38 LABORATORY BACTERIOLOGY 



however, to determine the acid and gas production in the test 

 tubes than to use the fermentation tubes, and it is cheaper. It 

 is convenient, therefore, to use these tubes with the sugar 

 media as follows : — 



1. If to determine power of organism to produce gas only 

 use the agar tubes. 



2. If to determine power of organism to ferment sugars pro- 

 ducing acids only use test tubes of bouillon. 



3. If to determine the quantity of gas produced and ap- 

 proximately its composition use the fermentation tube. In 

 this exercise all three are called for. 



