TUBERCULOSIS is an infectious disease which runs an acute, subacute, or even a markedly chronic course. Occasionally death supervenes merely days or weeks after infection, accompanied by astoundingly severe manifestations; in other cases the disease drags along for months, years, or even decades, and finally, after long and tedious suffering, results in a general disintegration; in yet other cases, the human organism may conquer and effect a cure. Tuberculosis may be localized in the various organs, or may be rapidly diffused through out the body. Its clinical pictures are manifold, its anatomical aspects varying, its portals of entry diverse. The common factor, which unites all these different manifestations which we group under the general title of tuberculosis, is the causative agent: the tubercle bacillus. The definition of tuberculosis is therefore an etiological one, in contradis tinction to the anatomical significance of the word tubercle, namely a nodule. It includes all those changes and conditions which are caused by the tubercle bacillus.
1882 Robert Koch discovered the tubercle bacillus to be the cause of tuberculosis, and thus segregated it as a specific dis ease, and enabled the varying clinical pictures (miliary tuberculosis, gelatinous tuberculous pneumonia, tabes mesenterica, acute hydro cephalus, etc.) to be united into the etiological group of tuberculosis. The infectiousness of tuberculous processes was previously known Cohnheim, and others) although disputed over and over. Koch's article dispelled all doubts. The tubercle bacillus is a rod 1.5– long, broad, slightly curved, classified by Lehmann as a mycobacterium under the hyphomycetes. It grows slowly when cul tivated, is immobile, and possesses a peculiar characteristic in being stained. It cannot be decolorized by acids after having been deeply stained by means of a dye and a mordant. Following such a procedure (see page 600) it. appears coarsely granular (Fig. 137). Sunlight kills the bacillus quickly; intense diffuse light less quickly.
Whereas Koch originally considered the human and bovine bacil lus as identical, in 1901 he changed this view and declared them to be different. First, because animal experimentation showed that cattle injected or fed with pure cultures of human tubercle do not develop general tuberculosis; secondly, because man, in spite of his consumption of the milk or flesh of tuberculous animals, rarely de velops primary intestinal tuberculosis. The investigations of P. and
E. Biedert and of Ganghofner coincide with this new view of Koch's. fin 1896 Theobald Smith showed the non-identity of the human and bovine tubercle bacillus.] They showed that the morbidity of tuber culosis in man and in cattle by no means run parallel; that on the contrary, where tuberculosis is widespread among cattle the mortality of this disease is comparatively low and vice versa. Koch's view as to the difference of species between the human and bovine bacillus has been actively denied by other authors (Johne, Arloing, and others). However at the present time the discussion revolves more about the point as to whether we are dealing with two species, different and totally separate, or with one species descended from a common ancestor, which has gradually accommodated itself to its host and to its particular parasitic life, and thus in the course of time has developed two different varieties (Baumgarten).
The Imperial Health Department in an article by Kossel and Weber has made the following pronouncement:—Among the bacilli of mam malian tuberculosis, two types may be distinguished, which are best designated as the human and the bovine types. These two types show characteristic differences as regards their morphology, cultural aspects, and virulence for rabbits and cattle. A metamorphosis of the human type into the bovine type as the result of experiments on rabbits, goats, and cattle was not observed. By means of the bacillus of the human type a progressive tuberculosis in cattle could not be produced. In tuberculous individuals the bovine type is found relatively seldom, and as yet only in children under eight years of age. The tuberculous individual is a source of danger for cattle only in the rare instance of his excreting bacilli of the bovine type. On the other hand, the human organism seems to be capable of receiving the bovine type of bacillus. Therefore the consumption of meat of tuberculous animals containing living bacilli of the bovine type, cannot be looked upon as insignificant for man. Especially is this true during childhood.