ORDINARY STAINING-SOLUTIONS. 145 



an impression cover-slip preparation of another colony 

 of the same organism. Compare the results. 



The Ordinary Staining-solutions. — The solu- 

 tions commonly employed in staining cover-slip prepa- 

 rations are, as has been stated, watery solutions of the 

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

 ylene-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 follows: 



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. Each 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. The bottles are then to be 

 labelled saturated alcoholic or watery solution of fuch- 

 sin, gentian-violet, or methylene-blue, as the case may 

 be. The alcoholic solutioTis are not directly employed for 

 staining-purposes. 



