62 



THE CULTIVATION OF BACTERIA. 



This preparation is chiefly used for determining whether the 

 bacteria secrete indol or not. It is necessary therefore to see 

 that the peptone preparation used be chemically pure, also 

 that the solution be free from the presence of carbohydrates. 



2. Glucose-, lactose-, and saccharose-bouillon. These are made 

 by adding to the bouillon after filtration and before steriliza- 

 tion from 1 to 2 per cent, of the desired kind of sugar. 



THE UTENSILS OF THE CULTIVATION OF BACTERIA. 



For making and keeping cultures the following instruments, 

 glassware, and utensils are required : 



1 . Perfectly clean glass tubes, 5 to. 7 inches long and J to 



FIG. 12. 



FIG. 13. 



Glass test-tube. 



Erlenmeyer flask. 



1J inches in diameter (Fig. 12). 

 with ordinary cotton-batting. 

 2. Erlenmeyer flasks (Fig. 13). 



These should be plugged 



