The principles of clinical pathology; a text-book fot students and physicians

Front matter

Class _ K . ft U 3

Book

Copyright)!

Preface To The Third Edition

In the present edition, a large part of which has been rewritten, the attempt has been made to include the results of work published since 1897. Yet, in spite of the great pains taken, I dare not assert that all has been included and that even important researches have not been left out. I do not beg indulgence for such omissions, but can only state that I have never intentionally neglected to mention an important research, and that I have endeavored to make the book as complete as possible. Whoever has attempted to follow the literature in so many fields will recognize how difficult it is to master even fairly well the great diversity of material.

L. Krehl.

Tubingen, August, 1904.

FROM THE PREFACE TO THE SECOND EDITION

The desire to write a book of this character arose from the conviction that two things are essential for a thorough knowledge of internal medicine. The first of these is skill in the art and technic of clinical medicine, which is only to be acquired by long and careful practice at the bedside. The second is the ability to judge disease in accordance with biological principles, for the study of disease is, ideally at least, an exact natural science.

It is unnecessary to discuss the question as to which of the two is the more important. Both are necessary, and a deficient knowledge of either is detrimental to the clinician. If the latter be neglected, he becomes a mere routinist; whereas if insufficient attention be paid to the former, he becomes an impractical theorist.

The whole tendency of modern times precludes the possibility that the practical side of medicine should be neglected, for the extreme value of medical art and technic is now universally recognized. Unfortunately, however, this recognition has led to a certain antagonism toward theoretical and scientific work. Yet we must remember that, now as always, the solid foundation of all clinical knowledge rests upon the sciences of anatomy, physiology, and pathology; that, without these, technical skill in medicine would avail but little; and that the activities and views of the medical profession sink

8 PREFACE TO THE SECOND EDITION

proportionately to their remoteness from the firm scientific foundations, and proportionately to the degree to which the clinician ceases to be a natural scientist. The purpose of this book, therefore, is to contribute to our knowledge of, and to awaken interest in, the theory of disease processes.

L. Krehl.

Leipzig, March, 1898.

Table Of Contents

PAGE

Introductory Note by Prof. Osler 13

Chapter I

Importance of the Circulation, 21 ; Pulmonary Circulation, 21 ; General Circulation, 22 ; Adaptability of the Heart, 23 ; Hypertrophy of the Heart, 28; Valvular Diseases, 30; Etiology of Valvular Disease, 30; Muscular Insufficiency, 33; Aortic Insufficiency, 34; Aortic Stenosis, 38; Mitral Stenosis, 39; Mitral Insufficiency, 40; Valvular Lesions of the Right Side, 41 ; Combined Valvular Lesions, 42 ; Hypertrophy of the Right Ventricle, 43 ; Hypertrophy of the Left Ventricle, 46; Hypertrophy of both Ventricles, 48; Cardiac Changes in Renal Disease, 49; The " Athlete's Heart," 53 ; The " Beer Heart," 54 ; Heart in Pregnancy, 55 ; Ability of the Heart to Hypertrophy, 55 ; Concentric and Eccentric Hypertrophy, 56; Inefficiencies of a Compensated Circulation, 57; Myocardial Changes in Hypertrophied Hearts, 60; Causes of Broken Compensation in Hypertrophied Hearts, 63; Causes of Primary Insufficiency of the Heart Muscle, 65 ; Results of Cardiac Weakness, 71 ; Disturbances of the Heart-Rate, 77; Tachycardia, 78; Bradycardia, 83; Arrhythmia, 87; Forms of Arrhythmia, 88; Causes of Arrhythmia, 93; Cardiac Impulse, 95; Heart Sounds, 96; Cardiac Murmurs, 100; Palpitation, 102; Cardiac Dyspncea, 103 ; Cardiac Pain, 105.

CHAPTER II. The Blood-Vessels and the Lymph 108

The Arterial Blood-Pressure, 109; Systolic and Diastolic Pressures: Pulse-Pressure, 109; Physiological Variations in Blood- Pressure, in; Pathologically Increased Blood-Pressure, in; Pathological Diminution in Blood-Pressure, 112; Arterial Pulse, 114; Venous Stasis, 115; Venous Murmurs, 115; (Edema, 116; Composition of Exudates, 121 ; Chylous and Chyliform Ascites, 121 ; Pulmonary (Edema, 122.

10 TABLE OF CONTENTS

Chapter III

The Red Blood-Corpuscles, 126; Anaemia from Hemorrhage, 126; General Considerations relative to Chronic Anaemias, 127; Chlorosis, 130; Secondary Anaemias, 133; Pernicious Anaemia, 136 ; Haemoglobinaemia, 141 ; Haemolytic Action of Alien Plasmas, 143 ; Paroxysmal Haemoglobinuria, 145 ; Other Causes which Injure the Red Blood-Corpuscles, 147; Systemic Effects from Rapid Destruction of Red Blood-Corpuscles, 148; The White Blood-Corpuscles, 149; Physiological Leucocytoses, 150; Pathological Leucocytoses, 152; Leucopenia, 154; Leukaemia and Pseudoleukaemia, 155 ; Plasma and Serum : Total Quantity of Blood, 162; Quantity of Fibrin, 162; Blood-Serum, 163; Cytolytic Properties of the Serum, 165 ; Antitoxins : The " Side- Chain" Theory, 167; Precipitins, 171; Agglutination, 172; Salts of the Serum, 174; Hydraemia, 174; Polycythaemia, 177; Plethora, 181.

Chapter IV

Portals of Entry, 184; Natural Inherited Immunity, 189; Natural Acquired Immunity, 190; Active Artificial Immunity, 193; Passive Artificial Immunity, 194; Phagocytosis and Immunity, 194; Conclusions, 195.

CHAPTER V. The Respiration 197

The External Respiration, 197 ; Means for Removing Harmful Material from the Air- Passages, 197 ; Stenosis of the Air- Passages, 201 ; Bronchial Asthma, 206 ; Paralysis of the Respiratory Muscles, 208; Loss of Pulmonary Elasticity: Emphysema, 209; Changes in Respiration of Nervous Origin : Cheynes-Stokes Phenomenon, 211; Pleural Effusions and Pneumothorax, 213; Atelectasis, 215; Effects of Obliteration of Air-Spaces, 216; Effects of Atmospheric Pressure, 217; Inhalation of Poisonous Gases, 220; Effects of Anaemia, 221; Respiratory Compensation, 223; Asphyxia, 225 ; The Internal Respiration, 226 ; Respiratory Sensations, 229.

Chapter VI

Mouth and GEsophagus, 231 ; Stomatitis, 231 ; Diminished Secretion of Saliva, 232 ; Ptyalism, 233 ; Composition and Reaction of Saliva, 234 ; Swallowing, 235 ; Oesophageal Stenosis, 236 ; Pressure Diverticula, 237; Primary Dilatation of the (Esophagus, 238; The Stomach, 239 ; The Disturbances of Gastric Secretion, 241 ; Hypersecretion of Gastric Juice, 242; Round Ulcer, 244; Effects

TABLE OF CONTENTS 11

PAGE

of Hypersecretion and Hyperacidity, 246; Subacidity and Anacidity, 247; Bacterial Action in the Stomach, 249; Disturbances of Motility, 252; Increased Peristalsis and Increased Motility, 254; Motor Insufficiency and Dilatation, 254; Causes of Dilatation, 256 ; Effects of Motor Insufficiency, 258 ; Belching and Vomiting, 260; Sensations from the Stomach, 262; Disturbances in the Secretion of Bile, 265 ; Gall-Stones, 266 ; Exclusion of Bile from Intestines, 271 ; Jaundice, 273 ; Other Hepatic Toxaemias, 277 ; Pancreatic Juice, 279 ; Fat Necroses, 281 ; Relation of the Bile to Pancreatic Disease, 282 ; Processes in the Intestines, 282; Effects of Poisons, 282 ; Abnormal Bacterial Processes within the Gastrointestinal Tract, 284 ; Pathology of Absorption, 291 ; Disturbances in the Intestinal Movements, 293 ; Diarrhoeas, 295 ; Constipation, 298; Obstruction, 301; Strangulation, 307; Meteorism, 308; Abnormal Intestinal Sensations, 310.

Chapter VII

Quantitative Variations in Metabolism of Fats and Proteids, 312; Caloric Needs of Body, 312; Proteid Needs of Body, 315; Inanition, 316; Effects of an Oversupply of Food, 319; Disturbances in Fat Metabolism, 322 ; Pathological Accumulations of Fat, 325 ; Pathological Destruction of Proteid Material, 330; Metabolism in Exophthalmic Goitre, 332; Qualitative Changes in Catabolism, 335; Autolysis, 335; Formation and Excretion of Ammonia, 337; Production of Organic Acids, 339; Diabetic and Other Toxic Comas, 342 ; Relation between Hepatic Disease and the Excretion of Ammonia, 344; Alkaptonuria, 345.

Chapter VIII

Disturbances in Carbohydrate Metabolism. Diabetes 347

Alimentary Glycosuria, 348; Phloridzin Glycosuria, 349; Renal Diabetes, 351 ; Transient Glycosurias, 351 ; Diabetes Mellitus, 352; Mild and Severe Forms, 352; Derivation of Sugar from Proteids and Fats, 353 ; Glycogenic Function of the Liver in Diabetes, 357 ; Consumption of Sugar in Diabetes, 358 ; Etiology of Diabetes, 361; Effects of Diabetes upon the Body, 362; Theory of Diabetes, 365.

Chapter IX

The Metabolism of the Purin Bodies. Gout 368

Gout, 370; Uric Acid in the Blood, 372; Uric Acid in the Urine, 373 ; The Cause of the Local Deposits of Urates, 374 ; Theory of Gout, 375-

12 TABLE OF CONTENTS

Chapter X. Page

Normal Regulation of the Body Temperature, 377; Heat- Stroke, 379; Heat Regulation in Fever, 381; Heat Production in Fever, 382 ; Heat Losses in Fever, 384 ; Metabolism in Fever, 388 ; Cause of the High Temperature, 392; Site of Heat Production, 393 ; Heat-Regulatory Mechanism in Fever, 395 ; Causes of Fever, 399; Variations in the Clinical Picture of Fever, 405; Nutrition in Fever, 406; Water Retention in Fever, 407; Significance of Fever, 408; Temperature in Collapse, 411 ; Subnormal Temperature, 412.

Chapter XI

Effects of an Increased Blood-Flow, 414; Diabetes Insipidus, 416; Effects of Diminished Blood-Flow, 417; Effects of Obstruction to the Escape of Urine, 418; Effects of Lesions of the Secreting Membrane, 419; Albuminuria, 420 ; Casts, 429; Effect of Changes in the Composition of the Blood, 429 ; Uraemia, 433 ; Urinary Passages, 436; Urinary Calculi, 438; Pain in the Urinary Passages, 441.

Chapter XII

Circulatory Disturbances, 443; Increased Cerebral Pressure, 446; Cerebral Concussion, 451; Disturbances of Motility, 452; Disturbances of Co-ordination, 456; Effect of Reflexes upon Motion, 462; Nervous Disturbances of Urination and Defecation, 463; Alterations of Reflexes, 464 ; Strychnine Poisoning and Tetanus, 467; Contractures, 468; Motor Irritative Symptoms, 471; Disturbances of Sensation, 473 ; Dizziness, 477 ; The Influence of the Nervous System upon Tissue Nutrition, 481 ; Muscular Atrophies, 483 ; Herpes Zoster, 490.

LIST OF ILLUSTRATIONS

PAGE

Fig. 1. — The effect of an extra stimulus applied to the ventricle ... 88

Fig. 2. — The effect of an extra stimulus applied to the auricle .... 89

Fig. 3. — Extrasystoles of the ventricular type 90

Fig. 4. — Extrasystoles of the auricular type 91

Fig. 5. — Tracing from a bigeminal pulse 92

INTRODUCTORY NOTE

Knowing its worth, I very gladly agreed to write a brief introductory preface to an American edition of Professor Krehl's well-known work. Not that it needs any words of commendation. A successful book in Germany, it has already been translated into several languages, and has long since passed beyond the probation stage; but a few words from me may serve to introduce it to the English-speaking profession. Those of us who were brought up on Williams's " Principles of Medicine" recall the pleasure and the profit derived from it, mingled now with the regret that we have no work of the same character to place in the hands of our senior students. This want Professor Krehl's book will supply. Herter's " Lectures on Chemical Pathology" cover part of the ground, and Cohnheim's well-known " Lectures on General Pathology" is somewhat similar. In Professor Krehl's work disease is studied as a perversion of physiological function, and the title " Clinical Pathology" expresses well the attempt which is made in it to fill the gap between empirical and scientific medicine. The facts presented are derived in part from studies upon patients, and in part from experiments upon animals, designed to explain clinical problems. The author has had the advantage of prolonged laboratory training, to which has been added that accurate knowledge of disease to be had only by years of study and teaching in the wards. For such a work as this there is at the present time great need. Every few years the laboratories seem to run ahead of the clinics, and it takes time before the facts of the one are fully appreciated by the other. In the complexity of the problems, sometimes in the fascination of the scientific side, we are apt to lose sight of the practical application

14 INTRODUCTORY NOTE

to diagnosis and to treatment of the facts obtained in the laboratories. The surgeons have invaded the medical wards with great advantage to our patients, and in many diseases to the great improvement in the art of diagnosis. How helpful it would be if clinicians had always at hand skilled physiologists, pathologists, and chemists to apply their most advanced technique to clinical problems, and not the technique alone, but the biological and chemical principles upon which medicine as an exact natural science is founded. Principles, as Plato reminds us, require constant revision and consideration ; and this book, representing a revision to date of the " Principles of Clinical Pathology," will be most helpful to all students and teachers who wish to know the scientific basis of our art.

William Osler.

Introduction

Pathological physiology is one among the sciences that contribute toward our knowledge of diseased processes. In his famous book on " General Pathology," Cohnheim has denned disease as a peculiar, abnormal course of the same processes that make up the life phenomena of healthy individuals. We term these vital processes normal when they occur in the majority of individuals and when these latter feel well and are able to accomplish their average amount of work.

In many instances, it is easy to determine whether the functions of the body are following a normal or an abnormal course ; in others, the question is a very difficult one to decide.

The whole series of living 1 beings, from the lowest up to the highest, are liable to be afflicted with disease. Yet different species, even though they are closely related, may vary considerably from one another, not only in their morphological but in their functional characteristics. For example, it would be pathological if a mammal excreted as much uric acid in its urine as does a normal bird. The question as to whether a given function is or is not normal can only be answered by comparing individuals of the same species.

These remarks might appear superfluous, inasmuch as the primary object of this book is to discuss pathological disturbances in man. Yet a satisfactory understanding of these latter is not possible except we make critical use of the data obtained from animals.

I shall not attempt to discuss the outlook that the method of comparative study opens for us in our knowledge of pathological processes. Hitherto this method of study has played but a minor role in developing this field, for the means and

'5 opportunities for pursuing this line of work have been lacking. Yet if pathology is to remain abreast of the other branches of biology, we must have a closer relationship between the pathological and the veterinarian laboratories, and the natural diseases of animals must be studied with a view to the light that they may throw on those of man. Even now, extensive use is made of animal experiments in the study of pathological processes and these experiments have become an almost indispensable aid in such study. In estimating the value of these experiments, however, due regard must be paid to the morphological and functional differences between man and the animals used.

Very considerable individual differences may occur even within a single species. For example, there are men whose stomach contents at the height of digestion contain no free hydrochloric acid, and, although such men differ in this respect from the great majority of their fellows, nevertheless they may show absolutely no digestive symptoms and no diminution in their capacity for work. In my opinion, such individuals can hardly be regarded as being sick, although it must be acknowledged that they stand near the border line between the normal and the pathological. Another class of men show for years clear and unmistakable functional disturbances in some organ or group of organs, and yet they are not incapacitated to the slightest degree for work. Theoretically such men are sick; practically, we hardly know whether to say they are sick or healthy.

The physician must be clear in his own mind about this great difference between the theoretical and the practical ; and although we are dealing in this book principally with the former, yet it will not be amiss to emphasize this fact, that many individuals who show definite pathological changes are perfectly healthy to all practical intents and purposes.

We should designate as diseased, therefore, all those life processes which differ from the ones that occur in the majority of the members of a species, and which, in addition, affect the individual's capacity for work or the duration of his life.

All theories of life processes, physiological as well as pathological, must be carried back to the elementary constituents of the body. Disease arises from changes in a certain set of cells, or of organs, or of groups of organs ; for the cells that normally work together are not necessarily grouped together, but they may be distributed over different parts of the body. We are learning more and more that certain functions necessitate the combined action of different classes of cells.

Functional disturbances naturally coincide with, and are caused by, physical, chemical, or morphological changes in the body cells. This dictum is in no way altered by the fact that these chemical and morphological changes may not be demonstrable with the methods at our disposal. It is customary to distinguish those disturbances in which no such changes in the cells have been found (functional disturbances) from those in which such changes have been demonstrated (organic lesions). Yet this distinction is a more or less accidental one, depending as it does upon what happens to be the state of our knowledge at the time when the division is made.

A complete theory of pathological phenomena must embrace not only a knowledge of the functional disturbances in the affected cells, but a knowledge of their chemical, physical, and morphological changes as well. At present, our knowledge in all these directions is satisfactory for only a few diseases. For others, it has developed along functional and anatomical lines, for a third group, along functional and chemical lines, and finally, for a fourth group, the functional changes alone are known to us and we are ignorant as to their anatomical or chemical basis.

The development of our knowledge in one or another of these directions depends in the first place upon the degree to which our methods of investigation can solve the problems presented. These methods will suffice for certain problems in certain diseases but not for others, so that we have an unequal development along different lines. In the second place, the master minds of the time tend to develop our knowledge along the lines that happen to interest them most, and these lines gain thereby a certain prominence. Controversies have been waged and still are waged as to which is of greatest importance, the functional, chemical, or morphological view of disease. The uselessness of such a controversy is apparent when we remember that all these changes necessarily go together and that we must look at a disease from every point of view. Nevertheless, it is true that one point of view may be more luminous than another in respect to any particular class of diseases.

Diseases result either from primary defects in the living protoplasm or from the protoplasm being placed under such abnormal conditions that it cannot compensate for the changes in its environment. In the first class of cases, the abnormality consists in an improper organization of the protoplasm. The affected individual is then either diseased from birth, or he is born apparently healthy but is unable to withstand the ordinary wear and tear of life as a normal person should. Consequently, the structure, composition, or functions of his tissues suffer. Such primary endogenous weakness apparently plays a not inconsiderable role in the etiology of disease.

Of greater importance, however, is the effect that injurious external influences exert upon the living substance of the body. When these injuries affect the composition, structure, or functions of the cells, they become causes of disease. These causes are of the most varied kinds. Heat and cold, humidity and dryness, electricity, chemicals, all these may affect the body; but more important than any of them is the penetration of abnormal forms of life into the body.

Whether a man shall become sick or not, depends, therefore, in the first place, upon the way that he is originally constituted

(endogenous causes), and, in the second place, upon the more or less accidental injuries to which he is exposed (exogenous causes). Furthermore, the effectiveness of the latter class of causes depends largely upon factors that lie within the individual. There are, indeed, poisons, which, in a certain dose, will kill practically any one, and there are infections that will attack all or nearly all individuals exposed to them. Nevertheless, the majority of all infectious and toxic processes affect only a certain proportion of the individuals exposed. The causes of this difference in susceptibility are naturally complex and not always the same ; but in the main they depend upon the physiological organization of the individual.

In a complete discussion of diseased phenomena, the vital processes and the alterations in these processes and in the elementary constituents of the body must be considered from various points of view. In the present book, we propose to present only one of these. Just as physiology deals with the functions of the normal body, so pathological physiology deals with the functions when organs are placed under pathological conditions; and this is the subject of our discourse.

The field covered by this book serves, in the main, to fill out the gap left in the subject of pathology after the subjects of general pathology and of special pathological anatomy have been eliminated. In classifying the material, I have followed the classification that is customary in the German universities, and I have utilized material that has especially appealed to me as a clinician. Many subjects that are usually discussed in our text-books on general pathology, such as local circulatory disturbances, have been omitted, even though they should rightly be included in a book of this character. Whether the choice of material has been a fortunate one or not, remains to be decided.

THE PRINCIPLES

Chapter I. . The Heart

The Importance of the Circulation. — The circulation is of fundamental importance to the body. It is not, of course, true, as was formerly believed, that the functions of the individual organs depend primarily upon the amount of material that they receive from the blood. Without doubt their activities depend rather upon the condition of the parenchyma cells and upon the stimuli which these receive from the nervous system. 1 Yet it is certain that, in warm-blooded animals at least, a sufficient supply of oxygen, salts, and food materials to the tissues is a necessary requisite for a normal course of life. Disturbances of the circulation are therefore of great importance, and the more complex the organ affected, the more serious are the results of such disturbances.

The Pulmonary Circulation. — A disordered condition of the circulatory system may have its origin either in the pump which propels the blood or in the tubes through which the blood flows. The right ventricle drives venous blood at a comparatively low pressure through the pulmonary vessels, which form

1 We are, however, now acquainted with at least one example demonstrating that the blood may normally carry a specific substance which Stimulates an organ to activity, — viz.. the secretin, stimulating the pancreas. — Ed.

a system of short tubes, whose combined area of cross-section is very great. Through the walls of these capillaries, the interchange of gases between the blood and the air in the lungs occurs; and since this interchange takes place quite rapidly, the pulmonary system of a large number of short tubes seems best fitted for the work to be performed. The vessels play a relatively subordinate part in controlling the circulation in the lungs, for the pulmonary arteries possess little, if any, tone. 2 So far as we know, the different parts of the lungs are functionally equal, and there seems to be no necessity for a variation in the blood-supply to different pulmonary areas. During a period of rest, when only a slight interchange of gases is necessary, the rate of blood-flow in the lungs is comparatively slow; but during exercise, when larger amounts of gases must be interchanged, a great quantity of blood is propelled through the lungs. The increased respiratory movements assist the action of the heart in maintaining this more rapid circulation.

The General Circulation. — The relations are quite different in the greater circulation. Here a higher blood-pressure prevails at the onset, its height depending upon the contractions of the left ventricle, and upon the size of the smaller arteries. Variable amounts of blood may be made to pass through different organs without any alteration of the general arterial pressure, for, as the resistance to the flow of blood through one organ is lessened, the resistance to the flow through another may be correspondingly increased. Such a mechanism is of the greatest service, for here all parts are not of equal functional value, as they are in the case of the lungs, and it may be necessary to furnish one organ with a rich supply of blood at one time, and then later to do the same for another. The activity of the muscle-fibres of the smaller arteries regulate the distribution of the blood without at the same time necessarily altering

' Knoll, Wiener Sitzungsber. mathem. naturw. Kl., 1899, iii. p. 5.

the general blood-pressure. Indeed, this latter must not sink below a certain point if the brain and eye are to perform their functions properly.

The flow of blood in the veins is caused in part by the slight blood-pressure transmitted through the capillaries from the arteries and in part by other accessory forces. Of these, we may mention the suction exerted by the heart and the thoracic cavity, as well as the pumping effect produced by the varying pressure of the muscles and fasciae upon those veins that are provided with valves.

The Adaptability of the Heart. — Any of the various parts of the cardiovascular apparatus may be diseased without necessarily disturbing the general circulation. This is due to the fact that this apparatus, like so many others in the animal body, possesses a compensatory mechanism. We need not regard this mechanism as the provision of a beneficent Providence, arming man against disease, nor need we regard it as a trait acquired in the struggles of the race against injurious agents. The compensatory mechanism for pathological processes is simply that which a healthy man possesses and uses in order to meet the varying physiological demands made upon the circulation.

The amount of work which the heart performs 3 may be approximately estimated if we know the volume of blood delivered at each systole, the velocity imparted to this blood, the peripheral resistance, and the number of heart-beats in a unit of time. In other words, it depends upon the size of the ventricular cavity in diastole, the number and intensity of the ventricular contractions, and the degree of constriction of the blood-vessels. The latter, in the lesser circulation, depends primarily upon the condition of the lungs, whereas in the greater circulation it depends upon the condition of the smooth

'R. Lewy, Ztft. f. klin. Med., vol. xxxi. pp. 321, 520; O. Frank, Ztft f. Biol., vol. xxxii. p. 428, and vol. xxxvii. p. 483.

muscle-fibres of the arteries and upon the vasomotor nerves which supply them.

During the life of a healthy individual, the blood flows at varying rates of speed, — rapidly when the cells need much oxygen or food material, slowly when this need is small. As stated above, it is possible that the blood-supply to an organ, or possibly to several organs, should vary greatly without affecting the general blood-flow. This is brought about by a contraction in one set of vessels, which contraction compensates for a dilatation in another set. Yet this compensation cannot meet all emergencies on account of the limited quantity of blood in the body. When large amounts of blood are needed in several parts of the body at the same time, they can only be furnished by increasing the speed of the general blood-stream.

We might think that propelling a larger amount of blood would not necessarily increase the work of the heart, for, as the volume of blood increased, the general blood-pressure might be so decreased that the two would counterbalance each other. As a matter of fact, however, this does not occur, and, indeed, could not occur, on account of the relations that exist between the amount of blood propelled, the general pressure, and the rate of flow. For example, if an extra supply of blood to the body were necessary, a diminution in the general arterial pressure would so reduce the difference in pressure between the arteries and the veins that the rate of flow in the capillaries would be insufficient to keep the heart supplied with fresh blood. Thus any great increase in the rate of flow is incompatible with a lessened arterial pressure, and consequently such an increased flow necessarily entails more work for the heart.

The work of the heart may be increased in another way, — viz., by increasing the peripheral resistance. The latter varies frequently and considerably even in health, for we know that the irritation of numerous sensory nerves will call forth contractions of the smaller arteries and therewith increased resistance. It is theoretically possible that this increased resistance should be overcome without additional work for the heart, provided that as the resistance is increased, the amount of blood delivered is correspondingly decreased. Such a condition, however, would slow the circulation so that the body could not perform its functions properly, and, as a matter of fact, it does not occur. We may therefore say that any marked increase in the peripheral resistance necessitates more work for the heart.

The heart is the best motor known to man. It performs equally well the small amount of work necessary when a man is at complete rest, and the large amount necessitated by great exertion. It therefore possesses the power of adapting itself to the varying demands made upon it. Not every man's heart is capable of the most extreme exertion, and a tailor in a large city could hardly furnish the circulation necessary for the ascent of the Matterhorn. The weight of the muscular tissue of the heart, and with this its capabilities, bears a certain relation to the weight of the skeletal muscles. The tailor is unable to ascend the mountain mainly because his general musculature is weak. If this be improved by training, then the heart also increases in its capabilities, and usually at a more rapid rate. Indeed, a healthy heart rarely fails in any effort. It possesses extreme adaptability, and what is of greater importance, the adaptation occurs precisely at the time when it is most needed. To this fact the body owes its remarkable capacity for work. For example, when a ventricle in diastole becomes unusually filled (even up to six times its customary capacity), 4 then with the next systole, it drives out not all the blood, perhaps, but at least several times the ordinary quantity. On the other hand, if the arterial resistance be suddenly increased, it is as promptly overcome by the succeeding ven-