THE STAINING OF BACTERIA 99 



rosaniline derives its staining action from the rosaniline. It 

 is therefore called a basic aniline dye. On the other hand, 

 ammonium piprate 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 cytoplasm 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.— Ulethyl- violet, R-5E (synonyms : Hoffmann's violet, 

 i dahlia). 



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

 Crystal violet. 

 Blue Stains. — Methylene-blue 1 (synonym : phenylene-blue). 

 Victoria-blue. 

 Thionin-blue. 

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



Safranin (synonyms : fuchsia, Girofte). 

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

 brown). 



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. 



It is most convenient to keep saturated alcoholic solutions 

 of the stains made up, and for use to dilute a little with 

 ten times its bulk of distilled water and filter. A solution of 

 good body is thus obtained. Most bacteria (except those of 

 tubercle, leprosy, and a few others) will stain in a short time in 

 such a fluid. Watery solutions may also be made up, e.g., a 

 saturated watery solution of methylene-blue or a 1 per cent, 

 solution of gentian-violet. Stains must always be filtered before 

 use ; otherwise there may be deposited on the preparation 

 granules which it is impossible to wash off. The violet stains 



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

 pound. 



