26 



drop of sterile water or bouillon. With the needle touch 

 the surface growth of the culture and then gently rinse the 

 end of the needle in the liquid on the covers. Spread the 

 liquid on the covers as before. From this point the procedure 

 is the same as that for the preparations made from the bouil- 

 lon culture. 



§ 29. Staining bacteria in cover-glass preparations. 

 ( I ) With alkaline methj'lene-blue. With the pipette place 

 a few drops of the staining solution on the film side of the 

 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 for- 

 ceps. 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, run a drop of distilled water under the 

 cover-glass which floats 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 bal.sam. (2) With 

 carbol-fuchsin. Cover the film on the cover-glass with the 

 stain and allow it to act for about one minute. Then rinse 

 it thoroughly in water after which cover it with xV% so- 

 lution 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 back ground. The bacteria should, as a 

 rule, be isolated and distinct, unless they are, the prepara- 

 tions are not satisfactory. 



Cover-glass preparations of bacteria are permanently 



