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 (-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. 1 



(b) 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 10 to 30 seconds. Then 

 rinse it thoroughly in water, after which cover it with T V% 

 solution of acetic acid or strong (95%) alcohol. Allow this 

 to act for from 5 to 10 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 

 rule, 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. 



