I 
RESEARCH FOR THE BACILLUS OF KOCH. 259 
culosis is a bacillus which is found in all the tuberculous lesions, 
and even in the products of the expectoration of phthisis. It 
can be cultivated indefinitely in artificial media, and when inocu¬ 
lated in the state of purity in various members of the animal 
species, reproduces exactly the disease from which it first pro¬ 
ceeds, under every variety and kind of form. These are the 
three principal conditions necessary to the actual scientific illus¬ 
tration of the subject, and which involve the admission, as demon¬ 
strated, of the assertion that such lower organism, or microbe, is 
the only cause of this contagious disease. In other words, it is 
to-day an acknowledged fact that tuberculosis is functional in the 
bacillus of Koch, as anthrax is functional in the bacteridie. 
One of the most important points of the discovery of Koch is 
the defining of the histo-chemical characters special to the tuber¬ 
culous bacillus, which belong exclusively to it, and which have 
never been observed in any other of the known micro organisms. 
When placed in contact with a slightly alkaline solution of any of 
the numerous coloring matters obtained from aniline, the bacillus 
of Koch fixes the coloring matter with such a power that if sub¬ 
mitted afterwards to the one-third solution of nitric acid it retains 
the given coloration, while all the other elements, whether cells 
or microbes, with which it may be mixed, lose it completely in a 
few minutes. Again, if, after the action of nitric acid, the prepar¬ 
ation is placed in another coloring solution, all the elements of 
the preparation take this second coloration, with the exception of 
the bacillus of Koch, which alone retains the first*. In this 
curious reaction we have the proof that the micro-purulent sputa 
of phthisis always contains bacilli, and at times in considerable 
quantities; and that, amongst the numerous micro organisms that 
may be found in the sputa, the bacilli of Koch alone resists the 
discoloration by nitric acid. 
From the publication of Koch’s discovery (in April, 1882), a 
great number of observers have essayed to repeat and to apply 
his experiments in such a manner that humane doctors of the 
* One exception, however, must be made in favor of the bacillus of Lepra, 
the action of which resembles that of tuberculosis ; but their difference, both in 
size and form, at once establishes their distinction. 
