THE ACTION OF CERTAIN BACTERIA ON SEWAGE 145 



aerobic conditions at room temperature, both the nitrites and 

 nitrates were increased, while the organic nitrogen was de- 

 creased. These changes % did not balance, leaving a large defi- 

 cit in the organic nitrogen which has not been satisfactorily 

 accounted for. 



B. subtilis. This micro-organism gave really consistent 

 results. They were obtained under aerobic conditions and 

 confined themselves to the free ammonia and the organic 

 nitrogen. There was in all of the experiments an increase in 

 the free ammonia with a decrease in the organic nitrogen that 

 practically balanced it. This activity was relatively very 

 great, amounting to as much as eight parts per million 

 at 37.5 C. and two parts per million at room temperature. 

 In regard to the nitrites and nitrates, the tendency was more 

 often to decrease than to increase them, but this action was 

 not constant. 



Under anaerobic conditions the action of the bacteria was 

 regular at 1ST. 5 C., both the free ammonia and the organic 

 nitrogen being decidedly decreased with an increase in the 

 nitrites and nitrates, the latter being very decided. At room 

 temperature the action was not so marked and in general 

 followed that of the aerobic conditions, showing an increase 

 in the free ammonia and a decrease in the organic nitrogen. 



From the results which were obtained, I believe that this 

 micro-organism and the entire group of allied micro-organisms 

 will bear much careful study in their relation to the bacterial 

 processes in the purification of sewage. 



The action of mixed cultures. I have already pointed 

 out that in mixed cultures B. coli was completely overgrown 

 in the anaerobic flasks, and was overgrown by all of the bac- 

 teria in the aerobic flasks, with the exception of B. pyocyaneus. 

 Also that B. subtilis and B. prof e us (vulgar us) overgrew the 

 other bacteria in both sets of flasks. When grown together they 

 about balanced each other. 



The fact that the chemical action very closely followed 

 the predominating bacteria was extremely interesting. The 

 action was in certain cases, as I will point out later, very dif- 

 ferent in the aerobic and anaerobic flasks with the same 



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