628 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
tions were begun and pursued to a successful termination. He 
inoculated not only with tubercular material from human beings, but 
also from cases of bovine tuberculosis, and he seemed to have proved 
experimentally the identity of the latter disease with human tuber- 
culosis. Villemin’s researches, from the number of his experiments, 
the careful manner in which they were carried out and the employ- 
ment of suitable control experiments, appeared to decide the question 
in favor of the infective theory of tuberculosis. The numerous 
workers who repeated Villemin’s experiments, after the same or 
modified methods, arrived at very contradictory results. The op- 
ponents of the infective theory strove to prove that true tuberculosis 
could be induced by inoculation with nontubercular material. To 
the decision of this question Cohnheim and Salomonsen contributed 
largely by selecting for imoculation 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 successful tubercular inocula- 
tion can be watched throughout by the experimenter until the 
pathological process has advanced so far that the whole organism— 
the neighboring lymphatic glands, the lungs, spleen, liver, and kid- 
neys—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 cultiva- 
tion, 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 ap- 
pearances 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 recog- 
nized 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 
