl alcohol, see alcohol. 
chloride, 115 
nitrite, 160 
Eucaine, 115 
Euquinin, 251 
Eustachian tube, 305 
Excretion of drugs in the saliva, 265 
pharmacodynamics of, 223 
Exophthalmic goitre, 271 
Expectorants, 182 
anodyne, 183 
demulcent, 182 
nauseant, 182 
saline, 182 
sedative, 182 
stimulating, 182 
Expiratory forces and muscles, 166 
Expired air, composition of, 170 
External secretions, 269 
Exteroceptive nerves, 68 
Eye, 289 
accessory structures of, 297 
anatomy of, 289 
blind spot, 297 
errors of refraction, 296 
hygiene of, 299 
pharmacodynamics of, 300 
reduced, 293 
refracting media, 292 
retinal image, 292 
schematic, 293 
Eye-ball, 289 
Eye-lids, 297 
Facial nerve, 90 
branches of, 90 
function of, 90 
Fainting, 150 
Farsightedness, 296 
Fat, 244 
absorption of, 234 
digestion of, 213, 217 
emulsification of, 213 
metabolism of, 239 
saponification of, 213 
Fatigue, 36 
effect of alcohol on, 43 
■ effect of caffeine on, 43 
Feces, 221 
Ferments, 188 
Ferratin, 126 
Ferric chloride, 25 
tincture of, 125 
Ferrous carbonate, pills of, 125 
iodide, syrup of, 125 
Fever, 248 
Fibrin, 122 
Fibrinogen, 122 
Fillet, lateral, 76 
mesial, 76 
Filum terminale, 58 
Fissures of the cerebrum, 81 
Flaxseed poultice, 183 
Flechsig's fasciculus, 67 
Food, 184 
accessory articles of diet, 185 
animal, 186 
cereal, 186 
composition of, 186 
disposition of, 237 
heat value of, 242 
iron, 126 
metabolism experiments, 243 
predigested, 225 
principles, classification of, 184 
quantities required daily, 242 
relative value of, 243 
vegetable, 187 
Forced expiration, 166 
inspiration, 166 
Forces aiding the movement of lymph and 
chyle, 154 
Formaldehyde, 29 
Fovea, 291 
Fruits, laxative, 227 
Galactose, 218 
Gall-bladder, 215 
Gambir, 25, 229 
Gamboge, 228 
Ganglia, 50 
sympathetic, 106 
Gaseous exchange in lungs, 172 
in tissues, 172 
Gases of blood, carbon dioxide, 172 
nitrogen, 172 
oxygen, 172 
relation of, 172 
tension of, 172 
Gastric digestion, 199 
duration of, 205 
glands, 200 
juice, 202 
appetite, 203, 223 
functions of, 203 
mode of secretion, 203 INDEX 
331 
Gastric juice, nerve mechanism for the secretion 
of, 203 
Gastric hormone, 203 
secretin, 203 
Gemmules, 47 
General action, 12 
anesthetics, 95 
Gentian, 224 
compound tincture of, 224 
Germicides, 28 
Ginger, 224 
Girdle, pelvic, 21 
scapular, 21 
Glands of internal secretion, 269 
action on metabolism, 250 
pharmacodynamics of, 281 
Globin, 118 
Glucosides, 228 
Glycerin, action on digestive apparatus, 227 
on epithelial tissue, 24, 26 
on respiration, 182 
Glycogen, 237 
in liver, 237 
in muscles, 237 
Glycogenase, 237 
Glycogenesis, 237 
Glycogenic function of the liver, 237 
of muscles, 237 
Glycogenolysis, 237 
control of, 237 
Glycolysis, 238 
Glycosuria, 238 
adrenal, 275 
alimentary, 239 
pancreatic, 239 
pituitary, 277 
Glycyrrhiza, see licorice. 
Goitre, exophthalmic, 271 
Goll, fasciculus of, 67 
Gonium pectorale, 2 
Gonorrhoea, 318 
Gower's spino-cerebellar tract, 67 
Granatum, 231 
Gray powder, 30 
Green vegetables, 187 
Guaiacol, 29, 183 
Guanidine, 273 
Guarana, 92 
Gustatory nerves, 88 
Gyri, 80 
Hairs, 263 
Haustra, 220 
Haversian canals, 18 
Hearing, 303 
Hearing, sense of, 303 
physiology of, 308 
Heart, 130 
action of digitalis on, 45, 155 
Heart, action of sympathetic nerve on, 140 
of vagus nerve on, 140 
anatomy of, 130 
auriculo-ventricular bundle, 135 
beat, nature of the stimulus, 135, 136 
frequency of, 134 
block, 133 
course of blood through, 134 
cycle of, 133 
drugs affecting, 43, 44, 45, 155, 156, 157, 
158 
filling of auricles and ventricles, 133 
hypertrophy of, 149 
intracardiac nerve cells, 138 
modifications of beat due to the action of 
drugs, 155 
muscle bundle of His, 135 
muscle fibers of, 133 
nerve mechanism of, 137 
origin and distribution of the sympathetic 
nerves to, 138 
and distribution of the vagus nerve to, 
137 
regurgitation, 149 
sino-auricular node, 135 
stenosis, 149 
valves, action of, 133 
work done by, 135 
Heart muscle, 133 
automaticity, 136 
conductivity, 135 
irritability, 135 
pharmacodynamics of, 43, 44, 45, 155, 
156, 157, 158 
properties of, 135 
rhythmicity, 136 
tonicity, 136 
Heat, 27, 247 
action on metabolism, 248 
body, 248 
on epithelial tissue, 27 
on excretion, 267 
hot water bag, 27, 183, 226 
poultices, 27, 183, 226 
Heat loss, 247 
production, 247 
regulating center, 248 
stroke, 248 
Hellebore, green, 157 
white, 157 
Hematin, 118 
Hematinics, 125 
Hemianopsia, 87 
Hemiplegia, 76, 86 
Hemoglobin, 118 
carbon monoxide, 118 
chemical composition of, 118 
quantity of, 118 
Hemolysis, 13 332 
INDEX 
Hemophilia, 123 
Hemostatics, 25, 128 
Heroine, action on central nerve system, 102 
on respiration, 182 
Hexamethylenamine, 29 
action on digestion, 223 
on excretion, 266 
High and low protein diet, 244 
Histamine, 44 
Histology, 4 
of bone tissue, 18 
of cardiac tissue, 133 
of connective tissue, 15 
of muscle tissue, 31 
of nerve tissue, 46 
Homatropine, 301 
Hormone, definition of, 203 
Horn, dorsal, of spinal cord, 58 
lateral, of spinal cord, 58 
ventral, of spinal cord, 58 
Howell's theory of coagulation, 123 
Hunger, 184 
Hyaloid membrane, 292 
Hyaloplasm, 6 
Hydragogues, 228 
Hydrastis, 26 
Hydremia, 265 
Hydrogen dioxide, 29 
Hydrotherapeutic measures, 249 
Hygiene of bones, 23 
circulation, 149 
digestion, 222 
eye, 299 
nerve system, 107 
reproductive organs, 316 
urinary apparatus, 260 
Hyoscine, action on central nerve system, 102 
on parasympathetic division, no 
Hyoscyamine, no 
Hyoscyamus, 102, no 
Hyperglycemia, 239 
Hypermetropia, 296 
Hyperpituitism, 277 
Hyperpnea, 169 
Hyperthyroidism, 271 
Hypnotic drugs, 100 
measures, 100 
Hypnotics, 100 
which abolish pain, 101 
which do not abolish pain, 100 
Hypoglossal nerve, 91 
Hypophysis, 275 
sicca, action on circulation, 156 
on internal secretion, 281 
on involuntary or smooth muscle, 44 
on metabolism, 250 
Hypopituitism, 277 
Hypothyroidism, 271 
Hysteric sedatives, 104 
Heo-colic sphincter, 219 
Incus, 304 
Indican, 221, 256 
Indol, 221 
Innervation, reciprocal, 65 
Insalivation, 192 
Inspiration, 166 
mechanical movements of thorax, 166 
muscles, 166 
Insula of Reil, 81 
Insulin, 239 
Intensity of drug action, 12 
Intercostal muscles, 166 
Internal capsule, 82 
functions of, 82 
Internal secretion, 269 
pharmacodynamics of, 281 
Internode, 48 
Interstitial cells of Leydig, 280 
Intestinal antiseptics, 29 
digestion, 207 
fermentation, 221 
juice, 217 
composition of, 217 
functions of, 217 
physiological action of, 217 
peristalsis, 218 
rhythmic segmentation, 218 
Intoxicants, 99 
Intra thoracic pressure, 168 
Invert sugar, 218 
Invertase, 218 
Iodides, action on excretion, 266 
on digestive apparatus, 223 
on internal secretion, 281 
on metabolism, 250 
on respiration, 183 
of mercury, see mercury. 
potassium, 30, 182, 183, 250, 266, 281 
sodium, 183, 250, 266, 281 
Iodine, action on epithelial tissue, 27 
on metabolism,'250, 281 
tincture of, 27, 183 
lodothyrin, 272 
Ipecac, action on digestive apparatus, 226 
on respiration, 182 
Iris, 295 
functions of, 295 
nerve mechanism of, 295 
reflex, 295 
Irish moss, 24 
Iron, action on epithelial tissue, 25 
on the blood, 125 
absorption of, 126 
excretion of, 126 
"food-," 126 
Irritability of heart, 135 
of muscles, 33 
of nerves, 51 INDEX 
333 
Irritation, n 
Islands of Langerhans, 280 
of Reil, 81 
Jalap, 228 
Jalapin, 228 
Joints, 22 
classification of, 22 
function of, 22 
Kamala, 231 
Kaolin, 24 
Karyokinesis, 9 
Keith-Flack node, see sino-auricular node. 
Kephalin, 123 
Ketosis, 238 
Kidney, 253 
histology of, 253 
nerves of, 255 
Kinase, definition of, 189 
Kino, 25, 229 
Knockout drops, 101 
Kola, 92 
Labyrinth of ear, 305 
sensations, 310 
Lacrimal apparatus, 297 
Lacteals, 233, 234 
Lactobacillus odontolyticus, 222 
Lactose, 218 
Lard, 24 
Large intestine, 219 
contents of, 220 
function of, 220 
movements of, 220 
nerve mechanism of, 220 
Larkspur, 30 
Laryngismus stridulus, 272 
Larynx, 312 
nerves of, 314 
structure of, 312 
Laughing gas, 98 
Laxatives, 227 
Lead acetate, 229 
Lecithin, 216 
Lemniscus, see fillet. 
Lens, crystalline, 289 
Lenticular nucleus, 82 
Leukocytes, 119 
functions of, 121 
migration of, 121 
number of, 119 
origin of, 120 
varieties of, 119 
Levulose, 218 
Licorice, 24, 182 
Ligaments, 22 
Light, 249, 289 
Lime water, 225, 230 
Lipase, 189 
Liquid petrolatum, 227 
Lithium citrate, 127 
Liver, 214 
conjugation of the products of protein putre- 
faction, 215 
elaboration of bile by, 215 
formation of urea in, 215, 240 
functions of, 215 
pharmacodynamics of, 265 
production of glycogen and sugar, 215, 
237 
storage of fat, 215 
structure of, 214 
Local action, 12 
analgesics, 104 
anesthetics, 114 
anodynes, 104 
antacids, 127, 225, 226 
emetics, 226 
remote, 13 
sedatives, 104, 226 
Localization of function in cerebrum, 85 
Lung motor, 179 
Lungs, movements of, 166 
pharmacodynamics of, 180, 265 
structure of the, 162 
Lycopodium, 24 
Lymph, 151 
composition of, 153 
flow of, 154 
formation of, 153 
functions of, 153 
Lymph-capillaries, 152 
-glands, 152 
-nodes, 152 
-vessels, 152 
Lymphagogues, 153 
Lymphatic ducts, 152 
Lymphocytes, 119 
Macula lutea, 291 
Maculae acusticae, 307 
Magma of magnesia, 225, 226, 227 
Magnesium citrate, 227 
solution of, 227 
sulphate, 227 
Male fern, 231 
Malleus, 304 
•Malt, 225 
extract of, 225 
Maltose, 189 
Mammary glands, 263 
Manganese, 126 
Marrow, 18 
Massage, 227 
Mastication, 191 
movements, 191 
nerve mechanism of, 191 334 
INDEX 
Mate, 92 
Matricaria, 224 
Meats, composition of, 186 
Mechanical laxative measures, 227 
Medial fillet, 76 
Medulla oblongata, 73 
centers of, 77 
functions of, 76 
reflex activities of, 76 
white matter of, 74 
Meibomian glands, 298 
Membrana tympani, 304 
function of, 309 
Meninges, 55 
Menstruation, 280 
Menthol, 27 
Mercuric chloride, 26, 27, 29,30 
iodide, 30 
Mercurous chloride, 29, 227, 228, 229, 230, 266 
iodide, 30 
Mercury, 30 
ammoniated, 30 
benzoate, 30 
bichloride, 26, 27, 29, 30 
with chalk, 30 
chloride, -ic, 26, 27, 29, 30 
chloride, -ous, 29, 227, 228, 229, 230, 266 
iodide, -ic, 30 
iodide, -ous, 30 
ointment, 30 
ammoniated, 30 
diluted, 30 
salicylate, 30 
salts an salivation, 223 
Metabolism, 237 
basal, 242 
of carbohydrates, 237 
of fats, 239 
on a mixed diet, 243 
of nucleo-proteins, 240 
pharmacodynamics of, 249 
, chemical stimuli, 249 
physical stimuli, 249 
on protein diet, 243 
of proteins, 240 
Metallic salts, astringent, 25, 26 
caustic, 26 
Methods of raising and maintaining the rise of 
body heat, 248, 267 
Methyl alcohol, 99 
Methylene blue, 29 
Micturition, 258 
Migration of leukocytes, 121 
Milk, 24, 266 
of magnesia, 225, 226, 227 
Mitosis, 9 
Mixed treatment, 30 
Monkshood, 157 
Morawitz's theory of coagulation, 123 
Morphine, acute poisoning by, 102 
treatment of, 102 
action on central nerve system, 101, 103 
on circulation, 159 
on digestive apparatus, 226, 229 
on metabolism, 249 
on respiration, 182, 183 
diacetyl, 102 
ethyl, 102 
methyl, 102 
Morphinism, 102 
Motility, 9 
Motor area of human brain, 85 
Motor-oculi nerve, 89 
Mouth digestion, 189 
Movements of the intestines, 218, 221 
of the lower jhw, 191 
of the lungs, 166 
of the stomach, 205 
Muscle, action currents of, 35 
carbohydrates of, 40 
cardiac, 42, 133 
pharmacodynamics of, 45 
chemistry of, 37 
contraction of, 34 
factors modifying, 35 
graphic representation of, 34 
modifying influences, 35 
mechanical work of, 35 
phenomena following stimulation, 34 
summation, 37 
tetanus, 37 
extractives of, 40 
fibers, 31 
fibrillae, 33 
involuntary, 40 
non-striated, 40 
physiological properties of, 33 
proteins of, 37 
rigor mortis, 40 
skeletal, 31 
structure of, 31 
physical properties of, 33 
smooth, 40 
striated, 31 
tissue, 31 
pharmacodynamics of, 43 
visceral, 40 
Muscles, energy liberated in, 35 
fatigue, 36 
involuntary, 40 
non-striated, 40 
pharmacodynamics of, 43 
sense, 68 
skeletal, 31 
smooth, 40 
striated, 31 
summation effects, 37 
tissue, 31 INDEX 
335 
Muscles, tissue, chemical composition, 37 
conductivity, 33 
elasticity, 33 
histology of, 31 
irritability, 33 
pharmacodynamics of, 43 
physical properties of, 33 
physiological properties of, 33 
tone, 33, 65, 106 
voluntary, 31 
work accomplished, 35 
Musical sounds, 308 
Musk, 104 
Mustard, action on digestive apparatus, 223, 
224, 226 
on epithelial tissue, 27 
on excretion, 267 
plaster, 183' 
Mydriatics, 300 
Myelin, 48 
sheath, 48 
Myenteric plexus, 206 
Myogen, 37 
Myopia, 296 
Myosin, 37 
Myosinogen, 37 
Myotics, 301 
Myrrh, 26 
Myxedema, 271 
Nails, 264 
Narcosis, 95, 100 
Narcotics, 95 
action on central nerve system, 95 
on circulation, 159 
on respiration, 182 
classification of, 95 
Narocaine, 115 
Nasal fossae, 286 
Nearsightedness, 296 
Neoarsphenamin, 30 
Neosalvarsan, 30 
Nerve, abducent, 90 
auditory, 90 
blocking, 115 
cell, 47 
trophic or nutritive action of, 52 
endings, 50 
facial, 99 
fibers, 48, 49 
afferent, 54 
excitatory, 54 
sensor, 54 
reflex excitatory, 54 
reflex inhibitory, 54 
sensorifacient, 54 
general sensibility, 54 
muscle sensibility, 54 
special sense, 54 
Nerve fibers, classification of, 53 
efferent, 53 
excitatory, 53 
motor, 53 
pilomotor, 53 
secretory, 53 
vasomotor, 53 
vicero-augmentor, 53 
viscero-accelerator, 53 
visceromotor, 53 
inhibitory, 53 
cardio-inhibitor, 53 
secreto-inhibitor, 53 
vaso-inhibitor, 53 
viscero-inhibitor, 53 
medullated, 48 
non-medullated, 49 
postganglionic, 105 
preganglionic, 105 
Nerve, glosso-pharyngeal, 90 
gustatory, 90, 285 
hypoglossal, 90 
oculo-motor, 89 
olfactory, 88 
optic, 88 
pneumogastric, 91 
spinal accessory, 91 
trigeminal, 89 
trochlear, 89 
Nerve control of respiration, 174 
Nerve impulse, 51 
nature of, 51 
velocity of, 52 
Nerve system, 55 
central, 55 
hygiene of, 107 
peripheral, 56 
pharmacodynamics of, 92 
autonomic system, 109 
central system, 92 
tissue, 46 
histology of, 46 
Nerves, autonomic system of, 105 
parasympathetic division of, 106 
pharmacodynamics of, no 
sympathetic division of, 106 
pharmacodynamics of, 112 
classification of, 53 
conductivity of, 52 
cranial, 88 
degeneration of, 52 
fatigue, 52 
irritability, 51 
peripheral endings of, 50 
physiological properties of, 51 
pilo-motor, 53 
relation of, to central nerve system, 
56 
spinal, 57. 336 
INDEX 
Neural groove, 55 
Neural tube, 55 
Neurocyte, 47 
Neuroglia, 46 
Neurolemma, 48 
Neuron, 46 
synapses of, 50 
varieties of, 49 
Neuroplasm, 47 
Neuropodia, 47 
Nicotine, 109 
Nissl granules, 47 
Nitrates, 266 
organic, 44, 160 
Nitrites, action on circulation, 160 
involuntary or smooth muscle tissue, 
44 
respiration, 183 
amyl, 44, 160 
ethyl, 160 
sodium, 44, 160 
Nitrogen equilibrium, 243 
monoxide, 98 
Nitroglycerin, 44, 160, 183 
Nitrous oxide, 96, 98 
Node of Ranvier, 48 
Normal saline solutions, 125 
Novocaine, 115 
Nucleolus, 6 
Nucleo-proteins, 240 
metabolism of, 240 
Nucleus, 6 
caudatus, 82 
cuneatus, 67 
gracilis, 67 
lenticular, 82 
pontis, 84 
salivatorius, 77, 195 
Nutgall, 25 
Nutrients, 184 
Nutritive equilibrium, 243 
Obesity, 281 
Oculo-motor nerve, 89 
Oil, castor, 227, 228, 230 
chenopodium, 230 
cinnamon, 104 
cloves, 104 
cottonseed, 24, 227 
action on epithelial tissues, 24 
digestive apparatus, 227 
croton, 27, 228 
action on epithelial tissues, 27 
digestive apparatus, 228 
juniper, 266 
olive, 24, 227 
action on epithelial tissues, 24 
digestive apparatus, 227 
sandalwood, 266 
Oil turpentine, 27 
action on epithelial tissues, 27 
digestive apparatus, 230 
excretion, 266 
wintergreen, 27 
Oils, fixed, 24 
action on epithelial tissue, 24 
volatile, 27, 29, 104, 224 
action on epithelial tissues, 27 
digestive apparatus, 224 
Olein, 213 
Olfactory nerve, 288 
sensations, kinds of, 288 
Opalina ranarum, 3 
Ophthalmic ganglion, 295 
Opium, see morphine. 
Optic disc, 291 
nerve, 290 
thalamus, 82 
functions of, 82 
Ora serrata, 290 
Organ, 4 
of Corti, 308, 310 
Organic silver compounds, 29 
Ossicles of ear, 309 
Osteoblasts, 18 
Otic ganglion, 195 
Ouabain, 156 
Ovarian extract, action on internal secretions, 
281 
metabolism, 250 
Ovaries as organs of internal secretion, 280 
Oxgall, 228 
Oxygen in blood, 118 
inhalations of, 189 
quantity absorbed daily, 170 
in tissues, 172 
Oxyhemoglobin, 118 
Pacinian corpuscle, 49, 284 
Palmitin, 213 
Pancreas, 210, 279 
action on metabolism, 238, 250 
Pancreatic juice, 211 
function of, 212 
secretion of, 211 
Pancreatin, 225 
Papillae, circumvallate, 285 
comical, 285 
filiform, 285 
fungiform, 285 
Paraldehyde, 101 
Paralysis, 11, 71, 86 
Parasiticides, 29 
Parasympathetic division of autonomic nerve 
system, 106 
pharmacodynamics of, no 
Parathyroids, 272 
effects of removal of, 272 INDEX 
337 
Paregoric, 183 
Parotid gland, 172 
Partial pressure of gases, 171 
Pasteurization, 28 
Pathogenic microorganisms, 28 
Pelletierine tannate, 231 
Pepper, 224 
Peppermint, oil of, 223, 224 
Pepsin, 202, 224 
Peptones, 204, 212 
Pericardium, 132 
Perineurium, 51 
Periosteum, 18 
Peripheral organs of the nerve system, 55 
Peristalsis, 218 
Peristaltic rush, 219 
Perspiration, 262 
drugs affecting, 267 
Petrolatum, 24 
liquid, 227 
action on epithelial tissues, 24 
digestive apparatus, 227 
Phagocytosis, 121 
Pharmacodynamics, of autonomic nerve system, 
109 
parasympathetic, division, no 
sympathetic, division, 112 
of the blood, 125 
of the cell, n 
of central nerve system, 92 
drugs which depress, 95 
drugs which stimulate, 92 
of the circulation, 155 
definition of, 5 
of digestive apparatus, 223 
of epithelial tissue, 24 
of excretion, 265 
of the eye, 300 
of internal secretions, 281 
of metabolism, 249 
of muscle tissue, 43 
cardiac, 43, 44, 45, 155, 156, 157, 158 
involuntary, 44 
non-striated, 44 
skeletal, 43 
smooth, 44 
striated, 43 
voluntary, 43 
of the respiration, 1807265 
Pharmacology, definition of, 5 
Phenacetin, see acetphenetidin. 
Phenol, action on central nerve system, 104 
on digestive apparatus, 226, 230 
on epithelial tissue, 26, 29 
Phenolphthalein, 227, 228 
Phenyl salicylate, 29 
Phenyl-cinchoninic acid, 252 
Physiological saline solutions, 125 
Bayliss, 125 
Physiological saline solutions, Dawson's, 125 
Locke's, 125 
Ringer's, 125 
U. S. P., 125 
Physiology, of the cell, 6 
definition of, 1 
Physostigmine, action on digestive apparatus, 
228 
the eye, 301 
the parasympathetic division, 112 
poisoning by, 112 
Pia mater, 55 
Pills, Blauds, 125 
of ferrous carbonate, 125 
Pilocarpine, action on digestive apparatus, 223 
excretion, 267 
the eye, 302 
the parasympathetic division, in 
salivary secretion, 223 
poisoning by, in 
Pituitary body, 275 
effects of removal of anterior lobe, 276 
of posterior lobe, 279 
functions of anterior lobe, 276 
of posterior lobe, 277 
influence of nerve system, 277 
pathologic conditions, 277 
Pituitary extract, action on circulation, 156 
on digestive apparatus,. 228 
on internal secretions, 281 
on involuntary or smooth muscle, 44 
on metabolism, 250 
Pituitrin, 277 
Plasma of blood, 121 
composition of, 122 
Pleura, 164 
Pneumogas trie or vagus nerve, 91 
Podophyllum, 228 
Poisons, definition of, 5 
Polypeptids, 212 
Pomegranate, 231 
Pons varolii, 73 
Portal vein, 233 
Potassium acetate, 127, 266 
arsenite, solution of, 126 
bitartrate, 127, 227 
carbonate, 26 
citrate, 127, 266 
hydroxide, 26 
iodide, 30 
action on excretion, 266 
on internal secretion, 281 
on metabolism, 250 
on respiration, 182 
permanganate, 29 
sodium tartrate, 127, 227 
Predigested foods, 225 
Prepared chalk, 225, 229 
Presbyopia, 294 338 
INDEX 
Pressor nerve fibers, 148 
Procaine, 115 
Proferment, 189 
Proprioceptive nerves, 68 
Protectives, 24 
Protein metabolism, 240 
Proteins, 185, 243 
chemical composition of, 185 
specific dynamic action, 244 
Proteoses, 204, 212 
Protoplasm, 2 
Pro to veratrine, 157 
Protozoa, 2 
Pseudopodium, 2 
Ptyalin, 196 
Ptyalism, 23 
Pulmonic blood vessels, 142, 153 
ventilation, 177 
Pul motor, 179 
Pulse, 145 
pressure, 145 
Punctum proximum, 294 
remotum, 294 
Pupil, 290 
drugs affecting the, 300 
Purgatives, 227 
acting by special affinity, 228 
drastic, 227, 228 
localization of action of, 228 
rapidity of action of, 228 
saline, 227, 228 
simple, 227 
Purkinje, cells of, 77 
Pustulants, 27 
Pyramidal tracts of spinal cord, 67 
Quassia, 224 
infusion of, 230 
Quinidine, 251 
Quinine, action on cardiac muscle, 45 
on central nerve system, 103 
on digestive apparatus, 223, 224, 230 
on involuntary or smooth muscle, 44 
on metabolism, 251 
on skeletal, voluntary or striated muscle, 
44 
Radium and X-ray emanations, 249 
Receptaculum chyli, 152 
Reciprocal innervation of antagonistic mus- 
cles, 65 
Red corpuscles, 117 
chemical composition of, 118 
function of, 118 
life history of, 118 
number of, 118 
Red nucleus, 68, 71 
Reduced hemoglobin, 118 
Reflex action, 63 
Reflex action, inhibition of, 65 
medulla oblongata, 76 
spinal cord, 63 
Reflex arc, 63 
emetics, 226 
irritability, 63 
time, 63 
Refracting media, 292 
action of, 292 
Refraction in abnormal eyes, 296 
Refractory period of nerve, 52 
Relation of gases in the blood, 172 
Remote action, 12 
local action, 13 
Renal duct, 253 
Rennet, 204 
Rennin, 204 
Reproductive apparatus, 316 
hygiene of the, 316 
Reserve air, 168 
Residual air, 168 
Resorcinol, 29 
Respiration, 161 
changes in composition of air during, 170 
of alveolar air, 171 
in composition of blood, 172 
in tissues, 172 
chemistry of, 170 
effects of a change of pressure of the blood 
gases on, 172 
expiratory muscles, 166 
external, 161 
inspiratory muscles, 166 
internal, 161 
mechanism of gaseous exchange, 171 
nerve mechanism of, 174 
number per minute, 169 
pharmacodynamics of, 180 
total respiratory exchange, 170 
volumes of air breathed, 168 
Respiratory apparatus, 161 
depressants, 181 
inspiratory center, see respiratory center. 
nerve control of, 175 
sedatives, 181 
stimulants, 180 
Respiratory center, 175 
effect of a change of pressure of blood 
gases on, 176 
influence of higher centers, 176 
influence of other afferent nerves, 175 
reflex stimulation, 175 
relation of vagus nerves, 175 
Respiratory epithelium, 163 
movements, 166 
on flow of blood through the intra- 
thoracic vessels, 168 
on the flow of lymph, 168 
of upper air passages, 161 INDEX 
339 
Respiratory, pressures, 167 
quotient, 171 
sounds, 169 
Retina, 290 
formation of image on, 292 
functions of, 297 
Rhubarb, 227, 228 
Rhythmic segmentation, 218 
Rigor mortis, 40 
Rima glottidis, 161 
Ringer's solution, 125 
Rochelle salts, 127, 227 
Routes for the absorbed food, 233 
Rubefacients, 27 
Rubro-spinal tract, 68, 71 
Rush peristalsis, 219 
Saccharose, 217 
Saccule, 307 
Salicylates, see salicylic acid. 
Salicylic acid, action on central nerve system, 103 
on digestive apparatus, 226, 228 
on epithelial tissue, 29 
on excretion, 267 
on metabolism, 252 
Saliva, 196 
composition of, 196 
drugs affecting the, 223 
excretion of drugs by, 223 
functions of, 196 
mode of secretion, 195 
nerve mechanism for secretion of, 194 
quantity of, 196 
Salivary glands, 192 
histologic changes in, during secretion, 193 
nerve mechanism for secretion of, 195 
pharmacodynamics of, 223 
Salivation, 223 
Salol, see phenyl salicylate. 
Salt-action, 13 
Salt, Epsom, 227 
Glauber's, 227 
Rochelle, 127, 227 
Salts, action on excretion, 266 
Salvarsan, 30 
Sandalwood, 29 
Santol, 183 
Santonin, 230 
Saponification, 213 
Sarcolemma, 33 
Sarcoplasm, 33 
Scammony, 228 
Schwann, white substance of, 48 
Sclera, 290 
Scoparius, 266 
Scopolamine, 102, no 
-morphine anesthesia, 103 
Sebaceous glands, 263 
Secondary sexual characteristics, 280 
Secretin, 211 
gastric, 203 
Secretion, external, 269 
internal, 269 
Sedatives, central, 100, 226 
hysteric, 104 
local, 104, 226 
respiratory, 181 
Seidlitz powder, 227 
Semicircular canals, 307 
Senega, 183 
Senna, 227, 228 
Sense organs, 282 
classification of, 282 
Sensor areas of the brain, 86 
Serpentaria, 224 
Serum, 127 
disease, 128 
Serums, 127 
antitoxic, 127 
Setchenow's center, 65 
Sheath, medullary, 48 
myelin, 48 
Sialogogues, 223 
Sight, sense of, 289 
Silver nitrate, 25, 26 
compounds, organic, 29 
Sino-auricular node, 135 
Six-o-six ("606"), 30 
Skeleton, 19 
appendicular portion, 21 
axial portion, 20 
bones of, 20-21 
bony, 19 
hygiene of, 23 
fibrous, 19 
Skin, 261 
appendages of, 262 
disinfection of, 29 
nerve endings in, 263, 283 
parasiticides, 29 
Skull, 20 
Slippery elm, 24 
Small intestine, 207 
glands of, 209 
movements of, 218 
nerve mechanism of, 210, 219 
Smell, end organ of, 288 
sense of, 286 
Soap, 227 
Soapsuds, 230 
Sodium acetate, action on blood, 127 
on excretion, 266 
benzoate, 29 
bicarbonate, action on blood, 126 
on digestive apparatus, 225, 226 
on excretion, 266 
bromide, 100, 182 
cacodylate, 126 340 
INDEX 
Sodium carbonate, 26 
chloride, physiological solution of, 125 
citrate, 125 
action on blood, 127 
on excretion, 266 
gallate, 26 
glycocholate, 228 
hydroxide, 26 
iodide,183, 250, 266, 281 
nitrate, 266 
nitrite, 44, 160, 183 
phosphate, 227 
effervescent, 227 
ricinoleate, 227 
salicylate, see salicylic acid. 
action on excretion, 267 
on metabolism, 252 
as a urinary antiseptic, 29 
sulphate, 227 
tannate, 26 
taurocholate, 228 
thiosulphate, 30 
sulphite, 30 
Solution, Fowler's, 126 
of magnesium citrate, 227 
physiological saline, 125 
Bayliss', 125 
Dawson's, 125 
Locke's, 125 
normal, 125 
Ringer's, 125 
U. S. P., 125 
of potassium arsenite, 126 
Somnifacients, 100 
Sounds, characteristics of, 308 
Speech, 312 
Sphincter, cardiae, 200 
ileocolic, 219 
pupillae, 290, 295 
pylori, 200 
urethrae, 259 
vesicae, 259 
Spigelia, 230 
Spinal accessory nerve, 91 
Spinal cord, 58 
encephalo-spinal conduction, 71 
fasciculi of, 66 
functions of, 61 
intersegmental conduction, 68 
tracts, 66 
irritability of, 63 
nerve cells, 59 
nerve fibers, 66 
reflex actions of, 63 
relation of spinal nerves to, 57 
segmentation of, 62 
shock, 63 
spinal nerve roots, functions of, 60 
spino-encephalic conduction, 68 
Spinal cord, structure of gray matter, 58 
functions of, 39 
structure of white matter, 60 
functions of, 68 
strychnine, effects of, 93 
Spinal cord, 58 
tracts of, 66 
classification of, 66 
functions of, 68 
Spinal nerves, origin of, 57 
roots of, 60 
Spirilla, 28 
Spirometer, 168 
Splanchnic nerves, influence of, on intestines, 
219 
on stomach, 206 
Spongioplasm, 6 
Squibb's diarrhea remedy, 229 
Squill, action on digestive apparatus, 226 
on excretion, 265 
Stapedius muscle, 305 
Stapes, 304 
Starch, digestion of, 196, 212 
action of epithelial tissue, 24 
Static sense, 310 
Steapsin, 213 
Stearin, 186, 213 
Sterilization, 28 
Sternum, 20, 164 
Stimulation, 11 
Stimuli, 9 
classification of, 9 
Stomach, 199 
absorption in, 206 
movements of, 205 
nerve mechanism of, 206 
Stomachics, 223 
Stovaine, 115 
Stramonium, 102, no 
Strophanthin, action on circulation, 156 
on excretion, 265 
Strophanthus, see strophanthin. 
Strychnine, action on digestive apparatus, 223, 
224 
on central nerve system, 93 
on circulation, 158 
on respiration, 181 
poisoning by, 93 
treatment of, 95 
Styptics, 25, 128 
Sublingual gland, 192 
Submaxillary gland, 192 
Sugar, action on excretion, 266 
influence of nerve system on, 237 
oxidation of, 238 
release, 237 
storage of, 237 
Sulphonal, 101 
Sulphondiethylmethane, 101 
Sulphonal, ioi INDEX 
341 
Sulphonethylmethane, 101 
Sulphonmethane, 101 
Sulphur, 227 
ointment, 30 
Sulphuric acid, 26 
Sumbul, 104 
Sun cholera mixture, 229 
Supplemental air, 168 
Suppositories, 227 
Suprarenal capsules or glands, 273 
Sweat glands, 262 
Sweat, influence of drugs on production of, 
267 
of nerve system on production of, 263 
Sympathetic ganglia, 106 
division of autonomic system, 106 
pharmacodynamics, of 109 
nerve system, 105 
resonance, 310 
Synapse, 50 
resistance at the, 64 
Synarthroses, 22 
Synovial fluid, 22 
membrane, 22 
Syphilis, 320 
Syrup of ferrous iodide, 125 
System, 4 
Systemic action, 12 
alkalinizers, 126 
antacids, 126 
Tactile sense, 68, 284 
Talc, 24 
Tannic acid, action on digestive apparatus, 229, 
230 
on epithelial tissue, 25 
Tar, 183 
Taraxacum, 224 
Tartar emetic, see antimony and potassium 
tartrate. 
Tartrates, action on blood, 127 
Taste, 285 
buds, 286 
kinds of taste sensation, 286 
nerve of, 286 
sense of, 285 
Tea, 92 
Tectorial membrane, 308 , 
Teeth, 189 
structure of, 190 
Telodendrion, 47 
Temperature of human body, 247 
changes in, 249 
drugs affecting, 249, 251 
human body, 247 
regulation of, 248 
sense, 68 
Teniacides, 231 
Teniafuges, 231 
Tension of gases in blood, 172 
in tissues, 172 
Tensor tympani muscle, 304 
function of, 309 
Tentorium cerebelli, 77 
Terpin hydrate, 182 
Testicles as organs of internal secretion, 280 
action of extract on metabolism, 250, 280 
Tetanus, 37 
Tetany, 273 
Tetronal, 101 
Tethelin, 277 
Thalamus, 82 
Theobromine, 160, 265 
sodio-salicylate, 266 
Theocine, 266 
Theophylline, 265 
Thermogenesis, 247 
Thermolysis, 247 
Thirst, 184 
Thoracic duct, 152 
Thorax, 164 
mechanical movements of, 166 
Thrombin, 122 
Thrombogen, 122 
Thrombokinase, 122 
Thromboplastin, 123 
Thromboplastins, 128 
Thymol, 29, 230 
Thymus, 279 
Thyroid gland, 269 
action of extracts on internal secretion, 281 
on metabolism, 250 
effects of absence or disease of, 269 
of hyperactivity of, 271 
effects of feeding, 272 
hormone of, 272 
pharmacodynamics of, 250, 281 
surgical removal of, 271 
Thyroxin, 272 
action on internal secretion, 281 
on metabolism, 250 
Tidal air, 168 
Tincture of ferric chloride, 125 
green soap, 29 
iodine, 27, 183 
larkspur, 30 
Tissue, adipose, 16 
areolar, 16 
cartilaginous, 17 
connective, 15 
definition of, 4 
epithelial, 14 
pharmacodynamics of, 24 
muscle tissue, 31 
pharmacodynamics of, 43 
nerve, 46 
pharmacodynamics of, 92 
osseous, 17 INDEX 
342 
Tissue spaces, 152 
white fibrous, 16 
yellow elastic, 16 
Tone, 33, 65, 106 
Tongue, 285 
Tonicity of muscle, 33 
Tonus, 33, 65, 106 
Total carbon dioxide exhaled, 170 
oxygen absorbed, 170 
respiratory exchange, 170 
Touch, sense of, 283 
Toxicology, definition of, 5 
Toxins, 127, 159 
Trachea, 161 
Transfusion, 125 
Trichloracetic acid, 26 
Trigeminal nerve, 89 
Trional, 101 
Triticum, 266 
Trochlear nerve, 89 
Tropocaine, 115 
Trypsin, 212 
Trypsinogen 212 
Tuberculin, 128 
Turek, fasciculus of, 66 
Twilight sleep, 103 
Tympanic membrane, 304 
function of, 309 
Tympanum, 304 
Tyramine, 44 
Upper air passages, 169 
Urea, 240 
action on excretion, 266 
antecedents of, 240 
seat of formation, 240 
Ureter, 253 
Uric acid, 240 
Urinary antiseptics, 29 
bladder, 253 
Urinary apparatus, 253 
drugs affecting, 265 
hygiene of, 260 
Urination, 258 
nerve mechanism of, 258 
Urine, 256 
composition of, 256 
mechanism of secretion, 259 
influence of nerve system, 258 
of blood pressure, 257 
quantity of, 256 
retention of, 261 
suppression of, 261 
Urotropin, see hexamethylenamine. 
Uterus, drugs affecting the, 44, 114 
Utricle, 307 
Vacuole, contractile, 2 
food, 2 
Vaccination, 128 
Vaccine, antirabic, 128 
gonococcus, 128 
typhoid, 128 
virus, 128 
Vaccines, 127, 128 
autogenous, 128 
lipo-, 128 
stock, 128 
Vagus nerve, 91 
influence on heart, 140 
relation of, to intra-cardiac ganglia 137 
Valerian, 104 
Valves of heart, 131, 132 
Valvular disease, 149 
Vas deferens, 280 
Vascular apparatus, 142 
nerve regulation of, 147 
stream bed, 146 
Vasoconstrictor drugs, 158 
centrally acting, 158 
peripherally acting, 159 
Vasodilatator drugs, 159 
centrally acting, 159 
peripherally acting, 160 
Vasomotor constrictor center, 147 
central stimulation, 147 
nerves to capillaries and veins, 149 
reflex stimulation, 147 
vasoconstrictor nerves, 147 
vasodilatator nerves, 148 
antidromic, 148 
Vegetable astringents, 25 
Veins, 143 
structure and function, 143, 145 
Velocity of blood, 146 
Ventilation, 177 
of the alveoli, 177 
Ventricles of central nerve system, 55 
of heart, 131, 132 
Veratrine, action pn circulation, 157 
on metabolism, 249 
on skeletal, voluntary or striated mus 
cle, 43 
Veratrum, see veratrine. 
Vermicide, 229 
Vermifuge, 229 
Vermis, 77 
Veronal, 101 
Vertebral column, 21 
Vertebrate body, appendicular portion of, 10 
axial portion of, 10 
cavities of, 10 
general plan of, 9 
abdominal, 10 
dorsal, 10 
neural, 10 
thoracic, 10 
ventral, 10 
surfaces of, 10 INDEX 
343 
Vesicants, 27 
Vestibule, 306 
Villi, 233 
functions of, 233 
structure of, 233 
Visceral muscle, 40 
functions of, 41 
pharmacodynamics of, 44 
properties of, 41 
Viscosity of blood, 117 
Vision, 289 
accommodation, 293 
ametropia, 296 
astigmatism, 297 
emmetropia, 293 
farsightedness, 296 
hypermetropia, 296, 299 
myopia, 296, 299 
nearsightedness, 296 
presbyopia, 294 
Visual purple, 297 
Vital capacity of lungs, 169 
Vitamins, 245 
Vitreous humor, 289, 292 
Vocal bands, 313 
sounds, 312 
Voice and speech, 312 
Voice production, mechanism of, 314 
Volumes of air breathed, 168 
Volvox, 3 
Vomiting, 206 
drugs inducing, 225 
nerve mechanism for, 206 
Wallerian degeneration, 52 
Water, 249, 250, 266 
absorption and excretion of, 233, 250, 257 
Water, action on metabolism, 249 
on excretion, 266 
carbonated, 250, 266 
distilled, 250 
Wash, black, 30 
yellow, 30 
White blood corpuscles, 119 
function of, 121 
migration of, 121 
origin of, 120 
physiologicalproperties, 121 
varieties of, 119 
White of egg, 24 
Witch hazel bark, 25, 229 
Work accomplished by muscles, 35 
effect of alcohol on the, 43 
of caffeine on the, 43 
Worms, intestinal, 229 
common round- (ascaris), 230 
hook- (uncinaria, necator, or ankylostomd) ,230 
pin- or thread- (oxyuris), 230 
tape-, 231 
varieties of, 231 
remedies, 229 
X-rays, 249 
Yellow wash, 30 
Zinc chloride, 26 
stearate, 24 
sulphate, 25 
action on epithelial tissue, 25 
on digestive apparatus, 226 
Zymogen, 189 
pepsinogen, 202 
trypsinogen, 212