«,rrv or CALIFORNIA UNIVERSITY OF CALIFORNIA QEFARTMENT OF CIVIL ENGINEERINC BERKELEY, CALIFORNIA PRINCIPLES OF SANITARY SCIENCE AND THE PUBLIC HEALTH *&&&. Principles of Sanitary Science and the Public Health WITH SPECIAL REFERENCE TO THE CAUSATION AND PREVENTION OF INFECTIOUS DISEASES BY WILLIAM T. SEDGWICK, Ph.D. j, PROFESSOR OF BIOLOGY AND LECTURER ON SANITARY SCIENCE AND THE PUBLIC HEALTH IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY, BOSTON; SOMETIME BIOLOGIST TO THE STATE BOARD OF HEALTH OF MASSACHUSETTS 11 With all deductions, the triumphs of sanitary reform as well as of medical science are perhaps the brightest page in the history of our century." — W. E. H. Lecky Nefo fgfltft THE MACMILLAN COMPANY LONDON : MACMILLAN AND CO., Ltd. 1922 All rights reserved Engineering Library Copyright, 1902, BY THE MACMILLAN COMPANY. TO &i)£ State iSoarti of f^altfj of Jftaggarfjusettg FAITHFUL THOUGH UNPAID GUARDIANS OF THE PEOPLE IN WHOSE HONORABLE SERVICE THE AUTHOR BEGAN AN ACQUAINTANCE WITH PUBLIC HYGIENE AND STRENGTHENED A LOVE FOR SANITARY SCIENCE WHICH HAVE INCITED HIM TO WRITE THIS BOOK AND ESPECIALLY TO Pfmrg $ictamg Watott, MM., Cfjatrman AND ^tram jjtanris Wills, €M. t lEngmeer Mtmbzt "Even to the State's best health:' — Timon of Athens. 5693 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 mod- ern conception of disease as due to imperfection, misbe- havior 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 dis- coveries 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 hith- erto 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 fer- ments 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, vu viii 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 in- terest and importance. Public hygiene and state medicine have become subjects compelling the attention of states- men 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 house- hold 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, domes- tic, 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 disturb- ance of a physical mechanism, and due to the fact that the mechanism is made of poor materials, or of good mate- rials 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 ap- proximately 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 compre- hend 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 hygi- ology, 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 impor- tance, 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 trans- ported. 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 consti. tutional 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 some- thing 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 sci- ence 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 sub- ject 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 archi- tects — of the Massachusetts Institute of Technology, and it has been prepared primarily for their use. It is be- lieved, 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 mate- rial, 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. CONTENTS PART I HEALTH AND DISEASE CHAPTER I PAGE On Health, Old Age and Disease. A Classification of Dis- eases ACCORDING TO THEIR PLACE OF ORIGIN. DEFINITIONS . 3 The Human Mechanism — Old Age — Death and its Causes — Disease, not Old Age, the Principal Nominal Agent of Death — An- other View of the Causes of Death — Intrinsic, Constitutional or Structural Defects of the Vital Machinery — Intrinsic or Constitu- tional Diseases — Extrinsic or Environmental Interferences with the Vital Machinery — Extrinsic or Environmental Diseases — The Pre- vention of Constitutional Disease the Special Function of Personal Hygiene — Environmental Diseases more readily controlled — Their Prevention the Special Function of Public Hygiene — The Pre- vention 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 Paracel- sus — 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 — Photo- graphs and Spores of Bacteria — A New Method for Bacterial Cul- tivation — Establishment of Bacteriology as a Science by Koch in 1 88 1 — 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 Dis- ease 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 morbi — 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 Resist- ance — 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 Struc- tural 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 Ali- mentary, Pulmonary and Genito-urinary Tracts — Toxins again — The Physiological Defences of the Living Body — "Vital Re- sistance " — " Susceptibility " and " Immunity " — The Precise Meaning of "Contagion" — Personal Contact (Contagion) vs. In- fection 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 Dis- ease. 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 Dis- posal and Purification; the Natural Purification of Sew- age by Fermentation and the Living Earth . . .• .123 The Genesis and Composition of Sewage — Its Dangerous Ele- ments and Properties — The Importance of its Sanitary Disposal — Primitive Methods of Disposal — Modern Methods — Disposal and Purification by Dilution — Disposal in Rivers — "The Self- Purifica- tion " of Streams — Disposal in Lakes — Disposal in Harbors, Estu- aries and the Sea — Principles involved in these Cases — Disposal and Purification on Land — The Living Earth — Intermittent Fil- tration — Experiments in England — In Massachusetts — The Law- rence 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 Infec- tious Materials in the Disposal and Purification of Sewage — Sew- age 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 — Diarrhceal 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 New- buryport (Mass.) — An Epidemic of Asiatic Cholera in Hamburg CONTENTS XVll PAGE (Germany) traced to an Infected Surface-water Supply — An Epi- demic 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 Inspec- tion and Protection of Watersheds — Expert Supervision an Abso- lute 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 Dis- trust of Uncooked Milk — Its Origin in Epidemics traced to Milk — The Fermentations of Milk — Normal vs. Fermented Milk — xviii CONTENTS PAGE Infantile Diarrhoea and Cholera Infantum — The Pollution of Ordi- nary Milk — Various Systems of Public Milk Supply in Villages, Cities, etc. — Milk Supply in Warm Countries — Epidemics of Ty- phoid Fever in Massachusetts traced to Infected Milk Supplies — Epidemics of Typhoid Fever traced to Skimmed Milk and Cream- eries — 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, Vegeta- bles, 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 Infec- tion 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 Shell- fish — The Contamination of Oyster Beds by Sewers — Fruits, Vege- tables, 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 — Quaran- tine — Isolation — Immunity, or the Prevention of Infection by Insusceptibility — Inoculation — Vaccination — Progress in Vacci- nation 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, Decomposi- tion and Decay — Intestinal Antisepsis — Sanitary Aspects of Re- frigeration and Cold Storage — Of Desiccation (Drying, Evapora- tion) — Of Smoking — Of Preserving — Of Canning — Of Pickling — Of Pasteurizing — Of Condensing. CONTENTS iax CHAPTER XIV PAGE On the Destruction or Removal of Infection — Disinfection and Disinfectants 334 Definitions — Disinfection by Chemical Agencies — Fire, Poisons, etc. — By Physical Agencies — Heat, Cold, Dryness, Light, Electricity, etc. — By Mechanical Means — Filtration, Sedimenta- tion, etc. — By Biological Agencies — Starvation, Old Age, " Un- favorable Environments," etc. — The Problem of Disposal of the Dead — Interment vs. Cremation — Special Disinfectants — Germi- cidal- efficiency Tests — Present State of the Art — Intestinal Disin- fection. PART III 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 Con- sumption 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 Dan- gers 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 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 essen- tially 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, 3 4 HEALTH, OLD AGE AND DISEASE 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 incompre- hensible and inexplicable. And so to others than physi- ologists the living body seems something altogether strange and wholly apart. The student of sanitary science must take up the physi- ologist'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 wonder- ful of all machines ; one before which the wisest of men stands very much as does the savage before the chro- nometer, 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, sub- ject 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 inju- ries. 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. Hence- forward 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, 6 HEALTH, OLD AGE AND DISEASE 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 ex- tremes 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 § i. — 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 per- fect 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 gen- eral 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 consti- tution 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, 1892. A PHYSIOLOGICAL ALLEGORY 7 namely, from old age. In the person of the deacon the Autocrat, himself a physiologist, has, consciously or uncon- sciously, stated the case as follows : — "Now in building of chaises, I tell you what, There is always somewhere 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." Accordingly the deacon proceeded to build his master- piece in such a way that — " The wheels were just as strong as the thills, And the floor was just as strong as the sills, And the panels just as strong as the floor, And the whippletree neither less nor more, And the back cross-bar as strong as the fore, And spring, and axle and hub encore" — with the result that after a whole century of life though there were indeed ..." traces of age in the one-hoss shay, A general flavor of mild decay," there was " nothing local as one may say ! " And when the end came from sheer old age,— ..." it went to pieces all at once — All at once, and nothing first — Just as bubbles do when they burst." Such is old age: the low-burning flame, which flickers and finally goes out ; the ripened fruit, which drops heavily to earth; the old mechanism, which after long years of 8 HEALTH, OLD AGE AND DISEASE service finally refuses to work, simply because it is worn out. All this is the natural and ordinary course of life. With this sanitary science has but little to do except to exercise a wholesome supervision and watchfulness and to provide the most favorable environment possible. With ordinary breakdowns from defects in the machine itself, in its construction, or its operation, sanitary science has also little if anything to do. Good stock comes by inheritance not by manufacture, as truly in men as in timber. Men do not gather grapes from thorns or figs from thistles. Neither do strong constitutions, as a rule, spring from weak ancestors or good lungs from tuberculous parentage. § 4. — Death and its Causes Life is the period of activity of the vital mechanism. Death marks the final stoppage of that machinery. Life is a perpetual struggle of the organism with its environ- ment. Death marks its final and unconditional surrender. In the higher forms of life death is the natural and inevi- table end of life. Old age marks the approach of death and is not less natural and inevitable. Doubtless the principal cause of death should be old age, the natural maturity of the organism, the gradual and irreparable wearing out of the vital machinery. Yet if we turn to any work on vital statistics, such as a Registration Report, we find far more prominence given to other factors of mortality. In the enumeration of the causes of death in the Registration Report of Massachusetts, for example, there are laid down five general classes of causes, namely, as follows : — I. Zymotic Diseases . . (Fevers, etc.) II. Constitutional Diseases . (Gout, Cancer, Scrofula, Dropsy, etc.) III. Local Diseases . . (Apoplexy, Heart Disease, etc.) IV. Developmental Diseases (Teething, Old Age, etc.) V. Violence . . . (Drowning, Murder, Accidents, etc.) THE PRINCIPAL AGENTS OF DEATH 9 If we look for old age, we find it under Class IV counted as a disease along with teething, — an equally normal process of the living organism. The great variety in the causes of death may be still more clearly seen by counting the subdivisions of the foregoing classes which are in number as follows in the Registration Report referred to : — 1 32 Causes of Death II 10 " " " III 48 " « « IV 10 " " " V 14 " " " It will be seen that Classes I-IV include seven-eighths of all the recognized causes of death. In other words, various forms of disease constitute seven-eighths of all the recognized causes of death, and it only requires a some- what closer examination of mortality tables to show that old age is assigned as the cause of death in a very small percentage of cases. § 5. — Disease, not Old Age, the Principal Agent of Death From the previous paragraph it is clear that disease is the cause of death most often assigned by physicians in filling out their official certificates; while old age, which may be considered the most natural cause, is compara- tively rare. But this is much more apparent than real, since it often happens that disease would have been power- less to cause death if the vital machinery had not already been weakened by age. To what extent death is really due to age it is, and always must be, impossible to say. The truth appears to be that many deaths occur under, and are attributed to, disease which would not have been able to cause death had the victim been either older or younger; while, on the other hand, death would not have occurred when it did if disease had been absent. There occurred in Massachusetts, in 1890, 45,108 deaths IO HEALTH, OLD AGE AND DISEASE from specified causes, and all but 1814, or four per cent, were assigned by the physicians reporting them to the effect of some disease. Disease, violence and old age, then, would appear to be the principal causes of death; disease causing about ninety-two per cent, violence four per cent, and old age four per cent, and if disease is thus in reality, as it is apparently, the principal agent of death, it is obviously to the prevention of disease that sanitary science must address itself. Hence has arisen its synonym " preventive medicine," i.e. such action as shall prevent the ravages of disease. § 6. — Another Classification of the Causes of Death A simpler, and for our purpose more helpful, view of the causes of death is one which seeks to classify them roughly according to their apparent place of origin, simply regarding them as either — (a) Intrinsic causes, or arising within the body proper, or (b) Extrinsic causes, arising outside the body or acting upon it from without. From this standpoint diseases may be regarded as due either to defects in the constitution or construction of the vital mechanism, or else to external unfavorable influences acting upon it. From the point of view of origin or causa- tion, all diseases may be divided into two classes, viz. : — I. Constitutional, or II. Environmental This classification, while open to many objections, is of the highest value to the physiologist and the sanitarian, for it brings the former face to face with intrinsic, struc- tural, or organic defects in the mechanism, while the atten- tion of the latter is concentrated upon those abnormal external influences which act unfavorably upon the organ- ism, and which he must seek, and may be able, to remove. BIOLOGY AND SANITATION u A count of the principal causes of death laid down in the Registration Report of Massachusetts shows that on this basis, and approximately speaking, there are there given — (i) Extrinsic or environmental causes of death .... 56 (2) Intrinsic or constitutional " " " .... 58 In other words, one-half of the principal assigned causes of death, from this point of view, may be said to proceed from within the organism and one-half from without ; one- half would therefore lie within the domain of the physiol- ogist and one-half within the field of the sanitarian. It will be found instructive to carry this line of thought considerably further, as in the next following sections, carefully keeping in mind the fact that many so-called intrinsic causes probably have in reality, though perhaps only remotely, an extrinsic source or origin. 11 Any arrangement of diseases is valuable so far as it helps the memory to retain useful facts ; any arrangement is useless or mischievous if it pretend to be a universal or g natural ' or ' scientific ' system. Diseases are not natural objects; they are physiological states, which we sometimes define by their cause, as plumbism [lead-poison- ing] and scabies [itch] ; sometimes by their histology, as sclerosis of the spinal cord and epithelial cancer of the lip ; sometimes by their constancy in transmission, as measles and typhus ; and sometimes by more or less con- stant concurrence of symptoms, as chorea and epilepsy." * § 7. — Intrinsic or Structural Defects of the Vital Machinery ; Constitutional Diseases The human body is a wonderful machine, an admirable piece of mechanism. Like other complicated machines, it has a definite structure and interdependent and recip- rocating parts. These are naturally adjusted to the per- 1 Pye-Smith, " Diseases of the Skin," London, 1893. 12 HEALTH, OLD AGE AND DISEASE formance of certain duties or functions, and a failure of one part may involve the failure of all other parts and thus of the entire vital apparatus. If, for example, the heart is defective and fails to do its duty, the circulation is affected unfavorably and the whole body suffers. It needs no further argument or illustration to show that a structural flaw or defect in the living machine may mean disaster and death, however favorable all external condi- tions may be. A condition of the blood, or a roughness upon the valves of the heart, which shall produce a clot, or a weakening of an arterial wall in the brain which shall finally produce cerebral hemorrhage or cause apoplexy, is an intrinsic or structural defect which may not be directly attributable to any unfavorable external condi- tion. It may be a flaw in the machine, an intrinsic and perhaps inherited defect of structure ; and, if so, it is remediable only by fundamental changes in organization which sanitary science cannot hope to establish, unless after many generations and by steps which are at present quite beyond its reach. Diseases of this class are dis- eases of construction, i.e. " intrinsic " or " constitutional." They belong as yet in the field of the biologist, the physi- ologist and the hygienist rather than that of the sanitarian ; to personal hygiene, rather than public hygiene or sanitary science. § 8. — Extrinsic or External Interferences with the Vital Machinery ; Environmental Diseases The human body is subject — sensitive, even — to exter- nal conditions : cold or heat, fire or water, may so act upon the human body as to produce death by freezing, burning, or drowning. Forces, such as gravity or electricity, may be causes of death by falling, crushing or execution. These and similar causes are clearly extrinsic or environ- mental, and come under the head of accident or violence — unless we except suicide as perhaps due to constitu- CONSTITUTIONAL VS. ENVIRONMENTAL DISEASE 13 tional peculiarities. Some diseases have already been spoken of as constitutional or intrinsic, but many dis- eases do not come under this head. The common expression which describes an infectious disease as an " attack" is noteworthy as indicating the popular recog- nition of the fact that disease often has its source out- side of the body. It is now believed that many diseases originate exclusively from unfavorable environmental in- fluences, and since the celebrated discovery of 1839 oi the vegetable nature of the cause of favus (honeycomb of the scalp), it has been found that not a few diseases are due to parasites, which invade the organism and inter- fere with its normal working. § 9. — The Prevention of Constitutional Diseases the Special Function of Personal Hygiene If diseases due to defects or flaws in the vital machinery are to be avoided, this is obviously to be done only by improving and perfecting the apparatus, which is a com- paratively slow and difficult matter. To make a family of weak constitution strong, is to reconstitute its entire physical basis ; and if this can be done at all, it may be only after generations shall have come and gone. It must be done by careful living and good feeding, wise inter- marriage and severe natural selection. To ward off adven- titious disease is, in these cases, not enough. The whole structure must be made over. Sanitation alone cannot hope to effect these changes. They must come from scientific hygiene carefully applied throughout long generations. § 10. — Extrinsic or Environmental Diseases mainly Pre- ventable and therefore within the Scope of Sanitation Diseases which arise from some invasion of the organism may possibly be warded off. As they virtually proceed OLD AGE AND DISEASE from the environment which, in theory at least, is under our control, they may be prevented. With such diseases the sanitary science of to-day is chiefly concerned. Sanita- tion has stamped out small-pox in many civilized com- munities. It is seeking to-day, with more or less success, to do away with typhoid fever. It boldly attacks epidemics of diphtheria and scarlet fever, and has recently sought to control tuberculosis and malaria. There can be no ques- tion that it has already won signal victories, and that its practitioners may reasonably hope for fresh laurels in the near future. § II. — The Prevention of Premature Death the Principal Function of Hygiene and Sanitary Science From what has been said above it would appear that dis- ease is the principal agent of death. But it must be kept in mind that disease (except in infants) is often facilitated in its work by age or enfeeblement, which gives it a foothold and incapacitates the organism for resisting its activity. Physiologists and physicians recognize differences of con- dition in which the body seems to possess great powers of resistance or endurance, or only small powers (p. 71). In this way it often happens that a structural or constitu- tional enfeeblement exposes the organism to the invasion of environmental disease ; as, for example, a low condition of vitality is generally believed to increase enormously the susceptibility to attacks of typhoid fever ; and as soldiers, enfeebled by long marches or bad feeding, appear to suffer unduly from certain camp diseases. A little reflection will show that death, as a rule, comes prematurely. Old age, the only theoretically normal and natural cause of death, is very rarely the one and only cause. Poor timber or poor materials or poor construction of the living machinery, alone or together making up a poor "constitution," or else violence, poison, parasites or THE FUNCTIONS OF HYGIENE 15 other unfavorable elements in the environment, usually bring on disease and death long before the appointed threescore years and ten, or the rarer fourscore years. Many die before they are born ; more before one year of life is over ; others under five years, ten or twenty. A few live on for thirty, forty or fifty years ; but for the great majority death comes before old age, before "the lean and slipper'd pantaloon." All this means that death is oftenest premature ; and the principal function of sani- tation and of the applications of hygiene in general is the prevention of premature death. Hygiene in its widest sense goes further, and seeks to elevate or maintain at a high level the standard of normal living. § 12. — Hygiene and Sanitary Science Sanitary science is the science of health. It is com- monly held to be, and commonly it is, much the same thing as hygiene. Sciences and arts, however, like living organisms, grow, differentiate and divide, and hygiene is no exception to the rule. The wonderful developments which have taken place within the last half century in our knowledge of the causes of disease, and especially those diseases proceeding from the environment, together with the corresponding advancement in our arts for their pre- vention or control, — the sanitary arts, — have brought about a differentiation of hygiene such that one portion of it now deals naturally and mainly with the environment of man, while another portion deals naturally and mainly with man himself. As the environment is usually shared in common by many persons, that branch of hygiene which deals mainly with the environment may conveniently be called " public " hygiene; while the remainder, dealing as it does chiefly with the individual, may properly be designated "personal " hygiene. Underlying both personal and public hygiene 1 6 HEALTH, OLD AGE AND DISEASE there are certain fundamental principles of the causation and prevention of disease which are absolutely essential to all sound practice of the sanitary arts. These, steadily growing in number and importance as the years go by, constitute the firm foundation on which both the theory and the practice of personal and public hygiene rest. Moreover, because they are founded largely upon experi- ment, and are in harmony with established laws of nature, they may be said to constitute the beginnings, at least, of a sanitary " science." Furthermore, inasmuch as the en- vironment is not only more accessible for treatment than the individual, but also far more under our influence and control, it has naturally come to pass that sanitary science consists very largely of principles derived from, and ap- plicable to, problems relating to the environment rather than the individual. Hence it happens that it is at pres- ent most often and most naturally associated with public hygiene or the public health rather than with general hygiene or with personal hygiene, or the health of the individual. The whole subject of proper food and clothing, for example, pertains to general or personal hygiene; but sanitary science is more especially concerned with infected food and clothing. Whether the citizens of Boston or Paris dress warmly enough, or too warmly; whether cot- ton, linen or wool is, on the whole, the most suitable for the climate of New York or London at all seasons or at any season — these are questions of general or of per- sonal hygiene ; but the question of infection by means of clothing made in the den of the sweater; the question of the disinfection of Egyptian rags arriving in the harbor of London or Boston ; the conveyance of disease germs by the clothing of persons dead of small-pox or scarlet fever — these are the peculiar property of sanitary science and the public health. To sanitary science and the public health belong also questions of polluted water, polluted SANITARY SCIENCE OR HYGIOLOGY 17 milk and polluted air; questions concerning the origin, dangers and disposal of sewage ; questions relating to dust and disease and to the natural history of epidemics. The practice of sanitary science is founded, as applied science must always be founded, upon a basis of estab- lished truth. Upon this sure basis we may construct a framework of philosophical explanation, or theory, by the aid of which we may hope to make or measure new dis- coveries. Though often unrecognized, some such working theory lies at the bottom of all sanitary endeavor. It has underlain the prayers and incantations of savages ; it under- lies all quarantine regulations ; it is at the foundation of all sanitary authority. The past fifty years have witnessed vast additions to our store of established truth, and vast changes in our stock of theory, underlying all the application of sanitary science. These additions we owe almost wholly to one simple mechanical discovery in the domain of physics — the discovery how to make an achromatic microscope objective. This discovery so facilitated and stimulated the use of the microscope that it has revolutionized ideas of the causation of disease; has established physiology upon a broad and firm foundation ; and has created new sciences of immense importance, such as general biology, pathology and bacteriology. § 13. — Definitions As a recapitulation of the foregoing paragraphs the following definitions may be found useful for beginners, although like most definitions they are only approximately correct and must not be taken too literally. HYGIENE Hygiene {general hygiene) is the whole science and art of the conservation and promotion of health both in mdi- 18 HEALTH, OLD AGE AND DISEASE viduals and in communities. It has for its function the prevention of premature death and the promotion of nor- mal life, health and happiness both directly by conservation and reenforcement of organisms and groups of oiganisms t and indirectly by the elimination or amelioration of unfa- vorable environmental conditions both local and general. The field of hygiene is immense, for it includes not only all of sanitary science and the sanitary arts, but a large part of physiology and even of biology as well. It includes not only questions of water supply, milk supply and sewerage, but also much of climatology, foods and feeding, clothing, heating, lighting, ventilation, vaccination, scavenging, the personal care of the body, work and overwork, sleep, rest, fatigue, exercise, play, sports, noise, crowding and over- crowding, and other subjects too numerous to mention but comprised in part under the heads of public hygiene and personal hygiene, municipal sanitation, school sanitation, household sanitation, offensive trades, unwholesome or dangerous trades, quarantine, toxicology, etc. PUBLIC HYGIENE Public hygiene is the science and the art of the conserva- tion and promotion of the public health. It has for its function the prevention of premature death and the promo- tion of normal life, health and happiness in communities chiefly by the elimination or amelioration of unfavorable environmental conditions common to many persons or com- munities either at one time or at different times. It includes especially hygienic problems common to groups or communities, such as camps, villages, towns and cities, e.g. water supplies, drainage, milk supplies, ice supplies, the control of infectious diseases, heating, light- ing, ventilation, school sanitation, municipal sanitation, and the like. The establishment of municipal gymnasia in many cities shows that the necessity of muscular exer- cise under the conditions of urban life is becoming a ques- DEFINITIONS 19 tion of public as it has long been of personal hygiene. There is undoubtedly a natural tendency for all questions of personal hygiene to become more and more problems of public hygiene. PERSONAL HYGIENE Personal hygiene is the science and art of the conservation and promotion of personal health, and has for its function the prevention of premature death and the promotion of nor- mal individual life, he alt J 1 and happiness chiefly by direct conservation and reenforcement of that physical mechanism which we call the human body. It includes especially problems relating to proper foods and feeding of the individual, his sleep and rest, his work and fatigue, his muscular exercise, stimulants and narcotics, the care of the eyes, the ears, the teeth, the bowels, the hair and other organs, clothing for special conditions, etc. SANITARY SCIENCE (HYGIOLOGY) Sanitary science (hygiology) is that body of hygienic or sanitary knowledge which having been sufficiently and criti- cally examined has been found so far as tested to be invari- ably true. Its phenomena are natural phenomena, its laws are natural laws, its principles are scientific principles. It includes those hygienic facts and theories which have been so thoroughly verified by repeated observation and experiment as to have become worthy to rank as scientific principles. A good example of such a body of fact and theory is that which underlies, and is correlated by, the germ theory of infectious disease, which is described in the next chapter. Like some other sciences, while largely inductive it is also in part deductive. THE SANITARY ARTS The sanitary arts are those methods and processes by which the applications of the principles of sanitary science of hygiene are effected. 20 HEALTH, OLD AGE AND DISEASE They include the practical processes involved in all sanitary engineering and architecture, e.g. in water-supply, sewerage, ventilation and heating, municipal sanitation, school hygiene, etc. Among the most important are the construction and operation of reservoirs, filters, con- duits, sewers, sewage fields and hygienic schoolhouses, the cultivation and preparation of vaccine, the manufac- ture of antitoxines, the inspection of foods and drugs, the examination of drinking waters, the disposal of garbage and refuse, the construction and maintenance of streets, the abatement of nuisances, the control of dangerous or offensive trades, etc. CHAPTER II ON ^ETIOLOGY or the causes of disease, ancient and MODERN THEORIES. THE ZYMOTIC (FERMENT) OR GERM THEORY OF INFECTIOUS DISEASE W How far the power of spirits and devils doth extend and whether they can cause this or any other disease, is a serious question and worthy to be considered. 11 — Burton's " Anatomy of Melancholy. 11 " Diseases and death are the consequences and effects of sin ; this is the idea which we have of them from Scripture. 11 — Cruden^ " Concordance." "Diseases have been generally considered as the inevitable inflic- tions of Providence. 11 — Malthus. " Diseases . . . will perhaps be never properly understood without an insight into the doctrine of fermentations. 11 — Boyle. " Side by side with these . . . has run the germ theory of epidemic disease. The notion was expressed by Kircher, and favored by Lin- naeus, that epidemic diseases may be due to germs which . . . enter the body, and produce disturbance by the development within the body of parasitic life. 11 — Tyndall. " Moreover, if inquiry into the origin and conditions of disease helps treatment, it is indispensable for the still better art of prevention. That depends entirely upon the extent of our knowledge of aetiology. 11 — Pye-Smith. The sanitarian must have sound working theories of disease. If he is to maintain and promote the public health, he must be familiar with the causes of disease and the avenues along which they travel. In order to prevent disease he must know, if possible, precisely what disease is. To-day all civilized and scientific persons re- gard disease, as has been indicated in the preceding chapter, as a state or condition of disturbance or abnor- 22 ^ETIOLOGY OR THE CAUSES OF DISEASE mality 1 which the body has unfortunately assumed or been placed in. Savage and uncivilized people, on the contrary, and the unscientific civilized, are apt to look upon disease as an entity, something to be pacified, cajoled or cast out. Very often this entity is personified, and illus- trates that subjective characteristic which is so marked a feature of primitive culture. § I. — The Demonic Theory of Disease* The earliest theories of disease with which we are ac- quainted are found among savage races, which naturally interpret fever, sickness, pain, madness and hysteria as due to the temporary or prolonged occupancy of the affected body by an evil spirit or demon. This is called the Demonic Theory. The same subjective, anthropomor- phic method of thought which sees in the sun, not a huge sphere of burning matter giving light and life to other worlds, but Apollo, a god, driving his chariot of fire daily across the sky ; or fills the woods with fauns and satyrs, and the streams with nymphs and naiads, naturally looks for the causes of disease in human or inhuman forms dis- torted and misshapen according to the fancy, but gifted with human cunning and more than human malignity. 3 1 " Disease is a state of a living organism . . . the disease itself is a per- turbation. . . . " — Allbutt, " Syst. Med.," I. xxiv. 2 For the substance, and to a great extent the form, of this entire section the author is indebted to various writings of that eminent authority on primitive culture, Professor E. B. Tylor. 3 " Among races of low culture, the conception of a ghost soul being made to account for the phenomena of life readily leads to a corresponding theory of morbid states of body and mind. As the man's proper soul causes the functions of normal life by its presence, while its more or less continued absence induces sleep, trance, and at last death, so the abnormal phenomena of disease have a sufficient explanation at hand, in the idea that some other soul or soul-like spirit is acting on or has entered the patient. Among the cases which most strongly suggest this, are : first, such derangements as hys- teria, epilepsy, and madness, where the raving and convulsions seem to PRIMITIVE THEORIES OF DISEASE 23 The demonic theory regards disease as a supernatural being or entity, not primarily as a process or condition, by-standers like the acts of some other being in possession of the patient's body, and even the patient is apt to think so when he ' comes to himself; and second, internal diseases where severe pain or wasting away may be ascribed to some unseen being wounding or gnawing within. This applicabil- ity of demoniacal possession as a theory to explain disease in general is best proved by the fact that it is so often thus applied by savage races. Especially, reasoning out the matter in similar ways, rude tribes in different countries have repeatedly arrived at the conclusion that diseases are caused by the surviving souls or ghosts of the dead who appear to the living in dreams and visions, thus proving at once their existence after death and their continued concern with mankind. This notion being once set on foot it becomes easy to the savage mind to identify the particular spirit, as when the Tasmanian ascribes a gnawing disease to his having unwittingly pronounced the name of a dead man, who, thus summoned, has crept into his body and is consuming his liver ; or when the sick Zulu believes that some dead ancestor he sees in a dream has caused his ailment, wanting to be propitiated with a sacrifice of an ox ; or when the Samoan persuades himself that the ancestral souls, who on occasion reveal themselves by talking through the voices of living members of the family, are the same beings who will take up their abode in the heads or stomachs of living men and cause their illness and death. ... In many, perhaps in most, cases, however, the disease demon is not specially described as a human ghost ; for instance, some Malay tribes in their simple theory of diseases are content to say that one kind of demon causes small-pox, another brings on swellings, and so on. . . . The savage theory of demoniacal pos- session has for its natural result the practice of exorcism or banishment of the spirit as the regular means of cure, as where, to select these from hundreds of instances, the Antilles Indians in Columbus's time went through the pretence of pulling the disease off the patient and blowing it away, bidding it begone to the mountain or the sea; or where the Patagonians, till lately, believing every sick person to be possessed by an evil demon, drove it away by beating at the bed's head a drum painted with figures of devils. " That such modern savage notions fairly represent the doctrines of disease- possession in the ancient world is proved by the records of the earliest civilized nations. The very charms still exist by which the ancient Egyptians resisted the attacks of the wicked souls, who, become demons, entered the bodies of men to torment them with diseases and drive them to furious madness. The doctrine of disease among the ancient Babylonians was that the swarming spirits of the air entered man's body, and it was the exorcist's duty to expel by incantations ' the noxious neck-spirit,' ' the burning spirit of the entrails which devours the man,' and to make the piercing pains in the head to fly away ' like grasshoppers ' into the sky. ... No record shows the ancient theory more clearly than the New Testament from the explicit way in which the 24 ETIOLOGY OR THE CAUSES OF DISEASE and the diseased condition is the result of the influence of some entity foreign to the patient, to something acting symptoms of the various affections are described, culminating in the patient declaring the name of his possessing demon, and answering in his person when addressed. The similarity of the symptoms with those which in barbarous countries are still accounted for in the ancient way may be seen from such statements as the following, by a well-known missionary (Rev. J. L. Wilson, * Western Africa,' page 207) : ' Demoniacal possessions are common, and the feats performed by those who are supposed to be under such influence are certainly not unlike those described in the New Testament. Frantic gestures, convulsions, foaming at the mouth, feats of supernatural strength, furious rav- ings, bodily lacerations, gnashing of teeth, and other things of a similar char- acter may be witnessed in both of the cases.' Among the early Christians the demoniacs or energumens formed a special class under the control of a clerical order of exorcists, and a mass of evidence drawn from such writers as Cyril, Tertullian, Chrysostom, and Minutius Felix shows that the symptoms of those possessed were such as modern physicians would class under hysteria, epilepsy, lunacy, etc. . . . Some theologians, while in deference to advanced medical knowledge they abandon the primitive theory of demons causing such diseases in our own time, place themselves in an embarrassing position by maintaining, on the supposed sanction of Scripture, that the same symptoms were really caused by demoniacal possession in the first century. . . . For our times this seems too like a discussion whether the earth was really flat in the ages when it was believed so, but became round since astronomers pro- vided a different explanation of the same phenomena. It is more profitable to notice how gradual the change of opinion has been from the doctrine of demon-possession to the scientific theory of disease, and how largely the older view still survives in the world. Not only in savage districts, but in countries whose native civilization is below the European level, such as India and China, the curious observer may still see the exorcist expel the malignant ghost or demon from the patient afflicted with fever, dizziness, frenzy, or any accountable ailment. . . . The unbroken continuance of the belief in medi- aeval Europe may be gathered from various works. . . . Even in the eigh- teenth century was published with ecclesiastical approval a regular exorcist's manual, the ' Fustis et Flagellum Doemonum,' Auctore R. P. F. Hieronimo Mengo (1727), which among its curious contents gives instructions how to get the better of those cunning demons who hide in the bodies of men and vex them with diseases, and which are apt, when expelled, to take refuge in the patient's hair. The gradual shifting of opinion is marked by the attempt to reconcile the older demonology with the newer medicine. The argument, which appears among the early Christian fathers, is worked out most elabo- rately in that curious museum of demonology, the ' Disquisitiones Magicse ' of Martin Delrio, published as late as 1720. While inveighing against those physicians who maintain that all diseases have natural causes, this learned Jesuit DISEASES AND DEMONIACAL POSSESSION 25 from or coming from the environment. Of any disease aris- ing from within, or due to any intrinsic or mechanical defect or derangement of an apparatus — such as faulty materials or construction — the savage has no conception. This idea requires anatomical information and the power to reflect from the merely objective point of view; in other words, the modern mechanical and scientific attitude of mind, the objective rather than the subjective capacity. Even here, however, the cure was logically applied. Sav- age therapeutics accurately followed savage pathology. If the disease were due to the possession of the patient by a demon or demons, nothing could be more logical or better medical practice than to seek somehow to cast them out. Exhortations, drums, or anything likely to influence the demon constituted a proper materia medica. Most admits that men may be dumb, epileptic, or lunatic without being obsessed; but what the demons do is that, finding the dispositions of epileptics suitable, they insinuate themselves into them ; also they attack lunatics, especially at full moon, when their brains are full of humors, or they introduce diseases by stirring up the black bile, sending blacks into the brain and cells of the nerves, and setting obstructions in the ears and eyes to cause deafness and blindness. Looking at the date of this celebrated work, we cannot wonder that in benighted districts of Europe the old diabolical possession and its accompany- ing exorcism may still now and then be met with, as in 1861 at Morzine in Savoy. The London Times, in November, 1876, contained an account of the casting out of devils by a priest in the Church of the Holy Spirit in Barcelona, during the preceding month. On one occasion, the patient, a young woman of seventeen or eighteen, lay on the floor before the altar, writhing in convul- sions, with distorted features and foaming at the mouth, while the priest carried on a dialogue with the devil, whom he addressed by the name of Rusbel, the fiend's answers being of course spoken by the voice of the frantic girl herself. At last a number of demons were supposed to come out of the patient's body, and such scenes were repeated for days in the presence of many spectators till a riot arose, and the civil authorities, intervening, put a stop to the whole affair. One of the last notable cases of this kind in England was that of George Lukins of Yatton, a knavish epileptic, out of whom seven devils were exorcised by seven clergymen, at the Temple Church at Bristol, on June 13, 1788.' — Tylor. ..." Thy demon, that's thy spirit that keeps thee." — " Antony and Cleopatra." 26 yETIOLOGY OR THE CAUSES OF DISEASE effective of all would be the voice of a master who should command their obedience and compel them to come out. It was even possible upon the demonic theory, crude and childish as it was, to have a legitimate "preventive medicine." "The very charms still exist by which the ancient Egyptians resisted the attacks of the wicked souls, who, become demons, entered the bodies of men to tor- ment them with disease and drive them to furious mad- ness." And we all know of survivals even to-day in the charms and amulets which are supposed to resist bad luck, and the more material horseshoe, rabbit's foot, horse- chestnut in the trousers pocket, etc., which shall ward off witches or disease from us or from our habitations. § 2. — The Theory of the Four Humors Long before the period of the highest development of Greek civilization, the primitive or demonic theory of dis- ease had ceased to satisfy the minds of cultivated men. Many traces of it indeed remain in the Homeric time; but with the arrival of the age of Pericles we have as his contemporary Hippocrates, already called "the Great," and ever since known as the " Father of Medicine." And now, apparently, for the first time, we find " a clear recog- nition of disease as being equally with life a process gov- erned by what we should now call natural laws. . . . The actual science of the Hippocratic school was of course very limited. In anatomy and physiology little advance has been made, and so of pathology in the sense of an expla- nation of morbid processes or knowledge of diseased struc- tures there could be very little. . . . The dominating theory of disease was the humoral, which has never since ceased to influence medical thought and practice. According to this celebrated theory, the body contains four humors, — blood, phlegm, yellow bile, and black bile, — a right proportion and mixture of which constitute ANCIENT AND MEDIEVAL THEORIES 2? health; improper proportion and irregular distribution, disease. It is doubtful whether the treatise in which this theory is fully expounded is as old as Hippocrates him- self ; but it was regarded as a Hippocratic doctrine, and when taken up and expanded by Galen, its terms not only became the common property of the profession, but passed into general literature and common language. Another Hippocratic doctrine, the influence of which is fortunately not even yet exhausted, is that of the healing power of nature." 1 Much of the language of this famous theory still lingers, as when we speak of a "bilious" condition, a "sanguine," "phlegmatic," or "melancholic" (black bile) temperament. It had the high merit under Hippo- crates of fixing attention upon natural rather than super- natural causes, upon the patient rather than demons. 2 § 3. — Romany Arabian and Mediceval Theories of Disease We need not follow in detail the shifting opinions of mankind as to the true causes of disease between the time of Hippocrates (500 b.c.) and that of Sydenham. In the decline of Greek culture and the Alexandrian period no new ideas of importance were successfully advanced or long maintained. The theory of the four humors, with various modifications and under various forms, prevailed, and even in the hands of Galen during the Roman period, though expanded and highly elaborated so that it became the standard authority for many centuries, remained essen- tially the same. During the Dark Ages no important new 1 J. F. Payne , M.D., on the " History of Medicine," Encyclopedia Bri- tannica, 9th ed., Vol. XVII, p. 800. 2 " The four Galenical humors, viz., the blood which took its origin in the liver, the phlegm secreted by the pituitary gland, the bile by the gall, and the black bile by the spleen. From the mixture of these humors arose the four natural 'temperaments': sanguine, in which the blood was predominant; phlegmatic or pituitous; bilious or choleric; atrabilious or melancholic; and from the ill-mixture of these ingredients resulted dyscrasia and new morbid humors, such as produced scurvy, scrofula and gout." — Pve-Smith. 28 AETIOLOGY OR THE CAUSES OF DISEASE ideas were introduced into Europe by the Arabian physi* cians, Avicenna and Rhazes; for these authors worked largely upon the foundations laid by Hippocrates and Galen, and their theories need not detain us. The period of scholasticism also yielded nothing in the theory of disease beyond the four humors, but only endless com- mentaries on Hippocrates and Galen similar in character to those in philosophy upon Aristotle. Even for some time after the revival of learning and the splendid period of the Renaissance, this very revival being in the hands of "medical humanists" led to a renewed respect for ancient authority, and more than ever Hippocrates and Galen were regarded as authorities while the theory of the four humors naturally held full sway. With Paracelsus (1480-1541), however, emphatic doubts began to be boldly expressed as to the sufficiency of the ancient theories. The study of anatomy in Italy in the sixteenth century under Vesalius, Fallopius, Fabricus and many others, followed as it was early in the seventeenth by Harvey's marvellous discovery of the circulation of the blood, to- gether with the general progress of knowledge, finally raised grave doubts in the best minds as to the true causes of disease, doubts which were powerfully supported by the occurrence in Europe in the fifteenth and sixteenth centu- ries of certain highly destructive epidemic diseases, some of them hitherto unknown and all quite inexplicable on the theory of the four humors. Meantime there arose two schools, called respectively the " iatro-physical " and "iatro-chemical," the former basing itself on physiology and mechanical explanations of disease, the latter on chem- ical or fermentative processes. " The intestine movement of particles," or "fermentation," was the essence of the latter, the application of physics and mechanics to the body that of the former. The name of Sylvius (1614- 1672) is widely known in connection with the iatro-chem- ical school. These schools, however, were compelled to THEORIES OF THE RENAISSANCE 29 struggle not only each with the other but both with the ancient (Hippocratic) doctrines. § 4. — The Theory of Sydenham Thomas Sydenham (1644- 1689), who has been called "the English Hippocrates," held as " his main avowed principle to do without hypothesis and study the actual diseases in an unbiassed manner." According to Syden- ham, " a disease is nothing more than an effort of nature to restore the health of the patient by the elimination of the morbific matter." This full recognition of a materies morbi was a distinct advance, and foreshadows the time when the materies morbi would itself be regarded as specific in specific diseases. Sydenham appears to have recognized the fact that there are specific diseases, but to have fixed his attention rather on specific remedies than specific causes. The latter were not fully recognized until after Pasteur's classic researches on the specific microbic ferments of the diseases of wine and beer (i860- 1864). . After Thomas Sydenham (d. 1689) " the reign of canonical authority in medicine was at an end, though the dogmatic spirit long survived." The philosopher John Locke was a close friend of Sydenham, and the following quotation from one of Locke's letters is noteworthy: "You cannot imagine how far a little observation carefully made by a man not tied up to the four humors (Galen), or sal, sulphur, and mercury (Paracelsus), or to acid and alkali (Sylvius and Willis), which have of late prevailed, will carry a man in the curing of diseases though very stub- born and dangerous ; and that with very little and common things, and almost no medicine at all." 1 § 5. — Theories of the Eighteenth Century The theories of disease in the eighteenth century reflect plainly the spirit of the times. On the one hand we find UNIVERSITY OF CALIFORNIA DEPARTMENT OF CIVIL ENGINEERING BERKELEY. CALIFORNIA 30 /ETIOLOGY OR THE CAUSES OF DISEASE views largely mechanical, physical and even astrological; and on the other, an opposing series more mystical, ani- mistic and even spiritualistic. As natural successors to Hippocrates, Galen and Sydenham, we find Boerhaave, Haller and Morgagni, while opposed to them and as natural successors to Paracelsus, Hoffmann, Stahl (author of the Phlogiston theory in chemistry) and Hahnemann, — all more or less supernaturalists. The labors of Boer- haave, Haller and Morgagni served to establish upon a sure foundation our present essentially physical and me- chanical views of constitutional disease (see pp. 1 1, 13), but shed very little light on the class of diseases now called " infections" (the fevers, etc.), which run a peculiar definite course and then disappear. But if these diseases baffled the naturalists of the eighteenth century, they were still less understood by the supernaturalists, of whom only one (Hahnemann) has succeeded in making himself felt in the nineteenth century by the perpetuation of a special " sys- tem " typical of the numerous "systems" of the eighteenth century. § 6. — The Theory of Hahnemann " Hahnemann taught that disease is to be regarded as consisting especially of the symptoms of it as experienced and expressed by the patient, or as detected by the physi- cian; in other words, that the chief symptoms, or the 'totality of the symptoms,' constitute the disease, and that disease is in no case caused by any material substance, but is only and always a peculiar, virtual, dynamic derange- ment of the health. ' Diseases ' (Introduction to the ' Organon,' p. 17) 'will not cease to be spiritual dynamic derangements of our spiritual vital principle.' He says on page 3 of the ■ Organon ' : ' For as far as the greatest number of diseases are of dynamic (spiritual) nature, their cause is therefore not perceptible to the senses ; ' and at page 18, referring to 'small-pox, a disease accompanied THEORIES OF THE EIGHTEENTH CENTURY 31' by almost general suppuration/ he asks, ' Is it possible to entertain the idea of a material morbific matter being introduced into the blood V He held that the psoric miasm, of which the itch is the outward and visible and comparatively harmless sign, was at the root of nearly all chronic disease, viz., of all chronic disease that was not due to syphilis or sycosis. ... In all countries the doctrine of homoeopathy is still without broad scientific recogni- tion. . . . Hahnemann despised any deep study of disease, and theorized about it instead. Had he carefully inquired into the nature and natural history of disease as Hippo- crates did, or as he himself inquired into the sensations of those who took infinitesimal doses, he would have done more for the world and his own reputation. Hahnemann was easily captivated by theories, but not very sound in his reasoning. But underlying all his system, as we have seen, was the idea that the causes of disease were impal- pable, immaterial, spiritual, dynamic. And this great foundation was rotten. Modern medicine is doing some of its best work in showing the material and the visible character of the causes of many of the commonest diseases, and suggests this in many cases where it has not as yet been demonstrated. The cause of many diseases is shown to be a living germ or particle which can be discerned under the microscope, can be carried on a lancet or in a tube and inserted under the skin so as to produce its pecul- iar disease. . . . The causes of other diseases are often not merely visible under a microscope, but coarsely visible. We have been lately told, on high authority, that to pro- duce certain forms of blood-poisoning one or two ounces at least of septic fluid are necessary. So with other forms of common disease. Alcohol does not destroy a liver or kidney in any dynamic or immaterial form, but in coarse quantities diligently repeated. The lead which paralyzes the painter's wrist is not a ' spiritual ' thing. It is an accumulation of matter in the wrong place, and enters his 32 /ETIOLOGY OR THE CAUSES OF DISEASE body in palpable quantities, and, what is more, can be recovered in similar quantities from his body. So with the uric acid or its salts in the blood of a person who has inherited his father's gout, and perhaps his port wine. It is not a ' spiritual ' affair at all, but can be demonstrated chemically and under the microscope. The itch, to whose mysterious workings Hahnemann attributed two-thirds of the internal diseases of the body, including mania, cancer, gout, etc., is easily demonstrated to be dependent on an ugly crab-like insect, which can be destroyed in a few hours with sulphur, when there is an end both of it and of the itch." * §7. — Theories of the Nineteenth Century If the eighteenth century is noteworthy for its numerous "systems " of medical theory, the nineteenth is equally conspicuous for its distrust of " systems." This was due doubtless in part to the natural swing of the pendulum, but whatever the cause may have been, there was unquestion- ably, in the first part of the century, a wholesome distrust of all " systems " and a return to a study of the " natural history of disease," what has been called a "rational empiricism " serving as the basis of medical practice. This " return to nature " was powerfully stimulated and facilitated by the rapid contemporary development of physical science, and above all by the invention of the achromatic microscope objective between 18 15 and 1830, so that the compound microscope, which had been so im- perfect as to be almost useless, became about 1835 a powerful and altogether novel instrument. Almost imme- diately results of capital importance were reached, for in 1837 an Italian investigator, Bassi, announced the dis- covery that muscardine, a contagious disease of silkworms, previously not understood, is really due to a parasitic 1 J. Grey Glover, M.D., on " Homceopathy," Encyclopedia Britannica, 9th ed., Vol. XII, pp. 126-129. THEORIES OF TO-DAY 33 fungus. Two years later the still more startling discovery was made by Schoenlein that favus, or "honeycomb" of the human scalp, a disease 1 long known, but never under- stood, is really due to a parasitic fungus growing at the roots of the hair. At almost the same moment botanists discovered that yeast, hitherto regarded as a mysterious " ferment," is also a microscopic fungus ; and the idea was boldly advanced that fermentation, which had long been held to be one of the causes of disease, was really due to microscopic fungi. The new microscope was also applied to the study of diseased tissue, and immediately disclosed ravages so coarse and obvious as to compel the idea of mechanical interference by palpable agents and to stimu- late further search not only for the footprints of disease, but for the mysterious makers of those footprints. Mean- time the applications of physics and chemistry to physi- ology by Johannes Muller and Wohler, Marshall Hall and Liebig, were drawing attention to the mechanical and material aspects of living things and the modern concep- tion of the body as a physical mechanism was becoming more firmly established. The pathologists likewise were making extraordinary progress in their explorations of the dead, and reporting constantly fresh examples of mechani- cal disturbance or interference, so that by the middle of the nineteenth century our theories of constitutional disease as largely due to poor timber or poor construction or mechanical breakdown were finally and probably forever established. 1 This is a rare affection of the scalp and body due to the presence of a fungus Achorion Schoenleinii. The disease was recognized and named by Bateman and figured by Alibert. But it was not till 1839 that Schoenlein published in Muller's Archiv the discovery that the yellow crusts of Favus were neither pustular nor sebaceous, but were composed of the mycelia and conidia of a parasitic fungus. Ringworm of the Scalp was only proved to depend on the presence of a cryptogamic parasite in 1844 by Malmsen, the Swedish microscopist. He named the fungus Trichophyton tonsurans. — Pye- Smith, I.e. D 34 ETIOLOGY OR THE CAUSES OF DISEASE The case was different, however, with certain diseases, such as the fevers, which run a definite course and disap- pear. These remained still unexplained and inexplicable. But their solution also was at hand. The obscure phenomena of fermentation, as we have seen above, had been claimed to be closely connected with disease by the iatro-chemical school of the seventeenth century, and this suggestion had apparently never been wholly lost sight of, though it was eclipsed in the eighteenth century by the rapid development of physiology. Modern chemistry began to unfold itself toward the close of the eighteenth century, and by the end of the first half of the nineteenth century, when the achromatic objective had been perfected, fermentation had assumed in the hands of Liebig great popular impor- tance. In 1837 tne fi rst serious attempt was made to collect and study the vital statistics of England, and a classifica- tion of diseases became necessary. For this classification of the various causes of death the following was at first used : — (1) Epidemic, endemic and contagious diseases. (2) Sporadic diseases. (3) Evident external causes. Some years later we find instead the following classi- fication : — (1) Zymotic diseases. (2) Constitutional diseases. (3) Local diseases. (4) Developmental diseases. (5) Violence. In other words, those diseases previously called "epi- demic, endemic and contagious" are now described as "zymotic"; and upon this term we may dwell somewhat at length. " The diseases of this class have been frequently spoken of as fermentations. . . . The property of communicating ORIGIN OF THE TERM "ZYMOTIC" 35 their action, and affecting analogous transformations in other bodies, is as important as it is characteristic in these diseases, which it is proposed therefore to call, in this sense, 'zymotic.' A single word, such as 'zymotics,' is required to replace in composition the long periphrasis * epidemic, endemic, and contagious diseases ' with a new name, and a definition of the kind of pathological process which the name is intended to indicate. . . . The early medical observers have directed attention to the analogies zymotic diseases have with combustion, fermentation, putrefaction, and poisoning. These analogies have been, to a certain extent, confirmed by the researches of modern chemistry. . . . This class includes fever, small-pox, plague, influenza, cholera, and the other diseases which have the peculiar character of suddenly attacking great numbers of people at intervals in unfavorable sanitary conditions. The diseases of this class distinguish one country from another, one year from another ; they have formed epochs in chronology, and, as Niebuhr has shown, have influ- enced not only the fate of cities, such as Athens and Florence, but of empires; they decimate armies, disable fleets ; they take the lives of criminals that justice has not condemned; they redouble the dangers of crowded hos- pitals ; they infest the habitations of the poor, and strike the artisan in his strength down from comfort into help- less poverty ; they carry away the infant from the mother's breast, and the old man at the end of life ; but their direst eruptions are excessively fatal to men in the prime and vigor of age. Pestilence and famine have always ob- tained the special attention of governments ; and epidemi- cal maladies have a special claim now to the attention of the statist, inasmuch as by prophylactic methods, of which vaccination is an example, and by hygienic arrangements, the ravages of epidemics may be greatly diminished. They are more than other diseases under public control, and may be diminished to a large extent by sanitary measures. 36 ETIOLOGY OR THE CAUSES OF DISEASE . . . New names are wanted to designate new groups of phenomena, and might perhaps be less equivocally desig- nated by letters of the alphabet ; but to assist the memory words have been employed which, by their etymology, will suggest the group. We do not, however, in any case accept the etymological sense as a definition or a descrip- tion of the group of causes which a name designates. Thus, parts of the body undergo a specific transformation in the diseases of the first class, and they have been desig- nated Zymotic Diseases (zymotici) in England, without any intention to imply that these diseases are fermenta- tions." 1 In spite of Dr. Farr's care not to assume close simi- larity between fermentations and zymotic disease, 2 the proof of such similarity was, even as he wrote, about to be brought forward by Pasteur. § 8. — The Germ Theory of Fermentation Alcoholic fermentation had been generally regarded as a purely chemical or a physical process until in 1838 Cagniard de Latour and Schwann showed that the yeast which accompanies it is a living plant. Liebig met this discovery with scorn and ridiculed the idea that yeast was the cause rather than the consequence of fermenta- tion in an article which Huxley has well called the most remarkable that ever appeared in a sober scientific jour- nal. Nevertheless, though with many hindrances because of the powerful opposition of Liebig, it slowly became 1 " Vital Statistics : A Memorial Volume of Selections from the Reports and Writings of Dr. William Farr," pp. 246, 249, 253. London, 1885. 2 The reluctance of Dr. Farr to connect zymotic diseases with fermenta- tions was not exceptional, and was probably due in part to the strenuous opposition of Liebig to that view. In 1863, Sir Robert Christison, in an " Address on Public Health " before the Association for the Encouragement of Social Science in Edinburgh, said of zymotic diseases, " They are so called from the Greek zyma, signifying ferment, on account of a rather fanciful resemblance between their origin and the process of fermentation." PASTEUR'S STUDIES ON BEER AND WINE 37 clear that the germ theory of fermentation is true, and that live yeast is the real " ferment " of the alcoholic fermen- tation. This biological theory was thoroughly and finally established by Louis Pasteur between 1857 an d 1863, and almost immediately led to the germ theory of disease through its extension by him to the diseases of beer and wine, which he traced to micro-organisms other than ordi- nary yeast invading the fermentable liquid and interfering with the usual alcoholic fermentation by producing unde- sirable fermentations of their own. At once it became clear to Pasteur (and soon after to the world) that specific fermentations are caused by specific ferments ; and, more- over, that a disease of wine or beer may be, and often is, simply an undesirable fermentation produced by an invad- ing ferment or germ. § 9. — The Germ or Zymotic {Ferment) Theory of Disease It could hardly fail to occur to any thoughtful person that if this were true for certain diseases of wine and beer, it might well be true also for certain diseases of animals; 1 for if we consider step by step the course of any familiar fermentation and then do the same for any familiar infec- tious disease, we shall discover between them a remarkable similarity. For this purpose we may take the fermenta- tion of apple juice, or cider, and small-pox. The juice of 1 " Les sciences gagnent toutes a se preter un mutuel appui. Lorsque, a la suite de mes premieres communications sur les fermentations, en 1857-1858, on put admettre que les ferments proprement dits sont des etres vivants, que des germes d'organismes microscopiques abondent a la surface de tous les objets dans l'atmosphere et dans les eaux, que l'hypothese d'une generation spontanee est presentment chimerique, que les vins, la biere, le vinaigre, le sang, Purine, et tous les liquides de l'economie n'eprouvent aucune de leurs alterations communes au contact de l'air pur, la medecine et la chirurgie jeterent les yeux sur ces clartes nouvelles. Un medecin francais, le Dr. Davaine, fit la premiere application heureuse de ces principes a la medecine, en 1863."— {Pasteur.) "La Vie de Pasteur," par Rene Vallery-Radot, p. 390. Paris, 1900. 38 ETIOLOGY OR THE CAUSES OF DISEASE apples is hermetically sealed and kept from exposure to air by the apple skin. In the making of cider this skin is broken, the juice is pressed out and of course exposed to the air, to dust, to the press, to the sides of the vessel which receives it, to the strainer through which it passes, etc. At first, and for some time, the juice is sweet, insipid, unfermented, but after some time it is plain that a change is going on. This change is called the " working" or active fermentation of the apple juice, and a closer exami- nation will show that it is accompanied by a slight rise of temperature or " heating " (which is a familiar phenomenon in many fermentations), as well as by obvious chemical changes resulting in the evolution of gas and the dis- appearance of sugar, in place of which alcohol makes its appearance, giving to the whole process the name of " alcoholic fermentation." The fermentation of any par- ticular portion of apple juice, however, is not indefinitely prolonged. On the contrary, after a comparatively short time the process comes to an end, the evolution of gas ceases, and rest supervenes. Since Pasteur's classical researches we know that what has really happened has been, first, the seeding of the apple juice by (wild) yeast; second, the slow growth of this during the quiescent period ; third, its active growth and "working" during the time of obvious fermentation ; and fourth, its gradual cessation of activity during the final period. In the case of the infectious disease known as small-pox the history is usually as follows : A susceptible patient must first be exposed to the disease, perhaps by contact with a person already affected, perhaps with clothing, letters, food or other ma- terials handled by such a person. After such exposure there is for a time no marked change ; but because the dis- ease has been shown by repeated experience to be never- theless gradually developing, as judged by the result and certain obscure premonitory symptoms afterward recalled, physicians have unanimously agreed to name this the FERMENTATION AND INFECTIOUS DISEASE 39 period of incubation. Sooner or later, headache, malaise, and other troubles appear, the patient becomes seriously and obviously ill, a physician is called in, a rise of tempera- ture or fever is discovered, the eruption and other marks of small-pox appear, and the patient is plainly affected by active disease accompanied by every indication of profound disturbance and chemical change. But at last, if death does not supervene, recovery ensues, and the patient gradually becomes free from the disease by which he was tempo- rarily overcome. We may add that the barrel of apple juice can undergo the alcoholic fermentation only once, and that the small-pox patient likewise, as a rule, has the small-pox only once. If now we tabulate side by side, and in order, the principal phenomena of an alcoholic fermentation such as that of apple juice, and those of an infectious disease such as small-pox, we shall discover a remarkable similarity between them. A Fermentation (Apple juice) Exposure of the juice to air, dust, etc. Repose and then slow change. (Growth of the ferment.) Active fermentation or "work- ing." Evolution of gas bub- bles, change of sugar to alcohol. Rise of tempera- ture. Gradual cessation of fermenta- tion. No further liability to alcoholic fermentation. An Infectious Disease (Small-pox) 1. Exposure of the patient to in- fection. 2. Incubation. (Slow and insid- ious progress of the disease.) 3. Active disease. Eruption, dis- turbance of the usual func- tions. Rise of temperature or fever. 4. Slow convalescence (or death) . 5. Immunity to small-pox. The striking analogy here shown suggests something more. It certainly justifies the suspicion of relationship, and shows well the natural fitness of the term "zymotic" (fermentative) for that class of diseases in which an anal- ogy so remarkable is manifest. 40 ETIOLOGY OR THE CAUSES OF DISEASE In the next chapter we shall obtain further indications of close relationship between fermentation and disease. Meanwhile, we cannot fail to observe that as soon as it was shown by Pasteur that the phases of an alcoholic fer- mentation are due to the introduction, growth and chemical work of a living ferment (yeast) finding its way into the apple juice from the air, dust or the outer skin of the apple, it became easy and natural to suspect that small-pox and similar diseases are somehow caused by similar living ferments finding their way into the body of the patient. Thus the " germ " theory of fermentation naturally led to a " germ " theory of infectious disease ; and movement in this direction became almost irresistible when Pasteur soon after established a fact of the very first importance, namely, that the diseases of wine and beer are "germ " diseases, due to their invasion by, and the growth within them of, undesirable micro-organisms (bacteria or wild yeasts). General attention was now drawn to the subject, and the germ theory of disease became very widely known when Pasteur, hitherto a mineralogist, chemist and biologist, turned aside from his laboratory studies on the fermenta- tions of wine, beer, vinegar and milk, and, in response to an urgent call from the French government, began a per- sonal investigation of a widespread animal disease, which had hitherto baffled all inquiry. This was the famous " silkworm disease " of which his son-in-law, M. V.-Radot, has given us an admirable popular account. Inasmuch as this brilliant effort of Pasteur was one of the most important factors in drawing universal attention to the germ theory of disease, and inasmuch as it is in itself an inspiring example of a scientific grappling with disease, we may quote at some length Radot's graphic description, as follows : — ZYMOTIC DISEASES OF BEER AND WINE 41 § 10. — Louis Pasteur and Infectious Diseases of Silk- worms 1 " The life of the population of certain departments in the South of France hangs on the existence of silkworms. In each house there is nothing to be seen but hurdles, over which the worms crawl. They are placed even in the kitchens, and often in well-to-do families they occupy the best rooms. In the largest cultivations, regular stages of these hurdles are raised one above the other, in immense sheds, under roofs of disjointed tiles, where thousands and thousands of silkworms crawl upon the litters, which they have the instinct never to leave. Great or small, the silkworm-rearing establishments exist everywhere. When people accost each other, instead of saying ' How are you ? ' they say 1 How are the silkworms ? ' In the night they get up to feed them or to keep up around them a suitable temperature. And then what anxiety is felt at the least change of weather ! Will not the mulberry leaves be wet ? Will the worms digest well ? Digestion is a matter of great im- portance to the health of the worms, which do nothing all their lives but eat ! Their appetites become especially insatiable during the last days of rearing. All the world is then astir, day and night. Sacks of leaves are incessantly brought in and spread out on the litters. Sometimes the noise of the worms munching these leaves resembles that of rain falling upon thick bushes. With what impatience is the moment waited for when the worms arrive at the last moulting ! Their bodies swollen with silk, they mount upon the brambles prepared for them, where they shut themselves up in their golden prisons and become chrysalides. What days of rejoicing are those in which the cocoons are gathered ; when, to use the words of Olivier de Serres, the silk harvest is garnered in ! . . . "In the epidemic which ravaged the silkworm nurseries in 1849, tne symptoms were numerous and changeable. Sometimes the disease exhibited itself immediately. Many of the eggs were sterile, or the worms died during the first days of their existence. Often the hatch- ing was excellent, and the worms arrived at their first moulting, but that moulting was a failure. A great number of the worms, taking little nourishment at each repast, remained smaller than the others, having a rather shining appearance and a blackish tint. Instead of all the worms going through the phases of this first moulting together, as is usually the case in a batch of silkworms, they began to present a marked inequality, which displayed itself more and more at each successive 1 " Louis Pasteur : His Life and Labors." By his Son-in-Law. Trans- lated by Lady Claud Hamilton. P. 127 et seq. N.Y., Appleton, 1885. 42 /ETIOLOGY OR THE CAUSES OF DISEASE moulting. Instead of the worms swarming on the tables, as if their number was uniformly augmenting, empty spaces were everywhere seen ; every morning corpses were collected on the litters. "Sometimes the disease manifested itself under still more painful circumstances. The batch would progress favorably to the third, and even to the fourth moulting, the uniform size and the health of the worms leaving nothing to be desired ; but after the fourth moulting the alarm of the husbandman began. The worms did not turn white, they retained a rusty tint, their appetite diminished, they even turned away from the leaves which were offered to them. Spots appeared on their bodies, black bruises irregularly scattered over the head, the rings, the false feet, and the spur. Here and there dead worms were to be seen. On lifting the litter, numbers of corpses would be found. Every batch attacked was a lost batch. In 1850 and 185 1 there were renewed fail- ures. Some cultivators, discouraged, attributed these accidents to bad eggs, and got their supplies from abroad. "At first everything went as well as could be wished. The year 1853, in which many of these eggs were reared in France, was one of the most productive of this century. As many as twenty-six millions of kilogrammes of cocoons were collected, which produced a revenue of 130,000,000 francs. But the year following, when the eggs produced by the moths of these fine crops of foreign origin were tried, a singular degeneracy was immediately recognized. The eggs were of no more value than the French eggs. It was, in fact, a struggle with an epi- demic. How was it to be arrested ? Would it be always necessary to have recourse to foreign seed ? And what if the epidemic spread into Italy, Spain, and the other silk-cultivating countries ? " The thing dreaded came to pass. The plague spread ; Spain and Italy were smitten. It became necessary to seek for eggs in the Islands of the Archipelago, in Greece, or in Turkey. These eggs, at first very good, became infected in their turn in their native country ; the epi- demic had spread even to that distance. The eggs were then procured from Syria and the provinces of the Caucasus. The plague followed the trade in the eggs. In 1864 all the cultivations, from whatever cor- ner of Europe they came, were either diseased or suspected of being so. In the extreme East, Japan alone still remained healthy. " Agricultural societies, governments, all the world, were preoccupied with this scourge and its invading march. It was said to be some malady like cholera which attacked the silkworms. Hundreds of pam- phlets were published each year. The most foolish remedies were pro- posed, as quite infallible, — from flowers of sulphur, cinders, and soot spread over the worms, or over the leaves of the mulberry, to gaseous fumigations of chlorine, of tar, and of sulphurous acid. Wine, rum, AN INFECTIOUS DISEASE OF SILKWORMS 43 absinthe, were prescribed for the worms, and after the absinthe it was advised to try creosote and nitrate of silver. In 1863 the Minister of Agriculture signed an agreement with an Italian who had offered for purchase a process destined to combat the disease of the silkworms, by which he (the Minister) engaged himself, in case the efficacy of the remedy was established, to pay 500,000 francs as an indemnity to the Italian silk cultivator. Experiments were instituted in twelve depart- ments, but without any favorable result. In 1865 the weight of the cocoons had fallen to four million kilogrammes. This entailed a loss of 100,000,000 francs. u The Senate was assailed by a despairing petition signed by thirty- six hundred mayors, municipal councillors, and capitalists of the silk- cultivating departments. The great scientific authority of M. Dumas, his knowledge of silk husbandry, his sympathy for one of the depart- ments most severely smitten, the Gard, his own native place, all con- tributed to cause him to be nominated Reporter of the Commission. While drawing up his report the idea occurred to him of trying to per- suade Pasteur to undertake researches as to the best means of combat- ing the epidemic. "Pasteur at first declined this offer. It was at the moment when the results of his investigations on organized ferments opened to him a wide career ; it was at the time when, as an application of his latest studies, he had just recognized the true theory of the manufacture of vinegar, and had discovered the cause of the diseases of wines ; it was, in short, at the moment when, after having thrown light upon the ques- tion of spontaneous generation, the infinitely little appeared infinitely great. He saw living ferments present everywhere, whether as agents of decomposition employed to render back to the atmosphere all that had lived, or as direct authors of contagious diseases. And now it was proposed to him to quit this path, where his footing was sure, which offered him an unlimited horizon in all directions, to enter on an unknown road, perhaps without an outlet. Might he not expose him- self to the loss of months, perhaps of years, in barren efforts ? " M. Dumas insisted. < I attach, 1 said he to his old pupil, now become his colleague and his friend, * an extreme value to your fixing your attention upon the question which interests my poor country. Its misery is beyond anything that you can imagine.' " ' But consider, 1 said Pasteur, ' that I have never handled a silk- worm.' "'So much the better,' replied M. Dumas. 'If you know nothing about the subject, you will have no other ideas than those which come to you from your own observations.' "Pasteur allowed himself to be persuaded . . . and on June 6, 1865, 44 AETIOLOGY OR THE CAUSES OF DISEASE started for Alais. The emotion he felt on the actual spot where the plague raged in all its force, in the presence of a problem requiring solution, caused him at once to forget the sacrifices he had made in quitting his laboratory at the Ecole Normale. He determined not to return to Paris until he had exhausted all the subjects requiring study, and had triumphed over the plague. " One of the most recent and the most comprehensive memoirs upon the terrible epidemic had been presented to the Academy of Sciences by M. de Quatrefages. One paragraph of this paper had forcibly struck Pasteur. M. de Quatrefages related that some Italian naturalists . . . had discovered in the worms and moths of the silkworm minute cor- puscles visible only with the microscope. . . . This instrument had already rendered such services to Pasteur in his delicate experiments on ferments that he was fascinated by the thought of resuming it again as an instrument of research. . . . " In a few hours after his arrival he had already proved the presence of corpuscles in certain worms, and was able to show them to the Presi- dent and several members of the Agricultural Committee, who had never seen them. . . . " It was necessary to know if there existed the relation of cause and effect between the corpuscles and the disease. This was the great point to be elucidated. . . . " One of the first cares of Pasteur was to settle the question as to the contagion of the disease. Many hypotheses had been formed regarding this contagion, but few experiments had been made, and none of them were decisive. Opinions, also, were very much divided. . . . " But whatever the divergences of opinion might be, every one, at all events, believed in the existence of a poisonous medium rendered epi- demic by some occult influence. Pasteur soon succeeded, by accurate experiments, in proving absolutely that the evil was contagious. . . . All the disasters that were known to have happened in the silkworm nurseries, their extent and their varied forms, were faithfully reproduced. Pasteur created at will any required manifestation of the disease. . . . " For five years Pasteur returned annually for some months to Alais. The little house nestling among the trees, called Pont-Guisket, became at the same time his habitation and his silkworm nursery. . . . " All the obscurity which enveloped the origin of the diseases of silk- worms had now been dispelled. Pasteur had arrived at such accurate knowledge both of the causes of the evil and their different manifesta- tions, that he was able to produce at will either pebrine or flacherie. He could so regulate the intensity of the disease as to cause it to appear on PASTEUR'S PERSISTENCE AND VICTORY 45 a given day, almost at a given hour. ... To triumph over this disease {pebrine), which was so threatening, Pasteur devised a series of obser- vations as simple as they were ingenious. . . . This process of pro- curing sound eggs is now universally adopted. . . . u But if Pasteur brought back wealth to ruined countries, if he had returned to Paris happy in the victory he had gained, he had also under- gone such fatigues, and had so overstrained himself in the use of the microscope while absorbed in his daily and varied experiments, that in October, 1 868, he was struck with paralysis of one side. Seeing, as he thought, death approaching, he dictated to his wife a last note on the studies which he had so much at heart. This note was communicated to the Academy of Sciences eight days after this terrible trial. " A soul like his, possessing so great a mastery over the body, ended by triumphing over the affliction. Paralyzed on the left side, Pasteur never recovered the use of his limbs. To this day (1884), sixteen years after the attack, he limps like a wounded man." § 11. — Sir Joseph {now Lord) Lister and Infectious Dis- eases of Wounds. Sanitary {Aseptic) Surgery Stirred by the investigations of Pasteur, and reflecting upon their significance, Sir Joseph Lister, already an eminent surgeon of Edinburgh, became convinced that many wound diseases are probably infectious and, if so, preventable. Accordingly, he set to work, and by the use of antiseptic dressings, sprays, instruments, etc., soon established his thesis and paved the way for the modern practice of sanitary or aseptic surgery, which was not only the first-fruit, but is also hitherto the most brilliant of the triumphs, of the germ theory of infectious disease. By its aid surgery has been not only revolutionized but also vastly extended. Operations formerly dreaded are now done with perfect assurance and constant success. The operating rooms of hospitals are built and conducted almost solely with reference to the exclusion or control of those micro-organisms (germs) which are now univer- sally recognized as the principal enemies of the patient and the worst foes of the surgeon. CHAPTER III ON THE RISE AND INFLUENCE OF BACTERIOLOGY. TRANS- FORMATION OF THE ZYMOTIC INTO THE ZYMOTOXIC THEORY OF INFECTIOUS DISEASE " Within the world of life to which we ourselves belong there is another living world, requiring the microscope for its discernment, but which, nevertheless, has the most important bearing on the welfare of the higher life-world." — Tyndall. " In der Aussenwelt, welche die alltagliche Umgebung des Menschen bildet und den Gegenstand der hygienischen Forschung ausmacht, findet der aufmerksame Beobachter in weitester Verbreitung Organismen, die an der Grenze der Sichtbarkeit stehen, selbst fiir das mit besten opti- schen Hulfsmitteln geriistete Auge, die aber mit ihrer ungeahnt aus- gedehnten, tief eingreifenden Thatigkeit eine hochwichtige Rolle im Haushalt der Natur und im Dasein des Menschen spielen. Sie bewirken die Zerstorung lebloser organischer Substanz, ... sie erregen die ver- schiedensten Gahrungen und sind uns unersetzliche Hiilfsmittel zur Bereitung unserer gewohnten Nahrungs- und Genussmittel ; sie be- fallen andererseits unsere Culturgewachse als Parasiten, die ihren Wirthen Degeneration und Tod bringen ; sie veranlassen gelegentlich schwerste Erkrankungen bei niederen und hoheren Thieren, und selbst den Menschen bedrohen sie mit morderischen Epidemien." — Flugge. § I. — The Achromatic Microscope Objective Reference was made in the last chapter to the influence of the newly discovered achromatic microscope objective upon the development of the germ theory of fermentation and its corollary the germ theory of disease. Its aid was also now being felt from a somewhat different direction, namely, from purely zoological and botanical studies of the lowest forms of life. Pasteur's studies on wine and beer, 46 EXPLORATION OF THE MICROSCOPIC WORLD 47 on the " organized corpuscles " of the air, and on the dis- eases of wine, beer and silkworms, had pointed downward into the world of the " infinitely little " as the source of those " germs " of life which seemed so small and yet so potent in fermentation and disease. All eyes, therefore, were turned in that direction, and extreme interest and curiosity were felt to know all that could be learned of the lowest forms of life, popularly described as " germs." This interest and curiosity were intensified, no doubt, by the rise just at this time of Darwinism, which also pointed downward for the beginnings of organic species to equally mysterious microscopic and primitive " germs " of life. As a result of these various inquiries one group of micro-organ- isms or germs, the Bacteria, then only recently studied by botanists, and lately located in the vegetable kingdom, became and has ever since remained of the first impor- tance to sanitarians and aetiologists. § 2. — Animalcula, Vibrionia, Bacteria The compound microscope is believed to have been invented about the middle of the seventeenth century, and micro-organisms, some of which were probably bacteria, were seen by Kircher (1650), figured by Leeuwenhoek (1680) and, because they were capable of motion, received as a group the name Thierchen or animalcula, i.e. "little animals'' or "animalcules." The compound microscope of the seventeenth century, however, was a very poor instrument and that of the eighteenth century little, if any, better. The best evidence of these facts is that many microscopists actually abandoned the use of the compound microscope of the day, preferring the simple microscope of lower power but comparative freedom from aberrations to the compound instrument of the time with its colored and distorted images. We need not be surprised, there- fore, to learn that the microscopists of the eighteenth 48 RISE AND INFLUENCE OF BACTERIOLOGY century made but small progress in the territory of the " animalcules." The first important and extensive advance upon the work of Leeuwenhoek was made a hundred and fifty years later, and with the aid of the newly discovered achromatic objective, by Ehrenberg (1838) and his con- temporaries. The vast horde of forms originally called "animalcules" had, it is true, by this time been separated into two or three main divisions, only one of which is of consequence to us, namely, the Vibrionia, a group of the infusorial animalcules ; and in 1850 the suspicion for the first time found expression that these are not all, or neces- sarily, animal forms, for in that year a young physician of Boston, Dr. Waldo Irving Burnett, read before the Amer- ican Association for the Advancement of Science a paper entitled "The Family of Vibrionia (Ehrenberg) not Animals but Plants." His proofs were unsatisfactory, but the idea steadily grew until in 1857 Nageli, the distinguished botanist of Munich, definitely and finally classified the Vibrionia as plants, giving to them the name of Schizo- mycetes — "fission plants." To show that the earlier names still prevailed for a time, however, we need only mention the fact that Pasteur in his earlier papers fre- quently refers to these forms as " infusorial animalcules " or "corpuscles." A long step forward was made when, in 1872, Ferdinand Cohn, of Breslau, began the publication of a series of papers entitled " Investigations on Bac- teria." 1 From that time onward the word " bacteria " has largely replaced the term "germs" in England, America and Germany. In France the term " microbes " seems to be preferred, and much can be urged in its favor. A synonym for this is extensively used in Germany, Great Britain and America, namely, "micro-organisms." Both terms are useful as including animal as well as plant forms ; and all of these terms may be said to be partial modern equivalents of the older term "animalcules." All of them 1 " Untersuchungen iiber Bacterien," Beitr'dge zur Biologic. GERMS, MICROBES, MICRO-ORGANISMS, BACTERIA 49 include living " ferments " capable of producing profound, though often invisible, changes in organic substances, and of causing singly or in cooperation those mysterious pro- cesses called fermentation, putrefaction, decay and some- times infectious disease. The bacteria alone belong exclu- sively to the vegetable kingdom. § 3. — The Foundations of Bacteriology laid by Louis Pasteur It has already been told in the previous chapter how the labors of Louis Pasteur served to establish the " germ " theory of fermentation and prepared the way for a "germ" theory of disease. His labors bore fruit also by laying for all time the secure foundations of what has since come to be a new branch of science, namely, bacteriology. Pasteur was not the first to use the microscope in studies on fer- mentation, but he was the first to employ careful culti- vations of the micro-organisms concerned, and special importance belongs to his constant attempts to secure " pure cultures " of yeast and other living ferments. It is true that he was compelled to rely altogether upon liquid cultivation, so that the actual purity of his cultures is open to some question ; but there is no doubt whatever that by his ingenious and successful use of these so-called " pure cultures" — which led him to the discovery of specific causative germs in certain specific diseases of wine and beer, as well as in normal fermentations, such as the acetic and lactic, not to mention the specific " corpuscles " of the silkworm diseases, — Pasteur earned the high privilege of being regarded as the " founder " of bacteriology. It may be well to state at this point, by way of anticipation and in order to avoid misunderstanding, that the honor of estab- lishing bacteriology as a science upon the foundation laid by Pasteur, belongs to Robert Koch, who, by proving (in 1876) that bacteria are the cause and not the consequence 50 RISE AND INFLUENCE OF BACTERIOLOGY of a particular disease (anthrax) and by introducing (in 1 88 1 ) an indispensable method of cultivation — the method of "solid" as opposed to "liquid" cultures — raised bac- teriology from a previously dubious position to one of high honor among the biological sciences. § 4. — Micro-organisms the Cause and not merely the Consequence of Disease The germ theory of disease was not without strenuous opponents. In particular, the objection was raised that there was as yet no evidence that the germs observed in any disease might not have been caused by the disease itself, they being the consequence and not the cause of it. This was really a sound and valid objection. It had been successfully raised by Liebig against Cagniard de Latour and Schwann, the discoverers of yeast as a living fer- ment, as early as 1839, an d na d been silenced in the case of Pasteur's studies on fermentation only with diffi- culty and by means of his use of needle inoculations and practically pure liquid cultivations. It was now (1865- 1875) urged with reason and with vehemence because many absurd claims were being made regarding the dis- covery of the " germs " of various diseases, based upon mere observation of microbes in the bodies of persons suf- fering from those disorders or else detected in their food or drink. In such a case it was entirely possible for any one to urge that the patient had first fallen ill and had then been invaded by the germs, the disease being primary and the germs purely secondary and adventitious. This view was forever disproved, and bacteriology for the first time established on a scientific basis by the splendid researches of Robert Koch upon splenic fever, or anthrax, between 1875 and 1878. Koch was a young physician of Woll- stein, in Prussia, when he began his studies on anthrax. This disease is not rare in Germany, Russia and other CULTIVATION OF SPLENIC FEVER GERMS 51 parts of Europe, and affects mainly cattle, sheep and horses, but also, at times, human subjects. On examining the bodies of cattle dead of anthrax, Koch found with the microscope (as Davaine in 1859 and others before him had found) minute rods or sticks in the blood and other organs, and especially in the spleen. To some observers this had seemed enough to prove that these were the " germs " of the disease ; but Koch did not rest here. Following the methods already employed by Pasteur in his researches on yeast, Koch transferred a needleful of blood or other tissue charged with the mysterious rods to a relatively large por- tion of the clear normal liquid which constitutes the aque- ous humor of the ox's eye. 1 After a few days, or even hours, the rods, being alive and able to grow in this liquid, had multiplied enormously, while the portion of tissue carried over with them being dead had not increased but rather diminished. From this first dish a needleful was now similarly transferred to a second large and fresh por- tion of aqueous humor, which was thus seeded in its turn. From this second a third was eventually seeded, and so on. A little reflection will show that at each transplanting, though many of the rods were carried over, very little, and always less and less, of the original tissue was transferred. Moreover, the rods transplanted soon included few or none of the original rods derived from the diseased animal, but only the innumerable descendants of these in more and more remote generations. It is easy to see that after a number of transplantings not only none of the original diseased tissue could have remained — those things only being represented that had the power of life, growth and reproduction, but also none of the original "germs." This method of cultivating the living plants — for the rods are 1 If it be asked how he hit upon the use of this liquid, the answer is that such transparent liquids had often been used in the study of animal tissues (histology), being known, because of their occurrence normally in the animal body, as " normal " fluids. 52 RISE AND INFLUENCE OF BACTERIOLOGY plants — was clearly a kind of horticulture, and it has be- come known as the method of liquid "cultures." It should not be forgotten that it was first used successfully (for yeast) by Louis Pasteur. If as a result of its use only one kind of micro-organism (yeast, bacterium) finally remains, such a culture is said to be " pure," or " a pure culture " ; pre- cisely as a wheat field free from everything but wheat would be a "pure culture" of wheat. Moreover, just as the ripe grains of wheat in a wheat field are not those which were planted but only their offspring, so the rods in Koch's cultures of the third or tenth generation were not those originally sown by the needle or directly derived from the diseased animals. But if the rods so derived really caused the disease known as anthrax, then their own offspring might reasonably be expected to have similar properties and powers, precisely as wheat grains have the properties of the seed wheat. Accordingly, Koch proceeded to in- oculate healthy susceptible animals with his pure cultures of anthrax rods, rightly thinking that if these were the germs of the disease they should be able to reproduce it. The result was perfectly conclusive : the inoculated animals promptly died of typical anthrax, and proof now existed, for the first time in the history of pathology, that a specific germ was and is the cause, and not merely the accompani- ment or the consequence, of at least one well-known speci- fic, infectious disease. An immediate result of this brilliant work of Koch was to give a fresh stimulus to the study of the bacteria, already in full cry since the beginning of the classic researches of Cohn, who, in 1875, added to his earlier results the highly important discovery that some bacteria can, and under certain circumstances do, produce spores which appear to be protective, highly tenacious of life, and very resistant to destruction by drying, heat, poisons, etc. Moreover, Koch not only readily discovered spores in the rods of anthrax, but also succeeded, as only a very few observers had done CRUCIAL TESTS ON LIVING ANIMALS 53 before him, in finding on other germs — notably certain large spiral forms in ditch water — cilia or lashes in active motion and presumably locomotor in function. These he (for the first time, in 1877) even succeeded in photographing. 1 §5. — A New Method of cultivating Bacteria and the Establishment of Bacteriology as a recognized Biologic Science by Robert Koch in 1881. Bacteria were probably first discovered in the latter part of the seventeenth century by Kircher and Leeuwenhoek, as has been stated already, but it was not until 1857 that microscopists were able satisfactorily to classify them as plants, and definitely locate them in the natural system. Pasteur observed many of them, for example a lactic ferment, a vinegar ferment and certain disease ferments of wine, beer, etc., and his work on these ferments, as well as on yeast, and especially his use of the method of "pure" liquid cultures, constitutes the basis of the modern science of bacteriology, no less than that of the germ theory of disease. Pasteur is, therefore, undoubtedly entitled to be known as the founder of bacteriology. And yet, owing to the intrinsic and peculiar difficulties of the subject, but little headway was made in exact knowledge of the bacte- ria themselves, and bacteriology as a distinct science was not established until, in 1881, a new and vastly improved method of cultivating bacteria was introduced by Robert Koch. This method, while extremely simple, was yet so effective and so fruitful that it forthwith became indis- pensable to many researches in biology. The method of cultivation which immediately proved so valuable is familiar to all biologists and is known as "Koch's method of solid cultures." Up to 1881 all cul- tures of yeast or bacteria hitherto made had been " liquid " cultures, such as were invented and used so effectively by 1 Cohn's Beitrage, Bd. II. 54 RISE AND INFLUENCE OF BACTERIOLOGY Pasteur in his establishment of the germ theory of fer- mentation and the germ theory of disease. Koch himself had used only liquid cultures in his great work on anthrax published in 1876; and Lister, Cohn and a host of others who studied fermentation and diseases be- tween 1869 and 1880 had used exclusively liquid cultures. In all these cases, however, it was very difficult to secure pure cultures because of the easy mingling in fluid media (such as bouillon or other fermentable or putrescible liquids) of various kinds of microbes, especially if the latter, as often happened, were endowed with the power of independent motion and could swim about. It was only by working on the basis of chance, and inoculating many flaskfuls by single needlefuls, that pure cultures could be got. This was tedious, uncertain, unsatisfactory, and in the hands of any but experts almost sure to lead to wrong conclusions. Thus it happened that during the twenty years after Pas- teur began to use liquid cultures, progress in bacteriology was slow and uncertain. We shall now see why, on the contrary, in the same number of years since Koch began his use of " solid " cultures, bacteriology has advanced by leaps and bounds. The method of solid culture overcomes the worst defects of the method of liquid culture, namely, first, the promiscu- ous mingling of different kinds of bacteria, and also, sec- ond, the time and labor consequently required to secure " pure " cultures. In this method the bouillon, or other liquid medium in which bacteria will thrive, is simply thickened while hot with gelatine or some similar substance such as Irish moss or agar-agar, so that when cooled the mass becomes a soft, moist jelly, capable of being melted by a gentle heat and solidified at the temperature of an ordinary room. It will be apparent on a moment's re- flection that any bacteria or similar micro-organisms pres- ent in the liquid must also be present in the solid mass, but with this important difference of condition, viz., that DISCOVERY OF THE TUBERCULOSIS MICROBE 55 whereas in the liquid they float or swim about promiscu- ously, and may become thoroughly intermingled, such is not the case in the solidified mass, in which each is brought to rest and held captive at some small distance at least from every other. Moreover, since the " solid " medium con- tains as abundant nutrients as the " liquid," the bacteria are firmly fixed in a solid which is at once their prison and their food. Accordingly, they continue to feed and multi- ply or reproduce, though each remains fixed at or very near the point where it was imprisoned. After a day or two, as a result of continued feeding and reproduction, microscopic heaps of bacteria are formed, which finally become visible to the naked eye as minute dots, and when still larger are known as "colonies." If the parent of the colony was, as is usually the case, a single isolated, individual bacterium, the colony, being composed solely of the descendants of this germ, will be a " pure " cul- ture, readily and immediately supplying the material for other pure cultures of the same species. The ease and the saving of time, the simplicity, certainty, and accuracy of the method are obvious. Its superiority to the method of liquid -cultures caused its immediate adoption, and it speedily led to the establishment of bacteriology as a recognized biological science. Almost immediately the new science began to yield wonderful fruit, for in the next year (1882) the whole world was startled at the announcement by Koch of his discovery of the micro-organism of tuberculosis, a bacillus usually found in the sputum of patients suffering from pulmonary consumption, capable of cultivation on solid media outside the human body, and able to produce the disease when inoculated into healthy susceptible animals, such as guinea-pigs. This announcement caused a pro- found sensation all over the world ; but so general and so conclusive was the confirmatory testimony that, in a sur- prisingly short time, it was accepted, and is now a matter 56 RISE AND INFLUENCE OF BACTERIOLOGY of history. The next year (1883) witnessed the discovery, also by Koch, of the micro-organism of Asiatic cholera, in this case not a true bacillus or rod, but a curved form ; hence at first described as a " comma " bacillus and after- ward as a spirillum or vibrio. One year more (1884) yielded the rich prizes of the bacillus of diphtheria and that of tetanus (lock-jaw), as well as new and careful studies by Gaffky, with the improved methods, upon the bacillus of typhoid fever which had been partially worked out previously by Eberth and Koch. Very much, of course, still remained to be done, not only in the search for the germs or living ferments of important and familiar dis- eases, but also in verifying the steps already taken ; but it is no exaggeration to say that within five years from the time of Koch's introduction of the method of solid cultures the new science of bacteriology had achieved a recognized and honorable position. Moreover, the zy- motic theory of infectious disease was now established, and the dreams of the iatro-chemists and of William Farr had come true. We shall next see how the theory of infectious disease as due to living ferments has been gradually further elaborated into a theory of ferment-poisons, or in other words transformed from a zymotic into a zymotoxic theory. §6. — How, precisely, do Living Ferments produce Disease ? A little reflection will show that there are several ways in which invading micro-organisms might conceivably pro- duce disease in the animal body; for example, (1) by mere physical obstruction, clogging the capillaries, veins and arteries, and interfering mechanically with the ordinary operation of the vascular and other mechanisms ; or (2) by chemical interference, such as (a) theft of food or other chemical compounds needed by the body, or (J?) by the DISCOVERY OF VARIOUS DISEASE GERMS 57 generation of substances harmful to the body and there- fore to be reckoned as essentially poisonous or "toxic." It is not necessary to do more than suggest these various possibilities inasmuch as it is now universally agreed that, while other influences should not be overlooked, the prin- cipal method of damage lies in the generation of toxic products {toxins), resulting from the operation of living ferments within or upon the organism. This will be more readily understood by returning for a moment to a con- sideration of the alcoholic fermentation. In the case of apple juice invaded by wild yeasts, it is indeed true that the yeasts multiply enormously and enough to cause a physical change, the turbidity of the liquid ; and also that sugar, a valuable food substance, disappears by the agency of the yeast. But the most striking phenomenon, and one which has been universally recognized as such, as is proved by the fact that this fermentation has long borne its specific name, is, that a new and toxic substance, alcohol, is generated during the fermentation. In a word, just as yeast may be considered the specific germ of the alcoholic fermentation, alcohol may be regarded as the toxic substance generated by it, i.e. alcohol may be re- garded as a toxin produced by yeast. We must hasten to remark, however, that the products of fermentation are not always or necessarily poisonous either in character or quantity, as may be seen in the case of the alcoholic fermentation just cited and in the vinegar, lactic and similar fermentations. It is "however interesting to observe that the character of the substances produced is in each case specific, — yeast producing alcohol, the anthrax germ producing anthrax poison or toxin, the diph- theria bacillus diphtherotoxin, the typhoid fever bacillus typhotoxin, the lock-jaw bacillus tetanotoxin, and so on. But if this be so, then this class of living ferments may easily do its damage by means of its products, which are harmful to the body just as poisons are, and the mystery 58 RISE AND INFLUENCE OF BACTERIOLOGY of an infectious disease becomes no greater, and perhaps no other, than a mystery of toxicology, such as exists, for example, in the case of poisoning by opium, belladonna, strychnine, and similar vegetable poisons. It is by reason- ing of this sort, based upon numerous observations and experiments, that the modern theory of infectious disease has reached the point to which we have now obviously come, namely, that the true theory of infectious disease is not merely a zymotic or ferment theory, but rather a zymotoxic ox ferment-poison theory. It is plain that the invading micro-organisms which pro- duce disease are essentially parasites, and that the germ theory of disease is a theory of parasitism. The term "zymotoxic" is here preferred to "parasitic" simply as being more definite and more precise. There can be but little doubt, however, that the growth of knowledge of parasitism materially aided the acceptance of the germ theory. Favus and muscardine have already been cited as early examples, and the discovery of trichinae in swine, and, in particular, the recognition that epidemics may be caused by these microscopic worms doubtless paved the way for a more speedy general acceptance of a parasitic or germ theory of infectious disease. To this aspect of the subject we shall return in the next chapter. § 7. — Sepsins, Ptomaines and Toxins It has long been recognized that spoiled meat, fish and other animal foods are sometimes dangerous to eat, and the popular assumption has been that they contained some deadly poisonous substance. As early as 18 14, according to Woodhead, Burrows in England described such a poi- sonous substance in putrefying fish ; while Kerner, in 1820, described a poisonous alkaloid which resulted apparently from the decomposition of albumen, and resembled in its physiological action a substance found by him in poison- BACTERIAL OR FERMENT POISONS 59 ous sausages. Kerner compared this with atropine, the alkaloid of belladonna, in its toxic effects. In i856Panum obtained from decomposing animal matter a characteristic product soluble in water or alcohol to which he gave the name "sepsin." No great attention, however, was paid to these substances until about 1870, when Selmi drew general attention to the subject, and gave to the so-called poisonous alkaloids the name " ptomaines," i.e. " cadav- eric " substances. Nencki and also Brieger soon obtained several of these from pure cultivations of bacteria, and since that time it has been generally recognized that it is easy to separate from substances which have undergone fermentation or putrefaction chemical compounds more or less characteristic of the fermentation or putrefaction in question. When these are poisonous, they are often de- scribed as ptomaines ; and the whole group is popularly known by this name, though it is obviously unfit for the purpose. Some writers have undertaken to apply the word " leucomaines " to those similarly derived but harmless. A more recent terminology describes the poisonous products of fermentation or putrefaction as toxins, and applies no name to the non-poisonous products. As we shall soon see, the ideas advanced in this paragraph have received widespread attention, and must be regarded as of the highest importance on account of their necessary con- nection with the subjects of susceptibility and immunity upon which we must dwell in the next chapter. § 8. — Transformation of the Zymotic Theory of Infectious Diseases into the Zymotoxic Theory of to-day. Recapitu- lation Enough has now been said to make it clear that the modern idea of an infectious disease is somewhat more than that of a fermentation or a case of parasitism. It is not merely that the body of the patient is invaded by 60 RISE AND INFLUENCE OF BACTERIOLOGY germs ; our theory goes much farther than this and shows us the germs growing, dividing and multiplying in the body of the patient, while at the same time each carries on its individual metabolic existence, acting upon its im- mediate environment, drawing to itself foods, and reacting by setting free the special products of its vital activity. It is not enough to suppose that the micro-organisms in question mechanically obstruct or physically disturb the delicate machinery of the living organism in which they multiply. The symptoms of infectious disease are rather those of toxic actions, actual poisonings of the body, accompanied by chills, fever, delirium and other symptoms of a profound disturbance. Moreover, the phases of infec- tious disease — the slow onset, the active illness, the recov- ery and the subsequent immunity — are all readily explained upon the modern theory of zymotoxic action. The slow onset is apparently due to the limited infection and the time required for the growth of the germs. The gradual increase of severity keeps pace with their multiplication and activity. The height of the disease corresponds to the height of their development. Its abatement to their decline. The subsequent immunity perhaps to the habitu- ation of the organism to their poison. The subject of immunity, however, is by no means well understood. It will be more fully considered in the next chapter. § 9. — Objections to the Germ Theory The principal objection to the germ theory was and is that already referred to as met and overcome by Koch, viz., that germs may be seemingly the consequence, not the cause, of disease. Another objection is that in certain diseases the most careful search has failed thus far to re- veal causative micro-organisms. The answer to this latter is simply that in the absence of all positive evidence of the true cause of disease we are at liberty to choose the THE ZYMOTOXIC THEORY OF DISEASE 6l most likely working hypothesis, and no hypothesis has yet been found for any infectious disease more reasonable or more probable than the germ theory. " A great scientific theory has never been accepted with- out opposition. The theory of gravitation, the theory of undulation, the theory of evolution, the dynamical theory of heat — all had to push their way through conflict to victory. And so it has been with the germ theory of com- municable diseases." 1 1 Tyndall, Essay on " Louis Pasteur, His Life and Labors." CHAPTER IV SANITARY ASPECTS OF THE STRUGGLE FOR EXISTENCE. PARASITISM. HEALTH AND DISEASE IN TERMS OF GEN- ERAL BIOLOGY. VITAL RESISTANCE, SUSCEPTIBILITY AND IMMUNITY " Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult — at least I have found it so — than constantly to bear this conclusion in mind." " Let it also be borne in mind how infinitely complex and close- fitting are the mutual relations of all organic beings to each other and to their physical conditions of life." — Darwin. " The Origin of Species." § i. — Sanitary Aspects of the Struggle for Existence In the preceding chapters stress has been laid on the potency of the agents of disease proceeding from the en- vironment. This, however, is only one aspect of the matter. In order that living ferments or their poisons shall be effective, there must be a susceptible subject upon which they can act. Thus it comes to pass that in any zymotic disease the energy and virulence of the attacking agents are virtually pitted against the resistance of the patient, and a struggle ensues which may be, and often is, on one side or on both sides a veritable struggle for existence. In this case the struggle is between organism and organism, between man and microbe. In "The Origin of Species" Darwin, in dealing with the struggle for existence, dwells chiefly upon similar struggles of living things one with another, and it is this aspect of the subject which is still most often emphasized. For the 62 THE PARABLE OF THE SOWER 63 hygienist, however, the struggle for existence means not only competition and battle and their consequences, not only the struggle of organism with organism, but also the broader struggle of the individuals with their whole environment. In the familiar parable of the sower we have a vivid picture of such a struggle for existence in the case of certain seeds : — " Behold, a sower went forth to sow ; And when he sowed, some seeds fell by the wayside, and the fowls came and devoured them up : Some fell upon stony places where they had not much earth ; and forthwith they sprung up, because they had no deepness of earth : And when the sun was up, they were scorched ; and because they had no root, they withered away. And some fell among thorns ; and the thorns sprung up, and choked them : But others fell into good ground, and brought forth fruit." In this parable both aspects of the struggle for exist- ence are dwelt upon : first the struggle of organism with organism, namely, of seeds with birds and with thorns ; and, second, of organism with lifeless environment, namely, with stony places, scorching sun and good earth. A similar breadth of view is required for the student of sani- tary science who seeks to gain a philosophic knowledge of the nature of disease; for disease may be the conse- quence not merely of organism struggling with organism, but also of organism struggling with lifeless environment. It is perhaps most often the result of both hostile organism and unfavorable lifeless environment acting together upon the human mechanism. Of the struggle of organism with organism parasitism affords a familiar and instruc- tive example. § 2. — Parasitism and Infectious Disease Some recognition of what is now known as parasitism must have occurred very early in the history of the human 64 THE "STRUGGLE FOR EXISTENCE" AND DISEASE race. It is exemplified, for example, in the case of the gourd which grew up and sheltered Jonah while he impa- tiently waited for the destruction of Nineveh, inasmuch as a worm was sent in the night to feed upon and destroy the gourd ; and it is said that Pliny was familiar with the parasitism of the mistletoe. The word " parasite," however, arose in a different connection and was only recently applied to plants and the lower animals, having been apparently first used for a person who unbidden eats beside, or at the table of, another, and therefore, of course, lives at his expense. A few cases of parasitism, such as that of the mistletoe, were recognized very early because they were so conspicuous that they could not readily be overlooked. The well-known lines of Swift 1 testify unmis- takably to a recognition of the same phenomenon. For the most part, however, parasitism remained comparatively unrecognized until the introduction of the compound micro- scope revealed its almost universal prevalence. Parasitism is now known to be one of the commonest features of the struggle for existence, and it is not neces- sarily, as it is often supposed to be, an abnormal and strange development — at least in its beginnings. If, in the search for food, a plant or animal happens to come in contact with and feed upon another, it may easily result that it shall gain great profit thereby, though if this habit becomes so extended as to lead to the destruction of the host, the parasite itself may also perish. It is not difficult to suppose that parasitism may have arisen from sapro- 1 " So, naturalists observe, a flea Has smaller fleas that on him prey; And these have smaller still to bite 'em. And so proceed ad infinitum." Of which a more popular, alliterative and generalized version is, — " Big bugs have little bugs Upon their backs to bite 'em; And little bugs have lesser bugs, And so ad infinitum." MICROBES SOMETIMES PARASITES 6$ phytism, in which plants or animals feeding upon dead or waste organic matters happened to become attached to living plants or animals, and it is easy to see how, under these circumstances, great advantage might accrue to the saprophyte. It is even possible to imagine how the ranks of parasites, thinned by the destruction of their hosts, or otherwise, might continually be recruited from among the saprophytes. The somewhat extended discussion of the germ theory of fermentation and disease in the previous chapter should not lead the reader to overlook the fact that many of the micro-organisms which are the prime movers of fermenta- tion and infectious disease must from another point of view often be regarded as parasites. The parasitic fungi have long been known in special cases to penetrate the tissues of their host precisely as microbes may "invade" the animal body. It has also been known that in doing this some solvent reagent was secreted by the fungus, and experi- ments have shown that it is possible to separate from par- ticular fungi substances which will corrode and destroy vegetable tissues. It thus appears that a close analogy is discoverable between the toxins or poisonous products of disease germs and these solvent reagents or tissue-poisons. It is customary to speak of the infectious diseases as essentially parasitic in their character, the disease germs being the parasites, and the organisms affected their hosts. This point of view is not only common, but exceedingly useful, for it places these diseases in the same category with certain well-known phenomena of parasitism (or sapro- phytism), and makes them thereby the more readily com- prehensible. The sanitarian in particular has reason to value this interpretation of infectious disease inasmuch as prevention of parasitism is, in theory at least, a compara- tively simple matter, namely, the destruction of the parasites in question and their control in the environment. When it comes, however, to an examination of the precise nature of F 66 THE "STRUGGLE FOR EXISTENCE" AND DISEASE the parasitism involved in infectious disease, we shall find it often necessary to regard the germs as parasites produc- ing chemical change and doing damage by the chemical changes which they effect, or the chemical bodies which they produce, rather than by the theft of food substances which is the more ordinary characteristic of parasitism. The germ theory is sometimes thus described as the parasitic theory of disease, and has also been called the " particulate " theory because the micro-organisms con- cerned are obviously material particles. This latter desig- nation is of value chiefly as emphasizing the reality of the materies rnorbi, or the fact that the causes of infectious disease are material particles and not merely immaterial conditions such as dynamical derangements of spiritual vital principles. The reader will be the better prepared to recognize the validity of the former term — the parasitic theory — if he will remember that just before the germ theory had taken definite shape two diseases, namely, muscardine in silkworms and fav us or honeycomb of the human scalp, had already been proved to be due to para- sitic fungi (see Chapter II, p. 32). Powerful support for a parasitic theory of disease had also been accumulating during the time of the growth of the germ theory of fer- mentation and disease, especially in connection with a terrible disease of man hitherto unsuspected, but by that time definitely known, namely, the disease caused by the parasite called the pork-worm {Trichina spiralis) and known as trichinosis. This disease is of special interest to sanitarians, inasmuch as the parasites which unquestion- ably produce it, while very minute are still scarcely to be called micro-organisms, and yet are so small that for a long time they escaped the detection which tapeworms, stomach- worms, etc., readily encountered. They thus form an interesting connecting link between the invisible micro- organisms and the coarsely visible tapeworms, etc., and the smaller fungi. (Cf. pp. 293, 296.) THE "PARASITIC" THEORY OF DISEASE 67 The whole matter may perhaps be summed up as fol- lows : from the widest point of view infectious diseases in common with all others are important and complicated phenomena in the universal struggle of organisms for existence. From a somewhat narrower point of view they are often to be regarded as cases of parasitism, the disease germ being the parasite and the organism affected being its host. From a still narrower point of view, and examin- ing the details of the struggle, the process appears to be essentially " toxic," the host being damaged by the para- site (or saprophyte) not so much by theft of material as by the products of its metabolic activity, namely, by chemical poisons known as " toxins." § 3. — The Lifeless Environment and Disease Any extended treatment of this subject would be beyond the province of a work like this, since such a discussion belongs rather to hygiene than to sanitary science. Nev- ertheless, the student of sanitary science cannot neglect the influence of the lifeless environment as a powerful factor in the causation and modification of infectious disease, even when it is not the principal factor. In such disease, for example, the time, the occurrence, the duration and even the energy of the attack, may be profoundly influ- enced by external environmental conditions such as season, temperature, dryness or light. We may, therefore, with advantage, consider somewhat carefully the relations be- tween organisms and their environments, whether living or lifeless, before passing on to the more recondite sub- jects of susceptibility, vital resistance and immunity. In addition to a comprehension of the fact that the living organism is essentially a delicate physical mechanism, the student requires an adequate knowledge of what is meant by the terms " organism " and " environment," and with this a recognition of the significance of the actions, reactions 68 THE "STRUGGLE FOR EXISTENCE" AND DISEASE and interactions which necessarily go on between organ- isms and their environments. In the language of biology an organism is a limited mass of living matter occupying a definite position in space and time. It is bounded on all sides by material substances, — earth, air, water, etc., — by which it is acted upon, and upon which it acts in return, and, on the whole, these actions and reactions are equal, though in opposite directions. Those portions of the material universe which thus act upon the organism are called its "environment," and a little reflec- tion will show that while it is the nearer portions which are most closely concerned and are, therefore, the most con- spicuous parts of " the environment," no part, in theory at least, is so remote as to have no influence. The whole material universe may be — must be — divided for any liv- ing thing into two parts, namely, that thing and its envi- ronment : the individual on the one hand, and the rest of the universe on the other, — very much as the ancient and mediaeval philosophers regarded man on the one hand as " microcosm " and the rest of the universe as " macrocosm." Biology teaches that if we would comprehend the doings of living things we must begin by taking this point of view. Viewed from this standpoint mankind becomes a host of masses of matter each bounded by the rest of the material universe, with which it must deal so long as it continues to live, and to which, no matter how prolonged the struggle, it must finally surrender. From the environment each must derive whatever of matter and energy it gains, and to it it must return whatever it loses. It may be profoundly affected by heat or cold, by lightning or earthquake, by fire or tempest ; and it may, on its part, react upon its environ- ment and displace the air by buildings or balloons, the sea by ships, the earth by mines or tunnels, or fire by incom- bustible substances. Every tree that lifts its branches into the aerial ocean reacts upon the atmosphere and, like every animal that burrows into the earth or builds its ORGANISMS AND ENVIRONMENTS 69 house or its nest in the air, reacts upon its environment. The encroachments of the sea may be resisted or overcome by dikes, of the wind by shelters, of the sunshine by shade. Everywhere in nature — and in man as a part of nature — we find actions and reactions incessantly going on, and these in the long run consist essentially of ex- changes of matter and of energy or of both, between masses of matter and their environments. § 4. — Health and Disease in Terms of General Biology Life has been defined as "the continuous adjustment of internal to external relations," and health might be de- fined on these terms as the normal state and performance of this adjustment. Disease would then be some serious disturbance or grave departure from this normal state or performance, and might conceivably be due to (1) a failure of the intrinsic powers of adjustment; or (2) some external condition so severe or unusual that the usual adjustment was impossible ; or (3) to a combination of these factors. From what was said in the first chapter (p. 12) it is clear that a failure of the mechanism itself to do its part, a failure of the intrinsic powers, such, for example, as old age effects, produces a constitutional dis- turbance or disease ; while external conditions, so hard or so unusual as to be met with difficulty or perhaps not at all, may well give rise to a disturbance or disease essen- tially environmental in its origin ; and the combined effect of imperfect mechanism or imperfect internal ad- justment with external relations difficult to deal with might lead to diseases seemingly environmental, but really no less truly constitutional in origin. A very little reflec- tion will show that to avoid disease and to forestall its effects there are required: (1) Mechanisms as capable as possible of adjustment to external relations, unfavorable as well as favorable. (2) Environments (external rela- yo THE "STRUGGLE FOR EXISTENCE" AND DISEASE tions) to which the mechanism may readily adjust itself, or making as small demands as possible upon its powers of adjustment. Of these two factors the former is on the whole far the less under our control at present. The mechanism may in- deed, as a rule, be strengthened by good air, good food, rest and other favorable conditions ; it may be weakened by bad air, bad food, fatigue and other unfavorable conditions ; so that it shall adjust more, or less, successfully its internal to any external relations. But while so much is unquestion- ably true, and while efforts looking in this direction lie at the basis of all sound hygiene and constitute one of its proper functions, it is still true that the external relations to which the internal relations of the mechanisms must be adjusted, are much more largely under our control. In other words, it is to a great extent within our power (in theory at least) to provide environments or external relations to which almost any living mechanism should be able to adjust its internal relations ; or, conversely, an environ- ment so unfavorable that few if any could possibly be able to adjust themselves to it. 1 § 5. — Three Principal Sanitary Conditions or States of Relation In actual life all these various conditions are readily observed. We find some persons so robust — that is to say, with mechanisms so capable of adjustment to external 1 " The man who lives to the age of a hundred years and who, during that time, suffers no pain, and is continually able to make use of the powers pecul- iar to his age, would by universal testimony be regarded as an example of health ; yet even the life of such an one would not always be at its best ; and health, like every other such name, is to be used in a relative sense. Into the life of the healthiest man disorders must frequently enter. Absolute health is an ideal conception, as the line of the mathematician, the ether of the physicist, and the atom of the chemist."— T. C. Allbutt, "System of Medi- cine," I, xxii. SANITARY PARADOXES 71 relations of whatever kind — that nothing seems to daunt them. They work hard, eat poor food, live in bad air and seemingly disobey all the rules of hygienic living, and yet possess apparently perfect health. Conversely, others surrounded by every sanitary contrivance, well fed, well housed and tenderly cared for, sicken and die in an envi- ronment apparently the most absolutely favorable. And finally, in the same community, are many who thrive as long as their external relations are good and easily dealt with (" favorable "), but who suffer just as soon as these become difficult to deal with ("unfavorable"). Furthermore, these groups are by no means fixed and invariable, but rather constantly subject to change both as to membership and mass. A period of unusual environ- mental severity of climate, temperature, infection, finan- cial or political buoyancy or depression, may promote or reduce from one rank to another, with the consequence not only of numerous changes in actual sanitary conditions in individuals, but even extensive improvement or deteriora- tion in the average public health of a community. Of this a good example is some effective change in external relations, such as a financial panic, causing anxiety, loss of employment, increased exposure, poorer feeding, loss of sleep, etc., but perhaps the best example is one in which a novel and direct action proceeds from the environment, unknown, it may be, until its work is done. Such a pro- found change in the external relations of an entire com- munity occurs when some epidemic, unsuspected, falls upon an entire city or town. There are on record many cases of this kind, some of which are described in the eighth chapter. If, for example, a public water supply becomes contaminated with the germs of an infectious disease such as typhoid fever, the general standard of health in the community using it will be lowered, the weak, as a group, will, on the whole become weaker, the strong, less strong, and some of each group will perish altogether 72 THE "STRUGGLE FOR EXISTENCE" AND DISEASE who would have lived longer if the infection had not reached them. The explanation of these three great groups — which we may call "the robust" or "the strong," "the well but not strong," and "the feeble" or "weak" — is simply that there are actually corresponding groups of organisms, or mechanisms, in every community. The "strong" are those endowed by nature, by inheritance, or it may be to some extent by training, with superior vital machinery. " The well but not strong " are similarly provided with machinery either poorer in quality or less successfully put together, while the "weak" or "feeble" are those hav- ing vital mechanisms so delicate in fibre or adjustment as to be always in need of attention or repair, even under ordinarily good conditions. It will be observed that no place is here left for those organisms which are altogether wanting in the power of " continuous adjustment of inter- nal to external relations." Such are those that perish, — some, before they are born ; some, vainly trying at birth to catch the first breath of life in order themselves to effect an oxygenation of their blood, hitherto provided for from the mother, from the novel atmospheric ocean in which if anywhere they must henceforward live ; some, later, in that struggle for existence which compels them to deal with bad food, or exposure, or infection, or with sorrow or shame. Few, comparatively, are able to adjust their internal to their external relations so successfully as to reach the familiar threescore years and ten; fewer still the fourscore years; and we have the authority of the psalmist that in the latter case it is only "by reason of strength " that the goal is reached : favorable environ- ments — favorable external relations — alone are not suffi- cient. The power of adjustment of internal relations is equally indispensable. THE STRONG AND THE WEAK 73 § 6. — Practical Importance of these Considerations The practical importance of these considerations is im- mense. Any one who deals chiefly with those more violent changes in the environment which produce great destruc- tion in a relatively short space of time is tempted to mini- mize the importance of forces acting more slowly over longer periods. The epidemiologist, for example, after witnessing the conspicuous effects of an outbreak of dis- ease affecting a whole community through impure food or drink, is strongly tempted to overlook the relatively remote effects of ordinary filth or foul air. And these are in fact far less striking, even when discoverable at all. But yet there is reason to believe that even quantitatively con- sidered they may do quite as much or even far more harm in the long run, for the great epidemics come seldom, affect a small number only, and pass quickly ; while filth and bad air act unfavorably upon a much larger number for a much longer time, keeping them frequently and per- haps constantly weakened, and enhancing always their susceptibility to specific disorders. Nor must we allow ourselves to be deceived by appear- ances. It is true that abounding health is often exhibited by those dwelling in most unwholesome places, and that many who never wash outlive many who do. But this does not mean that sanitary dwellings are superfluous, or that bathing is a waste of time. Nothing is plainer in sanitary science, as in human experience, than that " Cleanliness is next to Godliness," and that on the whole the first external condition of health is cleanliness. On looking closely we shall find that the cases observed are exceptional, or that the persons in question are the strong survivors of many now dead among whom they represent the survival of the fittest ; or that they have really bathed in their own sweat, thus shedding off the outer skin and with it much dirt and many micro-organisms; or finally, that although the sur- 74 THE "STRUGGLE FOR EXISTENCE" AND DISEASE viving younger members of the family may seem hale and hearty, the elders, while still young in years, show the effects of the struggle for existence and often break down or succumb to disease before their natural time. Darwin somewhere refers, more in sorrow than in anger, to those persons who have failed to understand him because they were utterly unable to appreciate the cumulative ef- fects of small changes acting over long periods of time. The sanitarian needs constantly to be warned against the neglect of small and seemingly insignificant factors of disease in the form of unfavorable conditions which by their prolonged action and cumulative effects may produce great results. §7. — Vital Resistance and Susceptibility The reader is now in a position to understand in its general aspects the term "vital resistance." In the last analysis this expression is used to describe that condition of the normal body, plant or animal, in which it is able to cope more or less successfully with unfavorable influences acting upon it from without, i.e. from the environment. There is, however, no quantitative measure of vital resist- ance ; but when it is regarded as small or altogether wanting, the term is no longer used, and the organism is said to be not vitally resistant, but "susceptible" or "vul- nerable " to disease. At the other extreme, when the vital resistance is complete, especially in regard to parasites, poisons, etc., the organism is said to be " immune," as are, for example, the arsenic eaters of Styria against ordinarily lethal doses of arsenic, and as are certain trees to certain parasites. Enough has perhaps already been said in the previous section in regard to susceptibility of different de- grees, but immunity is a matter of so much practical impor- tance that it will be necessary to consider it much more carefully in the following sections. CUMULATIVE EFFECTS OF UNSANITARY FACTORS 75 It has been suggested by Professor Theobald Smith that the mutual relations of vital resistance and infectious dis- ease may be the more clearly appreciated by expressing M them in the form of an equation, namely, D = — , in which D represents the disease, M the micro-organism and R the vital resistance of the organism attacked. Obviously, D will vary according to the relative values of M and R. It is even possible to carry this idea somewhat farther and to write the equation D — — - — , N representing the num- R ber of micro-organisms and V their virulence ; for there is good reason to suppose that the intensity of the disease de- pends on these factors as well as, though less than, on M, the specific character of the micro-organism involved. We are unable at present to resolve R into any component elements or even to picture to ourselves, except in the most general way, its origin or mechanics. We may, it is true, safely consider that it is bound up with chemical and physical processes which result in favorable chemical and physical conditions ; but concerning these processes, and to a great extent these conditions, we are at present almost completely ignorant. (Cf. pp. 98, 218.) § 8. — Immunity Examples of comparative immunity to infectious disease are familiar in the cases of all robust and healthy persons. Precisely what the basis of this immunity may be it would be difficult to say, but it is not inconceivable that in an organism which is a practically perfect mechanism the con- ditions should be such as to ward off effectually all micro- organisms, either by mechanical or physiological defences. Among the former would be healthy and vigorous skins and epithelia, which the invaders should find it impossible to penetrate ; among the latter, juices of the body of such composition as to be essentially toxic or destructive for f6 THE "STRUGGLE FOR EXISTENCE" AND DISEASE invading microbes. There is good reason to believe that such conditions are, in fact, some at least of those which constitute the robustly healthy organism immune to all ordinary infectious diseases. It has long been the ambition of dreamers to find some substance which should not only ward off the attacks of infectious disease but also interfere with the ordinary course of Nature, and postpone for a longer or shorter time the arrival of old age. Various elixirs of life have been put forward by enthusiasts, especially with a view to the latter result, and it must be allowed that, improbable as it is that this end will ever be achieved, it is not per- haps theoretically inconceivable. It is plain, however, that inasmuch as there frequently exists already a remarkable natural immunity to certain infectious diseases, the problem of artificial immunity to disease is one much easier; and when we learn, as is the fact, that such immunity has actually been produced in the case of some diseases, we may confidently expect that it shall be eventually brought about in the case of other diseases also. § 9. — Immunity to Small-pox. Inoculation The development of our knowledge in this direction is interesting and instructive. The first systematic steps toward securing artificial immunity from disease appear to have been taken in the case of small-pox. In the early part of the eighteenth century, Lady Mary Wortley Mon- tagu, the wife of the British ambassador at Constantinople, the daughter of a duke and the granddaughter of an earl, and a woman of rare gifts, in interesting letters sent from Constantinople to friends at home pointed out that the Turks, in pursuance of a custom apparently derived from the East, were in the habit of " inoculating " against small- pox. Lady Montagu wrote from Adrianople in 171 7: " Every year thousands undergo this operation, and the NATURAL VS. ARTIFICIAL IMMUNITY JJ French ambassador says pleasantly that they take the small-pox here by way of diversion, as they take the waters in other countries. There is no example of any one hav- ing died of it, and you may believe I am satisfied of the safety of their experiment since I intend to try it on my dear little son." Largely as a result of this correspondence the practice of inoculation was introduced into England, and thence carried to America. In both countries it be- came widely extended, and lasted for many years. It is said that the first person inoculated in England was Lady Montagu's daughter. George I and several members of his family were soon after inoculated, as were also many less noted persons, and the practice gradually became common. In the process of inoculation for small-pox, some " mat- ter" derived from a pustule of a small-pox patient was introduced under the skin of a healthy person who elected to suffer from the disease while well, and knowingly, rather than to run the risk of "taking" it when less well, unknowingly. The process was much the same as that employed in vaccination except that the " matter " used was derived directly from the pustules of a small-pox patient, and was not " vaccine " matter, i.e. was not derived either directly or indirectly from the cow. Inoculation had a very extended vogue and was justly regarded as a most important defence against small-pox ; and until the milder method of inoculating "vaccine " matter, i.e. matter derived from the cow, was devised by Jenner, no other method of prevention of small-pox, or, for that matter, of any infec- tious disease, was known or practised. The attitude of mankind at various times toward small- pox, inoculation and vaccination forms one of the most remarkable chapters in the history of the human race. It is impossible to-day to realize the dread and awful terror with which this horrible and most loathsome disease was justly regarded by our ancestors before the introduction of 78 THE "STRUGGLE FOR EXISTENCE" AND DISEASE inoculation and vaccination. A single brief quotation may help to give the reader some idea of the feeling in regard to it and its prevalence, even as late as the middle of the eighteenth century. "Small-pox has been for ages, and continues to be, the terror and destroyer of a great part of mankind. ... In the ordinary course and duration of human life scarce one in a thousand escapes the small- pox." . . . (Appendix to Dr. Brooke's "General Practice of Physic," London, 1766.) It would be easy to multiply authoritative statements of the fearful ravages of this dis- ease, and to bring forward testimony to its abundance, contagiousness and foul character. Fortunately, it has become to-day in civilized countries so uncommon that the former dread of it has largely disappeared from the popu- lar mind. Unfortunately, however, unfamiliarity with it has bred a contempt for it which leads many to despise, undervalue or refuse the means by which it is chiefly kept in abeyance. Such contempt is likely, if it becomes gen- eral, to carry with it its own punishment, for small-pox is so contagious that its recrudescence at any time in any community is natural and easy, if the very simple means in our possession for holding it in check are long neglected. The art of inoculation for the prevention of small-pox appears to have been long known and to have come to Constantinople from the East — from the Circassians in one direction and from the Chinese in another. By the Chinese the dried pustules are said to have been kept in bottles, inoculation being produced, when desired, by placing por- tions of these pustules in the nose of the patient. The results of inoculation appear to have been remarkably success- ful and under favorable circumstances to have approached, though they did not equal, those attained by vaccination. Sir George Baker, a dis- tinguished authority, writing in 1766, affirms, "According to the best information which I can procure, about seventeen thousand have been thus inoculated, of which number no more than five or six have died." Another writer of the same time says, "Scarce one in one hundred miscarries, whereas a fifth or a sixth part die of the natural small-pox." Dr. Hadow, of Warwick, is said to have practised inoculation for twenty-seven years, and out of 2143 persons inoculated only three "INOCULATION" AGAINST SMALL-POX 79 (children) died : of these one of an overdose of opium, one in very hot weather, the third of nose bleed. Much importance was attached by the best practitioners to " pre- paratory treatment " of various kinds, although in the East this was less regarded. Sir George Baker quotes Gatti, " who some time ago was much employed in inoculation at Paris" as "an enemy to any general plan of preparation. In all the Levant, he says, where the natural small-pox is as fatal as elsewhere, and where you may find old women who have inoculated ten thousand people without an accident, the only inquiry is, whether or no a person is prepared by Nature. All that is considered is whether the breath be sweet, the skin soft, and whether a little wound in it heals easily. Whenever these conditions are found, they inoculate without the least apprehension of danger." (" An Inquiry into the Merits of a Method of Inoculating the Small-pox," etc., London, 1766.) In America, where inoculation was also much practised before the introduction of vaccination, prepar- atory treatment was common, and Sir George Baker (/. c.) states on the authority of Dr. Huxham that " Dr. Benjamin Gale, of Connecticut, in New England, since he has given mercury and antimony in preparing persons for inoculation, has lost only one person out of eight hundred inoculated." (On inoculation in New England, see Dr. Zabdiel Boylston "An Historical Account," etc., Boston, 1730; in Massachusetts, see J. M. Toner, in Mass. Med. Soc. Trans., Vol. II, p. 151, Boston, 1867; in Great Britain, see W. Woodville, a Hist. Inoc. Small-pox," etc., London, 1796.) For Dr. Gale's paper see Phil. T?-ans. Roy. Soc, London, 1765. The drawback to inoculation was that persons inoculated had for the time being mild cases of genuine small-pox, and were therefore capa- ble of conveying the disease to others. They became, temporarily at least, " foci of infection," and were usually treated as such, being often gathered together in inoculation " hospitals " or establishments in relatively remote and inaccessible places, and kept meanwhile under more or less strict quarantine regulations. Those who voluntarily re- sorted thither for inoculation naturally went, or were sent, while in good health or well "prepared," and, for the time being, were completely separated from their families. It was a successful, but rather dangerous and troublesome method of combating the disease, and when vaccina- tion, equally and perhaps more protective and neither difficult nor dangerous, was introduced (in 1796), inoculation fell into disrepute and was finally forbidden by law (in 1840, in England). Like its successor and superior, inoculation of cow-pox (vaccination), the practice of inoculation of small-pox met with strenuous contemporary opposition, but the esteem in which it was held by the most eminent physicians and scientific men of the time is sufficient evidence of its value. " It 80 THE "STRUGGLE FOR EXISTENCE" AND DISEASE cannot be, likewise it ought not to be, concealed that some of the inoculated have died under this process even under the care of very able and experienced practitioners. But this number is so small that when compared with the mortality attending the natural smallpox it is reduced almost to a cypher." (Dimsdale, " The Present Method of Inoculating for the Smallpox," etc., London, 1767). Inoculation for small-pox will always remain for the student of hygiene one of the most interesting episodes in the development of sanitary science, 1 for it illustrates in the clearest manner some of the fundamental phenomena of infection, susceptibility, vital resistance and immunity — and these are among the principal problems of hygiology. § 10. — Vaccination Vaccination (Vacca, cow) is simply a modification of inoculation in which "matter " of cow-pox taken originally from the cow is substituted for " matter " of small-pox taken from man. It is immaterial for our present purpose whether cow-pox is or is not small-pox in the cow. The important fact is that inoculation of the matter of cow-pox into the body of human subjects is believed by those most competent to pronounce an opinion to prevent or weaken the virulence of small-pox in such subjects. Experts are unanimous in this opinion, and the methods and results of vaccination — the immortal discovery of Jenner in 1796 — are too familiar to require comment. By its universal application small-pox, as experience shows, can be not only held in check but virtually exterminated. In its infancy vaccination, like inoculation, had to en- counter strong opposition based upon ignorance and a natural dread. " Discoveries in physic, as in every other 1 Jonathan Edwards, the famous New England theologian, was installed as President of Princeton College on February 16, 1758, when small-pox was prevailing in the neighborhood. As an act of precaution he was inoculated, although after some hesitation and while he was in poor physical condition, and died thirty-four days after his inauguration. "VACCINATION" AGAINST SMALL-POX 8 1 science, are in their infancy liable to censure and opposi- tion ; and as the present system of inoculation is of so extraordinary a kind, it would not be strange if a greater portion of both than usual should fall to its share." (Dimsdale, /. c, 1767.) The remarkable fact is that long after its success has been abundantly demonstrated, and after its period of " infancy " may be regarded as having been long since passed, the practice of vaccination should still be not only rejected but also violently attacked by some persons of intelligence. The fundamental reason for this paradoxical state of things is, doubtless, that assigned above by Baron Dimsdale, namely, the "extraordinary " character of a treatment which consists in " inoculation " of any kind. Persons who of their own motion or on the advice of their physicians will cheerfully and even eagerly swallow " medi- cines," often of a poisonous character, the very names of which are unknown to them, will sometimes refuse to obey their medical advisers when these recommend vaccination, — the former custom being " ordinary " and hoary with age, the latter still comparatively novel and " extraordinary." The precise mechanism of that immunity which is the most remarkable and most valuable sequel of inoculation (or vaccination) is still a mystery. Some light, however, has been shed upon the problem by the discoveries of Pasteur, Metschnikoff and Behring, and their successors, to a consideration of which we may now turn. 1 {Cf. p. 318.) § 11. — Pasteur and Attenuation While germs or microbes characteristic of small-pox or of cow-pox have never yet been satisfactorily isolated, analogy compels us for the present to assume their exist- ence. A consideration of the corollaries resulting from the application of the germ theory to these long-known and 1 For an excellent short modern treatise, see " Vaccination," by S. M. Copeman (Macmillan), 1899. 82 THE "STRUGGLE FOR EXISTENCE" AND DISEASE world-famous diseases led Pasteur, in 1877, not indeed to a solution of the problem of immunity, but to an important extension of the art of vaccination, and new and inter- esting examples of the immunity-phenomenon. Pasteur reasoned that, if an infectious disease be really a struggle for supremacy between man and microbe, it is probable that in vaccination for small-pox the struggle is less severe for the patient because the germs of small-pox have some- how been weakened or enfeebled by their residence in the cow. If this hypothesis were correct, he might hope to lessen the virulence of any microbe by subjecting it to an unfavorable environment or treatment. Heat, cold, dilu- tion, starvation, overfeeding, etc., suggest themselves as possible agents for weakening virulence; and by experi- ment Pasteur actually produced enfeebled or " attenuated " cultures of anthrax, chicken cholera, etc., with which he was able successfully to " vaccinate " (if the term may still be used) various animals, rendering them more or less immune to the diseases respectively investigated. In a dramatic public demonstration, in 1880, Pasteur proved conclusively the practicability of his method, which, since that time, has passed into common use in France for the vaccination of domestic animals. 1 (Cf. pp. 321-324.) As a result of Pasteur's labors, fresh examples of immu- nity were provided, and the practicability of its artificial pro- duction was strongly emphasized ; but the basis of immunity or the physiological mechanics by which it comes to pass and persists remained as great a mystery as ever. § 12. — Metschnikoff and Phagocytosis A highly ingenious theory of immunity was suggested in 1882 by E. Metschnikoff, who, starting with the well- known fact that the white blood-cells are eating-cells (or 1 See " Louis Pasteur : His Life and Labors " (Radot), New York, Apple- ton, 1885, pp. 220-246. THE STRUGGLE OF MAN WITH MICROBE 83 phagocytes) and readily devour yeast-cells, bacteria-cells, etc., made elaborate and important investigations tending to show that, in the struggle between man and microbe which may be said to constitute the essence of an infec- tious disease, the battle is really between the white blood- cells and the microbes, after the latter have somehow secured entrance into the body proper, and especially into the blood-vessels. Metschnikoff's theory of immunity is therefore known as the theory of phagocytosis. It has the merits of simplicity and picturesqueness ; but, while doubtless containing much that is true, it fails at one of the most important points, namely, in explaining the persistence of immunity long after the disease is over except indeed on the somewhat too anthropomorphic theory that the pha- gocytes have become "trained" or "educated." It fails, also, to account satisfactorily for some of the remarkable phenomena afforded by blood-serum experiments, such as those now to be described. § 13. — Behring and Antitoxic Serums In 1892 an entirely new line of experiment was opened up by Behring and Kitasato in their work on diph- theria. It was discovered by them that the serum of an animal which had been made immune to the toxin of diph- theria was able, even in a test-tube, to neutralize or impair the virulence of such a toxin, and further that the serum of a non-immune animal was not able to do this. Clearly, then, substances exist in the serum of an immune animal which were not there before the process of immunization, and our present theory of immunity rests upon this fact. The process of immunization according to the serum theory may be described as follows : the microbe (or its toxin) irritates the cells of its host ; these produce defensive sub- stances or antidotes (antitoxins), which tend to neutralize the poison, or to inhibit the activity, of the microbe, or both. 84 THE "STRUGGLE FOR EXISTENCE" AND DISEASE If we assume victory for the cells, we have temporary im- munity or convalescence. Victory for the microbe means continued disease or death. If we may assume that the cells of the body continue to secrete more or less of the defensive substances, or that they remain for a long time peculiarly sensitive to even minute doses of the toxin in question, we can understand the persistence of more or less immunity. But these assumptions, while plausible and perhaps reasonable, are purely hypothetical. If we assume, as we may if we like, that the phagocytes of Metschnikoff are the principal productive sources of antitoxic substances, we have a certain harmony between the two rival theories which is, to say the least, conceivable. Much, however, remains to be done before any theory of immunity can be received as more than very imperfectly explaining all of the facts. 1 § 14. — Serum as Cure and Serum as Prevention The practical outcome of Behring's work has been of immense importance, especially in the cure and prevention of diphtheria. Patients suffering from this disease, and persons exposed or likely to be exposed to it, may and do have their own antitoxic serum reenforced by the antitoxic serum of the horse or other immune animal and thus are materially aided in their battle with the microbes. The process is simple. Microbes of diphtheria are cultivated in a richly nutrient liquid which gradually becomes charged with their toxin. The liquid is filtered, and portions of the toxin-bearing filtrate are subcutaneously injected into horses, beginning with small doses and continuing until the animal is immune to large doses. Blood is then drawn from the immune horse, and the serum from this blood is 1 For further remarks on Vital Resistance and Immunity, see Chapter V, § 6, and Chapter XIII. REVIEW OF THE ZYMOTOXIC THEORY 85 found to contain antitoxin in abundance. This serum is carefully filtered and then used subcutaneously as a reen- forcing remedy for persons actually ill with diphtheria, or as a preventive medicine by those who either may be or may have been " exposed " to it. The results of the serum treatment have everywhere been most significant and encouraging. § 15. — Recapitulation This brief statement of our present attitude in respect to infectious disease must suffice for the student of sanitary science. Those who desire to go further along these lines should consult the numerous excellent manuals of bacteri- ology, in which they will find a rich store of materials to draw upon. It is enough for the student of sanitary science to know that infectious diseases are now believed never to arise spontaneously or de novo, but only more or less directly from antecedent cases of the same disease. It is believed that in every instance there must be an actual invasion of, or at least contact with, the suscepti- ble patient by the micro-organism of the disease in ques- tion. Once inside or upon the patient, the micro-organisms may grow and multiply, producing at the same time their own peculiar toxin or toxins, precisely as yeast, whether in wine or beer or other fruit juices, produces alcohol as one outcome of its peculiar vital activity. The illness of the patient is believed to be due to the effect upon his body of these specific poisons, by which he may die, or to which he may become habituated. In the latter case he is said to be immune, very much as the smoker becomes immune to considerable doses of tobacco, or the arsenic eaters of Styria to heavy doses of arsenic, or opium eaters to opium. The physiological mechanism of immunity is still to a great extent a mystery, but one feature of it appears to be a cellular reaction to the foreign toxin, accompanied by the production of antidotal substances (antitoxins) capable of 86 THE "STRUGGLE FOR EXISTENCE" AND DISEASE neutralizing the microbic poisons (toxins). Whether the cells once affected may be said to have become " habitu- ated " to the poison, and if so what, precisely, such " habituation " means, is less clear, and further investiga- tions are required to elucidate this part of the problem. Meantime the practical value of the work already done is very great, and the antitoxic serum for diphtheria has become one of the most important weapons of the physi- cian and the sanitarian. 1 1 The author is indebted to Dr. J. H. McCollom, Instructor in Contagious Diseases in Harvard University, and Resident Physician, South Department (Contagious Diseases), Boston City Hospital, for the following facts: — Before the advent of antitoxin the fatality in cases of diphtheria (in hos- pitals) varied from 30 to 50 per cent. In 11,598 cases in the Asylums' Board Hospitals, London, without antitoxin, it was 30.3 per cent. In the same hospitals, with antitoxin? it has been 18.4 per cent. In the Boston City Hos- pital, without antitoxin, the recent fatality was 46 per cent; with antitoxin, it has been 12.9 per cent. Bayeux, in his work on diphtheria, gives 55 per cent without, and 16 per cent with, antitoxin, the latter figure being based on an analysis of more than 200,000 cases. Bayeux adds that not a single death has been clearly demonstrated to have been due to the use of the serum. Other statistics may be found in Quar. Pub. American Statistical Assoc, VII, 53 (June, 1901), and in 32a 1 Ann. Rep. State Board of Health of Massa- chusetts, for 1900, p. 768. PART II INFECTION AND CONTAGION: THEIR DISSEMINATION AND CONTROL CHAPTER V ON INFECTION AND CONTAGION I THE PATHS AND PORTALS BY WHICH THEY ENTER THE BODY J THE RESISTANCE WHICH THE BODY OFFERS J THE VEHICLES BY WHICH THEY ARE CONVEYED ; AND THE PLACES OF THEIR ORIGIN. ANIMALS AND THEIR EXCRETA AS SOURCES AND PRIME MOVERS OF INFECTION " Fur die Verbreitungsweise der Infectionskrankheiten kommen zunachst in Betracht die Infectionsquellen, die Transportwege, welche von dort zum Menschen fiihren, und die Invasionsstatten, an welchen das Eindringen der Infectionserreger in den gesunden Korper erfolgt. Sodann haben wir der individuellen Disposition und der Immunitat besondere Beachtung zu schenken, da diese Momente die Verbrei- tungsweise mancher Infectionskrankheiten in hohem Grade beeinflus- sen." — Flugge. " Exact scientific knowledge of the contagia and of their respective modes of operation is of supreme importance to the prevention of disease. With even such knowledge of them as already exists diseases which have in past times been most murderous .... can, if the knowledge be duly applied, be kept in subjection." — Simon. § i. — Infection, Infectious Substances and Infectious Diseases In order that apple juice shall be fermented by yeast micro-organisms must somehow find access to it. But the normal apple is protected from the invasion of yeast both by its skin — a mechanical or structural defence — and probably also by specific properties of its living cells, which properties, though they are not understood, are recognized and described by the term "vital resistance." The skin of the apple must be broken and vital resistance overcome 89 90 ON INFECTION AND CONTAGION before yeast can make its way into either juices or tissues, successfully " infecting " them and producing those changes which we call fermentation. It may even be said that the apple is " hermetically sealed " by its skin, for no sound apple can be infected or fermented by yeast unless its body has been penetrated either by living yeast cells or else, what is yet an open question, by soluble and diffusi- ble products of yeast. The word " infection " (from in and facer e) signifies " entrance " or, literally, " making into," and in sanitary science it means in the first place, a process, namely, the entrance into a living body, whether plant or animal, of something capable of producing disease. Contagion, as will be explained presently, is only a special kind of infec- tion. The words "infection" and " contagion " are also used, in the second place, in another sense, substantively, — "the infection," " the contagion," — to represent the infec- tious or contagious material itself. From what has been said in the preceding chapters it is plain that infection of the human body is usually its invasion by parasitic micro- organisms, each specific invasion constituting a specific infection ; and the " infectious diseases " are those which are produced by such invasions. The term " communica- ble " is also much used for this group of diseases. In practice the word "infection," when used for infectious materials, is usually applied to living materies morbi capa- ble of growth and multiplication in the body of the infected plant or animal and of transfer from one victim to another. Etymologically speaking, to be sure, it might be applied also to inorganic matters such as metallic poisons, — lead, copper, arsenic, etc., — or to organic but lifeless poisons, — such as the venom of serpents, the vegetable alkaloids, etc., — introduced in any way into the living organism ; but as these are doubtless also communicable (though rarely communicated), either term may be used at will, both being clearly inferior in descriptive accuracy to the term "zy- DEFINITIONS 91 motic," which, after all, is probably the most correct and comprehensive name for those diseases which are essen. tially attacks upon the plant or animal body by living fer- ments. That these ferments happen also to be more or less readily " communicable " is an incident only and not their principal characteristic; and that they are "infectious," or capable of entering the body, is a property which they share with diseases caused by other environmental agen- cies, such as lightning, arsenic and toadstools mistaken for mushrooms. § 2. — The Skin and Epithelia as Structural Defences of the Living Body against the Invasions of Disease As the normal apple is protected by its covering or skin, so the normal living body is protected by its cover- ings — skin and epithelia — from the invasion of parasitic or fermentative micro-organisms or their products. It is perhaps too much to say that the living body is hermetically sealed, and yet modern physiology teaches that one of the principal offices of the skin is protection against forces or substances acting from without, and that the cells of the more delicate epithelia covering the lung surfaces and the alimentary and genito-urinary tracts have as one of their specific duties a certain discriminating authority over the matters likely to pass through or to be absorbed by them. In somewhat more than a metaphorical sense, therefore, it may be safe to say that the living animal body is her- metically sealed against the invasion of matters proceed- ing from the environment. The phrase, once much used, which referred to any rupture of this seal as a " solution of continuity " undoubtedly referred to the same idea, and marks the recognition of the essential integrity of the body surfaces as one condition of health. In order that any germ, whether parasitic or not, shall find entrance into the living body, it must be able some- 92 ON INFECTION AND CONTAGION how to pass through the ordinary defences. In the case of the skin it would appear that an actual rupture must take place, as happens, for example, in a puncture, incision, bruise or other mechanical injury. In the case of the epithelia, it may be that a similar passage by force is neces- sary, or it may be that the living cells which here line the surface externally are, so to speak, off their guard or for the time being actually facilitate an invasion which, from their delicacy, is here more easily effected. At any rate, it is easy to see that for the actual entrance of micro- organisms into the body proper an unusual and direct passage must somehow be provided. As to the absorp- tion of the toxic products of germ life we shall have some- thing to say in § 5. It should not be forgotten that by " the body proper " is meant that portion of it enclosed within the skin and epithelia; the cavities of the alimentary canal and the genito-urinary tracts not being included, inasmuch as they are really portions of the environment merely passing through or dipping into the body-mass. § 3. — Infection by Way of the Skin. Invasion by Force The processes of infection by way of the alimentary canal and the genito-urinary tract, to be described in § 5, are typi- cal of a large class of the more obscure infectious diseases. There is, however, another and commoner path by which micro-organisms obtain entrance into the body proper, and that is directly through the skin, the diseases to which they give rise being known as "wound" diseases. Many of these are familiar, as, for example, the results of simple punctures made by small foreign bodies such as pins, needles, " slivers " and the like. When these carry in with them micro-organisms capable of setting up fermentation or inflammation, the infection thus produced may be either local or general : in the former case leading to the condi- SKIN AND EPITHELIA AS PORTALS OF INFECTION 93 tions familiar in such unimportant local wounds as those mentioned ; in the latter to septicaemia, or dangerous blood poisoning, a kind of fermentation of the whole body. Occa- sionally it happens that a wound made by a sliver or some other ordinarily insignificant object, such as a needle or a bee sting, is followed not merely by the usual local inflam- mation, but by a far more serious and extensive injury and even by speedy death. It is supposed that in these cases either the infection was of an unusual and severe type — by which is meant that the micro-organisms were unusually abundant or of some unusually virulent species- 1 - or else that the vital resistance of the cells and tissues of the victim happened to be poor in kind or at a low ebb, so that even ordinary micro-organisms met with specially favorable conditions. In a word, either the infection was unusually powerful or the patient was unusually susceptible. It is, of course, possible to conceive of a third condition resulting from an unfortunate coincidence or combination of the other two. § 4. — Wounds and the Diseases of Wounds The punctures and other simple infections by way of the skin just described belong in the same class with more serious interruptions of continuity such as gun-shot wounds, compound fractures, abrasions and the like, among which must be classified as of the highest practical im- portance surgical operations such as excisions of tumors, amputations, the tying of arteries, etc. In these cases the bullet, the surgeon's or dissector's knife, or other foreign body of relatively large size, may readily be a vehicle for the germs of infectious disease. It has already been pointed out how the classical inductions of Lister and his application of the germ theory and its corollaries to this class of diseases has led to results of the first importance in this direction, namely, to sanitary or aseptic surgery. (See p. 45.) 94 ON INFECTION AND CONTAGION There is one disease of wounds particularly interesting, for various reasons, to the sanitarian as well as to the sur- geon, namely, tetanus or "lock-jaw." It had long been known from observation and experience that certain punc- tures or incisions, especially those made by the entrance or laceration effected by dirty foreign bodies, were not infre- quently followed by a peculiar condition of the patient in which tetanic muscular spasms were a prominent feature, when, in 1884, Neisser isolated from garden soil a bacillus capable on inoculation into mice and rabbits of producing a similar disease. Further investigations have confirmed the discovery, and the natural history of the Bacillus tetani is now well known. It is frequently found in the earth and it is widely distributed in nature. It is anaerobic, i.e., it thrives best in the complete absence of oxygen. Culti- vated in bouillon, it produces a powerful poison (toxin) which appears to realize the early speculations of Dr. Farr, 1 and which, even in the absence of all living bacteria, is capable of producing typical tetanic convulsions. A sub- stance apparently identical with it has been separated from the muscles of patients dead of tetanus, and this substance, when injected into the lower animals, produces in them tetanic spasms. It may be added that an antitoxin capa- ble of neutralizing the toxin of tetanus has more recently also been prepared and used. The importance of the bites and stings or other punc- tures of the skin by insects, which has long been recog- nized theoretically, has recently received fresh emphasis and attention, owing to the results of investigations upon the hitherto obscure but widespread disease known as malaria. It is now believed that the female of a species of mosquito is the principal vehicle of this disease ; that the mosquito becomes itself inoculated by drawing the blood of malarial human subjects in whom the germ of malaria exists, often in the red blood-cells ; that in the mosquito the malarial 1 " Vital Statistics," I.e., pp. 244-245. Fig. 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. Conju- gation of 9 with one of the vibratile arms of gb. 11. Malaria germ resulting from such conjugation in stomach of mosquito. 12-16. Multiplication (encyst- ment and sporulation) of the malaria germ in the body of the mosquito, with production of many forms like 1 (cycle completed). 17. Female malarial mos- quito (Anopheles claviger) ; head of male below. 19-20. Mosquito larva and pupa. 21. Stomach of mosquito, showing tumors produced by 16. 22. Cross- section 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. MOSQUITOES, MALARIA, YELLOW FEVER 95 germ develops ; and that by the mosquito it is injected with the saliva as an inoculation into fresh victims during the bite or sucking of the animal. Dog-bite and accom- panying hydrophobic inoculations also plainly belong in this class of wound diseases. The researches of Laveran, Manson, Ross, Celli and others upon malaria, and mosquitoes as hosts of the malaria parasite, form one of the most brilliant and instructive chapters in the history of sanitary science and experi- mental medicine. The parasite, which infests the red blood-corpuscles of its victim, had been recognized for several years, but nothing whatever was known of its life outside the animal body or the method of its distribution until it was discovered that the female of at least one species of mosquito (Anopheles) is capable of acting as an effective vehicle of the micro-parasites (haematozoa). Further discoveries have shown that the Anopheles must itself become inoculated by sucking the blood of a malarial animal ; that the parasites undergo an important part of their development within the body of the mosquito (which is therefore a host as well as a vehicle of the microbes) ; and that they are conveyed to animals bitten by the mos- quito with the salivary poison injected during the bite. The mosquito, in short, is an intermediary host, precisely as is the hog in the life-cycle of Tcenia, the pork tape- worm. The practical importance of these discoveries is immense, for it has already been established by experi- ment that man may live in " malarious " districts with no risk of contracting malaria provided pains are taken to avoid absolutely all mosquito-bites ; and on the other hand, it has been shown that mosquitoes that have bitten mala- rial subjects may readily transmit the disease by their bites, and infect fresh victims even in regions hitherto abso- lutely free from malaria. More recently still evidence seemingly conclusive has been obtained — at great personal risk, and with admirable g6 ON INFECTION AND CONTAGION courage — by American investigators in Cuba that yellow fever is similarly transmissible by mosquitoes, and not readily, if at all, by infected bedding or other lifeless materials. Flies have of recent years come to be regarded as ready vehicles of infection, and especially of typhoid fever. Lime scattered over excrements in privies has been ob- served on the feet and legs of flies running over food set out for eating upon tables in the neighborhood, and if lime can be thus carried, there is no reason why microbes also may not be carried to food or drink. It is also prob- able that the bites of flies may convey infection, although this has not yet been established. It is believed, however, by experts that one of the principal sources of typhoid fever in army camps is the infection of food by flies acting as vehicles of the microbic infection. Those who would pursue these subjects further are re- ferred to the following works : Celli, " Malaria according to the New Researches " (English translation by Eyre and an Introduction by Dr. Patrick Manson), Longmans, Green & Co., 1900; Howard, L. O. " Mosquitoes : How they Live, How they carry Disease," etc., New York (McClure), 1901. § 5- — Infection by Way of the Alimentary Canal, Lungs and the Genito-urinary Tracts The alimentary canal being in free connection with the environment and really a portion of it, is naturally subject to invasion from various sources by various micro-organ- isms and similar extraneous matters ; and the same thing is true of lungs and genito-urinary tracts, though perhaps in less degree. The alimentary canal, moreover, is ordinarily well stocked with food materials for micro-organisms ; and although the gastric juice probably exerts an unfavorable influence upon them, it may be said that, on the whole, the warm and well-fed alimentary canal affords an excellent INFECTION IN DIPHTHERIA AND CHOLERA 97 breeding-ground for certain bacteria. But if bacteria mul- tiply enormously in the alimentary canal, they do so at the expense of materials found therein, and in the course of their multiplication must produce various substances of the nature either of by-products or excreta ; and some of these may conceivably be harmful either to the guardian epithelia lining the alimentary canal or to the tissues in general, if once they are absorbed and distributed by the circulation. Similarly, micro-organisms grow freely within the genital tracts, and feeding upon the exudations or secretions there found may multiply enormously, with the consequent pro- duction of deleterious substances which shall damage either the lining epithelia or, when absorbed, other tissues of the body, near or remote. Moreover, in both these cases the paralysis or destruction of the guardian epithelia may produce actual solution of continuity, which shall allow either the micro-organisms in question or their poi- sonous products to find ready entrance into the body proper. There is reason to believe that the bacillus of diphtheria, for example, works precisely in this way. Finding lodg- ment upon the tissues of the throat, it proceeds to grow and multiply upon the normal exudations and the food materials there present, and in the course of its vital activity pro- duces somehow some of that poisonous substance which is now well known as the " toxin " of diphtheria. This first paralyses or otherwise interferes with the normal activity of the cells lining the throat in its immediate vicinity, where- upon, these cells failing to do their duty, an abnormal exu- dation of lymph takes place, and this, coagulating, produces the well-known " white patches " so common in " the diph- theritic throat." At the same time a powerful poison, the toxin, is being absorbed into the general circulation, and causes those general or constitutional symptoms which are characteristic of the disease. In the case of Asiatic cholera, there appears to be first 98 ON INFECTION AND CONTAGION an invasion and then a genuine and extensive fermentation of the contents of the alimentary canal, with an enormous multiplication of the micro-organisms concerned, so that these can readily be detected in large numbers in the bowel discharges. At the same time the characteristic poison or toxin of Asiatic cholera is supposed to be liber- ated, and its absorption through the walls of the alimentary canal is supposed to give rise to constitutional symptoms characteristic of the disease and indicative of profound disturbance of the body proper, such as vomiting, fever, sweating and delirium. In these cases, as will be observed, it is not the germs themselves, at least in the first place, which penetrate into and ferment the body itself. It is rather by attacking the frontier, there and then setting up their own peculiar fermentations, and producing poisons which are easily absorbed, that these micro-organisms first do their harm and open the way for themselves or other germs to enter into the body proper. Nevertheless the process, even from the very start, is one of fermenta- tion, directly affecting either the body wall or materials, such as partially digested food or secretions, closely con- nected with and for the time being practically a part of it (Cf. § 3, p. 92.) § 6. — The Physiological Defences of the Living Body. Vital Resistance and Susceptibility once more The term "vital resistance " has been much used in the last few sections, coupled with the statement that its exact sig- nificance is unknown. It is unnecessary to argue again at this point that there is such a thing as vital resistance, or that it varies largely from time to time. The experience and observation of everyday life abundantly testify to these facts. Who has not witnessed, for example, that robust and abounding health which enables some persons to live happily and carelessly in poverty, filth, and squalor, while INFECTION THROUGH TOXIN-ABSORPTION 99 others, surrounded by every comfort and protection, perish on the least provocation ? Again, who has not, even in himself, known times when almost anything might be done with impunity, and other times when the least exposure or other unfavorable condition led to indisposition or illness ? Who has not remarked over and over again the immu- nity of youth, the fragility of age ? In no other way than by recognizing differences in resistance to unfavorable environments can these anomalies be explained, and the term " vital resistance " well sums up and describes facts established by the long and accumulated experience of the race. It describes the facts, but, as so often happens with terms applied to human experience, it does not explain them. Sanitary science, however, gladly accepting and using the terms " vital resistance " and " susceptibility," — the latter being the converse of the former, — seeks to go further and learn, if possible, the causes of these condi- tions, and the processes by which they are reached. It must be frankly admitted that thus far the search has not been wholly successful, and yet something has certainly been done, at least toward making things clearer and more comprehensible. (Cf. pp. 74-85.) It is easy to see that " vital resistance " must be largely constitutional. It must depend either upon the materials of which the body is built or on the way in which these are put together, or, more likely, upon both. In order to resist the attacks of micro-organisms upon epithelial sur- faces ; or to overcome them on their arrival if thrust in by force through the skin, as happens in wounds ; or in order to neutralize their poisons (toxins) if these succeed in break- ing down and passing through the epithelia or the skin, mechanical and chemical defences within the body — phys- iological defences — would seem to be most useful ; and it is therefore interesting to find, as we do, that the modern theories of "vital resistance" (which in its most perfect form is now called " immunity") proceed along these lines. IOO ON INFECTION AND CONTAGION A little reflection will show that micro-organisms on entering the body or any of its passages are immediately subjected to a peculiar environment, which for many species must be highly unfavorable. This may be said to be the simplest of the physiological defences. The first of these met with may be the gastric juice, which for many microbes is highly unfavorable on account of its acidity. The comparative immunity of plants to bacterial diseases and their relative susceptibility to the attacks of fungi has been accounted for in part on the ground of the greater acidity of their juices. Those microbes known as " disease germs," on the other hand, must be supposed to find the new conditions more or less favorable ; more if the patient is susceptible ; less if he is endowed with considerable vital resistance ; wholly unfavorable only if he is immune. Even milk, which is well known for its blandness and as a favorable culture medium for many bacteria, being literally crowded with certain species when it is stale, has been described as " germicidal," 1 so that the first and very likely the most important physiological defence of the liv- ing body may be the fact that merely as such it furnishes an unfavorable environment for many invading organisms. The bodies of micro-organisms perishing in the invaded territory, whether this be local or general, in the healthy animal soon disappear, and there is reason to believe that they are removed by the white corpuscles of the blood and the lymphatics, acting as scavengers. Whether these de- vouring cells (phagocytes) are soldiers as well as scaven- gers, whether or not they can kill as well as devour invading micro-organisms, is not wholly clear. The view that they can and do, and that acquired immunity depends largely on their training so that they shall do it successfully (Metschnikoff's theory of immunity by " phagocytosis "), while it has developed many interesting facts (as stated 1 " Ueber die Bakterienvernichtenden Eigenschaften der Milch," Baum- garten's Jahresbericht ueber Mikroorganismen, VI. 513, 529. INTERNAL DEFENCES AGAINST INFECTION IOI above), seems somewhat too picturesque and too an- thropomorphic. It is not much easier to understand with Behring and Roux how the cells of the tissues or the blood after one attack of an infectious disease, such as diphtheria, are so "affected" that they secrete regularly thereafter and in its absence a chemical antidote for the diphtheria toxin. Perhaps the truth is to be found in a combination of these various views. The physiological defences may very likely consist in (i) the fact that the living body merely as it stands offers to many micro-organisms an unfavorable en- vironment for their normal development ; (2) the fact that some microbes on entering are seized and devoured by phagocytes drawn to them by chemiotactic influences ; (3) the fact that over and above the general unfavorable- ness of environment, immune animals possess somehow, either naturally or acquired, the faculty of subjecting special invaders or their products (toxins) to the action of special chemical substances (antitoxins) which destroy their efficiency. It will be observed that in all these cases the defence consists essentially in a kind of internal or physiological disinfection, which whether real or not is conceivable enough. But besides this we have to recognize the .fact that the living cells of the epithelia appear to have a certain power of " selection," at present not understood, Doubtless this is no more mysterious than, for example, that power of selection which the absorbents appear to exercise, or that property of the cells of the stomach or intestine by virtue of which they are not digested by their own juices respectively. The fact, however, remains at present essen- tially unexplained. § 7. — The Precise Meaning of Contagion The terms " infection " and " contagion " as applied to processes rather than substances (for in the latter case 102 ON INFECTION AND CONTAGION they mean exactly the same thing) may now be further defined and explained. The former, strictly speaking, signifies "entrance," the latter "contact." Though often used as if synonymous, they are not best so used. Infection is the broader and larger term, and includes contagion. It signifies simply the entrance or " making into " the body of harmful material. This may be either living or lifeless, but the term is generally applied to the entrance or mak- ing in of living organisms by any method or avenue what- soever. Contagion, on the other hand, is only a particular kind of infection of living organisms or microbes in which the infecting substance is transferred from source to sub- ject by direct contact, as, for example, when the contagion or infection of small-pox is derived by the victim directly from contact with a preceding case. Infection is well illustrated by cases of typhoid fever or Asiatic cholera in which the bowel discharges of a person, A, find access to water or milk and are consumed with food or drink by another person, B. In this case B may never have seen, or heard of, or been anywhere near, A, and there may have been no contact whatever between them. In a word, con- tagion is direct, immediate — and generally personal — infection, while other forms of infection are more or less roundabout and indirect. Contagion operates, neverthe- less, in precisely the same way as infection. In all cases whether of infection or contagion there must be somehow a transfer of infectious material more or less directly from an antecedent or primary case as a cause, to a consequent or secondary case as an effect ; and it matters not, except as to details, whether the infectious material is derived immediately from the antecedent case by actual contact with it, or after the lapse of a long time and in obscure and roundabout ways. Both phenomena belong in the same category, though the more obvious is called "con- tagion" and the less obvious "infection." It would be better to drop altogether the term " contagion," and to INFECTION VS. CONTAGION 103 apply to all these cases the simple and accurate term " infection," * which, if we neglect the idea of entrance by force, has almost exactly the same significance as "inva- sion," and corresponds precisely to the popular term often applied to infectious disease, namely, an " attack." § 8. — Man and Other Animals the Principal Primary Sources of Infection We have now considered somewhat briefly the portals of entrance of infectious materials into the body proper, and have hinted at some of the vehicles of infection. Before dwelling long upon these it will be well to consider the original sources of infectious materials in the environment. Once we have determined the sources of infections, it will be comparatively easy to discover the avenues of communi- cation and the vehicles by which they travel. It was formerly supposed that the earth and various other non-living materials were prolific original sources of infec- tious disease, or in other words, that the germs of disease not only exist but thrive and multiply in the earth. It was thought, for example, and is still held by some, that the micro-organism of typhoid fever passes a portion of its life and undergoes a necessary portion of its development in the soil, especially in filthy soil, and similar ideas were held in regard to other infectious diseases. Doubtless the reason for this opinion was to be found in the fact that certain animal and vegetable parasites had been known for a long time to spend one portion of their lives in or upon some plant or animal other than, and often lower than, their most conspicuous host. This is true of the tapeworm, the Trichina, the blight of barberries, and many other para- 1 Much confusion in the use of these and related terms exists in the works of the earlier authors. Even Dr. Farr (I.e.) refers to " diseases propagated either by inoculation and contact (contagion) or by inhalation (infection)," and says " miasms produce diseases like ague, without being propagated by contagion." 104 ON INFECTION AND CONTAGION sites. The progress of inquiry, however, has not confirmed these ideas, except in special cases (such as that of tetanus y p. 94), for the ordinary infectious diseases. It has been said that some still hold to the idea in the case of typhoid fever; but the author believes, after a very considerable investigation of the question, and personal studies of epi- demics which he has had somewhat unusual opportuni- ties to witness, that this idea is not sound, and that every case of typhoid fever, at least in the latitude of New England, arises rather directly from an antecedent case, and in this way only. It is, of course, possible that in other latitudes, and under conditions particularly favora- ble, the typhoid bacillus may grow outside the human body. There is no question that under favorable condi- tions it can do this in laboratories ; but that it does so in nature in temperate climates, except under very unusual circumstances, does not seem to be indicated by the evi- dence at hand. It can unquestionably live for some time in nature, though apparently with diminishing virulence, and in diminishing numbers; but in northern latitudes and under ordinary conditions its prolonged survival, and especially its multiplication outside the body, must be doubted. A similar statement may be made in the case of many infectious diseases, and we may safely say that for the most part man and other animals are the original sources of infectious disease. But it should always be remem- bered that under tropical conditions, if only suitable food and moisture be present and other conditions favorable, the germs of infectious disease may live long and actually multiply outside the animal body. Since the above paragraphs were written the amazing revelations of the r61e played by mosquitoes in the convey- ance and the development of malaria have been made. From these it appears that here also a disease long associ- ated with swamps and mysterious " miasms " has its sources SOURCES AND PRIME-MOVERS OF INFECTION 105 only in animal bodies, for the malarial parasite comes from the bodies, of men and mosquitoes, which thus appear to be the only original sources of infection. § 9. — Man and Other Animals, and especially their Ex- creta, the Principal Primary Vehicles or Prime-movers of Infection If it be true that man and other animals are the principal original sources of infection, it must follow as a matter of course that their excreta are its principal original vehicles ; for the excreta represent the output of the organism, its contribution to the environment. Physiology teaches that the material output of the animal body consists of dis- charges from the alimentary and genito-urinary passages and from the skin, — the nose and lungs being regarded as branches of the alimentary apparatus, — and accord- ingly it is these discharges which must be the principal original vehicles of infectious disease from its place of origin to the environment. Diseases have, in the past, often been roughly classified according to their place of origin and the vehicles by which they are con- veyed. An important class of infectious maladies known as " diarrhceal " diseases is directly attributed to infections from the bowel discharges. Typhoid fever, Asiatic cholera, dysentery, diarrhoea, and cholera infantum are the most important members of this class. Of equal or even greater importance are those diseases known as "eruptive" dis- eases, which are readily scattered from seedings of the shed- off skin. In these cases, pustules form on the skin and, opening to the exterior, discharge their secretions there. To this class belong some of the worst diseases that afflict the human race, such as small-pox, typhus fever, scarlet fever, measles, chicken-pox and many more. Since the infectious material is in this case poured out upon the sur- face of the body, it is readily transferred by direct contact to the fingers, and thereby to the mouths or, when dried, 106 ON INFECTION AND CONTAGION by the wind, to the noses and lungs of other persons. Hence, the term " contagious " diseases, especially applied to this group. Again, a certain number of diseases affecting the mouth, throat, or lungs may be conveyed by means of the sputum or saliva thrown out of the mouth and eventually finding its way either when dried, pulver- ized and blown about by the wind, or through the agency of food contaminations, to other susceptible persons. In this group would naturally be found diphtheria and pul- monary tuberculosis. The other excreta, such as the urine and the breath, as well as the sweat, are not usually charged to the same extent with the carriage of disease. The expired air from the lungs, formerly so much dreaded by those who watched at the bedside, appears according to the careful investigations of bacteriologists to be the least dangerous of all the excreta, being practically germ-free. The rea- son for this is that the moist, spongy lungs act as an effi- cient filter, and not only refuse to yield up micro-organisms to the expired air, but even detain organisms arriving in the inspired air, so that the outgoing breath of a patient is from the bacteriological point of view actually purer than the inspired air. Recent researches, on the other hand, have shown that the urine may be a ready vehicle of the microbes of typhoid, and very likely of other, fevers. It is interesting to note, also, that the malarial parasite passes from mosquito to man with an excretion, the saliva. From man to mosquito it does not pass in this way, but rather as a contamination of stolen food, the sucked blood being itself infected. § 10. — Earth y Air, Water and Animals the Principal Secondary Vehicles of Infectious Disease But if the excreta are the principal original vehicles of infection, they are by no means the only vehicles, for they AIR, FOOD AND DRINK AS VEHICLES 107 may readily mingle with and transfer their burden of in- fection to almost any substance in the environment. From the skin the surrounding air may first become infected and then move on, laden with disease, so that disease — or rather its germs — may literally be borne on "the wings of the wind." Likewise, sputum from the mouth, or discharges from the bowels, may be impercepti- bly mingled with a stream, so that a cup of cold water — the time-honored symbol of purity and charity — may con- tain unseen and unsuspected the germs of deadly or dis- gusting diseases. Or, again, the earth impregnated with human excreta may be dried and pulverized, and, as dust infecting human throats, become the vehicle of diseases such as diphtheria or tuberculosis. Clearly, if animal life is the principal source of infection, and the excreta of ani- mals are its principal vehicles, these, being some solid, some liquid and some gaseous, are only too likely to find kindred substances in the environment with which they can mingle, and to which they can convey a portion at least of their burden of infection. We have already seen how insects may become the bearers of infection, and we may now turn, in the follow- ing chapters, to a detailed consideration of several other of the most important and most common vehicles of infec- tion, namely, dirt, dust, air, sewage, water, ice, milk, raw foods (such as oysters and salads) and the like, and the ways in which these can be protected or purified. CHAPTER VI ON DIRT AND DISEASE. THE LIVING EARTH. DIRT, DUST AND AIR AS VEHICLES OF INFECTION. FILTH, FILTH DIS- EASES AND THE PHILOSOPHY OF CLEANNESS " Uncleanness must ... be reckoned as the deadliest of our present removable causes of disease." — Sir John Simon. " Cleanliness covers the whole field of sanitary labor. It is the be- ginning and the end." — Dr. B. W. Richardson. The experience of the race has shown that one of the most effective vehicles of disease is dirt. The word " dirt " appears to be derived from an old Saxon word drit, mean- ing excrement ; but the modern form of the word " dirt " has taken on a more extended and less definite meaning. As ordinarily used it may be the synonym of dust, soil, filth or almost any form of uncleanness, whether such unclean- ness imply the presence of infection or only that of pollu- tion. Still it can hardly be denied that even at present the word "dirt" signifies something distinctly more filthy than do the words " earth," " soil " or " dust." It is easy to see in the origin of the word the reason for this, and after what has been said in the preceding chapters concerning the primary sources of infection and the efficiency of ex- crement as a vehicle, no surprise need be felt that dirt is regarded with suspicion by all intelligent and well- informed persons. § I . — Clean Earth and Infectious Dirt Unquestionably the general fear of dirt among the in- telligent is not in all cases discriminating. There may be, 108 DEFINITIONS IO9 and probably are, forms of dirt which carry with them very little of danger, and a certain recognition of this fact is shown in such expressions as " good clean earth." It appears to be true that while it is the earth that is most often associated with the idea of dirt, it is ordinarily only the surface of the earth which is thus looked upon with suspicion and aversion. One reason for this probably is that the surface or loamy layers of the soil are not infre- quently sticky and suggestive of organic matters, while the subsoil directly below the loam layer is generally more obviously mineral in its character and often clean, i.e. not sticky or " dirty." As a matter of fact the loamy layer so called is, in truth, richer in organic matters, and besides often containing innumerable earthworms is crowded with the bodies of micro-organisms. The earthworms by their ploughing actions, which Darwin has so admirably worked out, are constantly turning over the upper layers of the earth, carrying from the surface into the lower strata organic matters, and from below to the surface the more mineral subsoil. It follows, therefore, that not only is the surface of the earth contaminated by excrement of various kinds that falls upon it, but also, through the agency of earthworms, a considerable portion of the earth just below the surface, and especially, no doubt, the loamy layer already referred to. Accordingly, if we desire to define and classify the terms already used, we shall say that earth, broadly speaking and for the most part, is essentially mineral in character and clean in condition because free from any considerable amount of organic matter. It is also, therefore, ordinarily free from infection — uninfected as well as unpolluted. Soil, i.e. the surface layer of the earth, may be clean, and may be and ordinarily is fairly free from infectious materials, but inasmuch as it is exposed to contamination by dirt, i.e. excrement, and is being continually worked over by earthworms, it may be and usually is more or less 1 10 ON FILTH AND THE PHILOSOPHY OF CLEANNESS polluted or contaminated with organic matter. It may or may not be infected. Dirt in the original and most exact sense is simply excrement, but in the more ordinary use of the word is soil, i.e. the surface layer of the earth, which may or may not contain infectious materials. § 2. — The Living Earth It is one of the most marvellous revelations of bacteri- ology that the earth, long regarded as the type of lifeless- ness, is in fact, at least in its uppermost layers, teeming with life. Not only do many mammals, birds, reptiles, insects, and worms have their homes in the earth, but, as bacteri- ology teaches, also vast hosts of micro-organisms, more abundant by far than the grains of sand upon which they dwell. A single gram of garden soil may contain millions of micro-organisms, and much of the softness and sticki- ness of moist loam is probably due to the presence of such numbers of soft protoplasmic bodies. Thus it has come to pass that we are no longer at liberty to speak or think of the earth, at least in its upper layers, as dead and essentially mineral, but must regard it instead as highly organic and quivering with life. § 3. — Earth as a Vehicle of Disease. Tetanus or Lockjaw once More The earth is not only rich in germs, but may contain among these some that are pathogenic or disease-produc- ing. Reference has already been made to tetanus as caused by specific microbes found in the soil (pp. 94, 104), and these are especially interesting, inasmuch as they appear to lead regularly a saprophytic rather than a para- sitic life. In this respect we have reason to suppose that they (and a few others) differ from most pathogenic microbes, which fortunately do not, under ordinary con- THE LIVING EARTH III ditions, appear to thrive (though they may continue to live for a long time) outside the plant or animal body. § 4. — Dust and Disease Dust is pulverized soil or pulverized dirt, and only rarely pulverized and pure earth. It is therefore, as a rule, rich in bacteria, and may or may not contain infectious disease germs. Inasmuch as it is the surface of the earth which is ordinarily dried, pulverized and lifted into the air, it is easy to see that excrement of any kind, deposited upon the soil, sputum and other organic matters cast off by ani- mal bodies, — such as scales from the skin, bits of hair, dandruff and the like, — as well as the possible combina- tion of all these things with dirty water to make sewage, may when dried on the surface of the earth be also readily pulverized and lifted into the air as fine particles or motes of dust. At first sight, dust of this character might be supposed to be necessarily dangerous and even deadly, and there is very little doubt that infectious diseases are in fact frequently transmitted by dust which serves as a vehicle; but, on the other hand, it should not be for- gotten that there are certain compensating circumstances which tend to diminish the dangers of disease from this source. The unfavorable conditions to which micro-organ- isms are exposed in dust, namely, desiccation, possible ger- micidal action of light, unfavorable temperatures and the like, undoubtedly destroy many of them and weaken oth- ers, but, in spite of these various fortunate conditions, it still remains true that dust must always be regarded by the sanitarian as dangerous, not only because of the mechanical irritation of the delicate mucous membranes of the throat and other respiratory passages caused by the inorganic particles of which it is largely composed, but also because of the possibility of its containing virulent disease germs, such as those of tuberculosis or diphtheria 112 ON FILTH AND THE PHILOSOPHY OF CLEANNESS from the sputum of persons affected with these maladies ; as well as those of small-pox, scarlet fever, measles and the like, from the skin-scales of victims of these diseases ; and, to a less extent perhaps, the germs of typhoid fever and other diarrhceal diseases from the pulverized excreta of walking cases, or from night soil spread upon fields for manure and afterward dried and lifted into the air by- winds during the operations of hoeing, harrowing, plough- ing and the like. 1 §5. — The Atmosphere as a Vehicle of Disease ; Ancient and Modern Theories From the earliest times the atmosphere has been regarded with suspicion as a vehicle of disease. Miasms, pestilential vapors and various mysterious and unseen influences have been regarded as readily conveyed by the atmosphere, and obscure or occult effects not comprehended or else mis- understood have been attributed naturally enough to the omnipresent and always-moving atmosphere. It is one of the merits of the germ theory of infectious disease that it enables us to comprehend much more clearly than ever before the true nature of these supposed atmospheric influ- ences. From what has just been said in the last paragraph, it is easy to see that the atmosphere may under certain cir- cumstances be a ready carrier of infectious disease simply by serving as the vehicle for the floating organic matters and living particles which are lifted into it from the surface of the earth or from human bodies. Doubtless it is with these very much as it is with the birds of the air or the flying fish of the sea, which, caught up or springing from the earth or the sea, may for a longer or shorter time float, fly or swim in the atmosphere, but which after all belong 1 Those who wish to pursue this subject further may consult with advantage Tyndall's " Essays on the Floating Matter of the Air," New York (Appleton), and Prudden's " Dust and its Dangers," New York (Putnams). THE ATMOSPHERE AND DISEASE 113 to the earth and sooner or later return to it. It must not, however, be forgotten that the germs of the commoner con- tagious diseases, and especially of those known as " erup- tive," in which " peeling " of the skin occurs, may be and probably are often disseminated through the atmosphere, and that so much of truth existed in the primitive ideas of mankind. § 6. — Microbes of the Air The number of microbes in the atmosphere varies greatly. 1 In a dust-storm five feet above the surface of a macadamized street the author and one of his pupils, Mr. (now Dr.) John A. Rockwell, Jr., detected in ten litres of air two hundred thousand micro-organisms. Quiet air is usually relatively free from them (sewer air, for exam- ple, being often nearly or quite destitute of microbes), and the same is true of the atmosphere at high altitudes and in mid ocean. Even the expired air of the human lungs is quite free from germs, a fact doubtless due to the spongy and moist pulmonary surfaces which catch and detain in- coming microbes and a phenomenon of great interest and importance in the theory of infection. It is impossible to conceive of any other source or sources of infectious disease in the atmosphere than microbes." On the other hand, there is no difficulty in supposing that the ground air, rising and mingling with the ordinary atmos- phere, especially in periods of low barometer ; the gaseous exhalations of marshes, volcanoes, and the like ; the results 1 The presence of microbes in the air is easily demonstrated, and their number enumerated, by various methods described at length in works on bacteriology. One of the simplest methods is that devised by the author and Mr. (now Professor) G. R. Tucker. It consists in filtering a known volume of air through fine sugar or sand — the latter having been found by experience to be preferable — by means of an exhausted cylinder and a glass tube of special form, called an aerobioscope, capable of being converted at will into a " roll " tube. The micro-organisms are held back by the sand, and together with the latter are mixed with melted gelatin during the rolling process and afterwards incubated, cultivated, enumerated and studied. 1 114 ON FILTH AND THE PHILOSOPHY OF CLEANNESS of decomposition of dung-heaps, filth and other masses of decaying organic matter may, under certain circumstances, act as unfavorable environmental conditions and reduce the vital resistance to such a point that disease, which would otherwise have been absent, occurs. This simple view probably includes all or nearly all of the facts relat- ing to the atmosphere, strictly so called, as a source of disease, and probably suggests the true explanation of diseases supposed to be due to miasms, pestilential vapors, atmospheric and telluric influences, and the like. Even malaria, which has long been a puzzle to sanitarians, is apparently due not to any peculiar evil quality or disturb- ance of the atmosphere, such as the word implies, but rather to specific micro-organisms conveyed by the latter either directly as floating particles, or indirectly through insects or other living agents of transmission moving in or through the air (see pp. 94-96). Malaria has often been called paludistn or swamp fever ; but if the modern view is correct it is not swamp air, but swamp insects (mosquitoes), which under favorable circumstances transport the germs of paludism. § 7. — Filth Diseases. The Pythogenic Theory. Modem Views of Filth and Filth Diseases The principles which have been laid down in the pre- ceding chapters enable us to take up with regard to filth diseases a somewhat different view from that held in the third quarter of the nineteenth century. The term " filth diseases " was at that time used with the idea that filth might be not only a vehicle, but an actual breeder or gen- erator of infectious disease. This view even reached the dignity of a theory bearing a special name — the "pytho- genic " theory, — which is closely associated with the name of Murchison. According to Murchison, filth was danger- ous not merely because it was a vehicle of disease, or an THE "PYTHOGENIC" THEORY OF DISEASE 115 unfavorable condition, but also because it was a source of disease, the supposition being either that specific disease germs could be generated de novo from other germs in filth, under favorable circumstances, or that at least germs capable of producing disease found in filth the conditions for their more perfect development, some even requiring residence for a time in filth in order to reach their full maturity. In regard to typhoid fever, for example, it was held that the micro-organisms of the disease required a stay, longer or shorter, in the earth or heaps of filth, and only after such a period attained their natural and dan- gerous development. The older treatises on typhoid fever and the older teaching often referred to a residence in the earth as one phase in the ordinary development of the germs of typhoid fever. The pythogenic theory requires some consideration at this point, as it lies at the basis of much popular misconception of the origin of infectious disease and, by misleading, causes a neglect of the true sources of disease. It was first propounded by Murchison in a foot- note to a paper read before the Royal Medical and Chirurgical Society of London, April 27, 1858 {Med. Chirurg. Trans. 1858, p. 221): " In the course of this essay I shall bring forward what I consider positive proofs that this fever [typhoid] is produced by emanations from decaying organic matter, and I would therefore suggest for it the appellation of pythogenic fever — TrvOoyevrjs and yewcuo." Murchison's views were urged at great length and with much plausi- bility in the first edition of his work (1862) on continued fevers, in which occur statements like the following : "Pythogenic [typhoid] fever is often generated spontaneously by faecal fermentation 1 ' (p. 455). The doctrine was vigorously criticised and opposed by the "con- tagionists," especially by Dr. William Budd of Bristol, and in the second edition (1873) °f Murchison's "Continued Fevers" was con- siderably modified and restricted, although we find in that the follow- ing definition of pythogenic [typhoid] fever: "An endemic disease generated and propagated by certain forms of decomposing organic matter" (p. 417). And again : "It may be generated independently of a previous case by fermentation of faecal, and perhaps other, forms of organic matter. It may be communicated by the sick to persons in health, but even then the poison is not, like that of smallpox, given off Il6 ON FILTH AND THE PHILOSOPHY OF CLEANNESS from the body in a virulent form, but is developed by the decomposi- tion of the excreta after their discharge. Consequently an outbreak of enteric [typhoid] fever implies poisoning of air, water or other ingesta with decomposing excrement." In these statements it is easy to see that Murchison was a believer in the spontaneous generation of specific disease in or through filth, an idea unfortunately still widely prevalent, but wholly without foundation in fact. In regard to a closely related infectious disease typhus (jail fever, ship fever, spotted fever), which has often been attributed to filth as a source, whereas filth is probably only its efficient vehicle, Murchison went even further, asserting its spontaneous origin in such conditions as overcrowding and bad ventilation : " Typhus, the grand predisposing cause to which is destitution ; while the exciting cause or specific poison is generated by overcrowding of human beings with deficient ventilation" (Edin. Med. Journ., 1858, p. 322). The modern theories of filth and its dangers are very different from these. Filth is first and always a conven- ient vehicle of disease ; but as a rule, in temperate climates, it is probably nothing more than this unless it be also a de- pressing, or unfavorable, "predisposing" condition. The earlier view which saw in filth a necessary phase in the life-history of certain infectious micro-organisms is now abandoned, and it is to-day very doubtful whether the germs of most infectious diseases ordinarily find accumulations of filth suitable for their multiplication. There is no question that the micro-organisms of disease may under favorable conditions occur or survive for a long time in filth, and it is probable that under certain conditions of warmth, food- supply and the absence of enemies they may even multiply ; but it appears probable that such conditions do not often occur in nature, unless perhaps occasionally in tropical coun- tries. The most natural and the most favorable means for the conveyance of disease germs appears to be that which is quickest and most direct, namely, contagion, or the transfer directly from one individual to another without the inter- position of the earth, the atmosphere or other extraneous influences. Contrary to Murchison's view, the longer the journey, and the more the time spent in making the jour- FILTH AND FILTH DISEASES 117 ney, from patient to victim, the less is the likelihood of the successful transmission of the disease. The interposition of filth or earth or air or water doubtless tends in most cases to the diminution of danger, owing to the unfavorable conditions of one sort or another encountered by the germs en route. Filth is looked upon by the sanitarian of to-day, there- fore, as dangerous chiefly because it may contain the more or less attenuated germs of disease, and not so much as formerly because it may be a "breeding-place" for such germs. It is a vehicle rather than a source ; and when it is pulverized it may cause an atmosphere in its vicinity to become infected ; or when handled it may find its way to the mouth, or when occurring upon fruits, vegetables, in milk, in water or any other substances likely to enter the mouth without having first been sterilized, — and in all these cases it is obviously dangerous as a vehicle. With these views of filth and its sanitary significance the older notions of " filth-diseases " have faded away. Those diseases to-day are simply ordinary, zymotic (infec- tious) diseases in which the vehicle of the causative germs is filth of some sort. § 8. — The Philosophy of Cleanness From what has now been said, it is easy to perceive the modern philosophy of cleanness. Dirt is dangerous, not because it is " of the earth, earthy," but because it is too often " drit" or excrement; and the love of cleanness or the abhorrence of dirt, which is gradually becoming estab- lished in all highly civilized peoples, is doubtless a result- ant of the dearly bought experience of the race, which has shown that dirt is dangerous and therefore to be dreaded. Cleanness, or the absence of dirt, is not merely an aesthetic adornment, — though doubtless an acquired taste ; it is above all a sanitary safeguard, the importance of which Il8 ON FILTH AND THE PHILOSOPHY OF CLEANNESS has been learned by hard experience. In other words, to be clean is, in a measure, to be safe from infectious disease ; and cleanness applies not only to the person but extends also to the personal environment, and especially to the food supply, the water supply, the milk supply, etc. Probably, the greatest sanitary step ever taken by the race was the application of high temperatures to the prepa- ration of food, i.e. cookery. There is very little doubt that far more important than any increase in the digesti- bility of food effected by cookery is the destruction of parasites, visible and invisible, within it thus brought about. Charles Lamb was probably right in attributing the love of cookery to the improvement in the flavors of food which it occasions, as is described in his well-known version of the discovery in the case of roast pig ; and yet there is every reason to believe — as has only lately become recognized — that the sanitary improvement wrought by the discovery of cookery was even more important than either the gustatory or the nutritive improvement. It is difficult to see how infection could have been otherwise than very common and very disastrous before the invention of cook- ery, for even to this day uncooked food forms one of the principal vehicles for the conveyance of parasites and disease germs. § 9. — Personal versus Public Cleanness It follows as a matter of course that personal cleanness is more important than public cleanness. In other words, that the avoidance of personal filth is far more necessary than, for example, is cleanness of streets, dooryards, alleys and the like. And yet, as is pointed out and emphasized beyond (p. 221), public supplies are public dangers. If the public water supply, for example, be infected, no matter how scrupulously clean the residents of a city may be in respect to their persons, they will run very serious THE SANITARY SIGNIFICANCE OF COOKERY 119 risks of disease if they drink from it. The same thing may be said of the public milk supply; and nothing is more impressive to the practical sanitarian than to witness an epidemic of typhoid fever in a wealthy and well-cared- for quarter of a city, where the inhabitants are personally clean, the houses are unexceptionable, the plumbing per- fect, the drains in good condition, the tableware and linen spotless, and yet typhoid fever is present perhaps in nearly every family, because of a polluted and infected milk supply or water supply. It must never be forgotten that the sanitary chain is no stronger than its weakest part, and that, no matter how clean and wholesome all other conditions may be, if there is one point from which the germs of infectious disease may find admission into the body, danger may be imminent. Nothing is more instruc- tive than to discover cities or towns in which great com- plaint is made of filth in the streets, — from which, after all, comparatively little danger is likely to come, — while an impure water supply or milk supply is being used with absolute confidence, or blindness, or ignorance. § 10. — Public Drinking-cups and their Dangers It not infrequently happens that the same persons who complain loudly and rightly enough, perhaps, of dirty streets, and are quick to blame public officials for their laxity in this respect will, nevertheless, at fountains, in railway trains or in theatres, apply their own lips to public drink- ing-cups which a few minutes before have been touched by the lips of strangers, possibly suffering from infectious diseases, such as tuberculosis or diphtheria. It should require only a moment's consideration to show how great is the risk run under these circumstances, and how inconsistent is the criticism bestowed by one who thought- lessly takes these grave risks when he cries out at the relatively remote dangers of dirty streets. What has been 120 ON FILTH AND THE PHILOSOPHY OF CLEANNESS said about drinking-cups applies obviously to communion- cups, "roller" towels, razors in barber shops, unclean dishes, spoons, etc., and requires no further comment. The dangers of these things are too obvious to need emphasis. A sanitary fountain has been devised, and is in use in many places, to do away with the public drink- ing-cup, and in so far as it is successful in doing this, it deserves the warm commendation of sanitarians. The arrangement by which this is accomplished is very simple ; and for use in public places, schools, institutions and the like, it promises to be of great assistance. No cup what- ever is required, but any one who wishes simply leans over and drinks from a little fountain provided for the purpose. Every instant, of course, the water supply is changing, and if infectious micro-organisms should be for an instant deposited by A, they are necessarily the next instant washed away before B can come in contact with them. It has long been the custom in certain factories abun- dantly supplied with water, to keep rising, in the middle of a basin of convenient height, a small jet of water, from which the thirsty might drink. Small fountains of this kind can easily be arranged in many public places, doing away altogether with the common drinking-cup, which, wherever found, is a sanitary abomination. §n. — The Disposal of Dirt, Dust, Garbage and Refuse From the point of view of the sanitarian the disposal of garbage and refuse is largely a question of engineering. By " garbage " is usually meant the more solid organic wastes of the kitchen, the more liquid wastes being dis- charged through the sink-pipe into the sewer. By " refuse" is meant household wastes such as dirt, ashes, papers, boxes, dust, bottles and the like, which are only in part combustible. It is from the sanitary point of view de- sirable to get rid promptly and effectually of both garbage MUNICIPAL SANITATION 12 1 and refuse, for these may contain the germs of infectious disease, and their destruction or disinfection by fire — the quickest and most certain of all disinfectants — is highly desirable. What is not desirable is that garbage should be fed to cows used as sources of milk supply, not because of the dangers of infection, but because of the poor quality of milk likely to result. There is less objection, if any, to the disposal of garbage by feeding it to swine, or by carry- ing it to sea or by ploughing it into the living earth, which latter readily disposes of it as of stable manure. Various methods for the disposal of garbage and refuse are in use ; but while cremation, for the reasons given, is undoubtedly the most desirable, the sanitary aspects of the matter do not appear to be especially important so long as garbage and refuse are removed from dwellings or groups of dwell- ings, such as cities, and somehow effectively disposed of. Those who desire to enter further into this subject may be referred to Chapin's " Municipal Sanitation in the United States," Providence, R. I., 1901 ; to Goodrich's "Disposal of Town's Refuse," N. Y. (Wiley) ; London (P. S. King), 1 90 1 ; and to Baker's "Municipal Engineering and Sani- tation," N. Y. (Macmillan), 1902. § 12. — Cleanness, Asepsis and Antisepsis Inasmuch as dirt is richly laden with micro-organisms, the agents of fermentation, putrefaction and decay, it is plain that the absence of dirt, or cleanness, must go far to prevent these processes. It is clear, for example, that punctures of the skin made by instruments absolutely free from organisms cannot convey infection ; that the knife of the surgeon if absolutely clean cannot cause "dissecting wounds " ; that cookery of foods must tend to defer their decay: in short, that absolute cleanness is equivalent to asepsis, and partial cleanness is an antiseptic correspond- ing in efficiency to its extent. This is now so fully recog- nized that dirt is to-day regarded as the principal foe of 122 ON FILTH AND THE PHILOSOPHY OF CLEANNESS the surgeon; and probably the cleanest rooms that have ever been known either in modern times or in the past, are the operating rooms of the hospitals of to-day. In certain industrial pursuits experience is teaching a similar lesson. By drawing milk from healthy cows with extreme precautions as to cleanness, it is possible to have it keep sweet (if refrigerated) during the whole period of a trans-Atlantic voyage. Various other dairying processes are also favored, if not conditioned, by cleanness; can- ning and preserving are far more successfully carried out if done with scrupulous regard for cleanness; and it is no exaggeration to say that in all human affairs clean- ness — which means the exclusion or destruction of germ life — is the keynote of successful sanitation. CHAPTER VII ON SEWAGE AS A VEHICLE OF DISEASE. ITS PROPER DIS- POSAL AND PURIFICATION. THE NATURAL PURIFICATION OF SEWAGE BY FERMENTATION AND THE LIVING EARTH " If we neglect this subject, we cannot expect to do so with impu- nity." — Michael Faraday, on " The Filth of the Thames." London, 1854. " The sewer ... is, so to speak, the direct continuation of the . . . intestine." — William Budd, on "Typhoid Fever." London, 1873. "The bills of mortality are more obviously affected by drainage than by this or that method of practice." — Oliver Wendell Holmes, on "Border Lines of Knowledge," etc. Boston, 1862. § I . — The Disposal and Disinfection of Excreta Since there is reason to believe, as has been shown in Chapter V, that the excreta of man and other animals are the principal original vehicles of infection and contagion, one of the first problems of sanitation is the safe disposal and disinfection of excreta. Various devices for the dis- posal of the wastes of animal life have had their day, but only two need now be mentioned, viz., the " dry-earth " system and the "water-carriage," or "sewerage," system. The former was at one time in high repute, and in some cases, as in farm-houses, country-houses, and villages, is still useful, especially if water is scarce or difficult to get. It is open, however, to the grave sanitary objection that although dry earth deodorizes well, it does not necessarily disinfect; while on the practical side the system is much less convenient than disposal by water-carriage. The in- troduction of running water for other purposes, even into farm-houses and villages, has also greatly favored disposal 123 124 ON SEWAGE AND ITS PURIFICATION by sewerage ; so that the windmill and the cesspool have made unnecessary almost anywhere either the earth-closet or the privy. 1 In view of the now limited use of the dry- earth system we need not dwell upon it further. In the water-carriage (or sewerage) system, which is now so generally adopted and so familiar as to require no description the vehicle of infection is sewage. This sub- stance is of special and fundamental importance in sani- tary science, first, because of its character as a common carrier of excreta and a vehicle of infection; second, because of its ubiquity and abundance in modern life; and third, because it may contain not only the bowel discharges and urine of the diseased, but also the excreta from the mouth and the skin. In brief, sewage may be made up of all the original vehicles of disease, — the excreta from the skin; from the alimentary and pul- monary, and from the genito-urinary tracts ; and it is also subject to indirect infection from infected earth, air and water serving as secondary vehicles. The cleansing and disinfection of sewage is commonly described as its " purification," but before proceeding to consider this problem, one of the most pressing and one of the most difficult of the sanitary arts, we must inquire somewhat more closely concerning the nature of sewage, its origin and its fate. § 2. — Sewage : its Genesis and Composition The word "sewage" 2 signifies "drainage" and may be defined as the contents of drains ; but it must be distinctly 1 For an elaborate defence of the sanitary efficiency of the Dry-earth Sys- tem, see Buchanan, Twelfth Ann. Rep. Med. Off. Privy Council, 1869. Per contra, see Sinnhuber, Inaug. Diss. Konigsberg, under Esmarch. Baumgarten's fahresbericht, XII (1896), 844. 2 In common parlance the terms " sewage " and " sewerage " are often confounded. It is usual, however, as it is certainly preferable, to reserve the latter for the system of sewers, and to use always the word " sewage " for the liquid contents of sewers. SEWAGE VS. SEWERAGE 125 understood that the drains in this case shall be house drains and shall contain domestic drainage. The under-drains of a wet piece of uninhabited land, for example, contain drainage but no sewage, the idea of sewage being con- nected exclusively with the drainage of houses and human beings, or at least with the wastes of animal life. Sewage is composed ordinarily of the washings of sinks, the empty- ings of water-closets, the discharges from laundries, bake- shops, stables and similar places, together with the rain water from roofs and the washings of streets. It may also contain the refuse from slaughter-houses, pus and other substances from hospitals, the washings of markets — in fact, almost anything capable of carriage by water, and small enough to find entrance into sewers. The excreta of human beings, washings from the skin, sputum, bowel discharges, urine, — in short, all excreta excepting the breath, — may be present in sewage. Nevertheless, ordinary American sewage, on account of its vast dilution, is much less objectionable to look at than is commonly supposed and it often merely sug- gests in appearance dish-water or dilute milky liquids with some dirt in suspension. The average composition of the fresh domestic sewage of an American city (Law- rence, Mass.) for 1897 was, during the morning, when the sewage was relatively strong, as follows (parts per 100,000): — i< Albuminoid Ammonia M E 9 s X u Nitrogen as — ti °c3 ERIA Cubic n- RE u Total Soluble Insoluble Nitrates Nitrites Bact per Cen MET 3.19 1.26 .78 .48 13.36 .18 .Ol82 7-59 4,726,000 The sewage of European towns is usually much more concentrated than that of American cities, and is there- 126 ON SEWAGE AND ITS PURIFICATION fore darker in color, less watery or milky and more objectionable in appearance. § 3. — The Dangerous Elements and Properties of Sewage These consist chiefly in the disease-producing organisms which may be present. There is every reason to suppose that sewage free from such organisms might be swallowed without serious harm, and would be rather in the nature of a poor than a dangerous material. Inasmuch, however, as sewage contains or may contain the excreta of human beings or other animals, and inasmuch, further, as has been shown above, as it is by way of these excreta that infec- tion travels, sewage must always be regarded as dangerous, either to come into contact with, or to admit into the body through wounds, or in or upon food materials. There is reason to believe that the only really dangerous properties of sewage reside in the infectious elements referred to. The ordinary decomposition of sewage may indeed lead to the generation of objectionable gases, which shall tempo- rarily prejudice or damage the organism. But there is every reason to believe that the dangers of sewer gas have been much exaggerated, and that many cases of disease have been charged to sewer gas which were really due to the invasion of micro-organisms from other and very different sources. To the consideration of this question however, we shall return hereafter (Appendix, p. 347). § 4. — Importance of the Sanitary Disposal of Sewage Inasmuch as sewage may at any time contain any or all of the excretions of the animal body, and inasmuch further as these may contain actively infectious materials, the safe and proper disposal of sewage is one of the first necessi- ties of sanitary science and the public health. Among primitive and uncivilized peoples no special pains are taken for the disposal of sewage or the excreta of animals, but PRIMITIVE METHODS OF SEWAGE DISPOSAL 127 in civilized societies various and costly devices are em- ployed to this end. The most primitive method is that in which the wastes of life are simply deposited or thrown out upon the surface of the earth in the neighborhood of human habitations, and when the latter are widely separated little or no harm may result from this practice. When, for example, in country districts or elsewhere, the untidy housewife disposes of dish-water by simply throwing it from a window, no particular harm may result if the quan- tity thus disposed of is not too great, and the dousing of the soil below is not too frequent, especially if the soil be open, porous or sandy. We shall shortly see that in this case, and in the similar cases in which manure is applied to land in large quantities and in successive years, the organic wastes present are speedily mineralized or converted into inorganic matters, by the agency of bacteria residing in the soil in such overwhelming numbers as to form a density of population almost inconceivable, and entitling us to describe the surface layers of the earth as "the living earth." § 5. — Disposal of Sewage in Rivers Whenever a city or town introduces a system of sewers, it is easy and natural in many cases to dispose of the sew- age by simply letting it run from the principal sewer or sewers into a neighboring brook or river or other stream. It is easy, because the natural drainage is in the direction of the river, which is often little more than the principal natural drain of the neighborhood. It is natural, because the river being, as stated, the ordinary drain of the neigh- borhood, carries off not only the water which falls upon its watershed but also anything that will float upon or mingle with the water ; and in most cases even before it is proposed to introduce sewers, the stream has long been used as an easy means of ridding the neighborhood of 128 ON SEWAGE AND ITS PURIFICATION rubbish or wastes of various descriptions. It cannot be denied that, in case the amount of sewage to be got rid of is relatively small, and provided the stream is nowhere below used as a source of water supply, this practice may not necessarily be objectionable; but even in such cases it is generally unwise, because under slightly different condi- tions, such as growth of the population upon the water- shed, or unexpected drought, the presence of a relatively large amount of sewage may produce a nuisance, and prejudice the public health, finally transforming the stream from something capable of giving pleasure, into an open sewer shunned by all mankind. How, then, it will naturally be asked, has it happened that so many important cities and towns all over the world freely dispose of their sewage by simply turning it into the nearest watercourse ? The answer is easy. It is simply because until very lately engineers, chemists and sanitary experts, alike held as true a theory of the purification of watercourses which is now known to be false, or, at best, only a half truth. This was the famous theory of the " self- purification of streams," to a brief consideration of which we may now turn. § 6. — Theory of the Self -purification of Streams This theory was based upon the obvious fact that al- though a very large amount of sewage might be suddenly poured into a stream at a given point, so that at that point the pollution was conspicuous and self-evident, it was only necessary to follow the stream for a short distance to per- ceive that the water had distinctly improved in appearance. This result of mere inspection was strongly confirmed by the chemistry of the time, which proved by actual analysis that the organic matter in the water, and the results of decomposition, were decidedly less at the lower than the upper point. Naturally, only one conclusion could be THE "SELF-PURIFICATION" OF STREAMS 129 drawn from the premises. The stream had somehow puri- fied itself while flowing, and the corollary was deduced that " running water purifies itself." (Cf. p. 231.) The importance and far-reaching effects of this con- clusion can hardly be overestimated. Relying upon it, numerous cities and towns all over the world introduced water supplies derived from sewage-polluted streams, and infinite damage was done to the public health. The theory is now abandoned, or rather accepted only after so much modification that it is virtually new. There is, indeed, a considerable purification effected by streams, but it is mostly purification by dilution ; and, as we shall see in a later paragraph, distrust of this theory has produced pro- found changes in our points of view. The disposal of sewage in rivers is always to be deprecated unless the volume of sewage discharged is very small in proportion to the dry weather flowage of the stream in question. It is not to be tolerated if the river below is, at any point, however remote, used without purification as a source of water supply ; and it is often not desirable even with such purification. § 7. — Sewage Disposal in Lakes Some cities are so situated that it is convenient and natural for them to drain into bodies of fresh water, either lakes or ponds, in which there is little or no current such as always exists in a river. In these cases, the suc- cess of the practice, so far as the mere disposal of sewage goes, depends chiefly upon the proportion maintained be- tween the volume of sewage and the volume of the water into which it is discharged. This will be seen most clearly by simply considering the extremes, in which cases, for example, a large city empties its sewage into a small pond ; or, on the other hand, a small town pours its sewage into a large lake. In the former case, the results would be disastrous, the pond being very soon converted into a sew- 130 ON SEWAGE AND ITS PURIFICATION age pool. In the latter, no perceptible effect would be produced. Obviously, there must be a large class of cases, comprising cities and towns of moderate size located upon relatively large bodies of quiet water, which may drain with safety into lakes or ponds ; but it is equally clear that there is also another class of cases, comprising for the most part large cities, situated upon relatively small bodies of quiet water, which cannot drain into these without seriously prejudicing their purity and possibly producing a nuisance. Furthermore, the case is complicated seriously if either a city or a town draining into a lake or pond undertakes to derive its water supply from the same lake, or if any other city or town, no matter how remote, makes such use of the water. This aspect of the problem, however, need not detain us at this point but may be reserved for the con- sideration which it requires until a later chapter. It is enough in this connection to note that very many of the cities and towns of the United States do as a matter of fact dispose of their sewage by emptying it into lakes or ponds, and that, too, with entire success so far as the mere disposal of the sewage alone is concerned. Examples are the cities and towns bordering the Great Lakes, and in the list are some cities of large size such as Chicago, Mil- waukee, Duluth, Cleveland and Toronto. § 8. — Disposal in Harbors, Estuaries and the Sea Another class of cities and towns, and this includes some of the largest in the world, are so situated that their natural drainage is either directly into the sea, or into some tidal harbor or estuary. In these cases it is easy and natural to dispose of sewage by simply pouring it into the sea, harbor, or estuary at some convenient point or points ; and here, also, as in the preceding case, if the city or town is not too large in proportion to the volume of water at its doors, no harm comes from such disposal. There is, in this case, SEWAGE DISPOSAL IN LAKES AND THE SEA 131 the obvious advantage that such bodies of water are never used as sources of water supply, so that one serious ele- ment of difficulty which exists in the case of lakes and other bodies of fresh water may here be neglected. As a matter of fact, numerous cities and towns on our own coasts pour their sewage into salt or brackish waters, often with entire success and with the absence of all complaint. It is only, indeed, in very rare cases, that this system of disposal causes trouble, and in these instances the cities are usually situated not directly on the sea itself, but upon some narrow arm of the sea or some tidal river which virtually limits the size of the body of water into which the sewage is poured. Such a case is that of London, which is situated not upon the sea, but upon a tidal river, and even in the case of London the sources of complaint have been based more upon the alleged obstruction to navigation caused by deposits in the shallow river than upon sanitary grounds. No such complaints, at least of a serious character, have as yet arisen in the case of cities like New York, Philadelphia or Boston, or indeed, so far as the writer is aware, in any instance excepting that of London ; so that we may probably conclude that disposal in the sea or in its harbors or estuaries may safely be regarded as one of the most satisfactory methods of sewage disposal hitherto discovered or employed. § 9. — Principles involved in the Disposal of Sewage in Rivers, Lakes, Estuaries and the Sea In all these cases the fundamental principle of purifica- tion, and the basis of successful disposal, is simple dilution, by a relatively large volume of purer water. Other factors may or may not cooperate as, for example, in the case of a swiftly flowing river. The mere fact of removal some- times constitutes an important contribution to successful sewage disposal, the sewage being speedily carried away 132 ON SEWAGE AND ITS PURIFICATION to a point where its existence is of little consequence, as for example, may happen in an estuary or tidal river, the mere movement of the water constituting an efficient method of transportation of the sewage from a point where it would be objectionable to a point where its pres- ence is unobjectionable. But this is not all. Dilution is the fundamental phenomenon, and lies at the bottom of much of the purification which, undoubtedly, takes place in all these cases. Mere removal does not, in itself, contrib- ute to purification, while dilution certainly does do so. There are, however, other forces at work which contribute materially to purification by dilution, and these are best seen and studied in the case of the discharge of sewage into the relatively quiet waters of a lake, where they are not complicated or masked by currents, or by the flowing of a stream. Such instances are common and easily studied, and, as an example, we may take the case pre- sented by the sewage disposal of Burlington, Vt. (Cf. P- 234.) Burlington is a city of fifteen thousand inhabitants, situ- ated on Burlington Bay, a broad easterly expansion of Lake Champlain. The sewage of the city is collected into one large outfall sewer which empties near the southern extremity of the city directly upon the lake front into the waters of the lake. At this point Lake Champlain is so broad that the only currents perceptible are those produced by winds, and, accordingly, these move sometimes in one direction, sometimes in another, but as a rule are confined to the surface, so that, on the whole, there is very little motion of the lake water in any particular direction. The author has made repeated examinations of the sewage in the outfall sewer and of the mixed water and sewage at various points within one mile of the sewer outlet, and the results show that while the crude sewage is not materially different from that observed in most American cities, and contains in round numbers about one million of bacteria SEWAGE PURIFICATION BY DILUTION, ETC. 133 per cubic centimetre, the lake water even one hundred feet away shows already only perhaps a thousand, which num- ber rapidly declines as we recede from the sewer, until at a distance of a half mile and more it begins to be difficult to find any evidence of the presence of sewage, either by chemical or by bacteriological analyses. A little reflection will show that the mere dilution of the relatively small amount of sewage by the relatively enormous volume of the lake would alone account for most, if not all, of the facts in the case. But there is good reason to believe that other factors of purification exist and have their influence. In the first place, many of the sewage bacteria, and probably all of the most dangerous, are by preference thermophilous, or, so to speak, warm-blooded, having recently come from the bodies of warm-blooded animals in which they have existed and perhaps thriven. These, therefore, find the temperature of sewage hardly favorable to their continued existence or development, and when plunged into the still colder waters of the lake are subjected to conditions far less favorable. In the next place, in the bodies of their hosts these bacteria have found not only a favorable temperature, but also rich supplies of food. Once they begin to travel through soil pipes and sewers, their food becomes scarcer and less available, and when finally they mingle with the waters of the lake, which are relatively pure and destitute of organic matters, their pabulum must be distinctly scanty. At the same time, in sewage and in the lake, they are subject to the influence of gravity which tends to draw them down into the deeper, quieter layers and finally into the mud at the bottom, while predatory infusoria ranging through the water may devour them altogether. Lastly, if they tend to float or linger on the surface, they may there suffer from the germicidal action of the rays of light and perish. All of these unfavorable influences which accompany the ordinary process of dilution in lakes, rivers, estuaries 134 ON SEWAGE AND ITS PURIFICATION and the sea may be either hindered or exaggerated by movement of the water, such as occurs in a flowing stream, or in tides and other currents, and they, and all other con- ditions tending to the inhibition of the growth, or to the destruction altogether, of microbic life, may all be summed up in one phrase, namely, "unfavorable environment." There is reason to believe that the purification of sewage by dilution, in respect at least to its living, organic con- tents, is, as a matter of fact, considerable, though often incomplete, and that the forces enumerated and which we have described collectively as "unfavorable environment" play the principal part in whatever purification actually takes place. Inasmuch, however, as many micro-organisms are capable of successfully resisting for a long time the effects of an unfavorable environment, bacteria being in some cases especially resistant, it is easy to understand that the purification of sewage by dilution, even when accompanied by the factors mentioned, is often incomplete and never to be relied upon, except in the presence of sat- isfactory evidence. In the case of sewage disposal in salt water this is a refinement of small consequence, but in the case of fresh waters, such as lakes and rivers, which it may be desirable to use for public water supplies at points more or less remote from the place of disposal, the ques- tion assumes the highest possible importance, and to this aspect of the subject we shall return in Chapter IX. § 10. — Purification of Sewage by the Living Earth Reference has already been made above, in § 4, in some detail to the primitive method of sewage disposal in which the wastes of life are got rid of by simply throwing them upon the earth. In this case, and in the similar case in which manure is applied to land in large quantities and for many successive years, the organic wastes present are speedily mineralized, or converted into SEWAGE AND THE LIVING EARTH 135 inorganic matters by the agency of micro-organisms (bac- teria) which reside in the surface layers of the earth in astonishing numbers. The commonly received idea of the earth, that it is typically inorganic and lifeless, has been shown by modern researches to be singularly incorrect. Every one is aware that various living things, such as woodchucks, moles, snakes, and even certain birds, as well as numerous insects and innumerable plants, spend a part or the whole of their existence in the earth. And yet, when, in 1881, Darwin drew general attention to the enormous number of earth- worms living in the upper layers of the earth, his treatise occasioned widespread surprise. All these forms of life, however, are as nothing in comparison with the myriads of bacteria which have their home in the earth. A single grain of garden soil, for example, may contain as many as a hundred thousand of these microscopic organisms, and there is reason to believe that the soft, clammy feel of moist loam is in no small measure due to the presence of bacterial bodies. In many cases the inorganic grains which loam contains are mantled, as it were, by a jelly- like substance, probably produced by these organisms, and in which their bodies are embedded.. It is no exaggera- tion, therefore, at present, to speak of the surface layers of the earth, especially in fertile regions, as if they were alive, or of the upper layers of the earth itself as con- stituting a " living " rather than a lifeless earth. If now we consider what may take place when the organic wastes of life are thrown upon this porous, living earth, we may perhaps understand the remarkable process of purification which takes place. When, for example, the farmer periodically dresses his fields with manure consist- ing largely of the wastes of animal life, we need not be surprised if, after a time, these wastes seem to have dis- appeared, while the soil upon which they were placed has grown correspondingly soft and rich. Precisely as, under 136 ON SEWAGE AND ITS PURIFICATION similar circumstances, the earthworms which are present appear to flourish and multiply under the favorable condi- tions provided for them by the farmer, so, we have reason to believe, the infinitely smaller micro-organisms — which, like the earthworms, reside in the upper layers of the earth, — feed, flourish and multiply upon the food thus provided for them ; and exactly as the earthworms work over the materials upon which they feed, reducing them in chemical complexity, and turning organic into inorganic matters, so the myriads of micro-organisms which surround them on every hand do their appointed work, and min- eralize the organic wastes upon which they too feed and fatten. If what has just been said is true, it is easy to under- stand how it is that even repeated applications of large amounts of organic matters, such as stable manure, may be successfully made to a given area of land ; or how it hap- pens that the untidy housewife may, with comparative im- punity and for a long period, habitually throw from the window upon a limited piece of earth the organic wastes of the kitchen ; or, finally, the fact that some of the larg- est cities in the world, such as Berlin, successfully dispose of all their sewage by simply pouring it upon the land. There is every reason to believe that this method of sewage disposal, which is successfully in operation under either natural or artificial conditions all over the world, is, at the same time, one of the most primitive, one of the most practical, and one of the most perfect, systems hitherto employed by man. We may, therefore, in the next para- graphs, properly devote considerable attention to its theory and practice. By a curiously unfortunate use of words this process has come to be known by the altogether inadequate term "intermittent filtration." As we shall now see, intermittent filtration lies at the basis of all sewage disposal by irrigation and of all successful sewage- farming. LAND-DISPOSAL OF SEWAGE 137 § 11. — Intermittent Filtration In all cases of sewage disposal upon land, whether crops be grown upon the land or not, the fundamental processes at work are those involved in intermittent nitration, and this, as has been explained in the preceding paragraph, consists in biological and chemical treatment of, or reaction upon, sewage by the living earth. It has long been known that earth and soil are remark- ably effective in the purification of sewage. Everyday observation, such as that described in the preceding section in connection with the ordinary operations of agriculture, proves that land-disposal of organic wastes is perfectly natural and successful. The process, consisting as it does in a change of organic into inorganic matter, early attracted the attention of chemists, and inasmuch as the purification, chemically speaking, consists largely in oxidation of nitroge- nous bodies with conversion of the latter into nitrates, the essential phenomenon is often described as " nitrification." § 12. — English Experiments on Intermittent Filtration At first it was supposed that nitrification was due to the direct action of the oxygen of the air upon complex nitroge- nous bodies, but it was soon perceived that something more must be at work. It was evident, for instance, that stable manure exposed to an abundance of oxygen in the air re- mained unaffected, while if it were brought into contact with the soil in the ordinary process of agriculture, it speedily disappeared, giving rise to nitrates in abundance. Labora- tory experiments showed further that the nitrification could readily be set up by introducing earth into mixtures which it was desired to nitrify, so that it seemed perfectly clear that somehow the earth possessed a specific, nitrifying power. Some supposed that this was due to its porous character which might produce oxidation somewhat after the fashion of platinum sponge. 138 ON SEWAGE AND ITS PURIFICATION The first experiments on the disposal of sewage upon land or earth were laboratory experiments made by the Rivers Pollution Commissioners of Great Britain appointed in 1868, in connection with their investigations of the pollu- tion of rivers, and were most instructive. In these experi- ments, glass tubes, sixteen feet long and two inches in diameter, and glass cylinders, six feet long, and either ten and one-fourth or twelve inches in diameter, were filled with various kinds of soil. Each then received at the top (or in some cases at the bottom) known amounts of sewage which were discharged as effluent at the other end, and in the case of downward intermittent fil- tration were found to have been remarkably purified. A full report of these important investigations may be found in the First Report of the Rivers Pollution Commission appointed in 1868, published in 1870. (Mersey and Ribble Basins, Vol. I, pp. 60-70.) The facts developed by these experiments remained, however, largely unex- plained until a few years later when the investigations of other observers drew attention to the probable cooperation of micro-organisms in the processes of nitrification. More- over, the Commission's experiments were conducted on a laboratory scale, and were limited in number as well as in time. § 13. — The Problem Attacked in Massachusetts It remained for the State Board of Health of Massa- chusetts to take up the problem where the Commission had left it, and to make for the first time extensive and elaborate experiments upon a large scale with the aid of bacteriology as well as chemistry, upon the purification of sewage by land treatment or " intermittent filtration." In- asmuch as these investigations were the first to be made on a large scale and for a long time, and inasmuch as they have now become classical, we may describe EARLY INVESTIGATIONS IN ENGLAND 139 them, together with the conditions which led up to them, in some detail. 1 The state of Massachusetts, especially in its eastern portion, had become, by 1880, so thickly settled that the dis- posal of the sewage of the numerous cities and towns com- posing the metropolitan district having Boston as its centre was becoming a serious problem. Accordingly, in 1881, a Commission was appointed to consider and report upon the drainage of the Mystic and Charles River valleys. The report of these commissioners recommended a metro- politan district system which should preserve as far as practicable by general sewerage the purity of the water supplies of the cities included in this district. In 1884 the Massachusetts Drainage Commission was appointed, and in 1886 their report was published, giving a large amount of valuable information regarding sewage disposal theories and practices in England and on the Continent. Perhaps the most important work which they accomplished, how- ever, was their earnest recommendation that the common- wealth of Massachusetts should appoint a Commission or designate Guardians to conserve the purity of the inland waters of the state, such body to be provided with advisory rather than mandatory powers. " Let these guardians of inland waters be charged to acquaint them- selves with the actual condition of all waters within the state as respects their pollution or purity, and to inform themselves particularly as to the relation which that condition bears to the health and well-being of any part of the people of the commonwealth. Let them do away, as far as possible, with all remediable pollution, and use every means in their power to prevent further vitiation. Let them make it their business to advise and assist cities or towns desiring a supply of water or a system of sewerage. They shall put themselves at the disposal of manufac- turers and others using rivers, streams, or ponds, or in any way mis- 1 For an interesting and valuable historical statement of the rise and treat- ment of the drainage problem in a growing community, see Report of a Com- mission appointed to consider a General System of Drainage for the Valleys of Mystic, Blackstone, and Charles Rivers. Boston, 1886. 140 ON SEWAGE AND ITS PURIFICATION using them, to suggest the best means of minimizing the amount of dirt in their effluent, and to experiment upon methods of reducing or avoid- ing pollution. They shall warn the persistent violator of all reasonable regulation in the management of water, of the consequences of his acts. In a word, it shall be their especial function to guard the public interest and the public health in its relation with water, whether pure or defiled, with the ultimate hope, which must never be abandoned, that sooner or later ways may be found to redeem and preserve all the waters of the State. We propose to clothe the board with no other power than the power to examine, advise, and report, except in cases of violation of the statutes. Such cases, if persisted in after the notice, are to be referred to the attorney general for action. Other than this, its decisions must look for their sanction to their own intrinsic sense and soundness. Its last protest against wilful and obstinate defilement will be to the General Court. To that tribunal it shall report all the facts, leaving to its supreme discretion the final disposition of such offenders." 1 § 14. — Reorganization of the State Board of Health of Massachusetts The legislature of 1886 promptly adopted the recommen- dation of the Drainage Commission, and turned to the State Board of Health as the proper body to undertake the new and important functions which it was proposed to create. The Board was reconstituted and reorganized, and endowed not only with the usual powers and duties of a State Board of Health, but with entirely new and peculiar functions in regard to the water supplies and sewerage of the towns and cities of the commonwealth. The board was to become the expert sanitary adviser of the towns, and a fortiori of the legislature, in these particu- lars ; and it was to be liberally supported. As a special recognition of the new functions, Mr. Hiram F. Mills, of Lawrence, perhaps the most distinguished hydraulic engi- neer within the state, was made a member of the reorganized Board, and immediately took charge of the experiments upon intermittent nitration. 1 Massachusetts Drainage Commission Report (full reference given above), p. lxi. Boston, 1886. PROTECTION OF PURITY OF INLAND WATERS 141 The statute which provided the new functions for the Board was approved on June 9, 1886, and was entitled " An Act to protect the Purity of Inland Waters." In sub- stance, and to a large extent in form, it corresponds with one recommended by the Drainage Commission. It has proved to be one of the most novel and satisfactory enact- ments for the benefit of the public health ever undertaken in America. In one important respect the statute actually adopted differed from that recommended, namely, in pro- viding that the members of the Board should serve without pay. The special functions of the State Board of Health as laid down in this statue, concisely stated, were as fol- lows : — 1. To have the general care and oversight of all the inland waters of the commonwealth. 2. To recommend legislation and suitable plans for systems of main sewers for the state. 3. To cause examinations of the waters of ponds and streams to be made. 4. To recommend measures to prevent the pollution of waters. 5. To conduct experiments on the purification of drain- age. 6. To conduct experiments on the disposal of manu- facturing refuse. 7. To consult with and advise the authorities of cities and towns, or with others, with reference to water supply and drainage. 8. To consult with and advise manufacturers with refer- ence to the disposal of manufacturing refuse. 9. To bring to the notice of the attorney general all omissions to comply with existing laws. The act further provides that authorities of cities and towns, and all others intending to introduce systems of water supply or sewerage, shall submit to the Board out- lines of their proposed plans or schemes in relation to 142 ON SEWAGE AND ITS PURIFICATION these subjects ; and that manufacturers intending to en- gage in any business, drainage or refuse from which may tend to cause the pollution of any inland waters, shall also give notice to the Board of their intentions. The Board immediately proceeded to carry out the provisions of the act, and in its first report, dated January, 1887, it states in extenso precisely what it proposes to do if adequately supported, and concludes : — "In order to make the series of examinations above out- lined, including monthly analyses of all waters used for domestic supply in the state, and biological examinations of certain waters injuriously affected by animal life, to- gether with chemical analyses of other inland waters ; to conduct contemplated experiments upon the purification of sewage and refuse from industrial establishments ; to make the necessary investigations in order to advise cities, towns, corporations and individuals in regard to the best method of disposing of their sewage ; and to carry out the other provisions of Chapter 274, — the board estimates that the sum of #30,000 [for the first year] will be required." § 15. — The Lawrence Experiment Station of the State Board of Health of Massachusetts. The commonwealth cheerfully did its part, the legisla- ture granting the large sum asked for by the Board which thereupon proceeded to complete its organization for work along the lines indicated. It announced that it was ready to consult with and give advice to any Massachusetts city or town concerning its water supply or sewerage. At the same time it was distinctly held by the Board that, in order to give adequate and really expert advice, it must experi- ment and investigate. It was not to rest content with the scanty or imperfect knowledge of these subjects which was too often all that was available, or to accept without trial the methods or the results of scattered or local observers ; A SANITARY EXPERIMENT STATION 143 but, first, to investigate for itself the actual condition of the various water supplies of the state by all means in its power, whether engineering, chemical or biological; and, second, after having obtained all available information at home and abroad, to establish an experiment station, and make for itself investigations upon the long vexed ques- tions of the purification of sewage and drinking water. This station, the Lawrence Experiment Station, the first of the kind in America, if not in the world, was located in a building adapted for the purpose, which had been con- structed upon land on the left bank of the Merrimac River, belonging to the Essex Company and already used at an earlier date by Mr. Mills for experiments in hydraulics. § 16. — The Massachusetts Experiments at Lawrence The first problem attacked at the Lawrence Experiment Station was that of the best method for the disposal of sewage upon land. English and German experience had made it probable that much might be done in this direction in America ; but the knowledge available was very limited and of little or no practical value to American engineers, because the climates, soils, sewages, and civil and eco- nomic conditions of America are so different from those of Europe. Accordingly, in November, 1887, a series of careful experiments was begun, to test the purifying capac- ity of various soils and sands occurring in Massachusetts. For this purpose, a number of large wooden tubs or tanks built of cypress were cautiously filled with different soils, ranging from muck and garden loam on the one hand, through fine sand and coarse sand to mixed gravel stones, coarser materials, and pebbles on the other. The soil or sand to be tested was in each case supported by a stratum of stones and gravel, and underdrained through an effluent pipe which emptied into a large measuring basin. The sewage was also measured as it flowed on at the top, and 144 ON SEWAGE AND ITS PURIFICATION the whole experiment was under control in every respect. Each tank, or " filter," was sixteen feet in diameter, or one two-hundredth of an acre in area, and the filtering material in each case was five feet in depth. The sewage to be ex- perimented with was drawn from one of the main sewers of the city of Lawrence, and was ordinary domestic city sewage, free from manufacturing wastes. No experiments of this kind had ever before been undertaken on such a scale or with so much care. For the first time in the his- tory of science, engineers, chemists and biologists worked together under the direction of a master in hydraulics, toward one common end, — the promotion of the public health. The results crowned the endeavor. Intelligent by-stand- ers, who saw the sewage flowing upon the filters, at the out- set unhesitatingly predicted failure. They felt certain, and did not hesitate to express their belief, that in a fortnight, at the latest, the filters would become clogged and foul, and the whole neighborhood pestilential. They did not know that Berlin, the German capital, disposes of all its sewage upon land. They forgot that the farmer once a year, or oftener, manures his fields with filth, and that the hungry earth re- ceives the gift with open mouth, devours it, and soon cries out for more. As soon as a few days had passed, and the filters had become established, the effluent began to grow bright and clear. Chemical analyses showed that the out-put was now purified sewage, comparatively free from odor, and poor in organic matters. Bacterial analyses showed that while earlier, as sewage, it was swarming with the germs of putrefaction and decay, it now contained only a few bacteria. Further studies revealed the fact that the foulness of the sewage was not held back as by a strainer ; but rather that as wood by a slow fire is turned to ashes, the organic matters here were slowly reduced to min- eral substances. No disagreeable odor developed, and the filters showed no signs of clogging. Thus the very name THE MASSACHUSETTS EXPERIMENTS 145 "filter" became a misnomer. The by-standers were amazed, and could not repress their feelings of surprise and admiration. § 17. — Anatomy and Physiology of Intermittent Filters Meanwhile the data of the experiments were accumulat- ing. Winter came on, and still the " filters " did their work. Already it was proved that land-disposal of sewage was possible for America. But, curiously enough, those soils — such as muck and garden loam — which many had predicted would be the most useful, proved to be the least effective. They were too close in texture, too fine, too im- pervious ; while sand (such as ordinary mortar sand) or even fine gravel proved to be the most effective. And, on looking into the reason why, it was soon perceived that the whole process is a vital one. The soils are not mere strainers, for at the very outset they fail to work. They are rather like the living sponge, — an animal whose body is everywhere channelled with fine passages lined with living cells. The fine passages in the body of the filters are the spaces between the sand grains; the living cells are the micro-organisms which, after a few days, come to dwell upon the sand grains and line the passages. And very much as the living cells of a sponge detain and destroy the or- ganic particles passing by them, the bacteria resident upon the sand grains detain and work over the organic matters of the sewage poured upon the filter. Again, exactly as the living organisms of which a sponge is essentially composed require oxygen to support their respiration, so those inhabit- ing a filter must have abundant air. This means that the sewage, which is usually destitute of oxygen, must not be applied continuously, but intermittently r , so that air may follow it down through the filter and keep from suffoca- tion the purifying micro-organisms. And this also explains why intermittent downward filtration, under the right con- 146 ON SEWAGE AND ITS PURIFICATION ditions, is always successful, while continuous filtration, or upward intermittent filtration, of sewage inevitably fails. With the main principles once established, it remained only to learn the details of their application. Sand proved better than loam, because it allowed better ventilation. Fine sand proved better than coarse sand, because it seems to be the happy mean, giving full exposure to the air by distributing the sewage in thin films over a vast number of surfaces, but yet allowing sufficient ventilation. The practical results were quick to follow. Once the purifying values of sands of particular sizes were estab- lished, it remained only to obtain samples of sand from any town desiring to dispose of its sewage on land, and to ex- amine and compare them with known sands, to be able to predict for that community either success or failure. The town of Framingham soon constructed a large municipal filter under the advice of the Board, and it has proved an unqualified success. The city of Brockton soon after fol- lowed suit, and built an admirable system of intermittent sand filters for the disposal of its sewage. Henceforward any city or town — not only in Massachusetts, but in America, or in the world — may, if its soil be right, and other conditions favorable, adopt, with perfect confidence, systems for the land-disposal of sewage. § 18. — Theoretical Aspects of Intermittent Filtration Enough has now been said to make it clear that inter- mittent filtration is not really filtration at all, in the etymo- logical sense, but rather a biological and chemical process of extreme delicacy. A field of sandy soil may, it is true, be a very effective strainer ; but if worked intermittently, it is much more than this. A mere strainer soon chokes, and must be cleaned; but an intermittent filter does not readily choke, and is largely self-cleaning. This is a phe- nomenon which can be actually witnessed. When sewage THEORY OF INTERMITTENT FILTRATION 147 began to be applied to the several tanks outside the Law- rence Experiment Station, even the most intelligent of the workmen predicted that the filters would soon choke and become a nuisance ; but after two years of actual operation, hardly anything more remarkable or objectionable could be seen upon them than upon other fertile land. This simple ocular demonstration was confirmed by the results of analy- sis, and the mechanical theory is readily disproved by a com- parison of the chemical composition of the effluent with that of the affluent. In the life-history of an intermittent filter there is usually a period at the outset when there is but little, if anything, more than a mechanical purification ; but under the best conditions there speedily begins a change of the profoundest significance. The dissolved organic mat- ters no longer pass out as they came in ; the suspended matters for the most part cease to accumulate ; and both appear in the effluent under other forms. Obviously, me- chanical processes alone could not effect such changes; and besides, these changes may occur under conditions which exclude entirely the purely mechanical hypothesis. A most striking example of this kind is to be found in the operation of a tank composed of small stones, the spaces between which are, as compared with much of the organic matter of sewage, of infinitely large size ; yet the changes wrought by this filter are far more extensive, and the purifi- cation is far more complete, than in filters of peat or garden soil, which are mechanically nearly perfect strainers. It would be hard to find a better example of the possibilities of sewage filtration than such a tank supplies; yet this filter testifies in the clearest manner to the absolute insig- nificance of any merely mechanical factor in the purifica- tion of sewage by intermittent filtration. § 19. — Intermittent Filtration a Biological Process A theory much more reasonable than the mechanical hypothesis is that the action of an intermittent filter is 148 ON SEWAGE AND ITS PURIFICATION fundamentally chemical. Of the powers of intermittent filters to effect chemical changes there is no question, as the previous pages of this chapter abundantly testify. Moreover, the transformations effected are so thorough that the analogy of purification by fire must occur to every thoughtful observer. Very early, however, the existence of an additional factor began to be recognized. Thus the Rivers Pollution Commission in their experiments on inter- mittent filtration, although insisting upon the chemical character of the purification obtained, referred to the pro- cess as an act of respiration, adding, most unconsciously, the vital to the purely chemical idea : " From all of these experiments, then, it appears that the action of the filter must not be considered as merely mechanical. The process carried on in it is also chemical. ... A field of porous soil irrigated intermittently, virtually performs an act of respiration." (Cf. p. 150.) It has since been definitely established, moreover, that micro-organisms are an indispensable element in the con- stitution of a successful intermittent filter, so that the essentially chemical theory has given place to one essen- tially vital, or biological. " Upon the biological theory, an intermittent filter is no longer regarded as a mechanical strainer, nor is it merely a chemical furnace ; it resembles a living organism." 1 § 20. — Objections to Intermittent Filtration The Rivers Pollution Commissioners' a priori criticisms of the practical value of intermittent filtration are worthy of note as we bring this section to a close : — " Nevertheless there are three formidable objections to the general adoption of this process : first, it is entirely unremunerative, the amount of sewage applied to a given acre of land being probably in such a case 1 Experimental Investigations by the State Board of Health of Massachusetts upon the Purification of Sewage by Filtration, etc. p. 861. Boston, 1890. INTERMITTENT FILTRATION NOT REMUNERATIVE 149 too great to permit of the growth of any ordinary agricultural crop ; second, the whole of the manure ingredients of the sewage would be absolutely wasted ; and third, the collection of solid faecal matters upon the surface of the soil, with no vegetation to make use of them, would probably give rise to a formidable nuisance, especially in hot weather. We also entertain doubts as to the process being equally successful under ordinary management on a large scale, since the sewage would be likely to pass through the land in an unequal manner — in some places reach- ing the drains very rapidly, in others passing through the soil too slowly. . . . Filtration, properly conducted, results in the oxidation, and transformation of offensive organic substances in solution, as well as in the mere mechanical separation of the suspended solid matters which, when in motion, sewage conveys with it. If the process could be carried one step farther, and those harmless inorganic salts, which are carried off by the effluent water of a perfect sewage filter in too dilute a solution to be profitably extracted, could be converted into something positively useful, the remedy would be complete. We should have succeeded in not only abating an injurious nuisance, but in realizing a product which would help to refund expenses. This further step is possible in the great majority of cases ; and it is to the plan of using sewage in irrigation, as being in reality a filtration of the best kind, plus a conversion of its filthy contents into valuable products, that we have now to direct attention." — Rivers Pollution Commission of 1868 ', Re- port, Part I, p. 70. London, 1870. The objections here raised that the process is unremu- nerative and that the end products are wasted, still hold ; but the fear that a nuisance must result from the accumu- lation of matters on the surface of fields devoted to inter- mittent filtration, has been shown by experience to be groundless. We may now follow the line of thought laid down by the commissioners, and pass on to a con- sideration of sewage disposal by irrigation. §21. — Disposal and Purification of Sewage by Irrigation In the second report of the Commissioners appointed in 1868 to inquire into the best means of preventing the pol- lution of rivers (" Mersey and Ribble Basins "), p. 19, sew- age irrigation is referred to as a process — 150 ON SEWAGE AND ITS PURIFICATION "where sewage has been submitted, by means of irrigation, to the action of a vast mass of soil whose surface is covered with growing plants, which it feeds, whose depth is penetrated by their hungry roots, and whose whole substance provides an immense quantity of material efficient for sewage defalcation. . . . " If we except the laboratory experiments in the treatment of sewage in the intermittent downward nitration described in our first report . . . no other method of sewage defalcation approaches irrigation in the uniform excellence of its results. It is no doubt very desirable, in the interest of those towns where sewage cannot be dealt with by irrigation, that an experiment in intermittent downward filtration should be con- ducted on what may be considered a working scale, — when all those difficulties would arise which do not show themselves in a laboratory experiment, and when it would be proved whether the process can be conducted on the drainage water of, say, 20,000 people with the efficiency to which our laboratory experiments pointed, and without creating a nuisance. But the best result under that system would simply be the conversion of a polluting into a non-polluting stream. The injury done by town sewage would in that case disappear, but the agricultural value of it would be wholly lost. By using it in irrigation, on the other hand, the nuisance vanishes, while the fertilizing influence is retained and utilized." In the first report of the Commissioners, to which refer- ence has already been made in the preceding section, the purification of sewage by irrigation is well described as follows (Vol. I, p. 70) : — " We have still to discuss what may be called the agricultural remedy for the nuisance created by town sewage. In the first place, irrigation involves filtration. . . . But a filter, as has been already shown, is not a mere mechanical contrivance. It is a machine for oxidizing, and thus altogether transforming as well as for merely separating the filth of dirty water. And in this respect especially, irrigation necessarily includes filtration. Sewage traversing the soil undergoes a process to some extent analogous to that experienced by blood passing through the lungs in the act of breathing. A field of porous soil irrigated inter- mittently virtually performs an act of respiration, copying on an enor- mous scale the lung action of a breathing animal ; for it is alternately receiving and expiring air, and thus dealing as an oxidizing agent with the filthy fluid which is trickling through it. And a whole acre of soil three or four feet deep, presenting within it such an enormous lung sur- face, must be far superior as an oxidizer for dealing with the drainage SEWAGE DISPOSAL BY IRRIGATION 151 of one hundred people, to any filter that could be practically worked for this purpose. "To this item in the character of both irrigation and filtration as chemical processes, there must be added another cleansing agency also of a chemical kind, in which the former has very greatly the advantage. We refer to the actual appetite for certain dissolved impurities in filthy water, which soil, whether in a tank or covering a field, owes both to general surface attraction and to the chemical affinities which some of its ingredients possess. This appetite is doubtless very limited in its amount, but it is directly proportional to the quantity of material exer- cising it. The superior capability of this kind which the soil of a field possesses, in comparison with that in a limited filtration tank, depends partly on the immensely greater quantity of cleansing material which an acre drained perhaps four feet deep necessarily brings to bear upon the filthy fluid ; but also and especially on the fact that in the former case this appetite is, except in winter time, always kept alive and fresh by the action of plant growth in constantly removing the deposited impuri- ties, and rebuilding them into wholesome organic structures. " Considered then merely as a mechanical and chemical agency for cleansing the drainage water of our towns, it seems plain that a sufficient extent and depth of porous soil to be used in irrigation, having peri- odical intervals of rest, during which the soil drains and becomes refilled with air, certainly must be the best possible strainer, oxidizer, and filter of water which, like the sewer water of our towns, contains nauseous organic impurities, both suspended and dissolved. That it is so, analyses of effluent waters have satisfactorily proved, as will be illus- trated at length hereafter. Meanwhile we have further to consider the last great advantage of the soil over all other filters, in that it utilizes a considerable proportion of the substances which they only separate, or at best transform. "This is the second point in our discussion of the agricultural remedy for river pollution, so far as that is due to the influx of town sewage. Sewage filth is i fertilizing matter, 1 and therefore valuable as a manure. Every one is familiar with the idea that the fertility of a farm depends very much on the quantity of the live stock kept upon it. It is, in fact, an established maxim in agriculture that, apart from the use of imported and manufactured fertilizers, the maintenance of fertility depends very much upon the live stock which the farmer keeps upon the land, and the quantity of manure which he can thus apply to it "The process of filtration through sand, gravel, chalk, or certain kinds of soil if properly carried out is the most effective means for the purification of sewage to which reference has yet been made ; indeed^ 152 ON SEWAGE AND ITS PURIFICATION irrigation, as now carried out, owes no inconsiderable amount of its success to the contemporaneous effect of the filtration of the sewage through the soil of the irrigated fields ; for it is precisely in those cases in which the sewage is absorbed and disappears in porous land, that we have observed, in the effluent water from drains, the most complete purifying effect." — First Report, Rivers Pollution Commission of i886 t p. 60. § 22. — Sewage Farms. Objections to Sewage Disposal by Irrigation and Sewage Farming The disposal of sewage by means of irrigation naturally involves the establishment of sewage farms, that is, a special kind of farming in which a liquid fertilizer is supplied in abundance, sometimes in superabundance. Enough has already been said in the preceding sections to show the theoretical importance and value of sewage as a fertilizer. It cannot be denied that sewage possesses elements of large fertilizing value, and it should never be forgotten that it may at some time be made a far more powerful aid than it is to-day in increasing the food supply of mankind. On the other hand, there is good reason to believe that the practical value of sewage as a fertilizer falls far below its theoretical value, owing chiefly to its enormous dilution ; and that any combination of farming with sewage disposal is, closely examined, of doubtful economic wisdom, at least at present, in America. It does not by any means follow that, because sewage contains valuable fertilizing elements, it is therefore wise for every city and town having sewage to dispose of to undertake sewage farming. It must be borne in mind that the civilized world appears to have been everywhere, within the last decade, suffering from a period of agricultural depression due, no doubt, in great part, to the vast modern improvements in agricultural machinery, and especially to the wonderful modern facilities for trans- portation, which allow food to be carried from almost any point of supply or superabundance to points where it is SEWAGE FARMS AND SEWAGE FARMING 153 in demand, with extraordinary speed and cheapness ; and probably also to the remarkable advances which have been made in the arts of food-preserving, by means of which the superabundance of one season or place which was formerly wasted by decay may be conserved with success indefinitely, or until needed either there or at some remote point of the earth's surface. It is hardly necessary, therefore, in a period of depression in agriculture, such as has lately fallen upon much of the civilized world, to undertake agricultural opera- tions at a loss, and it is not surprising that objections to sewage farms have already arisen in some quarters from farmers who are obliged to compete with sewage farming. There can be no doubt that a greater area of land is re- quired for successful sewage disposal by sewage farms, than by mere intermittent filtration, and it is of very dubi- ous wisdom, at least in the United States where land in the neighborhood of cities is dear, where municipal servants are likely to be highly paid, and where, also, agri- cultural produce is cheap, to undertake sewage farming either for economic or aesthetic reasons. Moreover, as has already been suggested, there are other objections than the purely economic. Quite recently it was found somewhat difficult for the city of Paris to secure the privi- lege of adding to the area of its sewage fields because of the formidable opposition of the ordinary farming interests, which alleged with considerable vehemence that it was diffi- cult for them, unprovided as they were with sewage as a fertilizer, to compete successfully with the sewage farms already in existence, upon which larger crops could be more cheaply produced. There is also the sanitary objection, the force of which must to some extent be admitted, that vegetables and small fruits grown upon sewage fields and presumably watered with sewage are liable to become contaminated with infec- tious materials. We must probably allow that lettuce, cabbages, radishes, strawberries and similar vegetables IIVERSITY OF CALIFORNIA APARTMENT OF CIVIL ENGINEERS® PFRKPIFV r?At IP^bmi J 154 0N SEWAGE AND ITS PURIFICATION or fruits, if so watered or flooded, may possibly become thus contaminated. On the other hand, the testimony of vital statistics in towns and cities in which such vegetables or fruits are consumed appears to be distinctly reassuring, and the advocates of sewage farming assert with much positiveness, that little or no apprehension need be felt in this direction. Probably the truth is that, in some countries very often, and in all countries in some cases, the disposal of sewage by irrigation is the most suitable method to be employed or recommended ; but that in America, at least for the present, for the reasons stated above, or for other reasons peculiar to each locality, if land treatment of any kind is desirable or necessary, intermittent filtration is pref- erable. § 23. — The Partial Purification of Sewage by Chemical Precipitation In the first report of the Commissioners appointed in 1868 to inquire into the best means of the preventing the pollution of rivers (" Mersey and Ribble Basins "), Vol. I, p. 51, 1870, the Commissioners introduce their discussion of this subject as follows : — " The cleansing of sewage has engaged the attention of many chem- ists and others during the past ten or fifteen years ; and various plans, some exhibiting great merit and ingenuity, have been proposed for dealing with the offensive liquid. . . . The valuable constituents of sewage present to the chemist a mine of wealth, which despite so many failures has constantly stimulated him to renewed efforts for their extraction in a portable and consequently marketable form. "The chief valuable ingredients of sewage are, 1st, the different forms of combined nitrogen, and 2d, phosphoric acid. The money value of these constituents dissolved in one hundred tons of average sewage is about fifteen shillings, whilst the suspended matters contain only about two shillings' worth of them. " There is but little difficulty in extracting the suspended matters by filtration, but as these do not contain quite one-seventh of the total valuable constituents, the process, though simple, has never been re- munerative ; and inasmuch as it still leaves much putrescible organic SEWAGE DISPOSAL BY CHEMICAL PRECIPITATION 155 matter in solution, the mere extraction of the suspended matters of sewage, although doubtless tending to mitigate nuisance, does not pro- duce any substantial diminution of the polluting quality of the liquid. The operations of the chemist have, therefore, been directed chiefly to the soluble constituents of sewage; and have had for their object either the precipitation in a solid form of the valuable, but offensive, ingredients, so as to convert them into portable manure, or, secondly, the rendering them inoffensive by the action of disinfectants. Although these operations have not been altogether unsuccessful, they have hitherto entirely failed in purifying average sewage to such an extent as to render it admissible into running water. We have formed this opinion both from observations of the polluting effect of such chemi- cally purified sewage upon the streams into which it was admitted, and from the amount of putrescible organic matter revealed by the chemical analyses of the sewage after treatment. " It would obviously be rash to set any bounds to the possibilities of chemistry. Substances may, perhaps, be hereafter discovered capable of combining with and rendering insoluble the filthy constituents of our town drainage ; but we are compelled to admit that the present re- sources of this science hold out no hope that the foul matters dissolved in sewage will be precipitated and got rid of by the application of chemicals to the offensive liquid. The chemical affinities of these foul matters are so feeble, and the matters themselves are dissolved in such enormous volumes of water, that their precipitation is a problem of extreme difficulty. 11 — Second Report, Rivers Pollution Commission of 1868, pp. 18, 19. London, 1870. These conclusions may fairly be taken as representative of the best expert opinion thirty years ago. In the mean- time all attempts to make the chemical precipitation of sewage a source of pecuniary profit have been unsuccess- ful, and the most that is hoped for to-day is to keep the expense of the process within tolerable bounds. On the other hand, the sanitary results now obtained are decidedly better than those reported by the Rivers Pollution Com- missioners in the quotations given above. This method of sewage disposal is much used in Eng- land, either alone or in combination with disposal of the effluent by intermittent filtration or irrigation. The efflu- ent is usually well clarified, and shows a removal of about nine-tenths of the suspended matters and one-half of the 156 ON SEWAGE AND ITS PURIFICATION total organic matters. Experience has shown that such an effluent can safely be admitted into a stream of relatively- large size, provided it is not to be used for drinking pur- poses. One of the most carefully conducted establishments for the disposal of sewage by chemical precipitation is that at Worcester, Mass., and the chemical examinations of the effluent, there constantly made, show an average reduction of 95 per cent of the suspended and about 53 per eent of the dissolved organic matters of the sewage. It is fair to state, however, that Worcester has been called upon to defend the process before the law on complaint of Mill- bury, a town below Worcester, on. the Blackstone river into which the effluent from the Worcester purification plant is poured. Millbury has claimed that the purification of the effluent is inadequate, and that a nuisance which exists there is due to imperfect purification of the sewage of Worcester. On trial it appeared that there was among the most competent experts a great difference of opinion as to the sanitary efficiency of the process. The reader who cares to pursue the subject of chemical precipitation further is referred to the following : Hazen, " Experiments on the Chemical Precipitation Sewage," Massachusetts Special Report, State Board of Health, 1890, p. 734. Ibid. y " Chemical Precipitation of Sewage at the World's Fair, Chicago, 1893." Massachusetts Report, 1892, p. 595. "Annual Reports" of H. P. Eddy, Superintend- ent of Sewers, City of Worcester, Mass. Baker and Raf- ter, " Sewage Disposal in the United States." (D. Van Nostrand Co.), New York. § 24. — Sewage Disposal and Purification by Electricity The extensive development of electrical appliances has naturally led to various proposals for the purification of sewage by electrical means. It can hardly be said, how- ELECTRICAL PURIFICATION OF SEWAGE 157 ever, as yet, that any of these has attained a practical importance such as would entitle it to consideration. The principles involved in the electrical purification of sewage have been clearly stated, and the recent state of the subject ably summarized, by Professor (now President) Thomas M. Drown, 1 of Lehigh University, chemist to the State Board of Health of Massachusetts, in the following words : — " We may distinguish two classes of so-called electrical purification : first, those which electrolyze water, liberating oxygen at the positive pole ; and, second, those which electrolyze a solution of common salt and liberate chlorine in the same way. " The Webster process for the purification of sewage, of which a good deal was once heard, belonged mainly to the first class, although by reason of the chlorides contained in the sewage it fell also, in part, into the second class. The oxygen liberated at the positive pole, while in the nascent state, was supposed to oxidize some organic matter; but as the pole was composed of iron plates, the oxygen was mainly con- sumed in oxidizing this iron, and the oxide of iron thus formed acted as a precipitating agent on the sludge in the sewage. The process was thus mainly one of chemical precipitation of sewage by means of oxide of iron, which was formed by a current of electricity passing through the sewage. . . . " The possibility of oxidizing organic matter on the large scale by means of nascent oxygen liberated from water by the electric current will, probably, never be more than a dream. Attractive as the process seems, the necessary conditions for accomplishing it could probably never be realized on a city's water supply, or on its sewage. . . . " The more recent systems of purification of water and sewage by electricity belong in the second class, that is, the decomposition by electrolysis of a solution of common salt. . . . " The principal product, under ordinary conditions, is sodium hypo- chlorite. . . . "This, then, sodium hypochlorite, is the substance with which we have to deal in the method of electrical purification which depends on the electrolysis of a solution of salt or sea water. When the current of electricity has, in the manner above described, formed a sufficiently concentrated solution of sodium hypochlorite, this solution is mixed with the water or sewage to be purified. . . . 1 Journal New England Water Works Association, VIII (1894), pp. 183- 188. ■ On the Electrical Purification of Water [and Sewage]." 158 ON SEWAGE AND ITS PURIFICATION " The so-called ' electrical ' purification of water by treating it with an electrolyzed solution of salt is thus seen to be simply a process of disinfection by sodium hypochlorite ; electricity, as such, has nothing to do with it. . . . " Ozone is generally supposed to cover a multitude of sins of pollu- tion, and quickly to destroy them ; but we do not know much, if any- thing, about its germicidal power ; and there is certainly no good reason for attributing any of the disinfecting action of an electrolyzed salt solu- tion to ozone, even did we certainly know it to be present. " It is unfortunate that the advocates of this system of purification of water and sewage are not content to attribute the purifying action of the electrolyzed solution of salt solely to the hypochlorite formed. There is nothing gained by calling it ' electrozone, 1 or an ' electro-saline solu- tion,' for there is nothing mysterious about its action, as these terms would lead one to suppose. Nor is it proper to speak of this system of purification as in any sense an * electrical ' one. If one were to pur- chase two bottles of sodium hypochlorite of identically the same com- position, one prepared by a chemical process and the other by the electrolysis of a salt solution, he would not expect to find them called by different names. To call the latter an 'electrical disinfectant' would be simply fantastic." § 25. — Sewage Disposal and the Partial Self- Purification of Sewage by Means of Fermentation or Putrefaction. A recent and interesting development in the theory and practice of sewage disposal and purification is that known as the septic process, in which advantage is taken of the fact that sewage is a highly putrescible fluid richly charged with putrefactive bacteria, in order to decompose it by its own ordinary processes of bacterial fermentation or putre- faction, thus bringing it into a condition in which it is believed to be more readily nitrified when, subsequently, it is brought in contact with the living earth, and, in particu- lar, causing suspended matters (sludge) to pass partly or wholly into solution. The process consists simply in allowing ordinary town sewage to stagnate, ferment and putrefy in a tank or tanks for a somewhat longer time than usual. Under these circumstances, the sewage contains no free oxygen, SELF-PURIFICATION BY PUTREFACTION 159 and Pasteur's original idea of fermentation as " life without air" is fully realized. According to the evidence of vari- ous observers, the organic matter is thus more thoroughly decomposed, and the sewage is more quickly brought into a condition in which it is readily nitrified when, as is the practice, it is afterward run through slow sand filters in the usual methods of intermittent filtration, or by the in- genious modification of intermittent filtration known as "contact filters " proposed by Dibdin. Further details and a full account of the various processes employed may be found in a valuable paper by Professor L. P. Kinnicutt, entitled " Purification of Sewage by Bacterial Methods," Journal New England Water Works Association, Vol. XV, p. 119. Boston, 1900. See also the "Annual Reports" of the Connecticut State Sewerage Commission, begun in 1899. § 26. — Fate of the Infectious Matters in Sewage Disposal and Sewage Purification For the student of sanitary science, and from the prac- tical point of view, it is a question of the highest importance what becomes of the infectious materials in sewage when the latter is disposed of, or purified, by any of the various methods described above. In the case of disposal by dilution, there is reason to believe that much depends on the special conditions under which the dilution takes place. If, for example, a moder- ate amount of sewage is emptied into a relatively large body of quiet water, we may safely suppose that the infec- tious materials which it contains, namely, micro-organisms of various kinds, are for the most part unfavorably affected by the new environment with which they are likely to meet, and, under the influence of light, gravity, defective food supply and possibly predatory infusoria or other enemies, as well as unfavorable temperatures, gradually perish at a point not very distant from that at which they were dis- 160 ON SEWAGE AND ITS PURIFICATION charged. Indeed, it is impossible on any other hypothesis to explain the facts which have been observed in cases like those of Burlington, Cleveland, Chicago, Milwaukee, etc. It is quite otherwise, however, with those cases of puri- fication by dilution, in which the sewage forms a relatively large part of the body of the water into which it is emptied, and especially in those cases in which it is carried swiftly by running streams or currents within a short time to points comparatively remote from the place of disposal. In these cases, the same forces — light, gravity, temperature and, in general, unfavorable environment — would be operative, but yet the practical outcome might be that these were less availing, while the want of one other important ele- ment, time, would be favorable to the persistence of vitality of the micro-organisms which might therefore arrive, in a state of dilution to be sure, but yet, at comparatively remote points, quickly and therefore alive and virulent. It is for this reason that we are forced to conclude, contrary to the opinions held only a few years since, that quiet water, and not running water, purifies itself. But to this subject we shall return (in Chapter IX). When we come to the disposal of sewage upon land, we find the question of the fate of infectious materials in the sewage entirely different. If, as is always assumed, the sew- age to be purified is passed through, and not merely over, the earth, the micro-organisms which it contains are held back more or less completely, along with other suspended matters, by the living earth. One of the most striking phenomena of intermittent filtration which, as we have shown, is the fundamental process in all land treatment of sewage, is the disappearance of the very numerous living bacteria always present in the crude sewage. Some of these, no doubt, are mechanically detained in the upper layers of the living earth, the jelly-like masses which exist there being espe- cially favorable for entanglement of their cilia. Others perish from lack of food, either near the surface or, more FATE OF ITS INFECTIOUS MATERIALS 161 probably, in the lower layers of the filter, or still further down, in the now purified effluent which has been robbed of the food materials but lately abundant in it. In the sewage filters at the Lawrence Experiment Station it very early became evident that a high degree of nitrification was accompanied by a remarkable disappearance of bacteria, and repeated experiments have shown that the effluent from a good sewage filter is incapable of supporting any considerable population of bacteria. There is no doubt that under certain circumstances bacteria applied to the sur- face of an intermittent filter may live to find their way into the effluent, as was proved for the first time at the Law- rence Experiment Station by experiments made in 1888 and published in 1890. 1 The same thing was shown a little later by the experiments of Fraenkel and Piefke, 2 and the fact is now generally accepted. On the other hand, it is the universal testimony of those familiar with intermittent filters and sewage farms that the ordinary effluent waters derived from well-regulated filters may be, and often are, drunk with impunity. We do not know how small a number of pathogenic bacteria may under certain circumstances produce disease. But there is good reason to think that the danger of infection in any particu- lar case depends, in part at least, upon the size of the dose, which would mean the number of micro-organisms intro- duced into the body. It is not claimed that sewage efflu- ents are desirable for drinking waters ; but there is very little doubt that the effluents from well-regulated filters or sewage farms may be safely introduced into streams or other bodies of water, even those which are later to be used as sources of water supply. 1 " Experimental Investigations by the State Board of Health of Massachu- setts on the Purification of Sewage and Water," 1 888-1 890, p. 852. Boston, 1890. 2 Zeit. fur Hygiene, 8, 1890. See also Bertschinger, Vierteljahreschrift d. Naturforsch. Gesellsch. in Zurich, 1889.. M 162 ON SEWAGE AND ITS PURIFICATION If it be asked, what becomes of the infectious materials held back by the soil ? the answer is that they do not appear ordinarily to multiply, but rather to perish, along with the myriads of putrefactive bacteria which accompany them in the sewage. No fact is more striking in the history of the experimental niters at Lawrence than that these are vast charnel houses for bacteria. The sewage applied to the fil- ters contains, on the average, one or two millions of bacteria per cubic centimetre. The effluent drawn off at the bottom contains at most only hundreds or thousands, and this state of affairs is continuous day after day, month after month and year after year. And yet, at the same time, there appears to be a living resident population, tolerably con- stant in numbers, distributed through the different layers of the filter. In view of this and similar facts, we have above referred to the earth as the home of the bacteria ; but in view also of the enormous mortality of the bacteria in a sewage filter, it is equally clear that the earth may be no less truly their tomb ; and it appears to be here that the infectious micro-organisms present in the sewage find, fortunately, in this particular form of sewage disposal, their last resting-place. In the case of purification of sewage by chemical pre- cipitation, we may reasonably suppose that most of the infectious materials are carried down by the precipitant and got rid of in the sludge. In any event, however, the fate of the infectious materials in this case is of less im- portance, inasmuch as effluents from chemical precipitation works are not, as a rule, and cannot safely be, at least in America, admitted into a body of water used for drink- ing purposes. It has been urged in favor of the electrical purification of sewage that the infectious materials present are readily destroyed by the electric currents employed. But this, in view of various experiments touching the effect of electricity upon bacteria and other micro-organisms is, to say the SEWAGE FILTERS AS BACTERIAL TOMBS 163 least, doubtful; and if what has been stated above in regard to the real nature of this method of purification is true, the problem here does not differ essentially from that affecting chemical precipitation, which has just been considered. As to the effect produced by the natural, fermentation or septic, process, especially when combined with Dibdin's con- tact filters, such as are in use at Exeter and Manchester, in England, very little is as yet known ; but it is fair to sup- pose that the fermenting process in the tank, in the absence of oxygen, as well as the nitrifying process in the filters in the presence of oxygen, are highly unfavorable to the con- tinued life, and still less to the multiplication, of infectious materials. We may safely predict that these processes will prove to be entirely satisfactory so far as the puri- fication of the sewage in respect to infectious matters is concerned. CHAPTER VIII ON WATER AS A VEHICLE OF INFECTIOUS DISEASE. THE POLLUTION OF PUBLIC WATER SUPPLIES. NOTABLE EPI- DEMICS DUE TO INFECTED DRINKING WATER " My reports are incessantly showing the foulness of private supplies while as regards public water supplies ... it has again and again been shown that their conveniences and advantages are countervailed by dangers to life on a scale of gigantic magnitude." — Sir John Simon, Ninth Report, Medical Officer of the Privy Council, p. 34. London, 1867. " The events I am going to relate to you would, in the Middle Ages, have been ascribed to some mysterious influence or to supernatural per- secution. Science now enlightens us on the true cause of the evil, but at the same time imposes upon us the obligation to employ all the resources it gives us to combat the danger, which belongs to a class that human prudence can avoid." — Dr. Gueneau de Mussy, on lead poison- ing in the family of Louis Philippe from the water supply of the royal palace of Claremont. Inasmuch as sewage may contain any or all of the infec- tious materials from diseased animal bodies, and inasmuch, further, as it is a liquid readily miscible with water, — being itself hardly more than very dirty water, — while it is also produced in relatively large quantities by modern commu- nities, it is perhaps not to be wondered at that the germs of disease often find access to wells, springs, reservoirs and streams, from which water is destined sooner or later to be drawn for drinking purposes. § I. — Drinking Water as a Vehicle of Disease It has been shown above (Chapter V) that while infec- tious materials may sometimes enter the body through the 164 PURE VS. POLLUTED WATERS 165 skin, the more common and the easier avenues are those of the alimentary, pulmonary and genito-urinary tracts. Of all the substances admitted into the alimentary canal, the most abundant, and perhaps the most trusted, is water. The " cup of cold water " has long stood as the symbol of charity ; and yet, from the sanitary point of view, there is little or no doubt that water is one of the most dangerous vehicles of disease which passes through the gates leading into the human body. Water chemically pure should, of course, contain no infectious materials, although it is an interesting fact that in laboratory experiments it is possible to introduce into distilled water a considerable number of pathogenic bac- teria without producing any effect upon the water discover- able by the most refined chemical analysis. Again, it is quite possible, in laboratory experiments, to mingle with a specimen of water millions of the germs of typhoid fever or Asiatic cholera without effecting perceptibly its bright and attractive appearance. With these facts in mind it becomes comparatively easy to understand that water may appear bright and attractive to the eye and be acceptable to the palate, while yet containing myriads of disease germs. It should not be forgotten, however, that what has been stated is true only of laboratory experiments, and rarely, if ever, happens or is likely to happen under natural conditions or on a large scale. Natural waters, such as those of springs and wells, brooks and other streams from uninhabited districts, should con- tain, and ordinarily do contain, no infectious materials ; and such waters, although they may contain mud, or various vegetable and even animal matters, are commonly described as "pure." But it is very different with natural waters which have been exposed to pollution, especially by sewage. From what has already been said it is clear that the latter may and frequently does contain infectious materials ; so that if sewage in any form finds its way into drinking 166 WATER AS A VEHICLE OF INFECTIOUS DISEASE waters, these are more than likely to prove a convenient vehicle for the conveyance of infectious materials into the human body. Even if sewage has been somewhat purified by dilution or other treatment, its presence in waters used for drinking properly constitutes a source of anxiety, the precise danger involved depending in any special case upon the degree of purification which they have undergone; and it is obvious that the determination of the degree of purification in any particular case of pollution may be a special problem taxing the best resources of the sanitarian. § 2. — Diarrheal Diseases and Drinking Water A little reflection will show that while diseases of the skin, the throat, the lungs, the nose, etc., are accompanied by eruptions, exudations, expectorations or other discharges which may find their way into sewage, these are usually insignificant in amount in comparison with the bowel dis- charges. It is not surprising, therefore, to learn that diseases affecting the alimentary canal, and especially the intestine, particularly if accompanied by diarrhoea, are most conspicuous among the diseases conveyed by sew- age-polluted drinking water. It is now well established that certain bowel diseases, such as typhoid fever and Asiatic cholera, are readily conveyed by'drinking water, and numerous epidemics of these diseases have been traced to infected water supplies; but there is very little evidence of the conveyance of diseases of the skin, throat, lungs and nose by this particular vehicle. Moreover, there are certain members even of the group of diseases known as "diar- rhceal" which do not seem to be as readily conveyed by drink- ing water as are others of the same class. Cholera infantum, for example, is a common, severe and often fatal diarrhceal disease of children. But it seems seldom, if ever, traceable to polluted drinking water, with which typhoid fever and Asiatic cholera can very often be directly connected. SOME DISEASES NOT WATER-BORNE 167 § 3. — Typhoid Fever and Asiatic Cholera These two diseases, and especially typhoid fever, are of preeminent importance and interest to the student of sani- tary science, and for this reason a short account of their natural history will be given at this point as a preface to further consideration of them. As long ago as 1874 expert opinion had concluded that " the existence of specific poisons capable of producing cholera and typhoid fever is attested by evidence so abundant and strong as to be prac- tically irresistible. These poisons are contained in the discharges from the bowels of persons suffering from these diseases." — Rivers Pollution Commission of 1868, Sixth Report, p. 427. London, 1874. Typhoid fever is so called because it resembles, and was not formerly distinguishable from, typhus fever, otherwise known as "ship," "jail" or "spotted" fever. It is char- acterized by slow and insidious onset during a period lasting for about two weeks, and known as the " prodromal " period, during which the patient generally suffers from severe frontal headache, often having in addition backache, nose- bleed, diarrhoea and a general loss of strength which finally, in severe cases, compels him to take to his bed. By this time active fever is well established, the temperature rang- ing from ioo° to 105 or even higher, and characterized by a daily rise in the evening and a fall in the morning. During the period of active sickness, which usually lasts from four to eight weeks, delirium sometimes occurs, and other serious symptoms make their appearance. It is a characteristic of the disease, and one which distinguishes it from typhus fever, that in typhoid fever the small intestine undergoes more or less extensive and dangerous ulcerations ; and inasmuch as these ulcers burrow into the wall of the intestinal tube, they may either perforate it, allowing faecal matters to enter the peritoneal cavity, and causing speedy death from septicaemia, or they may involve important blood 168 WATER AS A VEHICLE OF INFECTIOUS DISEASE vessels, which becoming disintegrated cause profuse hemorrhages, often likewise followed by speedy death. Owing to the fact that the lower animals are not, so far as known, susceptible to typhoid fever, it has never been possible, as yet, to establish with absolute certainty the iden- tity of the specific germ of typhoid fever. At the same time there is a very general agreement that the so-called Koch-Eberth-GafTky bacillus is, in all probability, the real and. specific cause of the disease. The commonly accepted theory of the causation of typhoid fever is, that the specific bacilli, making their way into the alimentary canal in such vehicles as water, milk, dirt or dust, survive the journey through the stomach, and finding themselves in the intes- tine, there multiply and produce their own specific toxin, to the absorption of which are due the earlier symptoms of the disease. Simultaneously, or possibly subsequently, and presumably under the action of the same toxin, the guardian membranes of the alimentary tract are weakened or otherwise damaged, so that their usual resistance is somewhat enfeebled, and the bacilli make their way through them into the tissues of the body proper. Of all the tis- sues the spleen seems to be particularly affected; and it is from this organ that those bacilli are most easily recov- ered which are believed to be specific and characteristic of the disease. If these commonly accepted ideas are correct, it is obvious that the bowel discharges of typhoid fever patients must naturally contain large numbers of the germs of typhoid fever; and that if these discharges find their way into sewage, such sewage must be not only pol- luted with the ordinary bowel discharges, but also actually infected with the specific germs of the disease. Further- more, if this sewage happens to find its way into a water supply that supply is liable to become a vehicle of disease unless it shall somehow have been purified before it is used for drinking purposes. It should also be observed in pass- TYPHOID FEVER AND ASIATIC CHOLERA 169 ing that the journey from one human intestine to another may, conceivably at least, be very short, very direct and very quick; and it is also easy to understand that the virulence of the germs may well depend upon various conditions to which they have been submitted en route. Asiatic cholera is a disease in many respects similar to typhoid fever, but more violent, more rapid and more fatal. In this case, also, owing to the insusceptibility of the lower animals to the disease, it has been thus far impossible to prove absolutely that the Spirillum, or Vibrio, generally regarded as the cause of the disease, is surely such. Certain experiments, voluntarily made by human beings, and a large amount of circumstantial evidence, have made it, however, highly probable that the general belief that we know the real germ of this dis- ease is correct. (Cf. p. 98.) In this case, also, it is held that the germs having been taken into the alimentary canal with food or drink or, pos- sibly, air, survive the journey through the stomach, and, arriving in the intestine, there multiply enormously, pro- ducing at the same time their specific toxin, which, in cholera, is far more active and far more poisonous than that of typhoid fever. The toxin, being absorbed into the body proper, is supposed to cause those profound disturb- ances of the organism, and often even its rapid destruc- tion, which are so characteristic of the disease. In the case of typhoid fever it was until recently very difficult to demonstrate with certainty the presence of typhoid fever bacilli in the bowel discharges of patients suffering from that disease, so that we were actually in the humiliating position of attributing to these discharges the principal agency in the distribution of typhoid fever, while yet we were quite unable satisfactorily to prove the presence of the germs in the discharges. From this unfortunate dilemma we seem to have been relieved by the Widal serum test, so that at present it is held to be 170 WATER AS A VEHICLE OF INFECTIOUS DISEASE easy to make the demonstration so desirable. In the case of Asiatic cholera, on the other hand, the number of micro-organisms present in the bowel discharges is so enor- mous that it has been from the start easy to dem- onstrate their existence; and there is no difficulty in understanding how it is that the bowel discharges of a single patient suffering from this disease may not only pollute, but also specifically infect, a particular specimen of sewage, with which, in turn, infection may pass into a water supply and, under certain conditions, arrive in the alimentary canal of a person drinking the infected water. Here, also, it is easy to follow the infection from one intes- tine to another, and, as in the case of typhoid fever, the extent and virulence of the infection will obviously depend upon a number of conditions en route, such as time, temperature, food supply, gravity, light and mechanical obstructions. § 4. — An Epidemic of Asiatic Cholera traced to a Well. The Case of the Broad Street {London) Pump One of the earliest, one of the most famous, and one of the most instructive cases of the conveyance of disease by polluted water is that commonly known as the epidemic of Asiatic cholera connected with a Broad Street (Lon- don) well, which occurred in 1854. For its conspicuously circumscribed character, its violence and fatality, and espe- cially for the remarkable skill, thoroughness and success with which it was investigated, it will long remain one of the classical instances of the terrible efficiency of polluted water as a vehicle of disease. As a monument of sanitary research, of medical and engineering interest and of pene- trating inductive reasoning, it deserves the most careful study. No apology, therefore, need be made for giving of it here a somewhat extended account. 1 1 The complete original report is entitled " Report on the Cholera Out- break in the Parish of St. James, Westminster, during the Autumn of 1854. DRINKING WATER AND ASIATIC CHOLERA 1 71 (a) — The Parish of St. James, Westminster, in 1854 The parish of St. James, Westminster (London), occu- pied in 1854, 164 acres, and contained in 185 1, 36,406 inhabitants. It was divided into three subdistricts, viz., those of St. James's Square, Golden Square, and Berwick Street. As will be seen by the map (at p. 174), it was situated near a part of London now well known to travel- lers, not far from the junction of Regent and Oxford streets. It was bounded by May Fair and Hanover Square on the west, by All Souls and Marylebone on the north, St. Anne's and Soho on the east and Charing Cross and St. Martin' s-in-the-Fields on the east and south. In the cholera epidemics of 1832, 1 848-1 849, and 1853, St. James's Parish suffered somewhat but, on the aver- age, decidedly less than London as a whole. In 1854, how- ever, the reverse was the case. The Inquiry Committee estimated that in this year " the fatal attacks in St. James's Parish were probably not less than 700," and from this estimate computed a cholera death-rate, during 17 weeks under consideration, of 220 per 10,000 living in the parish, which was far above the highest in any other district. In the adjoining subdistrict of Hanover Square the ratio was 9 ; and in the Charing Cross district of St. Martin 's-in-the- Fields (including a hospital) it was 33. In 1848- 1849 the cholera mortality in St. James's Parish had been only 15 per 10,000 inhabitants. (J?) — The Search for the Source of the Epidemic Within the parish itself the disease in 1854 was ver y unequally distributed. In the St. James's Square district the cholera mortality was only 16 per 10,000, while in the Golden Square district it was 217, and in the Berwick Presented to the Vestry by the Cholera Inquiry Committee, July, 1855." London, J. Churchill, 1855. 172 WATER AS A VEHICLE OF INFECTIOUS DISEASE Street district, 212. It was plain that there had been a special cholera area, a localized, circumscribed district. This was eventually minutely studied in the most pains- taking fashion as to population, industries, previous sani- tary history, meteorological conditions and other general phenomena common to London as a whole; with the result that it was found to have shared with the rest of London " a previous long-continued absence of rain . . . ; a high state of temperature both of the air and of the Thames . . . ; an unusual stagnation of the lower strata of the atmosphere, highly favorable to its acquisition of impurity . . . ; and although it was impossible ... to fix the precise share which each of the conditions enumerated might separately have had in favoring the spread of cholera, the whole history of that malady, as well as of the epidemic of 1854, and indeed of the plagues of past epochs, justifies the supposition that their combined opera- tion, either by favoring a general impurity in the air or in some other way, concurred in a decided manner, last sum- mer and autumn (1854), to give temporary activity to the special cause of that disease." (Report of Cholera Inquiry Committee, pp. 38, 39.) The Inquiry Committee did not, however, rest satisfied with these vague speculations and conclusions. ". . . But, as previously shown in the history of this local outbreak, the resulting mortality was so dispro- portioned to that in the rest of the metropolis, and more particularly to that in the immediately surrounding dis- tricts, that we must seek more narrowly and locally for some peculiar conditions which may help to explain this serious visitation." Accordingly, special inquiries were made within the dis- trict involved in regard to its "elevation of site"; "soil and subsoil" (including an extended inquiry into the his- tory of a "pest-field," said to have been located within this area in 166 5- 1666, to which some had attributed the cholera of 1854); "surface and ground plan"; "streets and ASIATIC CHOLERA AND THE BROAD ST. PUMP 173 courts " ; " density of population " ; " character of the population"; "dwelling houses — internal economy as to space, light, ventilation and general cleanliness"; "dust- bins and accumulations in yards, cellars and areas " ; " cesspools, closets and house-drains " ; " sewers, their waterflow and atmospheric connection"; "public water supply " ; and " well-water supply." No peculiar condi- tion or adequate explanation of the origin of the epidemic was discovered in any of these, even after the most search- ing inquiry, except in the well-water supply. Abundant general defects were found in the other sanitary factors, but nothing peculiar to the cholera area, or, if peculiar, common to those attacked by the disease, could be found excepting the supply of well water. (c) — Suspicion falls upon the Broad Street Pump. The Investigations of Dr. John Snow. At the very beginning of ths outbreak, Dr. John Snow, with commendable energy, had taken the trouble to get the number and location of the fatal cases, as is stated in his own report (Report of Cholera Inquiry Committee, pp. IOO et seq.): — " I requested permission, on the 5th of September, to take a list, at the General Register Office, of the deaths from cholera registered during the week ending the 2d of September in the subdistricts of Golden Square and Ber- wick Street, St. James's, and St. Anne's, Soho, which was kindly granted. Eighty-nine (89) deaths from cholera were registered during the week in the three subdistricts. Of these only six (6) occurred on the first four days of the week ; four (4) occurred on Thursday, August 3 1 ; and the remaining 79 on Friday and Saturday. I considered, therefore, that the outbreak commenced on the Thursday ; and I made inquiry in detail respecting the 83 deaths registered as having taken place during the last three days of the week. 174 WATER AS A VEHICLE OF INFECTIOUS DISEASE " On proceeding to the spot I found that nearly all the deaths had taken place within a short distance of the pump in Broad Street. There were only ten (10) deaths in nouses situated decidedly nearer to another street pump. In five (5) of these cases the families of the deceased persons told me that they always sent to the pump in Broad Street, as they preferred the water to that of the pump which was nearer. In three other cases, the de- ceased were children who went to school near the pump in Broad Street. Two of them were known to have drunk the water, and the parents of the third think it probable that it did so. The other two deaths beyond the district which the pump supplies represent only the amount of mortality from cholera that was occurring before the eruption took place. " With regard to the 73 deaths occurring in the locality belonging, as it were, to the pump, there were 61 instances in which I was informed that the deceased persons used to drink the water from the pump in Broad Street, either constantly or occasionally. In six (6) instances I could get no information, owing to the death or the departure of every one connected with the deceased individuals; and in six (6) cases I was informed that the deceased persons did not drink the pump water before their illness. " The result of the inquiry consequently was that there had been no particular outbreak or increase of cholera in this part of London, except among the persons who were in the habit of drinking the water of the above-mentioned pump well. " I had an interview with the Board of Guardians of St. James's Parish on the evening of Thursday, 7th of Sep- tember, and represented the above circumstances to them. In consequence of what I said the handle of the pump was removed on the following day. . . . " The additional facts that I have been able to ascertain are in accordance with those above related ; and as regards ASIATIC CHOLERA AND THE BROAD ST. PUMP 175 the small number of those attacked who were believed not to have drunk the water from the Broad Street pump, it must be obvious that there are various ways in which the deceased persons may have taken it without the knowl- edge of their friends. The water was used for mixing with spirits in some of the public houses around. It was used likewise at dining rooms and coffee-shops. The keeper of a coffee-shop which was frequented by me- chanics, and where the pump water was supplied at dinner time, informed me on the 6th of September that she was already aware of nine of her customers who were dead." On the other hand, Dr. Snow discovered that while a workhouse (almshouse) in Poland Street was three-fourths surrounded by houses in which cholera deaths occurred, out of 535 inmates of the workhouse only five (5) cholera deaths occurred. The workhouse, however, had a well of its own in addition to the city supply, and never sent for water to the Broad Street pump. If the cholera mortality in the workhouse had been equal to that in its immediate vicinity, it should have had fifty deaths. A brewery in Broad Street employing seventy workmen was entirely exempt, but having a well of its own, and allowances of malt liquor having been customarily made to the employees, it appeared likely that the proprietor was right in his belief that resort was never had to the Broad Street well. It was quite otherwise in a cartridge factory at No. 38 Broad Street, where about two hundred work-people were employed, two tubs of drinking water having been kept on the premises and always filled from the Broad Street well. Among these employees eighteen died of cholera. Similar facts were elicited for other factories on the same street, all tending to show that in general those who drank the water from the Broad Street well suffered either from cholera or diarrhoea, while those who did not drink that water escaped. The whole chain of evidence was made 176 WATER AS A VEHICLE OF INFECTIOUS DISEASE absolutely conclusive by several remarkable and striking cases like the following : — " A gentleman in delicate health was sent for from Brighton to see his brother at No. 6 Poland Street, who was attacked with cholera and died in twelve hours, on the 1st of September. The gentleman arrived after his brother's death, and did not see the body. He only stayed about twenty minutes in the house, where he took a hasty and scanty luncheon of rump steak, taking with it a small tumbler of cold brandy-and-water, the water being from Broad Street pump. He went to Pentonville, and was attacked with cholera on the evening of the fol- lowing day, September the 2d, and died the next evening." " The deaths of Mrs. E and her niece, who drank the water from Broad Street at the West End, Hampstead, deserve especially to be noticed. I was informed by Mrs. E 's son that his mother had not been in the neighbor- hood of Broad Street for many months. A cart went from Broad Street to West End every day, and it was the cus- tom to take out a large bottle of the water from the pump in Broad Street, as she preferred it. The water was taken out on Thursday, the 31st of August, and she drank of it in the evening and also on Friday. She was seized with cholera on the evening of the latter day, and died on Sat- urday. A niece who was on a visit to this lady also drank of the water; she returned to her residence, a high and healthy part of Islington, was attacked with cholera, and died also. There was no cholera at this time, either at West End or in the neighborhood where the niece died. Besides these two persons only one servant partook of the water at West End, Hampstead, and she did not suffer, or, at least, not severely. She had diarrhoea." Dr. Snow's inquiry into the cases of cholera which were nearer other pumps showed that in most the victims had preferred, or had access to, the water of the Broad Street well, and in only a few cases was it impossible to trace ASIATIC CHOLERA AND THE BROAD ST. PUMP 177 any connection with that pump. Finally, Dr. Snow made a statistical statement of great value, which is here given in its original form. THE BROAD STREET (LONDON) WELL AND DEATHS FROM ASIATIC CHOLERA NEAR IT IN 1854 Number Number Date of Fatal Attacks Deaths Date of Fatal Attacks Deaths August 19 . . I Sept. II . . . 5 15 M 20 . . O " 12 . 1 6 « 21 . . 2 " 13 • 3 13 « 22 . . O O " 14 • 6 «< 23 • • O * 15 ■ 1 8 M 24 . . 2 " 16 . 4 6 <« 25 • • O O " 17 • 2 5 it 26 . . O " 18 . 3 2 <« 27 . . I " 19 . 3 M 28 . . O " 20 . «« 29 . . I " 21 . 2 M 30 . . 8 2 " 22 . 2 N 31 • • 56 3 " 23 . 3 Sept. I . . 143 70 " 24 . «< 2 . . 116 127 " 25 . <« 3 • • 54 76 " 26 . 2 M 4 • • 46 7i " 27 . M 5 • • 36 45 " 28 . 2 M 6 . . 20 37 " 29 . « 7 • • 28 32 " 30 • • M M 8 . . 9 • • 12 11 30 24 Date unknown . 45 « 10 . . 5 18 Total . . 616 616 (d) — The Rev. Mr. Whitehead 's Detailed Studies of Broad Street and Its Pump In addition to the original and general inquiry conducted from the time of the outbreak by Dr. Snow, the Rev. H. Whitehead, M.A., 1 curate of St. Luke's in Berwick Street, 1 "The Rev. H. Whitehead, M.A., to whom medicine is in a great measure indebted for that elaborate investigation of the cholera outbreak in the parish of St. James, Westminster (the Broad Street pump outbreak), which it is now known gives to Dr. Snow's opinion of its origin a probability 178 WATER AS A VEHICLE OF INFECTIOUS DISEASE and like Dr. Snow, a member of the Cholera Inquiry Com- mittee, whose knowledge of the district both before and during the epidemic, owing to his official position, gave him unusual advantages, made a most elaborate and pains- taking house-to-house investigation of one of the principal streets affected, viz., Broad Street itself. Mr. White- head's report, like that of Dr. Snow, is a model of careful and extended observation and study, cautious generalizing and rigid verification. It is an excellent instance of in- ductive scientific inquiry by a layman in sanitation. Mr. Whitehead found the number of houses on Broad Street, 49; the resident householders, 35; the total number of resident inhabitants, 896; the total number of deaths among these, 90. Deaths among non-residents (workmen, etc.) belonging to the street, 28. Total deaths chargeable to this street alone, 118. Only 10 houses out of 49 were free from cholera. The dates of attack of the fatal cases resident in this single street were as follows : — Date of Attack Number of Fatal Attacks Date of Attack Number of Fatal Attacks August 12 . " 28 . " 30 . " 31 • Sept. 1 . 2 . I I 6 26 24 9 Sept. 4 " 5 6 " 7 " 8 " 9 8 6 5 2 " 3 • 90 Mr. Whitehead's detailed investigation was not made until the spring of 1855, but in spite of this fact it supplied most interesting and important confirmatory evidence of Dr. Snow's theory that the Broad Street well was the source of the epidemic. Mr. Whitehead, moreover, went further practically amounting to a demonstration." — Mr. J. Netten Radcliffe, "On Cholera in London in 1866," Ninth Rep. Med. Officer of the Privy Council, p. 288. DRINKING WATER AND ASIATIC CHOLERA 1 79 than Dr. Snow, and endeavored to find out how the well came to be infected, why its infectious condition was so limited as it appeared to have been, and to answer various other questions which occurred in the course of his inquiry. As a result, he concluded that the well must have been most infected on August 31 ; that for some reason unknown a partial purification began on September 2, and thereafter proceeded rapidly. There was some evidence that on Aug- ust 30 the water was much less infected than on the 31st, so that its dangerous condition was apparently temporary only. He further discovered that in the house No. 40 Broad Street, which was the nearest house to the well, there had been not only four fatal cases of cholera contempora- neous with the epidemic, but certain earlier cases of an obscure nature, which might have been cholera, and that dejecta from these had been thrown without disinfection into a cesspool very near to the well. On his reporting these facts, in April, 1855, to the main committee, Mr. J. York, secretary and surveyor to the committee, was instructed to survey the locality and examine the well, cesspool and drains at No. 40 Broad Street. (e) Survey and Description of the Broad Street Well and its Surroundings Mr. York's report revealed a startling condition of af- fairs. The well was circular in section, 28 ft. 10 in. deep, 6 ft. in diameter, lined with brick, and when examined con- tained 7 ft. 6 in. of water. It was arched in at the top, dome fashion, and tightly closed at a level 3 ft. 6 in. below the street, by a cover occupying the crest of the dome. The bottom of the main drain of the house No. 40 Broad Street lay 9 ft. 2 in. above the water level, and one of its' sides was distant from the brick lining of the well only 2 ft. 8 in. It was — "constructed on the old-fashioned plan of a flat bottom, 12 in. wide, with brick sides rising about 12 in. high, and covered with old stone. 180 WATER AS A VEHICLE OF INFECTIOUS DISEASE As this drain had but a small fall, or inclination outward to the main sewer, the bottom was covered with an accumulation of soil deposit about 2 in. thick ; and upon clearing this soil away the mortar joints of the old stone bottom were found to be perished, as was also all the jointing of the brick sides, which had brought the brick work into the condition of a sieve, and through which the house drainage water must have percolated for a considerable period. . . . " After opening back the main drain, a cesspool intended for a trap, but misconstructed, was found in the area, 3 ft. 8 in. long, by 2 ft. 6 in. wide, and 3 ft. deep ; and upon or over a part of this cesspool a com- mon open privy (without water supply), for the use of the house, was erected, the cesspool being fully charged with soil. This privy was formed across the east end of the area, and upon removing the soil the brickwork of the cesspool was found to be in the same decayed condi- tion as the drain, and which may be better comprehended by stating that the bricks were easily lifted from their beds without any, the least, force ; so that any fluid could readily pass through the work, or, as was the case when first opened, over the top course of bricks of the trap, into the earth or made ground immediately under and adjoining the end wall eastward, this surface drainage being caused by the accumulation of soil in, and the misconstruction of, the cesspool. . . . " Thus, therefore, from the charged condition of the cesspool, the defective state of its brickwork, and also that of the drain, no doubt re- mains upon my mind that constant percolation, and for a considerable period, had been conveying fluid matter from the drains into the well ; but lest any doubt should arise upon this subject hereafter, I had two spaces of the brick steining, 2 ft. square each, taken out of the inside of the well — the first 13 ft. deep from the level of the street paving, the second 18 ft. deep, and a third was afterward opened still lower, when the washed appearance of the ground and gravel fully corroborated the assumption. In addition thereto, the ground was dug out between the cesspool and the well to 3 ft. below the bottom of the former, and its black, saturated, swampy condition clearly demonstrated the fact, as did also the small furrowed appearance of the underlying gravel observed from the inside of the well, from which the fine sand had been washed away during the process of filtration." — Report of J. York, Secretary and Surveyor to the Cholera Inquiry Committee. — L. c. It was thus established, as clearly as can be done by circumstantial evidence, that the great epidemic in St. James' Parish, Westminster, London, in 1854, was caused by the polluted water of the Broad Street well, which for a rr PAVEMENT. i ] f- I •i * 1 I 1 Yv WATER LINE ASIATIC CHOLERA AND the: broad street well. LONDON 1854. W. .WELL. 0_--_.__MAIN DRAIN OF HOUSE N0.40. VANOVlf. CELLARS UNDER STREET. C- ..CESSPOOL. P PRIVY. (AFTER MR. YORKfe ORIGINAL DRAWINGS.) ASIATIC CHOLERA AND THE BROAD ST. WELL 181 very few days was probably infected with cholera germs. It is much less clear how the well became infected, but it seems probable that the dejecta of a cholera patient found tolerably direct access to the well from the cesspool or drain of a house near by. There is no evidence whatever that the germs multiplied in the well, but rather much evidence that they rapidly died out. It is repeatedly stated in the report that the water was preferred for drinking because it was " cold," i.e. colder than the cistern water derived from the public water supply, and this condition would probably favor such dying out. That the water had long been polluted, there can be no doubt. There was evidence of this, and also some evidence that it was worse than usual at the time when it was prob- ably infected. One consumer spoke of it as having been at that time " offensive " in taste or odor. It is instructive to note that mere pollution seems to have done no obvi- ous harm. Specific infection, however, produced Asiatic cholera. Mr. Whitehead, in his singularly fair and candid report, raises an interesting question, viz., why, if an early and unrecognized case in the house in question brought about infection of the well, should not the four severer cases of undoubted cholera subsequently in the same house, with no known change in the drainage, have produced even greater disaster ? This question remains unanswered, ex- cept that after the removal of the pump handle on the 8th of September access to the well was shut off, and during the intermediate week the well may have been avoided by the frightened people ; or, owing to illness, less water may have been used in No. 40 Broad Street, so that the cesspool did not overflow ; or some other condi- tion, unknown, may have been changed. 1 82 WATER AS A VEHICLE OF INFECTIOUS DISEASE § 5. — An Epidemic of Asiatic Cholera in London in 1866 traced to a Polluted and Infected Surface Water Supply Dr. John Snow, in 1854, gave it as his opinion that not only wells but also public water supplies of far more gen- eral distribution, such as those furnished by cities or cor- porations and derived from rivers, may, under certain circumstances, be carriers of cholera. The great epidemics of Asiatic cholera in London in 1832, 1848-1849 and 1 85 3-1 8 54 had so strongly enforced this idea that in deal- ing with an important problem raised by epidemic cholera in London in 1866 Mr. J. Netten Radcliffe states that, " The predominant lesson derived from the outbreaks of 1 848- 1 849 and 1 85 3-1 8 54 was that the localities of chief prevalence of the disease were mainly, if not solely, de- termined by the degree of impurity of the water supply." 1 In 1866 Asiatic cholera, having again become epidemic in London, appeared in marked abundance in certain eastern districts of the city. A special investigation of its origin and distribution in those parts was made for the medical officer of the Privy Council (Mr., afterward Sir, John Simon), by Mr. J. Netten Radcliffe, whose very elabo- rate and painstaking report (published in extenso in the Ninth Report, London, 1867) served to fasten the blame for the excess in East London upon a special pollution and infection of a portion of the public water supply of the district, derived from the river Lea. 2 Briefly stated, it may be said that the epidemic of 1866 1 Ninth Rep. Med. Officer of the Privy Council, p. 295. See also Simon, Report on the Cholera Epidemics of London in 1848-1849 and 1853-1854 as affected by the Consumption of Impure Water. London, 1856. 2 Like some more recent students of English sanitation, Mr. Radcliffe seems to have been puzzled in regard to the correct spelling of this word. His note on the subject is therefore interesting. "The Rivers Pollution Com- missioners have spelled the name of this river Lee. All the standard maps and geographical works of reference spell the name Lea. I have adhered to the orthography commonly used." — Op. cit., p. 280. ASIATIC CHOLERA IN LONDON IN 1866 183 in England began on April 28 with a case in Bristol imported from Rotterdam. By May 15 the disease was prevailing among certain emigrants on board ships in the Mersey bound for New York. These emigrants had re- cently come from infected places on the continent. Scat- tered cases or outbreaks soon began to be reported from various parts of England, such as Swansea and South- ampton. The first death reported in London, according to Mr. Simon, was on July 18, and two days later an alarming number of cases appeared in East London. By July 21 it was clear that a special epidemic was pre- vailing in that region, and it is this special outbreak or " explosion " of cholera which forms the subject of Mr. Radcliffe's report. During the three months, — July, August and September, — there were registered in all England 10,365 deaths from cholera and 9570 deaths from diarrhoea. During the seven days ending August 4 there were in London alone 1053 deaths from cholera, and on one day (August 1) 204. The following comparison given by Mr. RadclifTe of the duration and mortality of the cholera epidemics in London in 1849, 1854, and 1866 is noteworthy : — Epidemic of Duration Deaths from Cholera Ratio to 10,000 Inhabitants Deaths from Diarrhoea Ratio to 10,000 Inhabitants 1849 1854 1866 23 weeks 23 weeks 23 weeks I3»565 10,684 5.548 5 1 43 18 2926 2551 2692 I3.O IO. I 8.8 " Cholera having been so less fatal in proportion to the number of persons attacked by the disease [in 1866] . . . the foregoing results would indicate increased, and perhaps increasing, safeguards in the metropolis." — Op. cit., p. 277. Mr. Radcliffe's investigation soon showed, however, that further safeguards, at least in respect to water supply, were urgently needed. 184 WATER AS A VEHICLE OF INFECTIOUS DISEASE Of the whole number of cholera deaths (5548), 3909 oc- curred in the east districts — "more than double the amount distributed over the rest of the metropolis." Moreover, it was in these districts that it increased most rapidly and to the highest point, and that it fell off afterward most quickly. Again, "no relative development of like magni- tude, suddenness, and shortness of duration had occurred in previous outbreaks of cholera in the metropolis," either in these or other districts. The brunt of the malady in 1849 and 1854 had fallen upon the south districts. " London was unquestionably less filthy at the time of the outbreak than in any previous outbreak. But the east districts could not claim a preeminence of filth. In the west of the metropolis and south of the river there were many localities as filthy. Neither Rotherhithe, nor Ber- mondsey, nor Southwark, nor Westminster, can be compared favorably with the east of London, yet the three former places suffered in a trifling degree as compared with the latter." — Op. cit., p. 293. Mr. Radcliffe carefully considered, in addition to "filth," such possible or supposed causes of cholera as "soil," " density of population," " sewerage," " locality," " meteor- ological states" and "altitude," and concluded that "not one of the conditions named . . . and believed to be liable to affect the progress and development of epidemic cholera, the disease being present, will account for more than very limited fluctuations of the outbreak, or for its localization in any particular spot in a restricted degree only. Any combination of these conditions is, moreover, equally inef- ficacious in explaining the peculiar localization and fluctua- tion in the east districts of the metropolis." (a) — Suspicion directed to the Public Water Supply of the Infected District The water supply alone remained to be considered, and " from the commencement of the localization of cholera in ASIATIC CHOLERA IN LONDON IN 1866 185 the east districts the probable association of this circum- scription with an impure water supply was forced upon the mind. . . . During the week ending the 28th of July it became obvious that the brunt of the outbreak had fallen upon the east districts; and in the bill of mortality for the week the registrar general directed attention to the fact that the field of prevalence of the disease was supplied with water from the East London Water Company's works." On August 1 the water company was notified that its supply was under suspicion, and the local sanitary author- ities were recommended by Mr. Simon to issue the following : — CHOLERA. NOTICE ! " The inhabitants of the District within which Cholera is prevailing are earnestly advised not to drink any water which has not previously been boiled. . . ." Further investigation satisfied Mr. Radcliffe that the "explosion" of cholera, which occurred just prior to July 21, had its origin in a temporary and limited infection of one portion of the East London Company's waterworks situated at Old Ford, on the river Lea. This river, con- siderably polluted by sewage in its upper reaches, was subjected to subsidence and filtration above, and at, Lea Bridge, respectively. Some of the filtered water was dis- tributed from this point, and no blame was attached to this portion of the supply. The remainder was conveyed farther into the metropolis by a closed iron conduit, to two covered reservoirs on the west bank of the Lea at Old Ford, and from this point pumped into the distributing mains. On the east side of the river at Old Ford were two uncov- ered reservoirs of large capacity, one of which had, at the time of the outbreak, direct connection with the covered reservoirs of filtered water. The open reservoirs were also 1 86 WATER AS A VEHICLE OF INFECTIOUS DISEASE connected with the filtering beds at Lea Bridge by an open and foul conduit, and they sometimes received the waste water from them unfiltered. They seem to have served as a reserve of unfiltered water to draw upon in case of clog- ging of the filter beds or in case of fire. It was admitted that the filter beds had, in fact, been seriously clogged just before the cholera outbreak, and it was in evidence that on at least one occasion, early in July, some 300,000 gallons of unfiltered water had been drawn from one of the uncovered reservoirs into the cov- ered reservoirs, to make good a deficiency in filtered water due to clogging of the filters. Precisely how this unfil- tered and impure water may have become infected by choleraic poison is not known. Mr. Radcliffe believed that soakage from the river, which was known to have been infected in its lower reaches, probably found access to the open reservoir. This is certainly possible, but it seems more likely that the infection may have found direct access to the river in the unpurified sewage of some city or town on the upper watershed above the point of intake of the East London Company's works. "In its course it (the river Lea) drains about 570 square miles of country, and before reaching Enfield Lock ... it receives the sewage of upward of 1 50,000 souls. It receives in its course, also, as affluents, several smaller streams, each in its degree a recipient of sewage." — Op. cit. y p. 296. The medical officer of the Privy Council, in his historical summary of the progress of the disease in England, states that even "within the next few days" after May 15 two cases were reported at Swansea, " and single cases in vari- ous other parts of the country." Of early July he writes, " evidently England was now being infected in many dif- ferent directions. Reports of new centres of infection became more and more frequent." It is not difficult to suppose that some one or more obscure case, or cases, may have occurred at this time or afterward upon the watershed TYPHOID FEVER IN LAUSEN, SWITZERLAND 187 of the Lea, and thus have directly infected that river, pol- luted as it plainly was with unpurified sewage. (J?) — The Obvious Value of Filtration as a Sanitary Safeguard On any hypothesis the supreme value and importance of filtration became manifest, for it was evidently only the unfiltered river water which did harm. The supply pumped from Lea Bridge was of filtered water derived from a highly polluted, and probably infected, river, and yet seems to have caused no spread of the disease. This apparently logical conclusion as to the value of fil- tration was, nevertheless, laid open to serious question a few years later, in consequence of the famous Lausen epidemic, to a consideration of which we may now turn. § 6. — An Epidemic of Typhoid Fever in Lausen, Switzer- land, due to an Infected Ground Water or Spring Typhoid fever derived from impure drinking water is now recognized as of common occurrence, and a great number of destructive epidemics have been traced to this source. The first to attract universal attention was that which occurred in Lausen, Switzerland, in 1872; and because of certain peculiar conditions connected with it, and especially because of its influence upon the theory and practice of the purification of water by filtration, it deserves the most care- ful consideration by all students of sanitation. The epidemic occurred in the little village of Lausen in the canton of Basel in Switzerland in August, 1872. Lausen was a well-kept village of 90 houses and 780 inhabitants, and had never, so far as known, suffered from a typhoid epidemic. For many years it had not had even a single case of typhoid fever, and it had escaped the cholera even when the surrounding country suffered from it. Suddenly, in August, 1872, an outbreak 1 88 WATER AS A VEHICLE OF INFECTIOUS DISEASE of typhoid fever occurred, affecting a large part of the entire population. A short distance south of Lausen was a little valley, the Fiirlerthal, separated from Lausen by a hill, the Stockhal- den, and in this valley, on June 19, upon an isolated farm, a peasant, who had recently been away from home, fell ill with a very severe case of typhoid fever, which he had apparently contracted during his absence. In the next two months there occurred three other cases in the neigh- borhood, — a girl, and the wife and the son of the peasant. No one in Lausen knew anything of these cases in the remote and lonely valley when suddenly, on August 7, ten cases of typhoid fever appeared in Lausen, and by the end of nine days, fifty-seven cases. The number rose in the first four weeks to more than one hundred, and by the end of the epidemic in October to about 130, or seventeen per cent of the population. Besides these, fourteen children who had spent their summer vacation in Lausen fell ill with the same disease in Basel. The fever was distributed quite evenly throughout the town, with the exception of certain houses which derived their water from their own wells and not from the public water supply. Attention was thus fixed upon the latter, which was obtained from a well or spring at the foot of the Stockhalden hill on the Lausen side. The well was walled up, covered and ap- parently protected, and from it the water was conducted to the village, where it was distributed by several public foun- tains. Only six houses used their own wells, and in these six there was not a single case of typhoid fever, while in almost all the other houses of the village, which depended upon the public water supply, cases of the disease existed. Suspicion was thus directed to the water supply as the source of the typhoid poison, very largely because no other source could well be imagined. A distribution of the disease from the farm through the air was hardly conceivable because houses in the Fiirlerthal, although lying upon the same plateau and TYPHOID FEVER IN LAUSEN, SWITZERLAND 189 naturally more accessible through the atmosphere, remained free from the disease, a fact which seemed to prove that the infected farmhouse could not have communicated the dis- ease to Lausen either through the ground water or through the air. In order, however, to clinch the evidence that the Lausen water supply had been infected, it became desirable to show some source from which an infection, so unusual and re- markable, could have come, and precisely how it had hap- pened. There had long been a belief that the Lausen well or spring was fed by and had a subterranean connection with a brook (the Fiirler brook) in the neighboring Fiirler valley ; and since this brook ran near the peasant's house and was known to have been freely polluted by the excreta of the typhoid fever patients, absolute proofs of the connec- tion between the well of Lausen and the Fiirler brook could not fail to be highly suggestive and important. Fortunately such proofs were not far to seek. Some ten years before, observations had been made which had showed an intimate connection between the brook and the well. At that time, without any known reason, there had suddenly appeared near the brook in the Fiirler valley below the hamlet, a hole about eight feet deep and three feet in diameter, at the bot- tom of which a considerable quantity of clear water was flowing. As an experiment, the water of the little Fiirler brook was at that time turned into this hole, with the result that it had all flowed away underground and disappeared, and an hour or two later the public fountains of Lausen which, on account of the dry weather prevailing at the time, were barely running, had begun flowing abundantly. The water from them, which was at first turbid, later became clear ; and they had continued to flow freely until the Fiirler brook was returned to its original bed and the hole had been filled up. But every year afterward, whenever the meadows below the site of the hole were irrigated or over- flowed by the waters of the brook, the Lausen fountains 190 WATER AS A VEHICLE OF INFECTIOUS DISEASE soon began to flow more freely. In the epidemic year (1872) the meadows had been overflowed as usual from the middle to the end of July, which was the very time when the brook had been infected by the excrements of the typhoid patients. The water supply of Lausen had in- creased as usual, had been turbid at the beginning and had had a disagreeable taste. And about three weeks after the beginning of the irrigation of the Fiirler meadows, typhoid fever had broken out, suddenly and violently, in Lausen. In order to make matters, if possible, more certain, the following experiments were made, but unfortunately not until the end of August when the water of the Lausen supply had again become clear. The hole which had appeared ten years earlier, and had afterward been filled up, was reopened, and the little brook was once more led into it; three hours later the Lausen fountains were yielding double their usual volume. A quantity of brine containing about eighteen hundred pounds of common salt was now poured into the brook as it entered the hole, whereupon there appeared very soon in the Lausen water, first a small, later a considerable and finally a very strong, reaction for chlorine, while the total solids increased to an amount three times as great as before the brine was added. In another experiment, five thousand pounds of flour (Mehl\ finely ground, were likewise added to the brook as it disappeared in the hole ; but this time there was no increase of the total solids, nor were any starch grains detected in the Lausen water. It was naturally concluded from these experiments that while the water of the brook undoubtedly passed through to Lausen and carried with it salts in solution, it neverthe- less underwent a filtration which forbade the passage of suspended matters as large as starch grains. Dr. Hagler, from whose report the foregoing facts are taken, was careful, however, to state that " it is not denied that small organized TYPHOID FEVER IN LAUSEN, SWITZERLAND 191 particles, such as typhoid fever germs, may nevertheless have been able to find a passage." As a matter of fact Dr. Hagler's minute account does to-day give us some indication that such germs might easily have passed from the brook to Lausen, for the turbidity of which he repeatedly speaks is evidence of the passage of particles probably as small as, and possibly smaller than, the germs of typhoid fever. ( Typhus und Trinkwasser, Vierteljahrschrift fur offentliehe Gesundheitspflege, VI, 1 54 ; also Sixth Report, Rivers Pol- lution Commission of 1868. London, 1874.) Unfortunately, this was before pure cultures of bacteria were known, and no experiments were made with suspended matters as small as bacteria. The conclusion was inevi- table that although filtration had in this case sufficed to remove starch grains, it had been powerless to remove the germs of typhoid fever; and, accordingly, filtration as a safeguard against disease in drinking water fell for a time into disrepute. 1 § 7. — An Epidemic of Typhoid Fever in Caterham and Red Hill (England ) traced to a Polluted and Infected Ground Water Supply A number of epidemics of typhoid fever had been already traced with more or less certainty to polluted water supplies when, in 1879, there appeared a serious outbreak of this disease in the towns of Caterham and Red Hill in England. The duty of investigation of this case was fortunately as- signed to Dr. Thorne-Thorne, and his report which appears in the Report of the Medical Officer of the Local Govern- ment Board for 1879, pp. 78-92, is a model of careful investigation and sound reasoning. Briefly summarized, it was as follows : The total number of cases affected 1 See a paper by the author on The Rise and Progress of Water-Supply Sanitation in the Nineteenth Century. Journal New England Water Works Association, XV (1901), p. 330, No. 4. 192 WATER AS A VEHICLE OF INFECTIOUS DISEASE during the epidemic proper was 352. The total number of deaths, 21. The disease was typical typhoid fever, the patients exhibiting the characteristic rose-spots and diar- rhoea and some of them suffering from severe pulmonary and intestinal complications, the latter including perfora- tion of the bowels which, in four cases, was the immediate cause of death. The first person attacked sickened on January 19, 1879; a second, on the 20th; two more on the 23d ; three on the 24th, and thenceforward up to Feb- ruary 2, to which date information was at first limited, fresh attacks in fresh houses occurred day by day. Caterham lies in the rural sanitary district of Godstone, and had a population of about 5800. It included at this time a portion called Lower Caterham, near the head of the Caterham valley, a valley bounded by chalk hills. The houses in this part consisted mainly of superior villa resi- dences. The other or upper part lies at a higher altitude. Here, also, are a number of villas, one of the asylums be- longing to the Metropolitan District Asylums Board, and certain barracks. The cases of typhoid fever referred to, and which had occurred in the fortnight ending February 2, were spread over a very wide area, some in Upper and some in Lower Caterham, extending to the extreme outskirts of both places. The families attacked belonged to no special class, both rich and poor having suffered. It was appar- ent that the disease could not have been conveyed by means of any general system of sewers for the majority of the houses drained into separate cesspools. There was also no possibility that there had been any common cause of infection in connection with the prevailing means of excrement disposal, because there was nothing in common with regard to such disposal. The possibility of infection by means of milk supply was next inquired into, but dis- proved. It was also evident that personal infection could not in any way have led to the outbreak. Finally, it was TYPHOID FEVER IN CATERHAM, ENGLAND 193 stated that for some years past the locality had been remarkably free from the disease, and only one isolated case could be heard of as having occurred during the twelve months preceding the outbreak, and this case was believed to have been imported. Caterham was supplied with water by the Caterham Waterworks Company, and of the forty-seven persons attacked during the fortnight in question, forty-five re- sided in houses supplied with this water. Suspicion was thus directed to the water supply, and was confirmed when it was ascertained that the two remaining patients, though living on premises having private wells, had been in the habit of spending the day at houses supplied with the company's water, and had admittedly used this water. It further appeared that in the Caterham Asylum, having nearly two thousand patients, no typhoid fever had ap- peared, and that there had been a similar absence of the disease among the five hundred men in the barracks. Both these establishments derived their entire water from a well sunk 462 feet into the chalk. In the meantime, information arrived that typhoid fever was also epidemic in Red Hill, a neighboring community. Red Hill had an estimated population of 9500, and included two or more villages, besides an asylum for idiots. It was about eight miles distant from Caterham, lay on a different geological formation, and was well sewered. Nevertheless, in regard to typhoid fever, the two places were remarkably similar. In both, the epidemic began at about the same time. The first two cases in Red Hill occurred on January 20 ; three more on the 21st; five more on the 22d; twelve on the 23d, and at the end of the first fortnight, namely, by February 2, the total number of houses affected was 96, and the number of patients had reached 132. There was nothing which threw suspicion upon the sewers. The community had been totally free from 194 WATER AS A VEHICLE OF INFECTIOUS DISEASE the disease for at least eighteen months, and there was no reason to suspect the milk supply. The water supply, on the other hand, was derived for the most part from the waterworks of the Caterham Waterworks Company, and a sanitary official, Mr. Jacob, independently of Dr. Thorne and the local officer in Caterham, had arrived at the conclusion that the Caterham water was in all probability the vehicle of the disease. Of the ninety-six houses affected during the first fortnight of the epidemic at Red Hill, ninety-one actually drew their water from the Caterham Company's mains, and the histories obtained with reference to the attacks in the remaining five cases were such as to confirm the impression that the Caterham Company's water had been the immediate cause of the epidemic. For example, at one of these houses where ultimately three persons were attacked, the supply, as was hitherto believed, had been exclusively derived from a rain water tank, but it was now ascertained that the Caterham Company's water was in addition procured surreptitiously ; that at another house, for which there was apparently no water supply, the company's water was procured from a neighbor's ; and with regard to the remainder, the patients infected were not only persons who were employed where the company's water was in use, but several of them had partaken of the water at their meals. Certain localities in Red Hill, namely, Meadvale, having about 1 60 houses, and in Red Hill itself a group of 30 houses supplied with wells, were practically exempt from typhoid fever. Still more striking was the case in Reigate, a town which forms the western ward of the burough of which Red Hill is the eastern ward. Rei- gate had a population of about 8500, provided, however, with a different water supply; and this region escaped entirely, only two cases, undoubtedly imported from Red Hill, having occurred there. All the facts ascertained in connection with the course TYPHOID FEVER IN RED HILL, ENGLAND 195 of the epidemic up to February 2 afforded very strong presumption that it had been caused by the use of the Caterham Company's water. Further developments made this view almost certain. The Waterworks Company derived its supply from two deep wells, situated about 30 feet apart, and about 490 feet deep. Both were several feet in diameter. Moreover, they were connected, by three adits in the chalk. From the wells the water was pumped to reser- voirs, in which it was submitted to Clark's softening process. The reservoirs freely communicated, and from them the supply was delivered by gravitation. During the preceding twelve months a third well had been made, 90 feet away from the others and of similar depth. From 1 86 1, and until the construction of the third boring, the water supplied by the company was held in high repute ; but since that time, and prior to the epidemic, complaints had been made with regard to the water. These were due to an unavoidable turbidity and to inter- ruptions in the process of softening. Apart from this turbidity and temporary hardness, there was no reason to believe that the water was objectionable; and consider- ing the deep sources of the supply, it was by no means apparent how the water could have been the means of pro- ducing an extensive epidemic of typhoid fever. Dr. Thorne inquired carefully into the possibility of contamination of the supply en route, but with negative results. He next sought to discover whether any contamination had taken place in the reservoirs or in the mains. But these sources also were satisfactorily excluded. Many other points re- lating to the method of distribution of the water were inquired into, but none led to any explanation of the cir- cumstances of the epidemic. It was next suggested that cesspool drainage or soakage of surface filth might have existed around the com- pany's wells. Certain cesspools were found in the vicinity, 196 WATER AS A VEHICLE OF INFECTIOUS DISEASE but after careful examination were excluded as probable sources of contamination. In the meantime facts were brought to light which led to an extension of the inquiry in another direction. It ap- peared that during the latter part of 1878 and the begin- ning of 1879, tne company had constructed an adit from one of their old wells up to the new boring, which was then being sunk. This adit was in the chalk at a depth of 445 feet. It was 6 feet by 4 feet in section and 90 feet long. A number of men were employed in the work, some of them being in the wells below, others on the surface. It was ascertained that one of the men who left work some time in January was reputed to have been ill, though no inquiries had been made concerning him since he quitted the works. This man was sought out, and eventually the following facts were obtained: — "J. K., aged thirty-two years, resided in Caterham, and was employed by the company as a laborer from October 25, 1878. The work assigned to him was that of ' loading-man, 1 he being employed in the adit below in attaching to a rope let down from above the buckets by which the excavated chalk was raised to the surface, and in again receiving those buckets when lowered full of bricks and cement required for the work in progress. From December 14 to December 29, J. K. was absent. When he returned he was in perfect health, but in about a week, that is, about January 5, 1879, ne kit himself ailing. His symptoms, which, according to his statement, steadily increased, were at first loss of appe- tite, recurring attacks of shivering alternating with a feeling of heat, great pains in the limbs which he attributed to rheumatism, but which, instead of being confined to any of the joints, were described both by himself and by his wife as an ' aching all over,' and diarrhoea. As the symptoms became aggravated, he was so exhausted during his work and became so 'giddified' that he was more than once drawn to the sur- face, and immediately on his return home he was compelled to go to bed. More than once his wife noticed that he was ' light-headed ' in his sleep. All this while the diarrhoea continued, the man making a great effort to remain at his work, because, as explained, he had had no employment between the 14th and the 29th of the previous month. " With reference to this man's diarrhoea, it is necessary to make the following explanation : Both from his own statement, and from that of TYPHOID FEVER IN CATERHAM AND RED HILL 197 others, it appears that all the men who worked in the adit were ex- pected to make such preparation before descending the well that no occasion should exist for relieving themselves below ; but should such necessity ever arise, and should there be at such a time any difficulty or delay in their being drawn to the surface, the buckets which were regu- larly being raised to the surface were to be used for that purpose. J. K. states that he strictly complied with these regulations before de- scending, but that, notwithstanding all his efforts, the purging under which he was laboring was such that he was compelled to evacuate whilst in the adit ' at least two or three times ' during each shift, the shifts lasting apparently from eight to twelve hours each, according to circumstances. Indeed, as time went on, the man's diarrhoea must have been considerable, for besides the attacks which came on whilst in the adit, he almost invariably suffered from it before descending, im- mediately after ascending, and also at his own house. So matters con- tinued until January 20, when work was again suspended for two days on account of a rise in the water level. But during the night of the 2 1 st he was so much worse that he was unable to rise next morning. According to his wife's statement, he found he could not stand when he got up, and returning to his bed, suffered from ' shivering down the back, aching, and exhaustion ' ; and later on severe abdominal pain came on which compelled him to lie with his knees drawn up ; he was also 'burning hot.' This pain was looked upon as 'cramp,' and was alleviated by linseed-meal poultices, which were applied by his wife. The more severe symptoms, including the diarrhoea, having subsided, he was two days afterward able to get up for a while, and from this time convalescence appears to have set in. No medical advice was sought, mainly, as he explained to me, owing to his straitened circum- stances. When I saw him, on February the 8th, he had the aspect of a man who had recently suffered from some acute disease ; he was still very weak, and it was obvious that he had greatly lost flesh." Dr. Thorne and Dr. Jacob with extreme care searched further into the history of this case, with the following result, in Dr. Thome's words : — " I have now no hesitation in taking it as a fact, that a man ill of enteric [typhoid] fever from January 5 to the end of the month was occupied during the first fortnight of that period at work in the well of the Caterham Waterworks Company. The fact, it will be observed, is not inferred from any consequences of it, but simply from what was seen and heard of the particular individual. " But now let us see what those consequences would have been. If 198 WATER AS A VEHICLE OF INFECTIOUS DISEASE this man's stools could by any means have found their way into the water of the well in which he had been working, and being enteric fever stools could thus have led to the development of the poison of that disease in the well, the effect on the water consumers ought to have been noticed within from about ten to fifteen days after the date when the diarrhoea first came on. And this, in effect, is precisely what did take place, the epidemic having commenced on January 19 and 20 in Caterham and Red Hill, respectively. This remarkable concurrence of dates led to a more detailed inquiry as to the course of the man's diarrhoea whilst working in the adit. He admitted that the purging was very copious, in short, that it ' ran from 1 him ; indeed, when at home, he was, because of the suddenness of its onset, unable to resort to the closet. He further admitted that, owing to his frequent use of the bucket whilst at work, complaints were made by his fellow-workmen on the surface ; but he stoutly denied that he had ever been so pressed by necessity, or so influenced by those complaints, as to relieve himself in the adit without waiting for a bucket. But even accepting his de- nial, there were undoubted means by which his evacuations could have found their way into the water. According to his statement, the bucket was used as a closet when it was empty, when half full, and when full ; he added, however, that when it was full he first took some of the chalk out and subsequently replaced it. During an earlier stage of my in- quiry I had occasion to descend one of these wells, and I noticed that any article let down by a rope, by its oscillations to and fro, came into constant and somewhat violent contact with the walls of the wells, and on inquiry of J. K. whether the same did not take place with the bucket, he admitted not only that this was so, but that some of its contents fre- quently fell over a stage into the water below. On further inquiry, he added that some portions of his evacuations probably did so also. And he further stated that the looseness of his bowels was such that the bucket itself must almost of necessity have been stained with them. This bucket, which was merely emptied out above, then received, as already explained, materials which were used in the construction of the works below. Here, then, were the stools of an enteric fever patient, from about January 5 onwards, getting into the Caterham Company's water and distributed with that water to the district served by the company. " Now we know from ample experience that enteric fever is produced, and produced with the maximum of certainty, when the specific evacua- tions of that disease are consumed by a population. Again, it is a mat- ter of experience that where enteric fever has been conveyed through water, some fortnight has to elapse between the distribution of the water and the occurrence of the disease among the community served TYPHOID FEVER IN CATERHAM AND RED HILL 199 by it. But a fortnight after January 5 to 19, i.e. from January 19 to February 2, the disease became widely spread throughout Caterham and Red Hill ; the distribution of the fever being limited, as we have already seen, to houses supplied with the water of the Caterham Com- pany. There can, I think, be no doubt that we have in the man J. K. the cause of the disease which followed. 1 ' A further study by Dr. Thorne made with similar care showed that wherever the Caterham water indubitably went, typhoid fever was also distributed. A part of this latter investigation was particularly interesting. The village of Warlingham, lying about three miles from the Caterham Company's Works, was supplied by that company with water, and yet had no typhoid fever. It appeared in the sequel, however, that in order to add to the Caterham Company's supply during certain portions of the time when the Caterham wells were undergoing alterations and furnishing a diminished supply, water had been pumped into the Caterham Company's mains by the Kenley Water- works Company; namely, continuously every night after November 26, 1878, to January 3, 1879; resumed again from January 5 to 10, then discontinued until the nights of the 14th and 15th, finally ceasing on the morning of the 1 6th. This water was therefore pumped into the Caterham Company's mains for the period January 5 to 9, during which the distribution of infection must have commenced. The Kenley water was not, however, mixed directly with the Caterham water. It was pumped in at one particular point, and that point was the extreme farther end of the Warlingham branch of the system. Furthermore, the ca- pacity of the main between Caterham and Warlingham, and of the branches of this main in Warlingham, was somewhat over 12,000 gallons. Accordingly, before the Kenley water could get to the Caterham Company's reservoirs, it had to fill the whole of the three-inch Warlingham main and its system of branches, besides one other larger main nearer to Caterham. It is therefore fair to suppose that the inhab- 200 WATER AS A VEHICLE OF INFECTIOUS DISEASE itants of Warlingham rarely, if at all, and probably never, during this time, received any of the Caterham water. In the end Dr. Thorne was led to believe that the almost com- plete exemption of Warlingham — for only a single case appeared there during the epidemic period — was powerful support to his views in regard to the true source of this epidemic. The total number of cases was 352, and the total number of deaths, 21, to the end of February. After that time only a few scattered cases occurred. The disease, as has been stated, was typical typhoid fever, the patients exhibit- ing the characteristic rose-spots, diarrhoea, etc. Most of the cases were of an exceptionally mild character, and the majority attacked were children. Amongst adults, women were more frequently attacked than men. The low fatality is noteworthy, and agrees with the theory of great dilution of the infectious material. § 8. — An Epidemic of Typhoid Fever in Plymouth {Penn- sylvania) traced to a Polluted Surface Water Supply One of the most instructive epidemics in the annals of sanitary science is the epidemic of typhoid fever which sprang from a polluted water supply in Plymouth, Penn., in the spring of 1885. Plymouth at that time was a mining town of about eight thousand inhabitants. It had grown up rapidly, and was not in good sanitary condition ; but it was provided with an apparently excellent, though limited, pub- lic water supply derived from a mountain stream, travers- ing an almost uninhabited watershed. There were, in fact, on the watershed only two houses so placed as to be able to contaminate the supply. It would appear from the ex- cellent report of Dr. L. H. Taylor, 1 of Wilkesbarre, from which the present account is drawn, that the inhabitants 1 First Annual Report, State Board of Health and Vital Statistics of Penn- sylvania, pp. 176-195. Harrisburg, Penn., j886. TYPHOID FEVER IN PLYMOUTH, PENN. 201 of one or both of these had nevertheless for some time, perhaps for years, been polluting the public supply of Plymouth with ordinary faecal matters ; but no harm was observed or even suspected until April, 1885, when, as was afterward discovered, the specific infection of typhoid fever was superadded to ordinary faecal pollution. Thereupon, out of a population of about 8000 persons, 11 04 con- tracted typhoid fever, and 114 died. The story may be briefly told. " The first case belonging to this epidemic occurred on April 9, and from this time on the disease spread rapidly. During the week begin- ning April 12, from fifty to one hundred new cases appeared daily, and on one day it is said two hundred new cases were reported. . . . Various theories were put forth, some declaring it [the epidemic] to be due to the filth of the town ; some that it was due to drinking polluted well water ; others, polluted river water ; and still others that it was due to a peculiar condition of nature, by no means explainable. " Among the various theories advanced, one of the first was that it was due to the accumulated filth of the town, which, being acted upon by the warm rays of the April sun, had suddenly become noxious, and the emanations, therefore, had caused the disease. This especially suited the ' typho-malarial ' theorists. But although Plymouth was not an espe- cially clean town, it was not, on the other hand, more filthy than other neighboring towns where the disease did not prevail, nor was it at this particular time in worse condition than in preceding years. . . . " All classes of people were attacked, the clean as well as the filthy, and all parts of the town affected, the highlands as well as the valley . . . and thoughtful minds naturally turned to the water supply as fur- nishing the true cause of the invasion." In addition to certain wells and springs the inhabitants had access to one or both of two public water supplies. A small portion of the town received regularly water from the Susquehanna River, pumped by the Delaware and Hudson Coal Company, and those who used this water exclusively did not suffer from the disease. The greater portion, how- ever, was supplied by the Plymouth Water Company, which in 1876 began supplying the town "with water of remarkable purity, from a neighboring mountain stream 202 WATER AS A VEHICLE OF INFECTIOUS DISEASE which had its source in a beautiful sand spring some miles away." On the stream had been built, successively, four storage reservoirs: No. i, the first, the lowest, and that serv- ing as the distributing reservoir (see diagram), having a capacity of 300,000 gallons ; No. 2, next above, a capacity of 1,700,000 gallons; No. 3, still higher, of 3,000,000 gal- lons ; and finally, No. 4, highest of all, of 5,000,000 gallons. In spite of this storage capacity, however, the supply was at times insufficient, and was then supplemented by direct pumping from the Susquehanna River, a stream polluted, and at times infected, by the sewage of Wilkesbarre, a city of 30,000 inhabitants, lying on the same river only three miles above. " Water from the river was first pumped . . . in 1878, and occasionally in succeeding years, e.g. in 1881, 91 days; in 1882-1883, ... 65 days; 1883-1884, 124 days; 1884 [additional], 118 days. This water, though objectionable, . . . has never been followed by any [re- ported] epidemic of typhoid fever." In the spring of 1885 resort was again had to the river, which was used just before the epidemic appeared, viz. from March 20 to 26, 1885. Dr. Taylor was therefore obliged to consider very carefully the possibility that the source of the epidemic lay in the river water. He was able, nevertheless, by various independent lines of evidence, to show conclusively that the great epidemic, which began with a single case on April 9, and by the end of another week had risen to alarming proportions, could not possibly be attributed to the use of the sewage-polluted river water. It was easy to show that the milk supply and the well- water and spring-water supplies could not furnish adequate explanation of the epidemic, so that there remained only the mountain supply of water to be investigated. " There remains but one possible cause for this most serious and de- plorable outbreak, and that is contamination of the water supplying the company's reservoirs. A glance at the accompanying map will show the location of this stream and of the several reservoirs. Above the 4TS RESERVOIR HOUSE FROM WHICH ^THE INFECTION CAME WELSH HILL. MAP or PLYMOUTH, PENN IN 1865. TYPHOID FEVER IN PLYMOUTH, PENN. 203 starting point of the water pipes there is but one house situated upon the banks of this stream, and one upon the banks of the fourth reservoir. " In the house between the third and fourth reservoirs, situated almost immediately upon the stream, there lives a man who but recently has recovered from the effects of a severe attack of typhoid fever. This patient went to Philadelphia, December 24, 1884, and while there, he thinks, contracted the disease. Whether he did thus contract the dis- ease in Philadelphia may, we think, admit of question. But it is never- theless true that he returned to his home, January 2, 1885, and for many weeks was seriously ill with genuine typhoid fever. Early in March he was convalescent and was out of bed. A relapse occurred about the middle of March, and he was very sick on the 16th. On March 16 and 17 he had hemorrhages of the bowels of so severe a type that, on March 18, his life was despaired of, even by his physician. "He, however, rallied, was quite ill for some time, but was con- valescent in April, so that his physician discontinued his visits after April 12. " During the course of his illness, his dejecta passed at night, with- out any attempt at disinfection, were thrown out upon the snow and frozen ground, toward and within a few feet of the edge of the high bank, which slopes precipitously down to the stream supplying the town with water. " The nurse in charge states explicitly that in emptying the chambers at night she did not stand on the porch to throw out the contents, but stepped down some distance and threw them into the creek. If she stepped but a few feet away from the porch, she would empty the ex- creta within twenty-five or thirty feet of the edge of the stream. " The dejecta passed during the day were emptied into a privy a little farther back, the contents of which lie almost upon the surface of the ground, and at the first thaw or rain they too would pass down the slop- ing bank and into the stream. These dejecta were thrown out from time to time until the accumulation no doubt equalled the daily passages from many such patients. They remained innoxious upon the snow and frozen ground until some time between March 25 and April 1, when they were washed into the stream and thence into the third reservoir. "The house in question does not stand in a ravine nor in a pro- tected spot, but in an open clearing, with land sloping toward the south, which clearing would naturally feel the effects of the sun's rays and part with its snow and accumulated filth sooner than the more protected re- gions which also drain into the stream, so without cavil the first water from the effects of the thaw to enter the third reservoir would be from the melted snow in the immediate vicinity of this house. 204 WATER AS A VEHICLE OF INFECTIOUS DISEASE "The maximum temperature . . . was on March 26,46.5° F. ; March 27, 56° ; March 28, 43° ; March 29, 37°, increasing rapidly until April 4, when a temperature of 70° F. was reached. "March 26, with a maximum temperature of 46.5 F., is the first day on which any considerable thaw could occur. Upon the evening of this day, the superintendent of the water company visited the reservoirs to ascertain whether it would be allowable to discontinue the pumping of river water. He found the first and second reservoirs almost entirely empty, while the third was filling rapidly, the short pipe which allows the water to discharge from the bottom of the third into the stream lead- ing to the second reservoir being tightly frozen. " He caused a fire to be built to melt the ice in this pipe, and then stopped the river pumps. The honest act of an honest man, and sim- ply in the discharge of his duty and with kindliest intent. But of what a catastrophe was he the unconscious usher and hastener ! The water, with its accumulated typhoid fever poison, was discharged from the bot- tom of the third reservoir, ran down to the second, on to the first, and was thence distributed to the town, in all probability between the 28th of March and the 4th or 5th of April. " In considering the possibility of one patient poisoning more than a thousand in Plymouth, we must bear in mind all the attending cir- cumstances : — " 1 . The accumulation of weeks — which equalled the dejecta from many ordinary patients, and which lay for a time dormant upon the snow and frozen ground. " 2. The nearness to the stream. The house is so situated that all of the excreta were thrown within a few yards of its banks, and the con- formation of the ground is such that its surface water could not possibly drain in any other direction. " 3. The unusually warm weather — which caused a sudden thaw and poured the surface water into the empty reservoir. " 4. The concentration of the poison in a small amount of water. " 5. The short distance to the town ; and finally, the possible previous preparation of the soil for the reception of this seed, which sprang at once into vigorous growth and ripened for an abundant harvest of death. « It would seem that the mere statement of facts, as found in the few preceding pages, is amply sufficient to explain the cause of this remark- able epidemic, and we need have no hesitation in declaring the pollution of the mountain stream, which supplies the reservoirs of the water com- pany of Plymouth, to be the sole cause of the remarkable outbreak of typhoid fever in this borough. TYPHOID FEVER IN PLYMOUTH, PENN. 205 " During the period of pumping from the Susquehanna, the water in that river was lower than it had been at any time for years, and the surface was frozen tight. The city of Wilkesbarre, containing thirty thousand inhabitants, delivers its sewage directly into the Susquehanna, the mouth of the lower sewer emptying only two miles above the Ply- mouth Pumping Station, while the current is very rapid between the two towns. The water is further contaminated by refuse water from five or six lines as well as by the garbage from the abattoirs at Wilkes- barre. Notwithstanding this unusually filthy condition of the Susque- hanna River, it is beyond question entirely innocent of causing the epidemic. . . ." Dr. Taylor's conclusions were confirmed in all essential particulars by other students of the epidemic, among whom may be mentioned Drs. Shakespeare and French of Phila- delphia ; Briggs of Buffalo ; and Biggs, Taylor, Edson and others, of New York. The first to suggest publicly the pollution of the mountain supply as the probable cause of the epidemic was Dr. R. Davis (in a Wilkesbarre newspaper published on April 29). We may readily agree with Dr. Taylor in his conclu- sions : — " It is safe to say that this was one of the most remarkable epidemics in the history of typhoid fever, and it teaches us some important lessons, at fearful cost. One is, that in any case of typhoid fever, no matter how mild, nor how far removed from the haunts of men, the greatest possible care should be exercised in thoroughly disinfecting the poisonous stools. The origin of all this sorrow and desolation occurred miles away, on the mountain side, far removed from the populous town, and in a soli- tary house situated upon the bank of a swift-running stream. The at- tending physician did not know that this stream supplied the reservoirs with drinking water. Here, if any place, it might seem excusable to take less than ordinary precautions ; but the sequel shows that in every case the most rigid attention to detail in destroying these poisonous germs should be enjoined upon nurses and others in charge of typhoid fever patients, while the history of this epidemic will but add another to the list of such histories which should serve to impress medical men, at least, with the great necessity for perfect cleanliness — a lesson which mankind at large is slow to learn. " Another lesson taught by this history comes more nearly home to us all. The water-companies throughout our land should be taught 206 WATER AS A VEHICLE OF INFECTIOUS DISEASE that they must furnish us the water for which we pay, from the very best source which the country affords. Not only should they avoid the use of river water contaminated by sewage, but they should be com- pelled to remove from the banks of their streams and reservoirs not only all probable, but all possible sources of pollution." Dr. M. S. French made an interesting estimate of the financial waste or loss involved in the Plymouth epidemic, and his paper, which follows that of Dr. Taylor (pp. 196- 217, /. c.\ contains also a complete and impressive list by name of those attacked with typhoid fever. Dr. French estimates the cost of the sickness — " expenses incurred by the epidemic " — at $67,100.17, of which $8,000 were spent in maintaining a temporary hospital. " Of those who were ill with the disease and recovered, the loss of earnings during their illness was found to be $30,020.08. Thus the total cost of the epidemic is reckoned at $97,120.25. By the 114 deaths, a monthly earning of $1,534.96 ceased, showing a loss of $18,419.52 per year in incomes." Dr. French does not, as he might have done, capitalize this latter sum, and add the result to the gross loss ; if he had done so, he might have concluded that the total cost of this disastrous epidemic was more than half a million of dollars. It will be observed that the fatality (1 14 deaths in 1 104 cases) was much higher than in the Caterham epi- demic (21 deaths in 352 cases), or 10.3 per cent against 5.9 per cent, and that this corresponds well with the probable relative concentration of the infectious material in the two epidemics. THE COST OF AN EPIDEMIC 20? § 9. — Typhoid Fever in Lowell, Lawrence and Other Cities on the Merrimac River In the valley of the Merrimac River, which is a large, swift stream draining a considerable portion of southern New Hampshire and northern Massachusetts, are situated a number of cities and towns of which the history in re- spect to typhoid fever is interesting and instructive. Situ- ated in the same valley, under closely similar climatic conditions, they are also, for the most part, manufacturing towns or cities, and have populations especially favorable for purposes of sanitary comparison. Lowell, Lawrence and Manchester are devoted chiefly to textile industries, and nearly the same might be said of Nashua and Con- cord, while Haverhill is what is called a "shoe" town, and Newburyport, while possessing some textile industries, is more diversified in this respect. In connection with his duties as biologist to the State Board of Health in Massachusetts, and especially with his work at the Lawrence Experiment Station of that Board, the author was already somewhat familiar with the sanitary history of the cities and towns situated in the Merrimac Valley, when, in December, 1890, a serious epidemic of typhoid fever having appeared in the city of Lowell, lying only nine miles above Lawrence, he was instructed by the Board to make a thorough investigation. At almost the same time he was also invited by the Water Commissioners of Lowell to conduct a similar inquiry on their behalf. Accordingly, clothed with ample authority and provided with every opportunity, he set to work. The population and death-rates from typhoid fever in the principal cities of the Merrimac for the two years preceding the outbreak of the great epidemic of 1 890-1 891 are shown in the following tables : — 208 WATER AS A VEHICLE OF INFECTIOUS DISEASE TYPHOID FEVER IN THE PRINCIPAL CITIES ON THE MERRIMAC RIVER Deaths per 100,000 Inhabitants (Population from United States Census of 1890) 1888-1889 < s a 3 "3 3 3 S a a, in | O M s « > La I i 4) b « 3 a b 3 I fa 3 S S u Concord, N. H .0 .0 .0 .0 5-9 17.6 i 7 .6 i 7 .6 11. 8 .0 •O .0 70-5 Manchester, N. H. . .0 2.3 4.6 .0 .0 4.6 .0 6.9 6.9 2-3 •O 2.3 29.9 Nashua, N. H. . . 5-3 .0 .0 .0 .0 15-9 31.8 5-3 10.6 -O .0 .0 68.9 Lowell, Mass. . . 10.4 7.8 3-9 3-9 3-9 10.4 6.5 9.2 9.2 5-3 6.6 9.2 86.3 Lawrence, Mass. . 11. 2 9.0 11. 2 2.2 9.0 .0 17.9 13-4 i3.4 4-4 15.6 17.9 125.2 Haverhill, Mass. . .0 .0 3-8 .0 3-8 3-8 3-8 .0 .0 3-8 3-8 .0 22.8 Newburyport, Mass. .0 .0 .0 .0 .0 .0 .0 .0 7.2 .0 7.2 .0 14.4 1889-1890 < V a 3 1— > "3 B 3 M 3 < h S V V i 1 55 ■ 1-. 1 B D w Q b 3 a 1 *-> b 3 C ■ Pi 2 4) O Concord, N. H 5-9 5-9 .O 5-9 .O .0 11.8 .0 .0 .0 .0 .0 29-5 Manchester, N. H. . . 2.3 .0 2-3 2.3 7.O 4-7 4-7 9-3 4-7 4-5 .0 .0 41.8 Nashua, N. H .0 .0 .O .0 .O .0 S-3 10.7 5-3 5-3 10.6 5-3 425 Lowell, Mass 9.2 6.6 4.0 1.3 6.6 9.2 4.0 11.9 11.9 6.4 7-7 5-i 83-9 Lawrence, Mass. . . . 8.9 8.9 II. 2 4.4 6. 7 156 8.9 6.7 13-4 iS-6 13-4 4.4 118.1 Haverhill, Mass. . . . 3-8 .0 .O 3-8 3-8 .0 7-5 .0 3-8 3-8 3-8 .0 30.3 Newburyport, Mass. . . .0 7.2 .O 14.4 .0 .0 .0 .0 7.2 .0 .0 28.8 TYPHOID FEVER IN THE MERRIMAC VALLEY 209 The death-rates for the epidemic years 1 890-1 891 are shown in the following table : — TYPHOID FEVER IN THE PRINCIPAL CITIES ON THE MERRIMAC RIVER Deaths per 100,000 Inhabitants (Population from United States Census of 1890) 1890-1891 a < * V e 3 3 M 3 < 1 i) Q. u •f O 1 V u i (J V Q b 1 3 c 1 s s ■a 2 « Concord, N. H 5-9 11.8 .0 .0 11. 8 I7.6 .0 .0 .0 .0 .0 5-9 53-o Manchester, N. H. .0 2.3 .0 2-3 4-6 6.9 .0 6.9 11.4 4.6 4.6 .0 43-6 Nashua, N. H. . . .0 .0 .0 .0 .0 .O .0 .0 .0 .0 5-3 .0 5-3 Lowell, Mass. . . 7.8 10.4 11.6 7.8 7.8 I2.9 12.9 36.3 32.3 24.6 18.1 12.9 195-4 Lawrence, Mass. . n. 2 .0 11. 2 2.2 2.2 4-5 11. 2 15.6 42.6 47.0 26.9 13-4 187.0 Haverhill, Mass. . 7-5 3-8 .0 7-5 .0 "•3 .0 3.8 .0 .0 .0 .0 33-9 Newburyport, Mass. .0 .0 7.2 .0 .0 14.4 21.6 .0 7.2 7.2 .0 .0 57-6 The death-rates for the same cities for the two years next after the great epidemic of 1 890-1 891 are shown in the following tables : — TYPHOID FEVER IN THE PRINCIPAL CITIES ON THE MERRIMAC RIVER Deaths per 100,000 Inhabitants (Population from United States Census of 1890) 1891-1893 a < >> *> c 3 *— » 3 to 3 W) 3 -< V 2 a V tfl 1 h B JO 1 1 e 2 3 a 1 fc a 3 fa ■8 to V Concord, N. H 5-9 .0 .O .0 17.6 .0 5.9 .0 .0 .0 .0 .0 29.4 Manchester, N. H. 2-3 .0 2-3 .0 .0 .0 .0 .0 .0 4.6 .0 2.3 ix-5 Nashua, N. H. . . .0 .0 .O .0 13.8 15.8 10.6 3i-7 5-3 5-3 5-3 .0 89.8 Lowell, Mass. . . 7-8 5-2 i-3 5.2 3.9 3-9 9.1 3-9 2.6 16.8 10.4 11.6 81.7 Lawrence, Mass. . 6.7 4-5 2.2 2.2 2.2 11.2 6.7 9.0 2.2 11. 2 15.6 17.9 91.6 Haverhill, Mass. . 7- 5 .0 .0 .0 3.8 .0 .0 3-8 3.8 75 3-8 .0 30.2 Newburyport, Mass. .0 7.2 7.2 .0 .0 .0 7.2 .0 7.2 .0 .0 .0 28.8 2IO WATER AS A VEHICLE OF INFECTIOUS DISEASE < V c 3 >> 3 V) 3 3 < 1 E « a V CO it V O O O ! > ! Q b 1 3 b 1 3 u fa £ «> Concord, N. H .0 5-9 .O .0 .O .0 .O .0 5-9 .0 .O .0 11.8 Manchester, N. H. 2-3 .0 4.6 6.9 .O 2.3 .O .0 2-3 2.3 .O .0 20.7 Nashua, N. H. . . .0 .0 .O .0 .O 5-3 .O 15-9 5-3 .0 5-3 .0 31.8 Lowell, Mass. . . 5-2 9.1 2.6 5-2 5-2 9-i 5-2 3-9 12.9 12.9 9.1 5-2 85-6 Lawrence, Mass. 6.7 2.2 4.5 9.0 4-5 .0 6.7 9.0 20.1 6.7 26.8 17.9 114.1 Haverhill, Mass. . 3.8 .0 3-8 3-8 .O 7-5 .0 3-8 22.5 .0 iS° 3-8 64.0 Newburyport, Mass. .0 14.4 .0 .0 .O .0 .0 .0 7.2 21.6 .0 7.2 50.4 The death-rates from typhoid fever for twelve-month periods in the principal cities on the Merrimac River, for five years in succession, are shown on the following table: — DEATH-RATES FROM TYPHOID FEVER, BY PERIODS OF TWELVE MONTHS, IN THE PRINCIPAL CITIES ON THE MERRIMAC RIVER, FOR THE FIVE YEARS, APRIL 1, 1888, TO MARCH 31, 1893. Deaths per 100,000 Inhabitants (Population from United States Census of 1890) From From From From From Average Apr., 1888, Apr., 1889, Apr., 1890, Apr., 1 891, Apr., 1892, Apr., 1888, to to to to to to Mar., 1889 Mar., 1890 Mar., 1891 Mar., 1892 Mar., 1893 Mar., 1893 Concord, N. H. . . . 70. S 29-5 53-o 29.4 11.8 38.8 Manchester, N. H. . . 29.9 41.8 43-6 "•5 20.7 395 Nashua, N. H. . . . 68.9 42.5 5-3 89.8 31.8 47 7 Lowell, Mass. . . . 86.3 83.9 195-4 81.7 85.6 106.61 * Lawrence, Mass. . . 125.2 118.1 187.0 91.6 114.1 127. 2. l Haverhill, Mass. . . 22.8 3°-3 33-9 30.2 64.0 46.3 Newburyport, Mass. 14.4 28.8 57-6 28.8 5