120 DAVID DAY WHITNEY 



this the jar was allowed to remain undisturbed for from twenty- 

 four to forty-six hours and then opened and the contents of the 

 watch glasses examined. In other experiments the saturation 

 of the culture water with oxygen in the glass tube was omitted 

 as the results by both methods seemed identical. 



The first set of experiments as recorded in table 7 were per- 

 formed with special reference to the protozoa in the zooglea in 

 order to determine what effect oxygen had on maintaining or 

 increasing the number of individuals in the culture water as 

 compared with other similar culture water subjected to ordinary 

 air conditions. In all the experiments recorded and in many 

 unrecorded ones a decided effect of the oxygen was noted. In 

 all culture waters subjected to oxygen, from eighteen to forty-six 

 hours, many more individual protozoa were counted in a definite 

 microscopic area than in the culture water subjected to air. 



The second set of experiments recorded in table 8 were per- 

 formed in order to determine what effect the oxygen had upon 

 the bacteria in the zooglea on which the protozoa or the rotifers 

 fed in the various waters such as were used by Shull and Ladoff. 

 At the end of twenty-four hours after being subjected to from 

 40 to 60 per cent of oxygen the culture water in the watch glasses 

 in 16 experiments out of 23 experiments showed a greater num- 

 ber of bacteria per cubic centimeter than did those subjected to 

 air. In one experiment there was no difference and in 6 experi- 

 ments there were fewer bacteria per cubic centimeter than in the 

 culture water subjected to air. The second important fact de- 

 termined was that no two watch glass cultures can be made that 

 are identical in food content, as judged by bacterial counts, either 

 at the beginning or at the end of the experiment except when it 

 is done by chance as in lots F and G of experiment 8 in table 8. 

 Before putting the zoogleal scum into the various culture waters 

 about 20 cc. of it was made up with its own culture water in a 

 separate dish and then stirred considerably in order to break up 

 the scum into small fragments. Then 1 cc. of this was added 

 to 4 cc. of the various culture waters. Immediately after this 

 bacterial plates were made and also again at the end of twenty- 

 four hours. The third point to be suggested is that in this 



