ORDINARY STAINING-SOLUTIONS. 147 



accomplished by the addition to the solutions of small 

 quantities of alkaline substances, or by dissolving the 

 staining-materials in strong watery solutions of either 

 aniline oil or carbolic acid, instead of simple water — in 

 other words, by employing special solvents and mor- 

 dants with the stains. 



Of the solutions thus prepared which may always be 

 employed upon bacteria that show a tendency to stain 

 imperfectly, there are three in common use — Loeffler's 

 alkaline methylene-blue solution; the Koch-Ehrlich 

 aniline-water solution of either f uchsin, gentian-\^olet, 

 or methylene-blue; and Ziehl's solution of f uchsin in 

 carbolic acid. These solutions are as follows: 



Lceffier^s alkaline mdhylene-blue solution : 



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

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



Koch-Ehrlich aniline-water solution. 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 alco- 

 holic solution of either f uchsin, methylene-blue, or gen- 

 tian-violet, preferably f uchsin or gentian-violet. 



ZiehVs carbol-fuchsin solviion : 



Distilled water 100 c.c. 



Carbolic acid (crystalline) 5 grammes. 



Alcohol 10 c.c. 



Fuchsin in substance 1 gramme. 



Or it may be prepared 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. 



