398 NATHAN BERMAN AND LEO F. RETTGER 



Proteus vulgaris manifested a peculiar behavior in the glucose 

 tubes containing the di-basic phosphate, in which it failed to 

 utilize the carbohydrate completely (see table 2). Even 0.2 

 per cent glucose was not completely fermented in the presence 

 of the buffer. These results were indeed unexpected, and the 

 tests were repeated, with identical results. It appears from 

 these data that Proteus vulgaris readily attacks the nitrogen- 

 containing substances in the absence of excessive acidity, and 

 in preference to the residuary carbohydrate. 



In all of the buffered media the methyl red test was negative, 

 while in the sugar-containing solutions the hydrogen ion con- 

 centration was sufficiently increased within twenty-four hours 

 to give the color reaction with methyl red. 



GENERAL DISCUSSION 



The influence of fermentable carbohydrates on nitrogen metab- 

 olism of bacteria is clearly shown in the foregoing experiments. 

 The failure of certain organisms to attack protein or other com- 

 plex nitrogenous foods in a medium containing carbohydrate is 

 due to the accumulation of products which inhibit growth. 

 The nitrogen which is required in the cell reproduction of the 

 bacteria in the sugar medium is supplied by relatively simple 

 substances, as for example amino acids and purin, bases, which 

 are always present in the ordinary media containing commercial 

 peptone or meat extract, although in small amount. 



The information furnished by the titratable acidity figures is 

 of little value. Reactions which would ordinarily be considered 

 too high apparently had no inhibitive action on continued 

 bacterial development. The futility of adjusting the reaction to 

 phenolphthalein was pointed out by Clark (1915) and further 

 emphasized by Burton and Rettger (1917). It is now well 

 known that culture fluids giving the same titration values may 

 differ markedly in their hydrogen ion concentration. As was 

 shown in the present work, a culture giving a methyl red nega- 

 tive test may have a titratable acidity twice as great as one 

 that is methyl red positive. 



