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appearance, and that therefore tuberculous bacilli are among the component parts 
typical of the tubercles and their products. The two single cases in which bacilli 
were not to be found concern the microscopic investigation of the pus of a tuber¬ 
culous abscess of the kidneys and the pus from the abscess of a vortex caries. That 
the bacilli were really wanting in these cases can nevertheless not be maintained, 
because here just such products of tuberculosis were examined as are almost regul¬ 
arly to be found without bacilli, owing to the fact that those originally present 
had vanished, as has been shown in the other examinations. Without doubt bacilli 
would have been found in these cases also if the original spots from which the pus 
came could have been examined. 
On the contrary, until now, however manifold the examinations of the most 
various disease processes in men and animals, the bacilli peculiar to tuberculosis 
have never been found in other diseases. Where this has been said to be the case 
the statements have proved themselves erroneous, proceeding from a wrong use of 
the methods of examination. 
A second important result is that the appearance of tuberculous bacilli marks 
the beginning of the tuberculous process. They appear just when the first changes 
in the cell elements of the tissue are noticeable. Not until the tuberculous bacilli 
are present do the heaps of epithelioid cells, the formation of giant cells, and the 
especially characteristic caseous products arising from the perishing of these cell 
elements, appear. Further, the presence and the number of the tuberculous bacilli 
are in closest connection with the progress of the tuberculous process. For where 
the tuberculosis bears a chronic character, only few and scattered bacilli are found; 
where, on the contrary, it is making rapid progress, numerous and thickly heaped 
bacilli are present; and where the tuberculous process has come to a standstill or 
has run its course, the bacilli vanish. 
These three facts, namely, that the tuberculous bacilli occur regularly and ex¬ 
clusively in tuberculosis; that they in time and place precede all the peculiar patholo¬ 
gical changes of tuberculosis; and that their number and their appearance and disap¬ 
pearance stand in direct relation to the course of tuberculosis—these facts allow us 
to conclude with great probability that tuberculous bacilli are not an accidental 
accompaniment of tuberculosis, but stand in an original connection with it. 
Such far-reaching consequences hang on the decision of this question, that 
one cannot rest in having brought it near to a solution, but must make the attempt 
to decide it with undeniable certainty. Moreover, a further investigation of the 
conditions of life and development of these parasites promised further important 
light on the aetiology of tuberculosis and on the ways and means of defending 
humanity against this most destructive disease. 
The only possibility of reaching this goal lay in taking the same way which 
had approved itself for the investigation of other bacteria diseases. The tuberculous 
bacilli must be isolated from the diseased organs, bred outside of the body in 
“ reinculturen ” (pure cultures), their behavior in this way investigated, and 
finally tuberculosis be artificially generated by such bacilli, freed from all admix¬ 
ture with the disease products. 
II.—ISOLATION AND REINCULTUREN OF TUBERCULOUS BACILLI. 
It could be seen in advance that the obtaining of reinculturen of tuberculous 
bacilli would be attended with difficulties, and therefore from the beginning the 
