AETIOLOGY OF TUBERCULOSIS. 
55 
Solitary, fncomplete and negative attempts to generate tuberculosis artificially 
were made towards the end of the last century. The first successful attempts 
were made by Klencke, who by inoculation of miliary and infiltrated tubercles 
from the human being into the cervical veins of rabbits, brought about a wide¬ 
spread tuberculosis of the lungs and liver. Klencke must therefore be pronounced 
the discoverer of experimental tuberculosis. He did not continue his attempts, 
and so they were almost forgotten. In a systematic and thorough manner experi¬ 
mental tuberculosis was worked out by Villemin. He not only inoculated tuber¬ 
culous substances from the human subject, but also from the pearl disease of cattle, 
and showed by experiment the identity of pearl disease and tuberculosis. Ville- 
min’s investigations seemed already, by the number of experiments, by their 
careful execution and comparison with opposing attempts bearing upon the same 
question, to have decided the question in favor of the infection theory. Never¬ 
theless the numerous investigators who repeated Villemin’s attempts according 
to the methods suggested by him or in modified ways, arrived at very contradictory 
results. The defenders of the infection theory, especially Klebs, sought to improve 
the experimental technique and to free it from the errors clinging to it; the op¬ 
ponents, on the contrary, strove to prove that the tuberculous substance possessed 
no virulent properties, and true tuberculosis could be produced by inoculation 
with material in which tuberculosis did not exist. This dispute was first settled 
by the experiments of Cohnheim and Salomonsen who, with this end in view, in¬ 
oculated the anterior chamber of the eyes of rabbits. It was an exceedingly 
happy idea to make use of the rabbit eye as the place of inoculation. From the 
nature of the case, those cases in which tuberculous substance only has been inoc¬ 
ulated must be distinguished from those in which other infectious material has 
been combined with the tuberculous virus. In subcutaneous inoculation, such 
materials often produce more or less widespread caseous infiltrations,which are 
not unlike the tuberculous cheesy products. In the eye, on the contrary, they cause 
an inflammation which rapidly runs its course, which can in no case be mistaken 
for the inoculated tuberculosis, which is slow and unique in its development. 
This inoculated tuberculosis, when the experiment is successful, takes such a 
course that it is always manifest to the investigator. After a somewhat prolonged 
stage of incubation little gray nodules appear in the iris, scarcely visible to the 
naked eye and proceeding from the transplanted portions of tuberculous substance. 
The number of these nodules increases gradually, they themselves grow, become 
yellowish in the center, become cheesy and show as well macroscopically as mi¬ 
croscopically all the typical characteristics of genuine tuberculous nodules. 
Tuberculous infection is, moreover, not confined to the eye, but spreads itself 
later through the entire organism; it attacks especially the neighboring lymphatic 
glands, the lungs, spleen, liver and kidneys. According to the united testimony 
of Cohnheim and Salomonsen and all other experimenters, who have repeated 
these attempts, an iris-tuberculosis has in no case followed the inoculation with 
non-tuberculous substances. More than this, a spontaneous case of iris-tuberculosis 
in rabbits has never been observed. This method of infection is therefore su¬ 
perior to all others in so far as that the influence of unintentional errors in attempt 
is shut out, errors which so easily creep into the experiments in subcutaneous 
inoculation and in transplantation into the abdominal cavity. The chance of 
