DIFFERENTIATION OF LEPROSY AND TUBERCLE BACILLI. 221 
3. The resistance to decolorisation. 
Originally Koch considered that while the B. tuberculosis 
required for its demonstration one of the complicated methods 
devised by himself or Ehrlich, the B. leprz could be readily 
stained by Weigert’s method of nuclear staining ; and also that 
while the B. tuberculosis was stained by alkaline methylene 
blue the leprosy bacillus remained unaffected. 
Babes showed that various violets (gentian violet, &c.) in 
simple solution would stain the B. tuberculosis, but stated 
that this bacillus was not stained by simple solutions of red or 
violet fuchsine, methylene blue, or eosin, while all these colours 
would stain the B. lepre. 
Baumgarten pointed out that both the bacilli were stained 
by watery solutions of fuchsine, but in contradiction to Babes 
asserted that neither was stained by watery or alcoholic solu- 
tions of methylene blue or eosin. 
Wesener found that it was possible to stain the B. tuber- 
culosis with any dye which stained the B. leprz, and agreed 
with Baumgarten that eosin and watery methylene blue stained 
neither. Alkaline methylene blue in diluted alcoholic solu- 
tion, however, stains both organisms, as does also (but very 
badly) acid solution of eosin. Bismarck brown and vesuvin 
stain neither. 
My own results agree in the main with those of Wesener. 
About such stains as fuchsine and the various violets all authors 
are agreed. It is not, however, easy to decide in all cases 
whether the stain is really taken up by the B. leprz or by the 
material present in the lepra cell. Ifa section rich in bacilli 
or lepra cells is stained with simple methylene blue (2 per cent. 
diluted alcoholic), Loffler’s solution, Friedlander’s stain, 
logwood, or even Bismarck brown, it is perfectly easy to dis- 
tinguish the lepra cells, and those parts of the section which 
can be shown by control staining to contain numerous bacilli. 
The cells are filled with a fairly strongly stained granular 
material, often of a different tint from the surrounding nuclei, 
and a similarly stained granular material interpenetrates those 
portions of the sections where bacilli are known to exist. 
