STAINING METHODS. 29 
the examination may be made without drying the surface upon 
which the stained bacteria are spread, the water taking the place of 
balsam in a permanent mount; or we may dry the film and use a 
drop of cedar oil between the slide and cover. 
While simple aqueous solutions of the aniline colors, when 
freshly prepared, will promptly stain most bacteria, certain agents 
-may be added to these which aid in the preservation of the solution, 
or which act as mordants, and are useful in special cases. 
We shall only give here a few of the standard solutions which 
are most frequently employed by experienced bacteriologists : 
1. Aniline-Gentian-Violet (Ehrlich). 
Saturated alcoholic solution of gentian violet, 
Aniline water, . ‘ : ‘i ‘ = : 100 cc. 
2. Aniline-Methyl- Violet (Ehrlich-Weigert), 
Saturated alcoholic solution of methyl violet, ‘ 11 ce. 
Absolute alcohol, . , : j : A 19 ee. 
Aniline water, ‘ : : : . j ‘ 100 ce. 
Aniline water for the above solutions is prepared by shaking in a 
test tube one part of aniline oil with twenty parts of distilled water, 
and, after allowing it to stand for a short time, filtering the saturated 
aqueous solution through a moistened filter. If the solution is not 
perfectly transparent it should be filtered a second time. 
3. Carbol-Fuchsin (Ziehl’s solution). 
Fuchsin, ; ‘ ‘ 4 : ; . ‘ - igm. 
Alcohol, 4 . i : 4 3 : ‘ 10 ce. 
Dissolve and add 100 ce. of a fiv 2-per-cent solution of carbolic acid. 
4. Alkaline Blue Solution (Léffler’s solution). 
Saturated solution of methylene blue, ; . ‘ 30 ce. 
Solution of caustic potash of 1:10,000, : 5 100 ce. 
These solutions keep better than the simple aqueous solutions, 
but after having been kept for a time they are likely to lose their 
staining power as a result of the precipitation of the aniline color. 
The following special methods of staining cover-glass prepara- 
tions will be found useful in certain cases: 
Gram’s Method.—The dried film upon a slide or cover glass is 
stained with an aqueous solution of methyl violet or with aniline- 
gentian-violet solution (No. 1); it is then placed in the iodine solution 
for a minute or two (iodine one part, potassic iodide two parts, water 
