AETIOLOGY OF TUBERCULOSIS. 
67 
Aside from the tuberculous bacilli, until now only one sort of bacteria has 
been known which takes color in the same way as the tuberculous bacilli; these 
are, as I have already mentioned in my first communication, the lepm-bacilli. 
This fact is so much the more worthy of notice, since not only the parasites belong¬ 
ing to tuberculosis and to lepra are similar in many ways and plainly nearly related, 
but, as is well known, those two diseases stand very near to each other anatom¬ 
ically as well as setiologically. To be sure, the coloring properties of the two sorts 
of bacilli are not identical. For although the lepra-bacilli can be colored by the 
same process as the tuberculous bacilli, the opposite is not the case. The first 
take, as is well known and as Neisser first proved, the nucleus-coloring of Weigert, 
which the last do not. However similar the two bacilli are in figure, size, &c., 
as soon as it comes to a diagnostic distinction, it becomes easy to recognize them 
through their different response to Weigert’s nucleus-coloring. 
The example of the lepra-bacilli already teaches that the tuberculous bacilli 
occupy in no way an entirely exceptional position in regard to their response to 
coloring matters; it is therefore not improbable that in course of time other sorts 
of bacteria will be found, which possess the same or similar coloring properties 
as the tuberculous bacilli. But any influence on the apprehension of the setiolog- 
ical importance of the tuberculous bacilli would not be exercised by such a discovery. 
For the special reaction against coloring matters is nevertheless not the only 
specific property of the tuberculous bacilli. They possess, as we shall see later 
also in biological relations, a number of other peculiarities, which give still more 
weighty reasons for separating them from the known bacteria as a specific sort. 
In all such considerations it is very much to the point to bring to remembrance 
how the same relations exist in inflammation of the spleen. One will then see 
that inflammation-of-the-spleen bacilli possess no specific coloring qualities and 
nevertheless, as is universally acknowledged, are bacteria of a distinct kind and 
form the cause of inflammation of the spleen. Exactly the same might be the 
case with tuberculous bacilli if they did not accidentally distinguish themselves 
from other bacteria by color-reaction. If the latter is nevertheless a fact, it is cer¬ 
tainly of value in diagnosis, but it is a great error to think that with the specific 
color-reaction of the tuberculous bacilli, their aetiological importance stands and 
falls. 
Further it appears to me not improbable that in the near future still further 
methods may be found by means of which tuberculous bacilli can be colored. 
Ehrlich’s coloring method has already experienced many modifications, of which 
theoretically the most worthy of notice is the fact found by Ziehl, that aniline can 
be replaced by other substances, such as phenol,—C 6 H 4 (OH) 2 —resorcine, &c. 
The statements of some authors, that the tuberculous bacilli may be dyed with 
pure fuchsine appear to hint that still other ways exist in which the coloring can 
succeed. The diagnostic importance of Ehrlich’s method, even if other methods 
which have no exclusive character are found, suffers by no means. For that 
remains in spite of all a well established fact, that by strict following of Ehrlich’s 
method the tuberculous bacilli conduct themselves in a manner wholly peculiar 
to them and are thereby to be distinguished from all till now known bacteria. 
The method has the value of a chemic reaction, which has made possible the dis¬ 
tinction of substances difficult to divide, nevertheless only under the condition 
