THE METHODS OF STAINING MICROBES 73 



alcohol until decolourised ; they are then placed in 

 oil of cloves, and finally mounted in Canada balsam. 

 As Gram's method only gives a faint colour to 

 the tissues, they may be stained a deeper colour 

 by immersing the sections (after decolourising with 

 alcohol) in an aqueous solution of vesuvin, eosin, or 

 Kanvier's picro-carminate of ammonia. They are 

 finally washed in alcohol, and mounted as already 

 described. 



One of the best methods for staining cover-glass 

 preparations is the one devised by Ehrlich. The 

 cover-glass preparations are made to float (with the 

 prepared face downwards) in a solution of fuchsine 

 made in the following manner : 5 cc. of aniline oil 

 and 100 cc. of distilled water are mixed together and 

 filtered. To the filtrate is added a concentrated 

 alcoholic solution of fuchsine. The preparations re- 

 main in this solution for fifteen minutes ; they are 

 then washed in nitric acid (one part of nitric acid to 

 two parts distilled water) and rinsed in distilled 

 water. An after-stain of methylene blue or vesuvin 

 gives the nuclei, etc., a blue or brown colour, while 

 the tubercle-bacilli or other pathogenic microbes are 

 stained red. The elegance of this method is that 

 the tubercle-bacilli impregnated with fuchsine resist 

 the action of nitric acid, whilst the saprophytic 

 microbes (present in sputum and saliva), nuclei, 

 etc., are immediately decolourised by the acid. 

 Both Ehrlich's and Koch's methods are also applic- 

 able for staining tubercular and other tissues. 



The Ehrlich- Weigert is another method for stain- 

 ing microbes in situ. The tissues are placed in a 



