STAINING AND EXAMINATION OF MICKO-ORGANISMS 45 



hence special devices and methods have to be resorted 

 to in these cases. A summary of the principal of these 

 special stains will now be given. The simplest modi- 

 fication is 



Lb'fflers alkaline methylene blue solution. To 100 c.c. 

 of a solution of caustic potash (1 : 10,000) add 30 c.c. 

 of a concentrated alcoholic solution of methylene blue. 

 This solution has a much stronger tinctorial power than 

 the simple aqueous solutions of aniline colours, and re- 

 tains, like all methylene blue solutions, its staining pro 

 perties if shut up in tightly stoppered bottles for years. 



Weigert's solution. Another simple modification 

 consists in adding ammonia, thus : To 90 '0 grms. of 

 distilled water add 0*5 grm. liq. ammonias, 10 grms. 

 of absolute alcohol, and 2'0 grms. of gentian violet. 



EhrlicKs solution and modifications. This solution 

 practically only differs from those we have described 

 above by reason of the alcoholic solution of the basic 

 dyestuff not being diluted with pure water but with 

 water which is saturated with aniline oil. Four to five 

 c.c. of aniline (the well-known oily substance manu- 

 factured in such large quantities from the benzene of 

 coal-tar, and which must not be used when it has 

 assumed a brown colour through prolonged exposure to 

 light) are shaken up with 100 c.c. of distilled water, by 

 which the greater portion of the aniline passes into 

 solution. This solution is passed through a damp 

 filter so that the excess of undissolved oily aniline 

 particles are retained by the filter, and to the clear 

 filtrate, or ' aniline water ' as it is called, are added 

 eleven c.c. of a concentrated alcoholic solution of either 

 fuchsine, gentian violet, or methyl violet. The whole 

 is then frequently shaken during twenty-four hours, 

 at the end of which time the liquid becomes clear 



