40 



The fermentation tubes are used to enable one to deter- 

 mine the quantity and kinds of gases produced and also the 

 anaerobic properties of the organism. 



EXERCISE XIII. 



THE EXAMINATION OF CULTURES (continued). 



§ 60. GeneraljDirections. Re-examine the cultures made 

 on special media and make notes on all changes which have 

 occurred in their appearance. 



Examine microscopically in hanging-drop preparations 

 the bacteria from the glucose-bouillon culture. 



Make 3 stained cover-gla.ss preparations from the milk 

 culture. Stain with the different dyes already used. 



Re-examine 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 (§ 2 f.). 



§ 61. Making cover-glass preparations from milk cul- 

 tures. Spread as thin a film as possible of the milk culture 

 on the cover-glass and allow it to dry in the air. Then pass 

 it 3 times through a flame. After flaming immerse the 

 preparation in a watch glass, or other receptacle, containing 

 a few cubic centimeters of ether to dissolve out the fat. 

 Then remove and after the ether has 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. 



