THE ACTION OF CERTAIN BACTERIA ON SEWAGE 147 



coli established itself so late in the incubation period that 

 the little chemical effect it might have had was not apparent. 



B. coli and B. proteus. In pure culture both of these 

 bacteria had a slight and irregular chemical action. However, 

 when grown together, the changes in composition were regu- 

 lar and consistent. In both the aerobic and anaerobic flasks 

 there was an increase in the free ammonia and a decrease in 

 the organic nitrogen. No changes were noted in either the 

 nitrites or nitrates. 



B. coli and B. subtilis. In the aerobic flasks the changes 

 were those of a pure culture of B. subtilis, i. e., 

 an increase in the free ammonia and a corresponding de- 

 crease in the organic nitrogen. Except in one case where there 

 was a slight increase in the nitrites, neither the nitrites or 

 nitrates showed any change. 



As I have noted, neither of the bacteria has a regular 

 chemical action at 37.5 C. under aerobic conditions. How- 

 ever, when grown together there is an increase in the free 

 ammonia and a decided decrease in the organic nitrogen. 

 This increase and decrease balanced each other. 



Neither the nitrites nor nitrates were affected in any way. 



Just what the explanation for this condition is, I am unable 

 to say at the present time, as B. coli was completely overgrown. 



B. subtilis and B. cloacae. In the aerobic flasks, in which 

 B. subtilis markedly overgrew B. cloacae, the chemical 

 changes were typical of B. subtilis. The free ammonia was in- 

 creased with corresponding decrease in the organic nitrogen. 

 The nitrates were decreased with an increase in the nitrites. 



In the anaerobic flasks where the overgrowth of B. subtilis 

 was not apparent, the chemical changes were in the main those 

 of B. cloacae, differing from those of the pure culture in the 

 tendency towards increasing the nitrites and nitrates. 



B. subtilis and B. mesentericus var. ruber. In the aerobic 

 flasks the action was irregular, resembling that of B. mesen- 

 tericus v<ir. ruber. Both the nitrites and nitrates were in- 

 creased. 



In the anaerobic flasks the free ammonia was increased 

 with a corresponding decrease in the organic nitrogen and 



