18 MICROSCOPIC EXAMINATION OF BACTERIA. 
around the bacteria and fixes them firmly to the 
glass. 
(/) Place a drop of stain ' on the cover-glass large 
enough td! cover the film. Allow it to stain for 
from two to ten minutes; the length of time de- 
pends on the stain, the strength of the staining 
solution, and the kind of bacteria.” 
Fic. 8.—Bottles for stains. 
(g) Wash in water, dry the unsmeared side on 
filter-paper, mount, film side down, in a drop of 
water on a clean slide, and examine with the } inch 
objective. 
‘Almost any of the anilin stains may be employed. 
Gentian-violet, basic fuchsin, and methylene-blue are those 
most commonly used. For methods of preparing these 
staining solutions, see Appendix, page 170. 
- ? It very rarely happens that bacteria are over-stained., 
But if such is the case, either a new film must be prepared 
or the stain drawn with weak acetic acid (1: 1000), or the 
cover-glass swept through 1 per cent. sulphuric acid. If 
the film is not sufficiently stained, repeat the staining 
process, 
