THE EXAMINATION OF CULTURES 4 1 



EXERCISE XIII 



THE EXAMINATION OF CULTURES {Continued') 



66. Work for this Exercise Reexamine the cultures made 



on special media and make notes on all changes which have 

 occurred in their appearance. 



Examine microscopically in hanging-drop preparations ^he 

 bacteria from the glucose- bouillon culture. 



Make 3 stained cover-glass preparations from the milk cul- 

 ture. Stain with the different dyes already used. 



•Reexamine all of the cultures previously made and make 

 careful notes of any changes in appearance. 



Reject all of the cultures made excepting those on agar from 

 the colony, which should be preserved, and clean the tubes and 

 Petri dishes (3,/). 



67. Making Cover-glass Preparations from Milk Cultures 



Spread as thin a film as possible of the milk culture on the 

 cover-glass and allow it to dry in the air. Immerse the prepa- 

 ration in a watch-glass, or other receptacle, containing a few cubic 

 centimetres of ether and absolute alcohol in equal parts, which 

 dissolves out the fat and fixes the film to the cover-glass at the 

 same time. Then remove and, after the ether and alcohol have 

 evaporated, stain as usual. The amount of albumen in the 

 milk will usually cause a heavy background, which will require 

 decolorizing with alcohol or weak acetic acid. 



