202 BACTERIOLOGY. 
alkaline methylene-blue solution, the Koch-Ehrlich 
aniline water solution, of either fuchsin, gentian-violet, 
or methylene-blue, and Ziehl’s solution of fuchsin in 
carbolic acid. These solutions are as follows : 
Loeffler’s Alkaline Methylene-blue Solution. This con- 
sists of concentrated alcoholic solution of methylene- 
blue, 30 ¢.c.; caustic potash in one ten thousandth 
solution, 100 e.e. 
Koch-Ehrlich Aniline Water Solution of Fuchsin or 
Gentian—violet is prepared as follows: To about 100 
c.c. of distilled water, aniline oil is added, drop by 
drop, until it has an opaque appearance, the solution 
being thoroughly shaken after the addition of each drop. 
Tt is then filtered into a beaker through moistened 
filter-paper until the filtrate is perfectly clear. To 
100 c.c. of the filtrate add 10 ¢.c. of absolute alcohol 
and 11 e.c. of the concentrated alcoholic solution of 
either fuchsin, methylene-blue, or gentian-violet. 
Ziehl’s Carbolic Fuchsin Solution. Distilled water, 
100 cc.; carbolic acid (crystalline), 5 grains; absolute 
alcohol, 10 c.c ; fuchsin, 1 grain; or it may be pre- 
pared by adding to a 5 per cent. watery solution of 
carbolic acid the saturated alcoholic solution of fuchsin 
until a metallic lustre appears on the surface of the 
fluid. 
The last two methods, combined with heating, are 
used to stain the bacteria intensely, so that the more 
resistant of them may retain their color when exposed 
to decolorizing agents. When so treated certain of 
the bacteria will retain their color, even when exposed 
to very strong decolorizers. The bacilli of tuberculosis 
and of leprosy are examples. They are both difficult 
to stain, but when once stained are equally resistant to 
