202 BACTERIOLOGY. 



alkaline methylene-blue solution, the Koch-Ehrlich 

 aniline water solution, of either fuchsin, gentian-violet, 

 or methylene-blue, and Ziehl's solution of fuchsin in 

 carbolic acid. These solutions are as follows : 



Loeffler's Alkaline Methylene-blue Solution. This con- 

 sists of concentrated alcoholic solution of methylene- 

 blue, 30 c.c.; caustic potash in one ten thousandth 

 solution, 100 c.c. 



Koch-Ehrlich Aniline Water Solution of Fuchsin or 

 Gentian-violet is prepared as follows: To about 100 

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

 drop, until it has an opaque appearance, the solution 

 being thoroughly shaken after the addition of each drop. 

 It is then filtered into a beaker through moistened 

 filter-paper until the filtrate is perfectly clear. To 

 100 c.c. of the filtrate add 10 c.c. of absolute alcohol 

 and 11 c.c. of the concentrated alcoholic solution of 

 either fuchsin, methylene-blue, or gentian- violet. 



Ziehl's Carbolic Fuchsin Solution. Distilled water, 

 100 cc. ; carbolic acid (crystalline), 5 grams; absolute 

 alcohol, 10 c.c ; fuchsin, 1 gram; or it may be pre- 

 pared 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 last two methods, combined with heating, are 

 used to stain the bacteria intensely, so that the more 

 resistant of them may retain their color when exposed 

 to decolorizing agents. When so treated certain of 

 the bacteria will retain their color, even when exposed 

 to very strong decolorizers. The bacilli of tuberculosis 

 and of leprosy are examples. They are both difficult 

 to stain, but when once stained are equally resistant to 



