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Popular Science Monthly/Volume 85/July 1914/Man and the Microbe

< Popular Science Monthly‎ | Volume 85‎ | July 1914

THE

POPULAR SCIENCE

MONTHLY

 

JULY, 1914




MAN AND THE MICROBE
By Professor C.-E. A. WINSLOW

THE AMERICAN MUSEUM OF NATURAL HISTORY, NEW YORK

A CASE of measles or typhoid fever is not only a most unpleasant kind of practical problem, but a natural history phenomenon of a mysterious and interesting sort. Here is a person who wakes up apparently well and goes about his daily tasks as usual. Gradually he is conscious of some strange clog in the machine, a dragging of the wheels, such as we experience when a carriage passes from a good road into a sandy by-way. Pains and aches begin to be felt in head and back. The general weakness increases, and, with or without a sharp chill, the patient gives up and takes to bed. Fever has set in. The vigorous and active human animal of the morning has been changed in a few hours to a mere wreck of his former self. What has happened? What subtle force has produced so sudden and mysterious a catastrophe?

The later history of such an attack is almost as remarkable as its inception. Most diseases go on and grow worse unless something definite is done to remove their exciting cause. If, however, your measles or typhoid patient be let alone, or only protected by hygienic precautions against certain secondary results, 99 times out of 100 in the case of measles, and 9 times out of 10 in the case of typhoid fever, he will get well. These are "self-limited" diseases, to use the old expressive term. They run a course of so many days or weeks, and then, unless death or some complication supervenes, there is a steady progressive recovery. The temperature falls, the mind clears, the strength returns, the patient is as he was before, with one important exception, that he is now, to a greater or less extent, and for a longer or shorter time, resistant or immune against the particular malady from which he has suffered. Think what a curious phenomenon this really is, divested of the cloak of familiarity with which it is commonly invested. What sort of strange process goes on in the body, which has a definite cycle like the life of an animal, fulfils its appointed round, and then draws to a close, leaving only the impress of immunity to mark its passage.

Nor is this all. There is another characteristic of this particular group of diseases, which is quite as remarkable as those associated with their inception and their cyclical course. They are catching, contagious, infectious, communicable. They do not occur singly, but spread from person to person, as flame leaps from tree to tree in a forest. The degree to which this quality is manifest varies widely. When measles was first carried to the unprotected inhabitants of the Faroe Islands, it spread indeed, like wildfire, to almost every person. When smallpox is brought into an unvaccinated community the same thing happens to-day. In other communicable diseases, like tuberculosis and typhoid fever, the transfer of infection is less inevitable and less direct. In all the maladies of this type, however, the same principle obtains. The disease neither originates within the patient nor comes, in the last analysis, from any influence of earth or water or air. It arises ultimately in every instance from a previous case of the same disease, from a specific spark of the same conflagation.

To the primitive mind, deeply tinged with anthropomorphism, the natural explanation of all disease was sought in the evil influence of a demon or other supernatural power. The plagues and pestilences in particular were punishments inflicted upon a people for their sins. There was no possibility of escaping such visitations except by the dubious expedient of flight; no hope except in the relaxation of the celestial anger of which they were the sign. As Defoe says of the cessation of the plague in London:

Nothing but the immediate finger of God, nothing but Omnipotent Power could have done it. The contagion despised all medicine; death raged in every corner; and had it gone on as it did then, a few weeks more would have cleared the town of all and everything that had a soul. Men everywhere began to despair; every heart failed them for fear; people were made desperate through the anguish of their souls, and the terrors of death sat in the very faces and countenance of the people.

The modern view that disease is not a divine infliction, but a natural phenomenon, with natural causes, which may be progressively grasped and controlled by the steady and disciplined activity of the human mind, we owe first to the wonderful nation whose genius came to its flower on the sea-girt promontories and islands of the Ægean twenty centuries ago. Of all our debts to Greece there is none greater than this, that the Greeks, first of all western nations, sought to find a natural rather than a supernatural explanation of the phenomena in the world about them. They often failed to find it, as was inevitable in the absence of the mass of observations needed for good induction. They fell back on poetic abstraction, almost as fanciful as the demons of their savage forefathers; in the case of the causation of disease, for example, upon the theory of the four humors developed to a position of commanding influence by Galen. Yet the great fact remained that whether the explanations of the Greeks were scientific or not, they aimed to be scientific, and they firmly implanted along with all their error, a zeal for the scientific truth about nature and a confident belief in the possibility of its ultimate attainment.

From Hippocrates down to our own times, then, we find that the explanation of diseases of all kinds has been sought by scientific men, not in the activities of spiritual beings, but in the workings of natural law. Results were almost nil, however, so far as the communicable diseases are concerned, until the nineteenth century when a sudden and rich fruition took place here, as in all fields of the biological sciences, as a result of a simple mechanical discovery, the lens-maker's trick of the achromatic objective, which made possible the modern high power microscope and revealed all at once a new and stupendous world—"The world of the infinitely little."

It is true that Leeuwenhoek and other early naturalists had seen the microbes with their primitive simple lenses. It is true that still earlier, in the sixteenth century, the Veronese physician, Fracastorius conceived the communicable diseases as due to "seminaria contagionum," minute particles capable of reproduction in appropriate media and having many of the attributes we know to be characteristic of the bacteria to-day. The Roman author Varro, in writing on the choice of sites for a farm house cautions the builder against the neighborhood of swampy ground "because certain minute animals, invisible to the eye, breed there, and borne by the air, reach the inside of the body by way of the mouth and nose, and cause diseases which are difficult to get rid of." Nevertheless, so far as any scientific demonstration of their nature was concerned, the communicable diseases remained as much a mystery in 1800 as in 400 B.C.

It was the achromatic objective, perfected about 1840, which first revealed the ubiquity of microbic life and its special richness in connection with the processes of fermentation and decay; and it was of profound moment in the history of medicine and sanitation when Pasteur proved, against the opposition and the ridicule of the great Liebig and a host of lesser critics, that fermentation was the result of the action of microbes, little living things which entered into the fermentable fluids and grew and multiplied there, the fermentation being the result of their powerful chemical secretions. The "little leaven that leaveneth the whole lump" was shown to be a self-propagating plant, and the many desirable and obnoxious decompositions to which sugary fluids are subject, each the result of a special microbe.

The analogy between fermentation and disease must have sprung into many minds, with the hope that the solution of the latter problem too might be found by the study of microscopic life. It was again Pasteur who by his rigid experimental method extracted the truth from the mass of good and bad guesses of those who had preceded him. In his study of the disease which threatened to wipe out the great silkworm industry of France, he again applied his microscope to the task, demonstrated the presence of living corpuscles in the bodies of the moths, whose offspring later succumbed to the disease, and saved the silk cultivators by a quarantine based on the destruction of eggs from such infected parents. In his later studies of anthrax and chicken cholera, he demonstrated that diseases of the higher animals too were due to specific microbes; and with his work and its extension by Robert Koch the mystery which for centuries had shrouded the communicable diseases was at last solved. Each case of sickness of this kind is a definite infection with a specific microscopic germ, which grows in the body as a mold grows in a jar of jelly and in its growth produces chemical poisons, which cause the weakness, pain, fever, delirium and the other manifestations of disease. The self-limited nature of such maladies is due, as Pasteur too showed, to the fact that the body cells react against the invaders in a specific and purposeful manner, which, if they finally triumph, leads to a more or less lasting state of immunity. The spread of communicable disease in the community is no longer a "pestilence that walketh in darkness," but the transfer in tangible ways of a small but definite animal or plant; and its control can be confidently looked for from the study of the life histories of these microscopic organisms and the working out of practical methods which shall prevent them from gaining access to our bodies.

The communicable diseases are merely striking examples of the more general biological phenomenon of parasitism described by Swift in the famous and often misquoted lines:

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.

It should be remembered that the word parasite was first coined for members of the human species. The parasite in Grecian times was the one who "sat beside" the great man, the hanger-on in the palace of the prince, who gained a precarious living at the expense of his complaisant host. We may hope that the type is less common in modern times and it is fair to remember that in the microbic world, as in our own, the parasite is an exception rather than the rule. The great majority of the bacteria are honest, industrious, useful citizens, who ripen our cream and butter and cheese, make our vinegar and lactic acid, dispose of our waste materials and play a most important part in maintaining the fertility of the soil. The tubercle bacillus and the malaria germ, like the thief and the murderer are perverted individual representatives of a generally sound stock.

There is another very important point of resemblance between the disease germ and the human parasite. Just as the man who has learned to live at the expense of society soon loses the capacity to do an honest day's work and would starve if left to his own resources, so the microbic parasites in adapting themselves to live at the expense of their human host have lost the capacity to gain a living in the world outside. They have been so modified in the course of evolution as to thrive in the rich warm fluids of the body and perish outside of it. If a hundred typhoid germs are discharged into a lake their fate is much the same as that of a hundred men under the same conditions. A few of the men may be good swimmers and a few may be lucky enough to cling to floating planks. Most die very quickly, however, and in the course of time all will surely perish. So with most disease germs in water or soil or anywhere outside the body. Certain pathogenic microbes may actually multiply in suitable media, in milk for example. As a rule, however, there is a steady decrease, rapid at first and slower afterward, but inevitably leading to extinction in a comparatively short period. We read of disease germs persisting in dust or ice for several months, and a very few may sometimes do so. Quantitative studies show, however, that the survivors are few indeed and that the danger from such remote infection is practically negligible. In the case of water, which has been more carefully studied than any other medium, we know, for example, that in a period of two or three weeks even gross infection will be removed by the natural mortality of the microbes. Dr. Houston, of London, who has done some of the most important work upon this subject, has repeatedly demonstrated his confidence in his results by drinking halfpint portions of water, merely kept in bottles for a few weeks in the laboratory after infection with millions of typhoid bacilli. Both bacteriological and epidemiological evidence indicates very clearly that it is only fresh, recent infectious material which plays an important part in the transmission of communicable disease.

This conclusion is one of the most important fruits of recent sanitary research; for it focuses attention sharply upon the human being, the original source of virulent disease germs, rather than upon vague and obscure miasms of the earth and air. It is people, primarily, and not things that we must guard against. Certain media, like milk and water, are important agents in the transfer of infection from person to person. Others, like air and dust and fomites (books, toys and the like which have been exposed to infection) are known to be far less dangerous than was supposed. Back of all such material agents of transmission, however, lies the human being, and the nearer to this source we get,—the more direct and rapid the transfer,—the greater is the danger.

Unfortunately, however, it is not only the obviously sick person who may be a center for the distribution of active disease. Another of the great contributions to sanitary science in the last ten years has been the recognition of the part played by incipient cases and "carriers," apparently well persons, who are nevertheless discharging from nose and throat or bowels the virulent germs of disease. Measles, for example, is spread chiefly in its incipient stage, when the child has no other symptom than a slight running at the nose and goes to school or to a party, thinking it has only a cold in the head. The carrier, properly so-called, may be a convalescent, entirely cured so far as his own symptoms are concerned, but still distributing virulent germs. From three to five per cent, of all typhoid cases continue to discharge typhoid bacilli for three months or more after convalescence. A recent milk borne epidemic in New York was due to infection from a carrier who had had typhoid in the West forty-six years before. Malarial infection is very frequently introduced into a community by Italian laborers who have themselves become immune to the parasites they carry, in their own country years before. Finally we have the most striking type of carrier, in which there is no present or past history of active disease at all. The famous cook, Typhoid Mary, for example, caused epidemics in eight different families where she worked, but so far as is known had never suffered herself. Two or three persons in a hundred in any normal population have been found on bacteriological examination to be carriers of the diphtheria bacillus, two or three in a thousand, of the typhoid bacillus. The problem of the carrier is one of the most serious of those which confront us since he is moving about in the world, mixing with others, perhaps taking part in the preparation and handling of food, and so may be proportionately much more dangerous than the sick person who is confined to his bed and under medical care.

It is a great step forward, however, to have learned that the human body, of the sick person or the carrier, is the primary source of infection; that every case of communicable disease is caused by the transfer of infectious material from such a person to a susceptible victim; and that the extent of the danger varies directly with the immediacy of the transfer. As this conception has been worked out in detail it has become clear that many of the supposed dangers of the pre-scientific period were of altogether minor import. To the older sanitarian the atmosphere was full of vague dangers, but its part in the spread of disease is now known to be exceedingly limited. In the immediate vicinity of a sick person or a carrier the air is infected by fine spray thrown out of the mouth in coughing, sneezing or loud speaking; but this is really a form of contact, not a general infection of the atmosphere. The mouth spray is a sort of rain which falls quickly to the ground, where it dries and the disease germs perish. It is true that dust collected from the surface in streets and rooms contains vast numbers of harmless germs and occasionally some disease-producing types. I am myself of the opinion that there may be real danger in breathing in such gross quantities of dust as one sometimes encounters in a dirty street on a windy day. This again, however, like the mouth spray, is an occasional and local pollution. Bacteriological studies, such as those carried on last winter in the New York schools, show that quiet indoor air contains comparatively few microbes of any kind and is singularly free from germs of human origin. So strong is the evidence of the insignificance of aerial infection that in some of the most modern hospitals, cases of various contagious diseases have been treated with perfect success in open wards, provided, of course, that the most rigid precaution be taken to prevent the direct transfer of infectious material by the hands and clothing of attendants.

One of the most striking examples of the exorcism of a bogey of the older sanitation by modern exact methods is the case of sewer gas. Dreaded as a prime spreader of disease ever since sewerage began, we now know that sewer and drain air is freer from microbes than the air of a city street, and that the microbes which are present are of the same harmless type in the two cases. From a careful series of experiments in Boston, it was calculated that if one placed the mouth over a house drain and breathed the drain air continuously for twenty-four hours the number of intestinal microbes ingested would be less than those taken in in drinking a quart of New York water, as it was before routine disinfection of the supply was introduced.

Disease germs do not enter the household through the sewer pipes or by flying in at the windows (unless borne on the wings of insects). They are not to any important extent brought in on books or toys or clothing, where, if any infection existed, it has mostly dried up and died. They are brought in directly by infected persons (carriers). They are brought in by insects. They are brought in by certain articles of food and drink. These three types of transmission, which have been alliteratively described as infection by fingers, flies and food, account for ninety nine cases of communicable diseases out of a hundred, and each of them deserves a somewhat more detailed consideration.

In order that a given food may be important as an agent in the transmission of disease there are three different conditions which must be met, and it is only in a few instances that all three are met at once. The substance must be exposed to infection, it must be delivered and used promptly and it must be eaten raw. For the great majority of our foods cookery furnishes an effective safeguard and, as has been often pointed out, the sanitary results of this practise must have played an important part in the evolution of the human race. Most processes of cookery destroy the disease germs and their toxins and make it possible to use such foods as the meat from slightly tuberculous animals with entire safety. It is fortunate that this is the case because the ideally healthy animal is as rare as the perfect human being, and the increasing burden of the cost of living makes it essential that we should utilize all food materials which can be consumed with safety. The common practise, in certain European countries, of eating meat only partially cooked often leads there to serious epidemics of meat poisoning, but in America such outbreaks are usually due to subsequent infection of cooked foods which have been improperly handled in the kitchen, rather than to original infection of the meat before it enters the house-hold.

Of the food materials which are eaten raw and might therefore be expected to play an important part in the wholesale transmission of disease, some, like certain fruits, are rendered safe by the fact that they are peeled before being eaten so that the edible portion has never been exposed to infection. Others are protected by the fact that long storage usually intervenes between exposure to pollution and ultimate consumption. Thus ice, though often cut on polluted streams, is one of the safest foods, as shown by careful bacteriological and epidemiological studies. Ninety per cent, of the bacteria in the water are thrown out in the physical process of freezing; and in a few weeks ninety-nine per cent, of any disease germs remaining will have perished.

Water and milk and raw shellfish are the three foods which in the highest degree fulfill all the requirements of a dangerous disease medium. If water is taken from streams or ponds or wells into which sewage enters, and is used for drinking without adequate storage or purification, the best possible opportunity is offered for a transfer of infection on a gigantic scale. The great epidemics of typhoid fever and cholera which used to sweep through European cities and more recently have continued to ravage American communities, bear eloquent testimony to this fact. With the cheap and effective methods of purifying water, by storage, filtration or disinfection, now at our disposal, there is no excuse for the delivery of a public water supply which is not absolutely safe. In uncivilized communities, which persist in using polluted supplies, and in the country where a local well is under suspicion, the householder may always, however, protect himself by using a Berkefeld or Pasteur filter, either of which types is efficient if properly cared for, or by boiling the water to be used for drinking.

Milk is second only to water as an agent in the transmission of disease. It is frequently infected with tubercle germs and sometimes with other pathogenic organisms from the cow. It is contaminated by dirt in the stable, and it is polluted at a dozen different points by the numerous individuals who handle it on its way through the dairy to the consumer. Furthermore, of all foods milk is the one which in some cases apparently permits an actual multiplication of disease germs and an increase instead of a diminution of virulence in transit. Epidemics of typhoid fever, diphtheria, scarlet fever and tonsilitis without number have been traced to milk, and to young children even the ordinary germs of decay in milk, aside from infection with specific diseases, are often fatal, as evidenced by the terrible toll of summer diarrhœa among infants, which is almost exclusively confined to those fed on cow's milk. Carefully protected milk, such as is certified by our medical societies, is of course much freer from danger than the ordinary product, but the history of epidemics which have affected the patrons of dairies where every possible precaution was taken shows that no raw milk can be considered a safe food. For infants, breast milk is the only proper nutriment, but for babies who can not possibly receive a mother's care, and for older children and adults, we have fortunately a simple and efficient protection in pasteurization. This process, which involves simply the heating of the milk to a temperature of 145° or thereabouts for a period of twenty minutes, represents the application of the saving grace of cookery to the food product which of all food products needs it most. Unlike scalding or boiling pasteurization does not alter the taste of milk, and one of the most effective ways of guarding the household against disease is to see that all milk which enters it is properly pasteurized. There is no more excuse for drinking raw cow's milk than for eating raw beef.

A third danger, but far less important than those inherent in water or milk, lies in the consumption of raw shellfish which have been grown, or more commonly fattened (swelled up and made to seem more plump by immersion for a time in brackish water), in tidal estuaries exposed to sewage pollution. Fortunately it appears that during the winter months oysters, at least, enter into a state of practical hibernation, closing their shells and taking in little water from outside. Under such conditions sewage bacteria, already present within the shell, soon die out and the oyster even when taken from polluted waters becomes a comparatively safe source of food. Most of the famous epidemics of typhoid fever caused by shellfish have occurred in the months from September to November, after the eating of raw shellfish begins and before hibernation has set in. The eating of raw or partially cooked shellfish (steamed clams, fried oysters, oyster stew) from unknown sources, particularly in the autumn months, is, however, a dangerous practise until the oyster industry is more thoroughly supervised than at present.

Finally, in connection with the transmission of disease by food, the danger of infection of any and all foods in the process of preparation should always be kept in view. If for example, sandwiches are prepared by a typhoid carrier, an epidemic is likely to result, as was the case recently in a town of Illinois. I have referred to Mary Mallon, our most famous American case of the carrier in the kitchen. After a brief incarceration by the New York City Health department, this woman was set free and she may now under another name be cooking for some one of the readers of this article. Not only water and milk and shellfish, but meats and vegetables and bread and forks and spoons and tumblers may be infected by a cook or a waitress who is a carrier, and many obscure cases of disease are traceable to this cause. The tragedy of such an occurrence was once personally brought home to me with keenness by the death of one of the most promising young sanitary engineers I have known—a student of mine at the Massachusetts Institute of Technology, who with many others was infected in a boarding house by a waitress who was nursing another servant ill with typhoid, in the intervals of her regular domestic duties. It is often impossible to prevent such catastrophes, but the danger should be kept in mind and all possible effort made to ascertain the health antecedents of those whom we take into our households.

The second of the common modes of disease transmission to which I have referred, spread by the agency of insects, is on the whole easier to control and in highly civilized communities is much less important than spread by articles of food. We must bring foods into our homes, and it is often hard to discriminate between the infected and the non-infected. Insects however can be entirely excluded from the household in cities, and may be kept under reasonable control even in the country. The most spectacular triumphs of modern sanitation have been achieved in the war against insect-borne disease and even before their sanitary importance was at all comprehended, rising standards of personal cleanliness, by the elimination of vermin, incidentally caused a marked reduction in diseases of this class. Our medieval ancestors with their rush strewn dining halls and their uncleansed bedding and clothing paid a heavy toll to the insect carriers of disease. Bubonic plague, the terrible Black Death of the Middle Ages, we know to be primarily a disease of the rat, commonly transmitted from rat to man and from man to man by the flea. Two great pandemics of this disease are recorded in history, one beginning in the sixth and the other in the eleventh century. In each case the pandemic started in Asia, spread to Constantinople and then through Europe, to almost all parts of the known world. At the height of the second great pandemic, in the fourteenth century, twenty-five million people—about one fourth of the population of Europe—were swept away and in the London plague year, immortalized by Defoe, 100,000 persons perished. A third great epidemic began in Hongkong in 1894 and again spread in India, killing 6,000,000 people between 1896 and 1907. Since that time infection has spread as far as Australia and Brazil. The rats in certain districts of England and the ground squirrels in California are known to be still infected with the plague bacillus. Yet no epidemics have occurred outside of Asia, simply because the rats and fleas which spread the disease are under control. If we lived in filth, as our forefathers did, there can be no doubt that we should be in the midst of a great world scourge of plague like that of the fourteenth century. So with typhus, or ship, or jail fever, which was one of the serious diseases of Europe and America a hundred years ago. It has now almost disappeared in western Europe and the United States, and its decrease was a mystery until it was shown that the germ is carried by the body louse. Personal cleanliness has automatically wiped out this disease, while typhoid fever, named from its supposed resemblance to typhus, and in olden times a malady of comparatively less importance, remains one of our grave sanitary problems.

The only household pest which still generally persists in city and country alike is the house-fly; and the public agitation against this insect has grown to such proportions in recent years that we may now look for substantial progress toward its elimination. The fly breeds in horse manure and other deposits of decomposing matter and it is always a carrier of filth, though only incidentally of disease. In paved and sewered cities there is little evidence that the fly is an important factor in disease transmission, but where human excreta are exposed, as in rural districts or cities with badly constructed privy vaults, the opportunity for flies to pick up the germs of typhoid fever and other diseases and carry them to food is so great that the danger becomes serious, particularly of course in the warm climates of our Southern States. During the Spanish War 142 out of every 1,000 of the men in our army camps contracted typhoid fever, and 15 out of every 1,000 died of it; and it was shown that the incidence of the disease was due mainly to careless disposal of excreta and consequent facilities for fly transmission. In Jacksonville, Fla., Richmond, Va., and other southern cities remarkable results in the reduction of typhoid and intestinal diseases have been attained by proper disposal of excreta and anti-fly campaigns. It is by no means a simple matter to control the multiplication of house-flies, but everything possible should be done, by trapping and by the cleaning up of possible breeding places, to reduce their numbers.

The transmission of typhoid fever by insects is, of course, only occasional and incidental, and even plague may at times assume a form in which it is spread directly from man to man by the discharges from the mouth. There is another class of diseases which are carried always and necessarily by insects, the germ passing through certain stages of its life history in man and others in the body of a particular insect host. The most important example in temperate climates is malaria. "Malaria," the bad air disease, was known to be somehow connected with night exhalations from swampy land and a large amount of curiously puzzling information about its prevalence was explained, only when it was shown fifteen years ago that it is transmitted by the bite of a particular mosquito which breeds in swampy pools and along the weed-grown margin of streams. It then became clear that marshlands did indeed cause malaria because their stagnant waters propagated the mosquitoes which carried the malaria germ from man to man. Malaria followed the turning up of the soil, not because emanations were set free in the process, but because digging produces pools of water which breed the insect hosts of the malarial microbe. The practical control of mosquitoes and the consequent elimination of malaria has been shown to be quite practicable, in temperate climates at least, by the drainage of marsh lands and the filling or oiling or stocking with fish of the smaller mosquito breeding pools.

The third mode of infection, by contact, the more or less direct transfer from person to person, is by far the most important factor in the spread of communicable disease in temperate climates. Malaria is our only important insect-borne disease. Typhoid may sometimes be spread by flies and often by water or milk—diphtheria and scarlet fever and tuberculosis and tonsilitis, sometimes by milk. On the other hand, diphtheria and scarlet fever and tuberculosis and, in cities with good water supplies, even typhoid fever, are all more commonly transmitted by contact than in any other way; and contact is practically the sole cause of smallpox, measles, epidemic cerebro-spinal meningitis, influenza, common colds and the venereal diseases. It is in the nose and throat, or on the hands of a human being, that disease germs generally enter our homes, and this sort of infection is obviously most difficult to detect and control. The child infected with measles yet showing no symptoms but those of a simple cold in the head, the person with a "little sore throat" which is the beginning of an attack of diphtheria, the friend who comes in with uncleansed hands to visit the cook after nursing a sister just put to bed with typhoid fever, the visitor who is "practically all over" whooping cough; these are the dangers against which it is so difficult to guard.

The term contact is a broad one and covers a wide variety of ways in which infective material may be spread from person to person. There are all degrees between such direct contact, as occurs when one person coughs over another person's hand, and the more remote infection carried by some object which has been recently handled; no absolute line can be drawn between what may be infective and what may not. If I handle an apple with infected hands and hand it to you and you eat it, we are dealing with clear and obvious contact. If I put it on the table and you find it and eat it an hour later, the connection is almost as direct, although some of the germs will probably be dead. If twenty-four elapses, most of the infection will be gone; if two weeks, practically all of it. Objects which are supposed to remain infective after a considerable period of time, are called fomites, and fomites' infection was once held to be an important factor in the spread of disease. The recent discoveries in regard to the rapid mortality of disease germs outside the body have made it clear, however, that objects are only dangerous when they have recently been exposed to fresh infection. The old stories of toys put away in a closet and causing scarlet fever after a lapse of several years are quite apocryphal. Such mysterious cases as were once explained in this fashion are now more reasonably attributed, and very often definitely traced, to direct contact with an unrecognized carrier case.

The danger of contact infection from such gross discharges as the sputum are sufficiently obvious. Material of quite as dangerous a nature is thrown out from the mouth as a fine spray in coughing, sneezing or loud speaking. Furthermore, it is a sad fact that cleanliness in a bacteriological sense is a very rare thing and the hands are usually more or less soiled with discharges from the nose and throat and too often from the intestines as well. Dr. C. V. Chapin, in his classic book, on "The Sources and Modes of Infection," has some striking paragraphs which, though not pleasant reading, must be pondered by all who would really understand how communicable disease is spread.

Probably the chief vehicle for the conveyance of nasal and oral secretions from one to another is the fingers. If one takes the trouble to watch for a short time his neighbors, or even himself, unless he has been particularly trained in such matters, he will be surprised to note the number of times that the fingers go to the mouth and the nose. Not only is the saliva made use of for a great variety of purposes, and numberless articles are for one reason or another placed in the mouth, but for no reason whatever, and all unconsciously, the fingers are with great frequency raised to the lips or the nose. Who can doubt that if the salivary glands secreted indigo the fingers would continually be stained a deep blue, and who can doubt that if the nasal and oral secretions contain the germs of disease these germs will be almost as constantly found upon the fingers? All successful commerce is reciprocal, and in this universal trade in human saliva the fingers not only bring foreign secretions to the mouth of their owner, but there exchanging them for his own, distribute the latter to everything that the hand touches. This happens not once but scores and hundreds of times during the day's round of the individual. The cook spreads his saliva on the muffins and rolls, the waitress infects the glasses and spoons, the moistened fingers of the peddler arrange his fruit, the thumb of the milkman is in his measure, the reader moistens the pages of his book, the conductor his transfer tickets, the "lady" the fingers of her glove. Every one is busily engaged in this distribution of saliva, so that the end of each day finds this secretion freely distributed on the doors, window sills, furniture and playthings in the home, the straps of trolley cars, the rails and counter and desks of shops and public buildings, and indeed upon everything that the hands of man touch. What avails it if the pathogens do die quickly? A fresh supply is furnished each day.

The control of contact transmission, the breaking of the chain of communication between the infected and the non-infected person, involves one or both of two measures. On the one hand, the spread of infective material from sick persons and carriers must be checked, so far as possible, and, on the other hand, the mouths of well persons must be guarded against infective material which, despite all our efforts, will to some extent be distributed in the world about us. The first half of this task involves the recognition of the sources of danger, and is of course greatly complicated by the presence of the unrecognized carriers. Much may be hoped, however, from the development of what may be called the sanitary conscience, the recognition on the part of each man, woman and child of the grave responsibility which he may incur by careless mingling with friends and neighbors when at the beginning or end of an attack of communicable disease. The isolation of even frank cases of the so-called mild diseases is still too often regarded as an unreasonable imposition by the uneducated (and the uneducated are by no means always those of the most limited incomes). We still hear "Every one must have measles and the children might as well have it as soon as possible." There has seldom been a more cruel superstitution. The children's diseases, measles, scarlet fever and whooping cough are no light matter. Each one of them kills more victims than smallpox, and in many cities often more than typhoid fever. In New York City in 1912, there were two deaths from smallpox, 500 from typhoid, 671 from measles, 614 from scarlet fever and 187 from whooping cough. Furthermore, the seriousness of these maladies decreases directly with the age of a child, so that each year for which an attack may be postponed is so much gained. With the progress of health education in the public schools we may look for the day when the social crime of spreading communicable disease will be realized at its full value, so that it will be recognized as wanton recklessness, not courage, to continue business or social intercourse when "coming down," half-sick with some as yet undefined but impending disease, and no thoughtful person will hasten to mix with his fellows when possibly still a carrier after an attack. In all these diseases there are two factors, the invading germ and the more or less susceptible host, and even a common cold is often due less to poor vitality than to fresh and virulent infection. Some day, perhaps, responsibility may be felt for the reckless dissemination of even this supposedly mild disease, of which Dr. Rosenau well says in his recent work on "Preventive Medicine and Hygiene": "Could the sum total of suffering, inconvenience, sequelæ and economic loss resulting from common colds be obtained, it would at once promote these infections from the trivial into the rank of the serious diseases."

It is of course, not essential that "isolation" of an infected person should mean solitary incarceration within four walls. In the Middle Ages the only protection against disease was quarantine, which in its derivative meaning was forty days' detention of all persons, well or sick. coming from an infected port. With the progress of sanitary science preventive measures have become at the same time more efficient and less irksome. When ships from cholera countries came to our eastern seaports two years ago, only a detention of a day or so was necessary, pending a bacteriological examination of the passengers and detection of the few carriers among them. Isolation of individuals takes the place of quarantine against nations, and a practical isolation may often be effected by simple precautions against the transfer of discharges, without interference with human intercourse. Disease germs do not fly across a room to seize on their prey. They are carried by direct material contact of some sort, by the discharge of mouth spray, by hand shaking, by the use of common drinking cups and the like. The careful consumptive, who guards others from his sputum and mouth spray and infected utensils, is no menace to his family and friends.

The essential point is that the discharges of the patient and all objects soiled thereby should be freed from living germs before they infected others. This is no easy task, as you will realize if you seriously try to carry it out. The common cold offers an excellent opportunity for a practical study of the problem. The next time some member of your family has a cold in the head, try to prevent its spreading further, and you will be surprised to note in how many ways discharges may be interchanged. If we seriously wish to prevent the further spread of infection from a case of communicable disease, an elaborate series of precautions must be taken. The dishes and spoons and forks used by the patient should be kept separate until they have been boiled. Handkerchiefs, towels and bed linen must be treated in the same way. A special wash basin should be set aside for the patient and faucets should be handled by him, not with the hand just to be cleaned, but with the interposition of a bit of paper. The hands of those who touch the patient or touch objects he has recently handled should be at once washed with some simple disinfectant like eighty per cent. alcohol. The mouths of the patient and of those in attendance on him should be kept as free as possible from infection by frequent gargling with a mild antiseptic, such as a mixture of one part of hydrogen peroxide, two of listerine and six of water.

The recognition that objects which have been in immediate contact with sick persons or carriers are the important, and the only important, sources of danger, has quite revolutionized our older ideas of disinfection. As Dr. Chapin, the pioneer in this field has pointed out, the disinfection of the general air and the surfaces of a room by formaldehyde is a burning of incense to the false gods of pre-scientific sanitation. He describes the doctor who comes into the sick room, sits chatting on the bed, puts a spoon in the patient's mouth, then handles it by the infected end, leaves it on the table, deposits some of the material he has smeared on his hand on the door handle and the rest on the faucet as he turns it to wash his hands; and attempts to atone for his sanitary sins by placing a bowl of so-called chlorides (which have about the disinfectant action of tap water) under the bed, and at the end of the attack by performing the sacrificial rite of the formaldehyde candle. As a matter of fact, the prevention of contact infection during the illness with immediate disinfection of excreta, soiled linen and the like, is a thousand times more important than any terminal disinfection after death or recovery. At the end of the illness there will be left on woodwork or furniture only an insignificant number of living virulent germs. If any do persist, they may be removed by a cleaning-up with hot water, soap and elbow-grease far more effectively than by formaldehyde or any other disinfectant.

The attempt to prevent the discharges of the sick from being spread abroad can, of course, only be partially successful at best. Furthermore, besides the frank cases of disease there will always be the unrecognized and in some cases unrecognizable, carriers. We must invoke here our second line of defence, the protection of the portal of the mouth against the infective germs, always likely to be present about us. This means the cultivation of an instinct of discrimination which I call the aseptic sense, an instinct which automatically keeps out of the mouth everything not bacteriologically clean. I have a baby of five who a year ago when told to open a door said, "Why mother just touched that handle and her cold germs are on it." At the kindergarten the children hold each other's hands, pass objects from one to another, work with common modeling clay, and then eat their lunch. My little girl is the only one who washes her hands first and I believe nothing could make her omit that ceremony. There is no phobia in this, no dread of "germs," merely a habitual instinct, no more irksome than the habit of taking off one's hat when meeting a lady in the street.

Is it worth while to trouble ourselves with these things? Our fathers lived happily enough without bothering their heads about them. True enough, but our fathers' brothers and sisters died in great numbers because of their ignorance. To-day there are, each twenty-four hours, 200 death beds in the city of New York. If the death rate of twenty years ago had been maintained, there would be 130 more. A forty per cent. decrease in the death rate has already resulted from the advances of sanitary science. Yet there is still upon us a great burden of preventable disease and death. The large, easy things, the purification of public water supplies, the pasteurization of milk supplies, are being accomplished. The insididous spread of contact infection can only be checked by the conduct of life of the individual citizen, by the diffusion of knowledge in the home and the factory, and by the building upon that knowledge of daily habits of personal cleanliness, which shall banish contact infection, as the insect-borne plagues have been banished by our emergence from the grosser filth conditions of the Middle Ages. These fruits of the sanitary conscience, these applications of the aseptic sense, are little things, and therefore hard things; but they are fraught with the possibility of large results in human health and human happiness.