202 
K. KOCH. 
cultures as with the natural tuberculous substances, only the first had a some¬ 
what quicker effect than the last. 
The products of the infection also were exactly like those obtained with 
the natural infectious material, as well in their microscopic structure as in 
their contents of tuberculous bacilli and in their virulent properties. 
By the most careful attention to all the prudential measures needful for 
the avoidance of mistakes in experimenting with tuberculosis, errors are with 
certainty excluded from these experiments. With reference to this it may 
also be made prominent here that in the same manner as with tuberculous 
bacilli, an extraordinary number of experiments with other disease-producing 
and non-disease-producing bacteria were made. These were also put into 
the anterior eye-chamber of rabbits, or were injected into their veins, they 
were subcutaneously inoculated into rabbits, guinea pigs, mice, etc., and in¬ 
jected into the abdominal cavity. Other bacteria were also used for experi¬ 
ments in inhalation according to the method already described. But tuber¬ 
culosis was never generated in these animals by these means. 
In these experiments made with pure cultures, also only the tuberculous 
bacilli completely freed from all original products of the disease, can have 
been the cause of the tuberculosis. The proof of the proposition that tuber¬ 
culosis is an infectious disease conditioned upon tuberculous bacilli, is here¬ 
with concluded. One could be sure to say, and it has been said, that the 
tuberculous bacilli are one cause for the occurrence of tuberculosis, but that 
besides these other things, for example other micro-parasites, can likewise 
generate tuberculosis. This supposition is, nevertheless, erroneous, because 
as we have seen, in all cases of genuine tuberculosis, tuberculous bacilli oc¬ 
cur, and the manner of their occurrence allows us to infer a causative con¬ 
nection with the disease. If in spite of this one would claim that besides the 
tuberculous bacilli still another special tuberculous virus exist, that would 
justify a claim that beside trichinae and itch-mites still another specific, until 
now unknown agent must exist as infectious material. We can, therefore, 
with right say that the tuberculous bacilli are not only one cause, but the 
only cause of tuberculosis, and that without tuberculous bacilli there is no 
tuberculosis. 
Therewith, tuberculosis is joined to inflammation of the spleen in knowl¬ 
edge of its aetiology. The tuberculous bacilli stand in just the same relation 
to tuberculosis as the inflammation of the spleen bacilli to that disease. 
G—THE RELATIONS OF THE TUBERCULOUS BACILLI TO THE 
AETIOLOGY OF TUBERCULOSIS. 
The investigations communicated in the preceding have already gained 
us so much knowledge of the biologic properties of the tuberculous bacilli, 
and their peculiar behavior in the body attacked by them, that by their help 
the aetiology of tuberculosis in its outlines may be stated with certainty. In 
time we shall certainly become more thoroughly acquainted with the proper¬ 
ties of tuberculous bacilli, and find out much that is new about them, which 
will extend our views of the aetiology of tuberculosis, and in many ways 
amend them; nevertheless, this conviction cannot prevent us from forming 
