92 MICROSCOPIC METHODS. 



nuclear chromatin, though sometimes more and sometimes 

 less actively. The bacterial stains par excellence are the 

 basic aniline dyes. These dyes are more or less compli- 

 cated compounds derived from the coal-tar product aniline 

 (C 6 H 5 . NH 2 ). Many of them have the constitution of salts. 

 Such compounds are divided into two groups according 

 as the staining action depends on the basic or the acid 

 portion of the molecule. Thus the acetate of rosaniline 

 derives its staining action from the rosaniline. It is there- 

 fore called a basic aniline dye. On the other hand, 

 ammonium picrate owes its action to the picric acid part of 

 the molecule. It is therefore termed an acid aniline dye. 

 These two groups have affinities for different parts of the 

 animal cell. The basic stains have a special affinity for the 

 nuclear chromatin, the acid for the protoplasm and various 

 formed elements. Thus it is that the former the basic 

 aniline dyes are especially the bacterial stains. 



The number of basic aniline stains is very large. The following 

 are the most commonly used : 1 



Violet Stains. Methyl-violet, R-5R (synonyms : Hoffmann's violet, 

 dahlia). 



Gentian-violet (synonyms : benzyl-violet, Pyoktanin). 



Crystal-violet. 



Blue Stains. Methylene-blue 2 (synonym : phenylene-blue). 



Victoria-blue. 



Thionin-blue. 



Red Stains. Basic fuchsin (synonyms: basic rubin, magenta). 



Safranin (synonyms : fuchsia, Girofle). 



Brown Stain. Bismarck-brown (synonyms : vesuvin, phenylene- 

 brown). 



It is of the greatest importance that the stains used by 

 the bacteriologist should be good, and therefore it is advisable 

 to obtain those prepared by Griibler of Leipzig. One is then 

 perfectly sure that one has got the right stain. 



1 For further information on this subject the student is referred to 

 Rawitz, " Leitfaden fur histologische Untersuchungen," Jena, 1895, fr m 

 which the following synonyms are taken. 



2 This is to be distinguished from methyl-blue which is a different com- 

 pound. 



