284 CHEN CHONG CHEN AND LEO F. RETTGER 



the formation of acid and gas, and the production of carbinol 

 and diacetyl. 



Much attention has also been given in recent years to the 

 differentiation of bacteria on the basis of nitrogen utilization, 

 in the form of ammonia, amino acids, di-amines, nitrates, etc. 

 For example, it was shown by Uschinsky that B. coli can attack 

 amino acids like asparagine in a purely synthetic medium, 

 whereas B. typhosus is as a rule unable to utilize it as a source 

 of nitrogen. Quite recently Koser (1918 and 1919) succeeded 

 in a somewhat similar manner in differentiating between the 

 B. coli and B. aerogenes types of organisms. 



In his extensive study of nitrogen utilization by bacteria in 

 media of definite chemical composition, Koser observed that B. 

 aerogenes readily attacks uric acid or hypoxanthine as the only 

 source of nitrogen, while B. coli is void of this property. In 

 other words, he found that the aerogenes type possesses the 

 unique power of seizing upon the nitrogen of the purin ring, 

 whereas the coli type leaves this portion of the uric acid molecule 

 intact, and fails in its development unless some other nitrogenous 

 substance which furnishes available nitrogen is present. 



In the present investigation all of the strains isolated from 

 feces and soils were employed in a further study of this phase of 

 bacterial nutrition. They were inoculated into the uric acid 

 synthetic medium of Koser. In a large series of tests other 

 purin bases were employed in the place of the uric acid, the basic 

 composition of the synthetic medium being the same as when 

 the uric acid was used. These substances were xanthine, caffein 

 and theobromin. The uric acid synthetic medium as prepared 

 by Koser has the following composition : 



Distilled ammonia-free water 1000.0 cc. 



NaCl 5.0 grams 



MgS0 4 0.2 gram 



CaCl 2 0.1 gram 



KjHPO* 0.1 gram 



Glycerol 30.0 grams 



Uric acid 0.5 gram 



The medium was tubed in 5 cc. portions and sterilized for 

 fifteen minutes at 12 pounds extra pressure. The test tubes 



