198 LABORATORY EXERCISES IN BACTERIOLOGY. 



STAINING SOLUTIONS. 



1 . There should be kept in the laboratory supplies of the following stock solutions : 

 saturated alcoholic solutions of (a) basic fuchsin, (6) gentian violet, (c) methylene-blue, 

 (d) thionine, (e) eosin, (/) vesumn. These are prepared from strong alcohol and an 

 excess of the stain; as used, more alcohol may be added, always with the caution that 

 some excess of undissolved stain remains. Each student has in his locker his individual 

 tray of tubes (Fig. 59), in which watery solutions of the above are kept. One cubic 

 centimeter of the saturated alcoholic solution of aniline dye to ten or twelve cubic 

 centimeters of distilled water are used in the preparation of the latter aqueous solutions. 

 Each tube is provided with tubules as in a chemical wash-flask, for discharge of the 

 stain as needed, a wad of absorbent cotton in the lower end of the exit tubule serving 

 as a filter. Owing to the fact that these watery solutions quickly deteriorate, they 

 should not be used if old, and should never be made up in large quantities. 



2. The following special stains and other fluids frequently used in staining are also 

 to be kept in stock: 



(a) Ziehl's Carbol-fuchsin: 



Fuchsin, I 



Absolute alcohol, 10 



Five per cent, aqueous sol. carbolic apid, 90 



FIG. 59. TRAY OF STAINING TUBES. 



Used in staining mycobacterium of tuberculosis, etc. This solution keeps well for 

 several months. The carbolic acid in its composition is added as a mordant. In 

 preparation throw the fuchsin on a filter paper and after mixing the alcohol and the 

 acid solution percolate until the stain is all dissolved. Filter before use. Contact with 

 films four or five minutes if warm, longer if cold. 



(6) Gabbet's Solution: 



Methylene-blue, 2 



Twenty-five per cent. aq. sol. of sulphuric acid, 100 



Used as decolorizing agent and as counterstain after carbol-fuchsin. Acid solution 

 should be cooled before being added to the stain. In preparation throw stain on a 

 filter paper and percolate the acid solution until the stain is all dissolved. This solution 

 is not liable to decomposition. Filter before use. Contact with film, cold, for from 

 half a minute to two minutes. 



(c) Loe filer's Blue Solution: 



Sat. ale. sol. methylene-blue, 3 



I : 10,000 aq. sol. potassium hydroxide, IO 



