Principles of sanitary science and the public health, with special reference to the causation and prevention of infectious diseases

Front matter

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Preface

With the single exception of the change effected by the acceptance of the theory of organic evolution, there has probably been no modification of human opinion within the nineteenth century more wonderful, or more profoundly affecting the general conduct of human life, than that in our attitude toward the nature, the causation and the prevention of disease. The modern conception of the living body, whether plant or animal, as essentially a physical mechanism, is largely the result of discoveries in the domain of physics and chemistry begun, indeed, but not perfected, before the recent century. The modern conception of disease as due to imperfection, misbehavior or disturbance of a physical mechanism depended for its development on an acquaintance with the physiology of the body and its microscopic structure which did not exist before the introduction, in the third decade, of the achromatic objective. The microscopical renaissance which began with this pregnant invention speedily led to discoveries of the first importance in the normal structure of organized bodies; disclosed in abnormal tissues the material ravages, and, in some cases, the parasitic origin of disease ; brought into full view a flora and a fauna hitherto unseen or only half seen ; and, by the end of the fifth decade, was throwing a new and increasingly powerful light on the long-vexed question of the relation of ferments and fermentation to decomposition, putrefaction and disease. At the end of the sixth decade a new theory of infectious disease — the "germ" theory — had arisen, vin PREFACE

and in the hands of Pasteur, Lister and many others was already bearing fruit.

The last quarter of the century has witnessed the firm establishment and fruitful development of these several conceptions. The principal theories to which they have given birth have been thoroughly tested, and stand to-day for the most part as accepted scientific principles ; while their applications to the practical conduct of life have everywhere been followed by results of extraordinary interest and importance. Public hygiene and state medicine have become subjects compelling the attention of statesmen and affecting the welfare of nations. Sanitary law has been endowed with unusual privileges and powers, and sanitary regulations controlling the commerce of the civilized world are debated in international congresses. Sanitary science and preventive medicine, terms practically unknown before this century, have become almost household words. Sanitary arts of great range and importance have grown up ; vast sums are annually spent for private, and especially for public, sanitation ; and human life has been made safer, longer and probably happier.

Standing on the threshold of the twentieth century, and surrounded by the innumerable municipal, medical, domestic, public and private sanitary safeguards which have already sprung from these discoveries so that, in spite of facilities for the spread of disease by the development of easy international transportation, such as the world has never before known, pestilences and plagues are no longer greatly dreaded, it is hard to realize that our not very remote ancestors regarded disease as an insoluble mystery, an inscrutable visitation of divine Providence, or as the penalty and consequence of sin. Under such beliefs there could be no sanitary science. But if disease be disturbance of a physical mechanism, and due to the fact that the mechanism is made of poor materials, or of good materials badly put together, or that it is badly operated, or

PREFACE ix

that it is interfered with by unfavorable environmental conditions, it becomes easy to comprehend at least approximately the causes of diseases, and in many cases to remove or forestall them. It is precisely this which the science and art of hygiene seek to do, namely, to comprehend the nature of the human body and its diseases, in order as far as possible to prevent the latter. Hygiene is the science and art of the conservation and improvement of normal living, the prevention not merely of premature death but of abnormal life ; and sanitary science, or hygiology, is simply the body of scientific doctrine, or the principles, underlying the sanitary arts.

The time has not yet come for a scientific treatise on the whole subject of hygiene. The application of many of the results of experimental science to the welfare of man, extensive and valuable though they are, must still wait until their relations to everyday life become clearer. Climatology, clothing, warming and ventilation, foods and feeding are subjects undoubtedly of the very first importance, but not as yet reducible in their relation to human life to simple scientific terms. It is otherwise, however, with an important class of diseases proceeding from the controllable environment and known as " communicable " or "infectious." In principle, at least, these are now well understood and capable of being scientifically dealt with. Their causes are known, as are also the sources in which they originate, and the vehicles by which they are transported. Their characteristic operations and effects are rapidly becoming familiar everyday facts. Their control, therefore, in theory at least, becomes easy and in a broad sense a problem of engineering, which subject has been defined as the scientific control and use of the forces and materials of nature for the benefit of man. So much, at least, of medical or sanitary engineering rests upon a sound scientific basis, and for this the term "sanitary science," as distinguished from " hygiene," may conveniently be

X PREFACE

employed. If, hereafter, our knowledge of the constitutional diseases, and the ordinary conduct of individual life, comes to rest upon foundations equally sure, simple and scientific, either term — hygiene or sanitary science — may be dropped, for the two will be strictly synonymous. Until that time comes it will probably conduce to a just recognition of the real situation if we keep the term " hygiene " more as an end to be sought for than as something possessed, and endeavor by the constant extension of the boundaries of knowledge and the application of the principles of science, to enlarge the field of sanitary science until its boundaries become coterminous with those of hygiene. The mutual relations of hygiene, sanitary science, public hygiene and personal hygiene are dwelt upon at some length at the end of the first chapter, and to that place those are referred who care to pursue this subject further.

The present volume is the direct outgrowth of a course of lectures on Sanitary Science and the Public Health given for several years by the author to certain senior students — chiefly engineers, biologists, chemists and architects — of the Massachusetts Institute of Technology, and it has been prepared primarily for their use. It is believed, however, that a larger circle of students and some physicians, publicists and general readers may be glad to have access to the same material. If any apology is required for the occasional use of examples drawn from the author's personal experience, chiefly in Massachusetts, it may be said that these have been referred to, not because the author regards them as of paramount importance, but because he has preferred to deal as far as possible at first hand with matters within his own knowledge rather than to depend upon the digests or even the original reports of others.

It must not be forgotten that this volume deals with the principles, rather than the arts, of sanitation, nor that it is

PREFACE

XI based upon lectures given to beginners. It is intended to be no more than an elementary treatise on the subject ; and while it is believed that it contains some new material, and some old material treated from new points of view, no special claim is made for originality either in substance or in method of presentation. The author has chiefly sought to bring together and to present in a simple and logical form those fundamental scientific principles on which the great practical arts of modern sanitation securely rest. The subject is so vast and touches human welfare at so many points that it has seemed wise to omit many things altogether, and to make in many cases only brief and summary statements where more extended treatment would have been easy and perhaps desirable. It is hoped, however, that clearness and accuracy have nowhere been sacrificed to mere condensation.

The author has prepared the present work in the earnest hope that it may find a useful place in sanitary education, both professional and popular, for he holds with Lord Derby that " sanitary instruction is even more important than sanitary legislation."

The Biological Laboratories,

Massachusetts Institute of Technology,

December, 1901.

FlG. I. {After Leuckart-Chun s Wall- Diagram.) —ANOPHELES AND THE MALARIA Germ, i, 2. The malaria germ (Plasmodium) introduced by a mosquito bite into human blood. 3-5. After penetrating a red-blood cell ; its growth at the expense of the latter. 6. Its vegetative multiplication. 7, 8. Crescentic forms (for further development the germs must at this point be transferred from the man to mosquito). 9. Female germ-cell ; 9 a, 9 b, Male germ-cell. 10. Conjugation of 9 with one of the vibratile arms of go. 11. Malaria germ resulting from such conjugation in stomach of mosquito. 12-16. Multiplication (encystment and sporulation) of the malaria germ in the body of the mosquito, with production of many forms like 1 (cycle completed). 17. Female malarial mosquito (Anopheles claviger) ; head of male below. 19-20. Mosquito larva and pupa. 21. Stomach of mosquito, showing tumors produced by 16. 22. Crosssection of salivary gland of mosquito, showing malarial microbes which have wandered into it (from the tumors in 21) and now ready to be transferred with saliva into persons bitten.

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CONTENTS PART I

HEALTH AND DISEASE

Chapter I

On Health, Old Age and Disease. A Classification of Diseases ACCORDING TO THEIR PLACE OF ORIGIN. DEFINITIONS

The Human Mechanism — Old Age — Death and its Causes — Disease, not Old Age, the Principal Nominal Agent of Death — Another View of the Causes of Death — Intrinsic, Constitutional or Structural Defects of the Vital Machinery — Intrinsic or Constitutional Diseases — Extrinsic or Environmental Interferences with the Vital Machinery — Extrinsic or Environmental Diseases — The Prevention of Constitutional Disease the Special Function of Personal Hygiene — Environmental Diseases more readily controlled — Their Prevention the Special Function of Public Hygiene — The Prevention of Premature Death the Principal Function of Hygiene and Sanitation — Hygiene and Sanitary Science — Definitions.

Chapter II

On ^Etiology or the Causes of Disease; Ancient and Modern Theories. The Zymotic (Ferment) or Germ Theory of

Infectious Disease 21

The Primitive or Daemonic Theory — Theory of the Four Humors — Roman, Arabian and Mediaeval Theories — Theory of Paracelsus — Physical and Chemical Theories — Theory of Sydenham — theories of the Eighteenth Century — Influence of Haller and Morgagni — Theory of Hahnemann— ^Theories of the Nineteenth Century*— The Germ Theory of Fermentation — The Zymotic or Germ Theory of Infectious Disease — Louis Pasteur and Infectious Diseases of Silkworms — Joseph Lister and Infectious Diseases of Wounds — Sanitary (Aseptic) Surgery the First Fruit of the Germ Theory.

xiv CONTENTS

Chapter III Page

On the Rise and Influence of Bacteriology. Transformation of the Zymotic into the Zymotoxic Theory of Infectious Disease 46

The Achromatic Objective — Animalcula, Vibrionia, Bacteria — The Beginnings of Bacteriology — Its Foundations securely laid by Louis Pasteur — Robert Koch proves that Micro-organisms are the Cause and not merely the Consequence of Splenic Fever — Photographs and Spores of Bacteria — A New Method for Bacterial Cultivation — Establishment of Bacteriology as a Science by Koch in 1881 — Quick Discovery by its Aid of the Germs of Tuberculosis, Typhoid Fever, Asiatic Cholera, Diphtheria and Tetanus — How precisely do Germs produce Disease ? — Sepsins, Ptomaines and Toxins — Transformation of the Zymotic Theory of Infectious Disease into the Zymotoxic Theory of To-day — Objections to the Germ Theory.

Chapter IV

Sanitary Aspects of the Struggle for Existence. Parasitism. Health and Disease in Terms of General Biology. Vital Resistance, Susceptibility and Immunity .... 62

Sanitary Aspects of the Struggle for Existence — The Parable of the Sower — Parasitism and Infectious Disease — Parasites and their Hosts — The Germ Theory a Theory of Parasitism — Materies tnorbi — The Lifeless Environment and Disease — Organisms and their Environments — Health and Disease in Terms of General Biology — Three Principal Sanitary Conditions or States of Relation — Their Practical Importance — Sanitary Paradoxes — Vital Resistance — Susceptibility — Immunity — Inoculation for Small-pox — Jenner and Vaccination — Pasteur and Attenuation — Metschnikoff and Phagocytosis — Behring and Antitoxic Serums — Serum as Cure and Serum as Prevention — Summary.

CONTENTS xv

Part II

INFECTION AND CONTAGION: THEIR DISSEMINA- TION AND CONTROL. FUNDAMENTAL PROB- LEMS OF PUBLIC SANITATION

Chapter V Page

On Infection and Contagion : the Paths and Portals by which they enter the body; the resistance which it offers; the Vehicles by which they are conveyed; and the Places of their Origin. Animals and their Excreta as Sources and Prime Movers of Infection 89

The Meaning of " Infection " — The Skin and Epithelia as Structural Defences of the Living Body against the Invasions of Disease

— " The Solution of Continuity " — Infection by Way of the Skin

— Wounds and the Diseases of Wounds — Tetanus or "Lockjaw"

— Insects as Vehicles — ^Mosquitoes and Malaria, Yellow Fever^ etc. — Flies and Typhoid Fever — Infection by Way of the Alimentary, Pulmonary and Genito-urinary Tracts — Toxins again — The Physiological Defences of the Living Body — "Vital Resistance " — " Susceptibility " and " Immunity " — The Precise Meaning of " Contagion " — Personal Contact (Contagion) vs. Infection and their Relative Efficiency in the Distribution of Disease

— Man and Other Animals the Principal Primary Sources of Infection — Man and Other Animals and especially their Excreta its Principal Primary Vehicles — Earth, Air, Water and Animals (Insects, etc.) the Principal Secondary Vehicles of Infectious Disease.

Chapter VI

On Dirt and Disease. The Living Earth. Dirt, Dust and Air as Vehicles of Infection. Filth and Filth Diseases and the Philosophy of Cleanness 108

^Precise Meaning of the Terms " Dirt," " Earth," " Soil," " Dust£_ etc. — Their Popular Significance as derived from Experience — Clean Earth vs. Dirty and Infectious Earth — Modern Ideas of a Living Earth — Earth as a Vehicle of Disease — Tetanus — Dust as a Vehicle — Its Dangers — The Atmosphere as a Vehicle of Disease; Ancient and Modern Theories — Pestilential Vapors; Atmospheric Influences; Miasmata — Microbes of the Air — Filth and Filth Diseases — The Pythogenic Theory — Modern Views of Filth and Disease — The Philosophy of Cleanness — Personal vs. Public xvi CONTENTS

PAGE

Cleanness — Public Drinking Cups, Towels, Razors, etc., and their Dangers — The Disposal of Dirt, Dust, Garbage and Refuse — Cleanliness — Its Aseptic and Antiseptic Value.

Chapter VII

On Sewage as a Vehicle of Infectious Disease : its Proper Disposal and Purification; the Natural Purification of Sewage by Fermentation and the Living Earth . . . .123

The Genesis and Composition of Sewage — Its Dangerous Elements and Properties — The Importance of its Sanitary Disposal — Primitive Methods of Disposal — Modern Methods — Disposal and Purification by Dilution — Disposal in Rivers — "The Self- Purification" of Streams — Disposal in Lakes — Disposal in Harbors, Estuaries and the Sea — Principles involved in these Cases — Disposal and Purification on Land — The Living Earth — Intermittent Filtration — Experiments in England — In Massachusetts — The Lawrence Experiment Station — Theory of Intermittent Filtration — * A Bio-chemical Process — Objections to Intermittent Filtration — Disposal of Sewage by Irrigation — Sewage Farms — Objections to Sewage Disposal by Irrigation and Sewage Farming — Disposal and Partial Purification of Sewage by Chemical Precipitation — By Electricity — By Fermentation or Putrefaction — Fate of the Infectious Materials in the Disposal and Purification of Sewage — Sewage Fields and Sewage Filters as Bacterial Tombs.

Chapter VIII

On Water as a Vehicle of Infectious Disease. The Pollution of Public Water Supplies. Notable Epidemics due to

Infected Drinking Water 164

Drinking Water as a Vehicle of Disease — Diarrhoeal Diseases and Drinking Water — Typhoid Fever and Asiatic Cholera — An Epidemic of Asiatic Cholera traced to a Polluted and Infected Well : the Case of the Broad Street (London) Pump — An Epidemic of Asiatic Cholera in London in 1866 traced to an Infected Public Surface-water Supply — An Epidemic of Typhoid Fever in Lausen (Switzerland) traced to an Infected Public Ground-water Supply — An Epidemic of Typhoid Fever in Caterham (England) traced to a Polluted Ground-water Supply — An Epidemic of Typhoid Fever in Plymouth (Pennsylvania) traced to a Polluted Surface-water Supply — Typhoid Fever in Lowell, Lawrence and Other Cities on the Merrimac River — Pollution vs. Infection — The Case of Newburyport (Mass.) — An Epidemic of Asiatic Cholera in Hamburg

CONTENTS xvii

PAGE

(Germany) traced to an Infected Surface-water Supply — An Epidemic of Typhoid Fever in New Haven (Conn.) traced to an Infected Surface-water Supply — Diseases Other than Typhoid Fever and Asiatic Cholera traced to Polluted Drinking Waters — Dysentery and Diarrhoea — Concluding Remarks on Drinking Water as a Vehicle of Disease.

CHAPTER IX On the Establishment and Conservation of Purity in Public

Water Supplies 221

Public Supplies as Public Dangers — The Atmosphere as the Source of Water Supply — The Pollution of Rain Water and of Snow by Dust — Influence of the Earth upon the Purity of Rain Water — " The Living Earth " again — Ground-waters and their Pollution and Purification — The Conservation of Purity in Ground Waters; Microscopical Organisms and Noxious Tastes or Odors — Surface Waters and their Pollution — "The Self-purification of Streams" once more — Quiet Water rather than Running Water purifies itself — Natural Processes of Water Purification — Purification by Storage — By Slow Sand Filtration — Artificial Processes of Water Purification — Rapid Mechanical Filters — Conservation of Purity in Surface Waters — Recapitulation — Protection by Statute of the Purity of Inland Waters in Massachusetts — Sanitary Protection of Public Water Supplies — Advanced Legislation — Sanitary Inspection and Protection of Watersheds — Expert Supervision an Absolute Requirement of Sanitary Science.

Chapter X

On Ice as a Vehicle of Infectious Disease. The Pollution of Ice. Ice Supply and the Public Health . . . .251

The Use of Ice in Drinks — Does Polluted Water purify itself in Freezing ? — Epidemics charged to Infected Ice — Investigations of the Purity of Ice by Various Observers — Ice as a Vehicle of Infectious Disease — The Pollution of Ice — General Inferences and Conclusions.

Chapter XI

On Milk as a Vehicle of Infectious Disease. The Pollution and Infection of Milk. Epidemics traced to Infected Milk. Milk Supply and the Public Health . . .263

Milk as Food for Microbes and Mankind — The Modern Distrust of Uncooked Milk — Its Origin in Epidemics traced to Milk — The Fermentations of Milk — Normal vs. Fermented Milk — xviil CONTENTS

PAGE

Infantile Diarrhoea and Cholera Infantum — The Pollution of Ordinary Milk — Various Systems of Public Milk Supply in Villages, Cities, etc. — Milk Supply in Warm Countries — Epidemics of Typhoid Fever in Massachusetts traced to Infected Milk Supplies — Epidemics of Typhoid Fever traced to Skimmed Milk and Creameries — The Question of Tuberculosis in Milk — Scarlet Fever and Diphtheria — The Protection of Milk Supplies from Pollution — Their Protection from Infection — Safeguards against Polluted and Infected Milk — Sterilization — Pasteurization — Condensation — Modification — Model Dairies — The Outlook for Improved Milk Supplies.

Chapter XII

On Certain Uncooked Foods (Meats, Oysters, Fruits, Vegetables, Ice Creams, etc.) as Vehicles of Infectious Disease.

The Sanitary Significance of Cookery 293

An Infectious Disease {Trichinosis) produced by Microscopic Worms in Raw Pork — Trichina spiralis — The Question of Infection by Tuberculous Meat — Raw Oysters as a Vehicle of Disease — An Epidemic of Typhoid Fever traced to Infected Oysters — English and French Opinion in Regard to Dangers from Raw Shellfish — The Contamination of Oyster Beds by Sewers — Fruits, Vegetables, Ice Creams, etc., as Vehicles of Disease — The Sanitary Significance of Cookery.

CHAPTER XIII On the Prevention and Inhibition of Infection, Decomposition

and Decay. Asepsis and Antisepsis 311

Asepsis, or the Prevention of Infection by Exclusion — Quarantine — Isolation — Immunity, or the Prevention of Infection by Insusceptibility — Inoculation — Vaccination — Progress in Vaccination due to the Labors of Pasteur — A Public Demonstration of Protective Inoculation or " Vaccination " for Anthrax — Antisepsis, or the Inhibition of Infection by Antiseptics — Antiseptics and the Theory of their Action — The Control of Infection, Decomposition and Decay — Intestinal Antisepsis — Sanitary Aspects of Refrigeration and Cold Storage — Of Desiccation (Drying, Evaporation) — Of Smoking — Of Preserving — Of Canning — Of Pickling — Of Pasteurizing — Of Condensing.

Contents

CHAPTER XIV xitf

On the Destruction or Removal of Infection — Disinfection

and Disinfectants 334

Appendix

On Some Popular Beliefs as to Certain Special and Peculiar

Causes of Disease 347

The Belief in Dangers from Sewer Gas — The Belief in Dangers from Well Water — The Belief in Dangers from Broken Drains — The Belief in Dangers from Bad Smells — The Belief that Consumption is Inherited and therefore a Constitutional Disease — The Probable Truth about Endemic Disease — The Belief in Dangers from Atmospheric and Telluric Disturbances — The Belief in Dangers from Damp Cellars — The Belief in Dangers from Human Breath — The Probable Truth about Disease from Putrefaction and Decay — From Spoiled Meats — From Ice Cream Poisoning — From Canned Foods.

Part I Health And Disease

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SANITARY SCIENCE AND THE PUBLIC HEALTH

Chapter I

ON HEALTH, OLD AGE AND DISEASE. A CLASSIFICATION OF DISEASES ACCORDING TO THEIR PLACE OF ORIGIN. DEFINITIONS

"The fundamental conception of the living body as a physical mechanism ... is the distinctive feature of modern as contrasted with ancient physiology." — Huxley.

"To die of age, is a rare, singular and extraordinarie death." — Montaigne.

§ I. — The Human Mechanism

We must endeavor to obtain at the outset clear ideas of what is meant by the words " health " and " disease," which, to physiologists at least, are terms of precise and definite meaning indicating actual states or conditions of the living body. A moment's consideration will show that it is essentially no more difficult to comprehend the idea of a general state or condition of a living body than a general state or condition of a lifeless body, such as a stone or a piece of iron or a watch or a locomotive.

Closely examined, the living body reveals itself as a machine or mechanism composed of parts (called organs) precisely as a watch does. Very much in the same sense that a watch is a time-piece a living body is a life-piece. If a watch appears to be in good order and running well, we say that it is a good and normal time-piece. So also if the human body appears to be in good order and working well, we call it a normal or healthy body ; but if it be out of order and not working well, we say that it is in a state of " disease," either temporary or permanent. In a word, health is the normal, and disease the abnormal, condition of the living mechanism. Nor is this a mere analogy or abstraction. To the biologist it calls up a picture — the picture of health or the picture of disease. For precisely as the experienced watchmaker carries in his mind's eye and can at any moment summon up a mental image of intricate, correlated and interdependent parts — springs, wheels, bearings — lying concealed within, but which, taken together and in a certain definite and orderly relation one to another, make up the works of a delicately adjusted chronometer in actual operation, and constitute a valuable time-keeper; so the physiologist, familiar with bones, muscles and nerves, with good red blood and beating heart, all cooperating to a common end, — the healthy, normal life of the organism, — can summon up at will the picture of normal, vigorous, almost superfluous vitality in some vascular life-keeper. And in one sense, hardly more wonderful to him is the pulsing, vibrant, living mechanism than to the jeweller the accurate chronometer of delicate adjustment. To the savage the watch would be incomprehensible and inexplicable. And so to others than physiologists the living body seems something altogether strange and wholly apart.

The student of sanitary science must take up the physiologist's point of view. He must look upon the living body as a mechanism ; a mechanism of curious origin and history and of marvellous complexity; the most wonderful of all machines ; one before which the wisest of men stands very much as does the savage before the chronometer, ignorant of its origin, ignorant of its ultimate construction, ignorant of its fate; but yet unlike the

THE HUMAN MECHANISM 5

savage because without superstition and without fear; knowing that the body is nevertheless a mechanism, subject to natural laws, and with all its parts cooperating to one end, — the life-keeping function of the whole. The living body is like a machine, also, in that it receives all its energy from without and is merely a transformer of energy; in that it is profoundly sensitive (as is a watch) to its environment — to heat, to cold, to mechanical injuries. This living machine may be well built or ill; of good timber or poor; it may be sound and flawless or defective in construction. These are accidents of birth or ancestry; effects of good feeding or bad, of normal living or abnormal.

§ 2. — The Making of the Body. Youth and Maturity

Unlike the watch, the living mechanism is not made, but grows. With the fusion of two unlike cells — ovum and spermatozoon — the life of the individual begins. Henceforward its increase in size, its acquirement of organs and tissues, its powers and properties, are due, not as in the making of a watch to the assembling and cooperation of parts already perfected, but to processes of its own, to cell growth, cell multiplication, cell differentiation — balanced, adjusted, directed and controlled chiefly from within. The first portion of this development takes place within the body of the parent, and is called intra-uterine or embryonic life ; the second is a helpless state outside the body, but under parental care, the period of infancy ; a third, somewhat less dependent but ill-defined, is the period of childhood and adolescence. These three periods — the periods of youth — ripen into adult life or maturity, and this passes on into old age. Only very rarely does the mechanism last longer than a century. Usually, long before this it has stopped in death, which may have marked the end of life at birth, or even long before it, in infancy, in childhood, in maturity or in age. The period of growth and the period of decline — infancy and old age — appear to be the periods when death is least successfully resisted. As has been finely said : " In this last respect the two extremes of life resemble one another. The freshly lighted taper and that which is burnt down to the socket are both easily extinguished by the slightest puff of wind." 1

§ 3 .__ Old Age

Finally the living mechanism may wear out — it must wear out. No machine, however perfect, can run or be run forever. However smooth its bearings, however perfect its adjustments, dust and friction, and wear and tear, do their work, and in time the machine becomes old. So, also, is it with the human mechanism. No matter how well cared for, or how cleverly managed, old age finally creeps over it ; the rust of rheumatism gathers in its joints; its bearings grow eccentric ; its movements irregular and halting; until by and by something breaks, and death stops the whole machinery. Death is the final stoppage of the living mechanism. But while theoretically this comes only when all parts are worn out, and as the simple, natural cessation of function from sheer and general debility of each and every organ, it does not in fact come very often in this way. The machine breaks down ; it does not wear out. Some organ or part gives out comparatively early, and by failure to do its part destroys the whole.

Facts like these may or may not have inspired the author of the " One-Hoss Shay," who, in his famous poem has described the building of the body ; its defects of constitution and construction ; the ordinary causes of its death ; and, finally, the theoretic possibility of so making a living body that it shall die at last only because it is worn out,

1 P. H. Pye-Smith, "Lumleian Lectures," London, 189a.

A PHYSIOLOGICAL ALLEGORY 7

namely, from old age. In the person of the deacon the Autocrat, himself a physiologist, has, consciously or unconsciously, stated the case as follows : —

" Now in building of chaises, I tell you what, There is always so?newhere a weakest spot, — In hub, tire, felloe, in spring or thill, In panel, or cross-bar, or floor, or sill, In screw, bolt, thoroughbrace, — lurking still, Find it somewhere you must and will, — Above or below, or within or without, — And that's the reason, beyond a doubt, A chaise breaks down, but doesn't wear out."

His remedy for this unfortunate state of things was, —

" only jest T' make that place uz strong uz the rest."