24 LABORATORY BACTERIOLOGY 
this point the procedure is the same as that for the preparations 
made from the bouillon culture. 
34. Staining bacteria in cover-glass preparations. (a) With 
alkaline methylene blue. With the pipette place a few drops 
of the staining solution on the film side of the fixed prepa- 
ration, which is either held horizontally with the fine forceps 
or left resting on the tray. Allow the stain to act for 2 or 
3 minutes; then carefully rinse it off in water, holding the 
cover firmly by one edge with the forceps. After thoroughly 
rinsing, place the preparation, film downward, on a clean slide 
and dry the upper surface with a piece of filter paper. It is 
now ready for the microscopic examination. Use first the 
dry lens (4-in. obj.) and then the oil-immersion objective. If 
the specimen is a good one and it is desirable to preserve it, 
wipe off the drop of oil with a piece of lens paper and run a 
drop of distilled water under the cover glass, which will float it, 
when it can be easily removed with the forceps. Place it on 
the tray, film upward, and when dry, mount it in a neutral or 
slightly alkaline Canada balsam.’ 
(4) With carbol fuchsin. Moisten the film side of the 
cover glass with water (using the pipette); then cover it with 
the stain and allow it to act for from ro to 30 seconds. [Then 
rinse it thoroughly in water, after which cover it with »>% 
solution of acetic acid or strong (95%) alcohol. Allow this 
to act for from 5 to ro seconds, and again thoroughly rinse 
in water and examine as above. (For other decolorizers, see 
text-books.) 
Upon ‘examination the preparation should be free from 
deposits or stained background. The bacteria should, as a 
tule, be isolated and distinct ; unless they are the preparations 
are not satisfactory. 
1 To neutralize balsam, add some pure sodium carbonate to it and 
allow it to stand for about a month in a warm place, shaking it from 
time to time. Then allow the sodium to settle. The clear supernatant 
balsam will be found to be slightly alkaline. 
