22 LABORATORY BACTERIOLOGY 



From this point the procedure is the same as that for the 

 preparations made from the bouillon culture. 



32. Staining Bacteria in Cover-glass Preparations. — (i) 

 With alkaline methylene-blue. With the pipette place a few 

 drops of the staining solution on the film side of the fixed 

 preparation, 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 off the stain 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 objec- 

 tive. 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, 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 alkaline 

 Canada balsam. 



(2) With carbol fuchsin. Cover the film on the cover- 

 glass with the stain and allow it to act for about i minute. 

 Then rinse it thoroughly in water, after which cover it with ^% 

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

 act 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. 



Cover-glass preparations of bacteria are permanently mounted 

 in the same manner as similar preparations made from the 

 blood or other tissues in histology, the process being to put a 

 drop of balsam on the centre of the slide and place the prep- 

 aration, film downward, over it and apply slight pressure. 

 Label the preparation, giving the name of the organism, its 



