Preventable Diseases

by Woods Hutchinson

On the other hand, it is anything but safe to accept Koch's practical dictum and neglect the meat and milk of cattle as a source of danger in tuberculosis. First, because the degree of our immunity against the bovine bacilli is still far from settled; and, second, because, while bacteriologists are fairly agreed that the avian, the bovine, and the human represent three distinct and different variations, if not species, of the bacillus, they are almost equally agreed that they are probably the descendants of one common species, which may possibly be a bacillus commonly found upon meadow grasses, particularly the well-known timothy, and hence very frequently in the excreta of cattle, and known as the grass bacillus or dung bacillus of Mœller. This bacillus has all the staining, morphological, and even growth characteristics of the tubercle bacillus except that it produces only local irritation and little nodular masses, if injected into animals. Our knowledge of its existence is, however, of great practical importance, inasmuch as it warned us that in our earlier studies of the bacilli contained in milk and butter we have been mistaking this organism for a genuine tubercle bacillus. As a consequence, of late years our tests for the presence of tubercle bacilli in milk are made not only by searching for the organism with the microscope, but also by injecting the centrifugated sediment of the infected milk into guinea pigs, to see if it proves infectious. Many of our earlier statements as to the presence of tubercle bacilli in milk and butter are now invalidated on this account.

Not only are the three varieties of tubercle bacilli probably of common origin, but they may, under certain peculiar conditions, be transformed into one another, or, at least, enabled to live under the conditions favorable to one another. This was shown nearly fifteen years ago by the ingenious experiments of Nocard, the great veterinary pathologist. He took a culture of bovine bacilli, which were entirely harmless to fowls, and, inclosing them in a collodion capsule, inserted them into the peritoneal cavity of a hen. The collodion capsule permitted the fluids of the body to enter and provide food for the bacilli, but prevented the admission of the leucocytes to attack and destroy them. After several weeks the capsule was removed, the bacilli found still alive, and transferred to another capsule in another fowl. When this process had been repeated some five or six times, the last generation of bacilli was injected into another fowl, which promptly developed tuberculosis, showing that by gradually exposing the bacilli for successive generations to the high temperature of the bird's body (from five to fifteen degrees above that of the mammal), they had become acclimated, as it were, and capable of developing. So that it is certainly quite conceivable that bovine bacilli introduced in milk or meat might manage to find a haven of refuge or lodgment in some out-of-the-way gland or tissue of the human body, and there avoid destruction for a sufficiently long time to become acclimated and later infect the entire system.

This is the method which several leaders in bacteriology, including Behring (of antitoxin fame), believe to be the principal source and method of infection of the human species. The large majority, however, of bacteriologists and clinicians are of the opinion that ninety per cent of all cases of human tuberculosis are contracted from some human source. So that, while we should on no account slacken our fight against tuberculosis in either cattle or birds, and should encourage in every way veterinarians and breeders to aim for its total destruction,—a consummation which would be well worth all it would cost them, purely upon economic grounds, just as the extermination of human tuberculosis would be to the human race,—yet we need not bear the burden of feeling that the odds against us in the fight for the salvation of our own species are so enormous as they would be, had we no natural protection against infection from animals and birds.

The more carefully we study all causes of tuberculosis in children, the larger and larger percentage of them do we find to be clearly traceable to infection from some member of the family or household. In Berlin, for instance, Kayserling reports that seventy per cent of all cases discovered can be traced to direct infection from some previous human case.

Lastly, what of the left wing of our army of extermination, composed of those light-horse auxiliaries—the general progress and new developments of civilization, and the net results upon the individual of the experiences of his ancestors, which we designate by the term "heredity"? For many years we were in serious doubt how far we could depend upon the loyalty of this group of auxiliaries, and many of the faint-hearted among us were inclined to regard their sympathies as really against us rather than with us, and prepared to see them desert to the enemy at any time. It was pointed out, as of great apparent weight, that consumption was decidedly and emphatically a disease of civilization; that it was born of the tendency of men to gather themselves into clans and nations and crowd themselves into villages and those hives of industry called cities; that the percentage of deaths from tuberculosis in any community of a nation or any ward of a city was high in direct proportion to the density of its population; and that the whole tendency of civilization was to increase this concentration, this congestion of ground space, this piling of room upon room, of story upon story. How could we possibly, in reason, expect that the influences which had caused the disease could help us to cure it?

But the improbable has already happened. Never has there been a more rapid and extraordinary growth of our great cities as contrasted with our rural districts, never has there been a greater concentration of population in restricted areas than during the past thirty-five years. And yet, the prevalence of tuberculosis in that time, in all civilized countries of the earth, has shown not only no increase, but a decrease of from thirty-five to fifty per cent. To-day the world power which has the largest percentage of its inhabitants gathered within the limits of its great cities, England, has the lowest death-rate in the civilized world from tuberculosis, although closely pressed within the last few years by the United States, whose percentage of urban population is almost equally large, while England's sister island, Ireland, with one of the highest percentages of rural and the lowest of urban population, has one of the highest death-rates from tuberculosis, and one which is, unfortunately, increasing.

The real cure for the evils of civilization would appear to be more civilization, or, better, perhaps, higher civilization. Nor are these exceptional instances. Take practically any city, state, or province in the civilized world, which has had an adequate system of recording all births and deaths for more than thirty years, and you will find a decrease in the percentage of deaths from tuberculosis in that time of from twenty to forty per cent. The city of New York's death-roll, for instance, from tuberculosis, per one thousand living, is some thirty-five per cent less than it was thirty years ago. So that our fight against the disease is beginning to bear fruit already. As Osler puts it, we run barely half the risk of dying of tuberculosis that our parents did and barely one-fourth of that of our grandparents.

But this gratifying improvement goes deeper, and is even more significant than this. It is, of course, only natural to expect that our vigorous fight against the spread of the infection of the disease would give us definite results. But the interesting feature of the situation is that this diminution in England and in Germany, for instance, began not merely twenty, but thirty, forty, even fifty years ago—two decades before we even knew that tuberculosis was an infectious disease with a contagion that could be fought.

In the case of England, for instance, we have the, at first sight, anomalous and even improbable fact that the rate of decline in the death-rate from tuberculosis for the twenty years preceding the discovery of Koch's bacillus was almost as great as it has been in the twenty years since. In other words, the general tendency, born of civilization, toward sanitary reform, better housing, better drainage, higher wages and consequently more abundant food, rigid inspection of food materials, factory laws, etc., is of itself fighting against and diminishing the prevalence of the "great white plague" by improving the resisting power and building up the health of the individual. Civilization is curing its own ills.

It must be remembered that vital statistics, showing the decrease of a given disease within the past forty or fifty years, probably represent not merely a real decrease of the amount indicated by the figures but an even greater one in fact; because each succeeding decade, as our knowledge of disease and the perfection of our statistical machinery improves and increases, is sure to show a prompter recognition and a more thorough and complete reporting of all cases of the disease occurring. Statistics, for instance, showing a moderate apparent rate of increase of a disease within the last thirty years are looked upon by statisticians as really indicating that it is at a standstill. It is almost certain that at least from ten to twenty per cent more of the cases actually occurring will be recognized during life and reported after death than was possible with our more limited knowledge and less effective methods of registration thirty years ago. So we need not hesitate to encourage ourselves to renewed effort by the reflection that we are enlisted in a winning campaign, one in which the battle-line is already making steady and even rapid progress, and which can have only one termination so long as we retain our courage and our common-sense.