THE ORDINARY STAINING SOLUTIONS. 141 



aniline oil or carbolic acid, instead of simple water in 

 other words, by employing mordants 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 fuchsin, gentian-violet, 

 or methylene-blue, and ZiehPs solution of fuchsin in 

 carbolic acid. These solutions are as follows : 



Lceffler'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 fuchsin, methylene-blue, or 

 gentian-violet, preferably fuchsin or gentian-violet. 



Ziehl's carbolic-juchsin solution : 



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. 



The Koch-Ehrlich solution decomposes after having 

 been made for a time, so that it is better to prepare 

 it fresh when needed in small quantities than to ein- 



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