144 UNIVERSITY OF WISCONSIN STUDIES 
that the standard methods may tend to give results too low, 
and that possibly some of the nitrogen is liberated. 
B. cloacae.—In general it may be said that this micro-or- 
ganism did not materially differ from B. col. The greatest 
action was on the nitrites and nitrates, which were decreased 
markedly in both the anaerobic and aerobic flasks. There was 
also a decided tendency to decrease the amount of free am- 
monia, although this was not constant. 
B. pyocyaneus.—At 37.5° C. the action was irregular. At 
times the nitrites and nitrates were increased and under ap- 
parently the same conditions they were decreased. The 
same holds true for the free ammonia and organic nitrogen. 
There was nothing to indicate that the oxygen content of the 
samples had any effect on the action. 
At room temperature the action on the free ammonia and 
organie nitrogen had the same irregular tendencies that were 
noted above. 
This irregularity was also noted in the aerobic flasks in 
connection with the nitrites and nitrates. In the anaerobic 
flasks the nitrates were decreased with an increase in the ni- 
trites. This increase and decrease nearly balanced. 
B. proteus.—This also showed a marked irregularity in its 
action at 37.5° C. At room temperature the action was more 
constant, the free ammonia being increased with a correspond- 
ing decrease in the organic nitrogen. The nitrates were in- 
creased with a corresponding decrease in the nitrites. This 
activity was more marked in the anaerobic than in the aerobic 
flasks, and I believe that with this micro-organism, better 
results can be obtained under anaerdbic, or nearly anaerobic 
conditions, than where the oxygen content is relatively high. 
B. mesentericus var. ruber.—This has nearly the same 
characteristics as the previous micro-organism, the action being 
irregular in the experiments conducted at 37.5° C. while 
those at room temperature were more constant, especially 
under anaerobic conditions. At the lower temperature the 
free ammonia was increased and the organic nitrogen was 
decreased. The nitrites were, in the majority of the experi- 
ments, increased, with no changes noted in the nitrates. Under 
