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 ‘‘ satu- 
rated alcoholic solution,’’ of whatever dye has been 
employed. The alcoholic solutions are not themselves 
empioyed 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 
