THE STAINING OF BACTERIA. 97 



These dyes are more or less complicated compounds derived 

 from the coal-tar product aniline (CgHg . NHj). 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 therefore 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 : ^ — 



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

 dahlia) . 



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



Crystal violet. 

 Blue Stains. — Methylene-blue ^ (synonym : phenylene-blue) . 



Victoria-blue. 



Thionin-blue. 

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



Safranin (synonyms : fuchsia, Girofld). 

 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 Sy Griibler of Leipzig. One is then per- 

 fectly sure that one has got the right stain. 



Of the stains specified, the violets and reds are the most 

 intense in action, especially the former. It is thus easy in using 

 them to overstain a specimen. Of the blues, methylene-blue 

 probably gives the best differentiation Of structure, and it is 

 difficult to overstain with it. Thionin-blue also gives good dif- 

 ferentiation and does not readily overstain. Its tone is deeper 



^ For further information on this subject the student is referred to Rawitz, 

 " Leitfaden fiir histologische Untersuchungen," Jena, 1895, from which the synonyms 

 used in the text are taken. 



2 This is to be distinguished from methyl-blue, which is a different compound. 

 H 



