128 BACTERIOLOGY. 



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 satu- 

 rated alcoholic or watery solution of fuchsin, gentian- 

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

 alcoholic solutions will not answer for staining purposes. 



The solutions with which the staining is accomplished 

 are made from these alcoholic solutions in the following 

 way : 



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

 three-fourths filled with distilled water and the concen- 

 trated alcoholic or watery solution of the dye is then 



FIG. 21. 



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

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

 given that the color does not become too dense. The 

 .best results are obtained when it is just transparent 

 as viewed through a layer of about 12 to 14 mm. 

 thick. 



These represent the staining solutions in everyday 

 use. They are kept in bottles supplied with stoppers 



