MICROSCOPIC EXAMINATION 



127 



l>asic dyes are generally employed as salts of hydrochloric 

 ; while the acid dyes occur as sodium of potassium salts. 

 EHRLICH'S CLASSIFICATION OF THE ANILINE DYES.* 



i r 



Red 



A. Basic -[ Violet 



Aniline dyes 



Blue 



( Fuchsin 



j Rubin 



( Diamond red 



f Gentian violet 

 | Methyl violet 

 -] Crystal violet 

 | Dahlia 

 [ Tliioniiie 



f Methylene blue 

 j Victoria blue 



L Green { Methyl green 



f Vesuvin 



\ Bismarck brown 



f Eosin 



f \ Fluorescin 

 I B. Acid 



1 ( Acid fuchsin 

 Sapranine 

 ( Picric acid 



Of the aniline stains the violet and red are the most in- 

 tense in action. With them it is easy to overstain the speci- 

 men. Of the blues, methylene blue is one of the best for many 

 purposes, especially the differentiation of structure, and it 

 is difficult to overstain with it. 



These dyes are more or less crystalline powders and 

 while some are definite chemical compounds, others are mix- 

 tures. For this reason various brands are met with on the 

 market and exact duplication of stains is not always possible. 

 In purchasing these dyes one can procure the crystalline or 

 powder form from which the various solutions are prepared. 

 If desired, the staining solutions can be procured from the 

 dealers. Bacteriologists as a rule use Griibler stains. In 

 addition to the appended formulae for preparing the ordinary 

 staining solutions, there are special staining processes for cer- 

 tain species, such for example, as the tubercle bacterium ; and 



* Quoted by Thoinot and Masselin. Precis de Microbie, 1896, p. 

 166. 



