1C2 'MICROSCOPIC METHODS 



chromatin, though sometimes more and sometimes less actively. 

 The bacterial stains par excellence are the basic aniline dyes. 

 These dyes are more or less complicated 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 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 1 (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. 



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 

 than that of methylene-blue, and it approaches the violets in tint. 

 Bismarck-brown is a weak stain, but is useful for some purposes. 

 Formerly it was much used in photomicrographic work, as it was 

 less actinic than the other stains. It is not, however, needed 

 now, on account of the improved sensitiveness of plates. 



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

 pound. 



