2 3 o POPULAR SCIENCE MONTHLY 



appeared to decide the question in favor of the infective theory of 

 tuberculosis. The numerous workers who repeated Villemin's experi- 

 ments, after the same or modified methods, arrived at very contradic- 

 tory results. The opponents of the infective theory strove to prove 

 that true tuberculosis could be induced by inoculation with non- 

 tubercular material. To the decision of this question Cohnheim and 

 Salomonsen contributed largely by selecting for inoculation the anterior 

 chamber of a rabbit's eye. The great advantage which this method 

 possesses over all others arises from the fact that the course of a suc- 

 cessful tubercular inoculation can be watched throughout by the experi- 

 menter until the pathological process has advanced so far that the whole 

 organism — the neighboring lymphatic glands, the lungs, spleen, liver 

 and kidneys — becomes tuberculous. A further point in favor of this 

 method of inoculation is that spontaneous tuberculosis of the eye has 

 never been observed in rabbits. It was reserved for the genius of Robert 

 Koch to discover nearly twenty years later, in 1882, by the employment 

 first of an original staining method, the tubercle bacillus in sections of 

 tuberculous organs, and next by the use of a special method of artificial 

 cultivation, to secure growths of the bacillus free from all admixture 

 with extraneous matter. With these pure cultivations he succeeded, as 

 you well know, in reproducing in certain domestic animals all the 

 characteristic appearances of tuberculosis in man. Furthermore, Koch's 

 studies of this period convinced him of the unity of causation of the 

 various tubercular affections met with in man and also of those met 

 with in the common domestic animals. Refusing to be daunted by the 

 fact that tuberculosis tends to appear under different aspects in each 

 species, and directing his attention not upon the gross appearances of 

 the disease, but focusing it upon the microscopical appearances of 

 the primary tubercle, which as he said recurs with typical regularity 

 in all the different processes in man, Koch recognized the essential 

 identity of the apparently widely different forms of tuberculosis in the 

 various species of animals. It does not detract from the immense value 

 of his work that Koch failed to distinguish between the tubercle bacilli 

 isolated from the tubercular tissue in fowls, cattle and man. This 

 failure was by no means accidental, for the possibility of the existence 

 of differences in nature of the cultures depending upon their origins 

 was clearly in his mind. Many of you will recall the long list of cul- 

 tures which is given in the paper on tuberculosis published in 1884. 

 In regard to this list Koch says : " It may cause some surprise that so 

 relatively large a number of cultures was set on foot when a few would 

 have sufficed for observing the behavior of bacilli in cultures. It 

 seemed to me, however, not improbable that though bacilli from varying 

 forms of tuberculosis — perlsucht, lupus, phthisis, etc., presented no dif- 

 ferences microscopically, yet, that in cultures differences might become 



