164 



BACTERIOLOGY. 



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 fuch- 

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

 be. The alcoholic solutions are not diredly employed for 

 staining-purposes. 



The solutions with which staining is accomplished 

 are made from the stock solutions in the following 

 way : 



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

 three-fourths filled with distilled water and the con- 

 centrated alcoholic or watery solution of the dye 

 added, little by little, until one can just see through 

 the solution. It is then ready for use. Care must be 

 taken that the color does not become too dense. The 

 best results are obtained when this dilution is just 



Fig. 35. 



Back of bottles for staining-solutious. 



transparent as viewed through a layer about 12 to 

 14 mm. thick. A solution consisting of 5 parts of the 



