MICROSCOPICAL EXAMINATION. 201 



we can take from time to time the amount necessary to 

 make up the watery solutions for use. The stock satu- 

 rated alcoholic solutions are made by pouring into a bot- 

 tle enough of the dye in substance to fill them to about 

 one-quarter of their capacity. The bottle should then 

 be filled with alcohol, 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 dis- 

 solved, 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 sedi- 

 ment of undissolved coloring-matter is seen upon the 

 bottom of the bottle. This will then be labelled t( satu- 

 rated alcoholic solution, 77 of whatever dye has been 

 employed. The alcoholic solutions are not themselves 

 employed for staining purposes. The solution for use 

 is made by filling a small bottle three-fourths with dis- 

 tilled water, and then adding the concentrated alcoholic 

 solution of the dye, little by little, until one can just 

 see through the solution. Care must be taken that the 

 color does not become too dense. Small wooden cases 

 come prepared for holding about one-half dozen bottles 

 of the staining solutions. This number will answer 

 for all routine purposes of the student or physician. 



For certain bacteria, which stain only imperfectly 

 with these solutions, it is necessary to employ some 

 agent that will increase the penetrating action of the 

 dyes. We have learned that the addition to a solu- 

 tion of a small quantity of alkaline substance, or by 

 dissolving the staining materials in strong watery solu- 

 tions of either aniline oil or carbolic acid, instead of 

 simple water, will accomplish this. Of the solutions 

 thus prepared there are three in common use: Loeffler's 



