1889.] MICROSCOPICAL JOURNAL. 211 



BACTERIOLOGY.* 



The Basic Aniline Colors. f — These colors are soluble in water, 

 and for the most part in one or all of the decolorizing agents. In use, 

 a weak, watery solution colors at first the intercellular substance and 

 the cell body, while the nuclei remain unstained. Through the subse- 

 quent treatment with alcohol, glycerine, or acetic acid, an inversion of 

 the staining takes place, by which the elements previously colored be- 

 come colorless while the previously colorless nuclei are stained. In the 

 use of the stronger solutions the staining follows (without any discern- 

 ible inversion) directly and quickly ; and, in general, its intensity is in 

 proportion to the concentration of the solution. In a quite concen- 

 trated watery solution overstaining may occur, which can be reduced 

 to the proper degree by subsequent decolorization. 



If the dyes are dissolved in the decolorizing agents — such as absolute 

 alcohol, acetic acid, or thick glycerine — they stain slightly or not at all. 

 Instead of using some decolorizing agent subsequently to reduce the 

 intensity of the staining to a proper degree in preparations which have 

 been overstained in watery solutions, in many cases a solution of the 

 dye-stuff in a mixture of water with alcohol (Herrmann), glycerine 

 (Schaefer), or acetic acid (Ehrlich), may be used. 



The basic aniline-dyes are used in the following solutions : 



i. Concentrated watery solutions. These are either used directly or 

 after dilution to the desired degree with distilled water. The solutions 

 are prepared with distilled water (which has been previously boiled), 

 so that an excess of the coloring-matter remains undissolved. They 

 must always be filtered before using. Only a small quantity of these 

 watery solutions should be made at a time. 



2. Concentrated alcoholic solutions. The solution of an excess of 

 the coloring material is brought about in the best way by absolute al- 

 cohol, or, in want of this, by the officinal 90 per cent, spirit of the 

 Pharmacopoeia. 



In general, one can calculate about 20 to 25 grammes of the dye-stufi 

 to 100 grammes of the spirit or alcohol. These solutions are kept pre- 

 pared, and are not used directly for staining, but are mixed with a cer- 

 tain amount of distilled or aniline water. In place of concentrated 

 watery solutions the alcoholic solutions can be used if five or six drops 

 are added to a small watch-glass of distilled water. This mixture is 

 often designated as the dilute alcoholic solution. 



From the watery or alcoholic solutions of the basic aniline colors the 

 various staining fluids are prepared. The preparations that are more 

 commonly employed in staining bacteria are Koch- Ehrlich 's solution 

 of methyl-violet or fuchsin (described in the April number of this 

 Journal} , and the alkaline methylene blue solution. 



Alkaline Methylene Blue. — The alkaline preparation of methy- 

 lene blue is undoubtedly the staining fluid most universally employed in 

 staining micro-organisms. With it bacteria are very satisfactorily stained 

 either in cover-glass preparations made directly from animal tissues, 



* Conducted by V. A. Moore. 



t Hueppe. Die Methoden der Bakterien-Forschung, p. 52. 



