130 BACTERIOLOGY. 



basic aniline dyes — fuchsin, gentian-violet, and raethy- 

 lene-blue. These solutions may be prepared either by 

 directly dissolving the dyes in substance in water until 

 the proper degree of concentration has been reached, or 

 by preparing them from concentrated watery or alco- 

 holic solutions of the dyes which may be kept on hand 

 as stock. The latter method is that commonly prac- 

 tised. 



The solutions of the colors which are in constant use 

 in staining are prepared as followed : 



Prepare as stock, saturated alcoholic or watery solu- 

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

 These solutions are best prepared by pouring into clean 

 bottles enough of the dyes in substance to fill them to 

 about one-fourth of their capacity. The bottle should 

 then be filled with alcohol or with water, tightly corked, 

 well shaken, and allowed to stand for twenty-four hours. 

 If at the end of this time 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. This will then be labelled 

 saturated alcoholic or watery solution of fuchsin, gen- 

 tian-violet, or methylene-blue, as the case may be. 

 These alcoholic solutions are not employed for staining 

 purposes. 



The solutions with which the staining is accomplished 

 are made from these alcoholic solutions in the follow- 

 ing way : 



An ordinary test-tube of about 13 mm. diameter is 

 three- fourths filled with distilled M'ater and the concen- 

 trated alcoholic or watery solution of the dye is then 



