THE ACTION OF CERTAIN BACTERIA ON SEWAGE 143 
having been isolated from or are representative of groups 
normally occurring in sewage. 
The bio-chemistry of these bacteria, when grown on artifi- 
cial media, shows that they possess characteristics which, 
theoretically at least, should be of value in breaking down a 
complex organic substance such as sewage. The only excep- 
tion to this statement is possibly the power of B. coli to reduce 
nitrates. It will also be recalled that all of them are faculta- 
tive anaerobes. 
The action of the bacteria when grown in mixed cultures 
brought out two. very interesting points. One was the behavior 
of B. coli. Invariably in the anaerobic flasks it was com- 
pletely overgrown in the twenty-four hour period. Under 
aerobic conditions it overgrew B. pyocyaneus, but was over- 
grown by other bacteria. 
The other fact was that both B. proteus and B. subtilis over- 
grew the other bacteria in the proportion of three to one 
under all conditions. When these two were grown together 
they about balanced each other at the end of the twenty-four 
hour period. 
THE ACTION OF PURE CULTURES 
The action of pure cultures was studied under two conditions 
of temperature, at 37.5° C. and at room temperature. A 
summary of the results follows: 
B. coliThere was a marked tendency to decrease the 
nitrites and nitrates, with a very decided decrease in the 
organic nitrogen. This was more marked in the anaerobic 
flasks than the aerobic flasks, and was much more vigorous 
at 37.5° C. There was very little action on the free ammonia, 
although the general tendency was to decrease it. 
It was noted that the correction for the amount of organic 
nitrogen added to the sample in the bouillon tended to give, 
in all of the experiments, a reduction of the organic nitrogen. 
This was studied in the hope that some intermediate decom- 
position products might be found to account for it. At the 
present time I am unable to explain it in any other way than 
