164 BACTERIOLOGY 



the basic aniline dyes fuchsin, gentian-violet, and methyl- 

 ene-blue. These solutions may be made either by directly 

 dissolving the dyes in substance in water until the proper 

 degree of concentration has been reached, or by using con- 

 centrated watery or alcoholic solutions of the dyes which 

 may be kept on hand as stock. The latter method is the 

 one commonly practised. 



The solutions of the colors which are in constant use in 

 staining are prepared as follows: 



Prepare as stock, saturated alcoholic or watery solutions 

 of fuchsin, gentian- violet, and methylene-blue. These 

 solutions are best made by pouring into clean bottles enough 

 of the dyes in substance to fill them to about one-fourth of 

 their capacity. Each bottle should then be filled with 

 alcohol or with water, tightly corked, well shaken, and 

 allowed to stand for twenty-four hours. If by then all the 

 staining-material has been dissolved, more should be added, 

 the bottle being again shaken and allowed to stand for 

 another twenty-four hours; this must be repeated until 

 a permanent sediment of undissolved coloring-matter is 

 seen upon the bottom of the bottle. The bottles are then 

 to be labelled "saturated alcoholic" or "watery" solution 

 of fuchsin, gentian-violet, or methylene-blue, as the case 

 may be. These alcoholic solutions are not directly employed 

 for staining-purposes. 



The solutions with which staining is accomplished are 

 made from the stock solutions by adding 5 c.-c. of the latter 

 to 95 c.c. of distilled water. These represent the staining- 

 solutions in every-day use. They may be kept in bottles 

 supplied with stoppers and pipettes (Fig. 33), and when 

 used are dropped upon the preparation to be stained. 



For certain bacteria which stain only imperfectly with 



