Preventable Diseases

by Woods Hutchinson

Not only is the method spreading rapidly among the more intelligent class of breeders, but many progressive countries of Europe and states of our Union require the passing of the tuberculin test as a requisite to the admission within their borders of cattle intended for breeding purposes. So that, while the problem is still an enormous one, it is now confidently believed that complete eradication of bovine tuberculosis is only a question of time.

The other instance furnishes a much more crucial test, as it is carried out upon wild animals under the unfavorable conditions of captivity in a strange climate, like our slum-dwellers from sunny Italy, and comes home to us more closely in many respects, inasmuch as it is concerned with our nearest animal relatives on the biological side—monkeys and apes, in zoölogical gardens.

Tuberculosis is a perfectly frightful scourge to these unfortunate captives, causing not infrequently thirty, fifty, and even sixty per cent of the deaths. This, however, is only in keeping with their frightful general mortality. The collection of monkeys in the London Zoo, for instance, some fifteen years ago, was absolutely exterminated by disease and started over afresh every three years, a death-rate of thirty-five per cent per annum as compared with our human rate of about two per cent per annum. Here, it would seem, was an instance where there was little need to call in the bacillus. Brought from a tropical climate to one of raw, damp fog and smoke, from the freedom of the air-roads through the tree-tops to the confinement of dismal and often dirty cages in a stuffy, overheated house, condemned to a diet which at best could be but a feeble and far-distant imitation of their natural food, it seemed little wonder that they "jes' natcherly pined away an' died."

But let the results speak. A thorough system of quarantine was enforced, beginning with one of the Vienna gardens, and finally reaching one of its most brilliant and successful exemplifications in our own New York Zoölogical Gardens in the Bronx. All animals purchased or donated were tested with tuberculin, and those that reacted were either painlessly destroyed or disposed of. Those which appeared to be immune were kept in a thoroughly healthy, sanitary quarantine station for six months or a year, and again tested by tuberculin before being introduced into the cages. The original stock of monkeys was treated in the same manner or else destroyed completely, and the houses and cages thoroughly cleaned and sterilized or new ones constructed. Keepers employed in the monkey-house were carefully tested for signs of tuberculosis, and rejected or excluded if any appeared. Signs were posted forbidding any expectoration or feeding of the animals (which latter is often done with nuts or fruit which had been cracked or bitten before being handed to the monkeys) by the general public, and these rules were strictly enforced.

At the same time the houses were thoroughly ventilated and exposed to sunlight as much as possible, and the animals were turned out into open air cages whenever the weather would possibly permit. As a result the mortality from tuberculosis promptly sank from thirty per cent to five or six per cent. In our Bronx Zoo, for instance, it has become decidedly rare as a cause of death in monkeys, no case having occurred in the monkey-house for eighteen months past. What is even more gratifying, the general mortality declined also, though in less proportion, so that, instead of losing twenty-five to thirty per cent of the animals in the house every year, a mortality of ten to fifteen per cent is now considered large.

And to think that we might achieve the same results in our own species if we would only treat ourselves as well as we do our monkey captives! To "make a monkey of one's self" might have its advantages from a sanitary point of view.

"But this method," some one will remind us, "would silence only a part of the enemy's infection batteries." Even supposing that we could prevent the spread of the disease from human sources, what of the animal consumptives and their deadly bacilli? If the milk that we drink, and the beef, pork, and poultry that we eat, are liable to convey the infection, what hope have we of ever stopping the invasion?

The question is a serious one. But here again a thorough and careful study of the enemy's position has shown the danger to be far less than it appeared at first sight. Even bacilli have what the French call "the defects of their virtues." Their astonishing and most disquieting powers of adjustment, of accommodation to the surroundings in which they find themselves, namely, the tissues and body-fluids of some particular host whom they attack, bring certain limitations with them. Just in so far as they have adjusted themselves to live in and overcome the opposition of the body-tissues of a certain species of animals, just to that degree they have incapacitated themselves to live in the tissues of any other species.

Some of the most interesting and far-reachingly important work that has been done in the bacteriology of tuberculosis of late years has concerned itself with the changes that have taken place in different varieties and strains of tubercle bacilli as the result of adjusting themselves to particular environments. The subject is so enormous that only the crudest outlines can be given here, and so new that it is impossible to announce any positive conclusions. But these appear to be the dominant tendencies of thought in the field so far.

Though nearly all domestic animals and birds, and a majority of wild animals under captivity, are subject to the attack of tuberculosis, practically all the infections hitherto studied are caused by one of three great varieties or species of the tubercle bacillus: the human, infesting our own species; the bovine, attacking cattle; and the avian, inhabiting the tissues of birds, especially the domestic fowl. These three varieties or species so closely resemble one another that they were at one time regarded as identical, and we can well remember the wave of dismay which swept over the medical world when Robert Koch announced that the "perlsucht" of cattle was a genuine and unquestioned tuberculosis due to an unmistakable tubercle bacillus. But as these varieties were thoroughly and carefully studied, it was soon found that they presented definite marks of differentiation, until now they are universally admitted to be distinct varieties, each with its own life peculiarities, and, according to some authorities, even distinct species.