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, . . 5 cc. 



Aniline water, ....... 100 cc. 



2. Aniline- Methyl- Violet (Ehrlich- Weigert). 



Saturated alcoholic solution of methyl violet, . .11 cc. 

 Absolute alcohol, ...... 10 cc. 



Aniline water, ....... 100 cc. 



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, ......... 1 gm. 



Alcohol, . . . . . . . 10 cc. 



Dissolve and add 100 cc. of a fi\ 3-per-cent solution of carbolic acid. 



4. Alkaline Blue Solution (Loffler's solution). 



Saturated solution of methyl ene blue, ... 30 cc. 



Solution of caustic potash of 1:10,000, . . 100 cc. 



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 



