66 
R. KOCH. 
other relations. For while usually the little grains of the plasma-cells conduct 
themselves like the cell-grains and show a different coloring from the tuberculous 
bacilli, I have lately seen a preparation, made by Dr. Benda’s assistant in the 
pathological institute in Gottingen, in which tuberculous bacilli were not to be 
found, but on the contrary the grains of the plasma-cells showed themselves colored 
blue. Probably in this case the object from which the section was prepared had 
received a treatment with cromic acid or had not been hardened quickly enough 
in alcohol. 
Accident comes to our help in proving the existence of tuberculous bacilli, since 
not alone the parts of the tissue take a different coloring, but also all other bacteria 
which I have known until now and examined, with the exception of the lepra- 
bacilli to be mentioned later, also react in an opposite manner from the tuberculous 
bacilli under Ehrlich’s method of coloring. Bacteria coming from the mouth are 
almost always to be found in phtisic sputum. I have never seen that one of 
these numerous sorts of bacteria showed the same color-reaction as the tuberculous 
bacilli. This observation has been confirmed by many reliable investigations, and 
can be considered as an established fact. The same is true of the tuberculous 
bacilli occurring in the contents of the intestines, when tuberculous ulcers are 
present. When this sort of discharge is prepared and colored in the prescribed 
manner on the covering glass, it appears to consist almost wholly of bacteria; 
they fill the layer in such thick masses. But without exception they take a dif¬ 
ferent color from the tuberculous bacilli, and especially is this the case in the smaller 
sorts of bacilli, which might perhaps lead one to mistake them for. A peculiar 
behavior is shown by a large sort of bacilli, which form somewhat large, oval 
spores standing on ends, in that the spores often keep a plainly manifest, some¬ 
times indeed an intense blue color, while the substance of the bacillus is itself dyed 
brown. According to all appearance these spores only take the color a short time 
after their formation, but remain uncolored after they are older. Among the 
many spores of the contents of the intestines which belong to other sorts of bacilli, 
until now none have been found which took the color of the tuberculous bacilli. 
Also the spores of the inflammation-of-the-spleen bacilli, hay bacilli and others, 
which Dr. Gaffke examined at my instance with reference to this color-reaction, 
remained uncolored. On the contrary Dr. Gaffke found during these investigations 
that the spores of “ shimmel-pilze ” take a strong blue. Also a certain kind of yeast 
seems to take the color. Since a mistaking of tuberculous bacilli for the above 
mentioned spores and yeast is impossible, their diagnosis so far as it rests upon 
the color-reaction is not thereby prejudiced. 
Of late I have examined many sorts of bacteria-bearing substances, such as 
decaying meat infusion, decomposing urine, blood milk, vegetable infusion, mire 
from swamps with Ehrlich’s coloring method, but have never found bacteria 
which take the same color-reaction as the tuberculous bacilli. I must therefore 
consider all claims for the appearance of bacteria which conduct themselves in 
regard to color exactly like the tuberculous bacilli, and which are said to be found 
in sputum, decaying liquids, the contents of the intestines in healthy men and in 
swamp-mud, for mistakes and resting upon an erroneous use of the coloring 
method. I feel myself so much the more justified in this opinion since I almost 
daily see examples of the difficulties which the use of this certainly rather com¬ 
plicated color technique offers to most people. 
