274 CHEN CHONG CHEN AND LEO F. RETTGER 



a simultaneous acid and alkaline fermentation in which the 

 salts of organic acids produced from glucose are converted into 

 carbonates or bi-carbonates, which in turn cause the reversion 

 in reaction in a B. aerogenes culture. 



In our attempts to follow up the work of Ayers and Rupp the 

 Sorensen method of determining primary amino acid was em- 

 ployed, in addition to the ammonia determination method of 

 Folin. It was hoped that some definite relationship between 

 the formol titration and the ammonia figures could be established. 



The Clark and Lubs peptone-phosphate-glucose medium was 

 again made use of. Flasks containing 500 cc. of the medium were 

 inoculated with a loopful (standard 4 mm. loop) of a twenty- 

 four-hour culture of B. aerogenes grown in the same medium, and 

 incubated at 30°C. At the end of 1, 2, 3, 5, and 10 day intervals 

 the required amount of culture material was removed and sub- 

 jected to the tests for sugar, amino acids, ammonia and hydrogen 

 ion concentration. Eight representative strains of bacteria were 

 selected for the test. Two were B. coli isolated from animal 

 feces, and the remaining six aerogenes types from various appar- 

 ently uncontaminated soils. 



In the following table the Sorensen titration figures are recorded 

 as the numbers of cubic centimeters of w NaOH required to 

 neutralize 100 cc. of the test medium. The ammonia figures are 

 given as milligrams of ammonia per 100 cc. of the culture fluid. 



The results show several interesting points. A close relation- 

 ship appears to exist between the sugar utilization and the hydro- 

 gen ion concentration. In the aerogenes cultures the complete 

 reversion of reaction took place within five days' incubation, 

 and the sugar supply was practically exhausted in the same 

 period. On the other hand, in the coli cultures the glucose was 

 only partly fermented, and the hydrogen ion concentration 

 remained constant after three days of incubation. No definite 

 relationship between the Sorensen titration and the ammonia 

 figures could be established. Irregularity of ammonia production 

 is noticeable. One point stands out clearly from the rest; the 

 amount of ammonia recorded in the B. aerogenes cultures was no 

 greater, after ten days' incubation than in the control. 



