SPECIAL STAINING SOLUTIONS. 129 



and pipettes (Fig. 21), and when used are dropped upon 

 the preparation to be stained. After remaining upon 

 the preparation for about thirty seconds, they are 

 washed off in water and the preparation can then be 

 examined. 



For certain bacteria which stain only imperfectly with 

 these simple solutions it is necessary to employ some 

 agent that will increase the penetrating action of the 

 dyes. Experience has taught us that this can be accom- 

 plished by the addition to the solutions of small quan- 

 tities of alkaline substances or by dissolving the staining 

 materials in strong watery solutions of either aniline oil 

 or carbolic acid, instead of simple water. 



Of the solutions thus prepared which may always be 

 employed upon bacteria which show a tendency to stain 

 imperfectly, there are three in common use Loffler's 

 alkaline methylene-blue solution, the Koch-Ehrlich ani- 

 line-water solution of either fuchsin, gentian-violet, or 

 methyleue-blue, and Ziehl's solution of fuchsin in car- 

 bolic acid. These solutions are as follows: 



Loffler's alkaline methylene-blue solution : 



Concentrated alcoholic solution of methylene-blue 30 c.c. 

 Caustic potash in 1 : 10,000 solution . . 100 c.c. 



Koch-Ehrlich aniline-water solutions. To about 100 

 c c. of distilled water aniline oil is added, drop by drop, 

 and the solution thoroughly shaken after each addition 

 until it is of an opaque appearance. It is then filtered 

 through moistened filter-paper until the filtrate is per- 

 fectly clear. To 100 c.c. of the clear filtrate add 10 c.c. 

 of absolute alcohol and 11 c.c. of the concentrated al- 

 coholic solution of either fuchsiu, methylene-blue, or 

 gentian-violet, preferably fuchsin or gentian-violet. 



