FEEDING P.\EAMECIUM KNOWN BACTERIA 159 



the percentages for the three-day intervals that an increased 

 death rate sometimes accompanied an increased metaboHsm. 

 This suggests that an accelerated rate of metaboUsm may be 

 paralleled by an excessive mortality, as if the unusual expendi- 

 ture of energy was destructive to weak individuals. With the 

 exception of these occasional increases, the death rate of A'C 

 remained less than that for C. The significance factor for the 

 difference between C and A'C, 9.832, indicates a marked ac- 

 celeration of metabolism in animals fed with A'C 



The analysis of the conditions obtaining in the feeding of the 

 above mixtures is aided by a series of graphs of the division rates 

 averaged for three-day intervals during the five periods of ob- 

 servation. An inspection of these graphs shows the superiority 

 of the A'C mixture. It is true that for the first ten intervals, 

 the average division rate, 1.712, was less than that for M, which 

 was in excess of 2 (table 3 a). A fission rate greater than 2 is 

 unusual for Paramecium aurelia, yet the rate for A'C exceeded 2, 

 twelve intervals out of a total of forty-four. The rate for the 

 mixture A'B'C, used for a total of forty-two intervals, exceeded 

 2 nine times, thus approximating A'C. The division rate of 

 the control, C, did not exceed 2 in any of the averages for three- 

 day intervals. Although the daily rate rose above this figure or 

 equaled it 174 times between August and March, these high 

 rates did not occur with suff.cient frequency to bring any single 

 average for a three-day interval up to 2. 



Certain minor fluctuations in the rhythms are to be seen on 

 an inspection of the graphs. These fluctuations are independent 

 of those for the three-day intervals and of the occurrence of endo- 

 mixis. They are evidence of an alternating elevation and de- 

 pression of the metabolic rate which seems to be independent of 

 food. They occur in all cultures and are fairly synchronous ir- 

 respective of the type of food used. The temperature of the 

 laboratory was fairly constant; that for the liquid in which the 

 animals were living was necessarily more constant than the air 

 of the room, and this even temperature obtained throughout the 

 course of the work save for a part of the winter when there was 

 some variation. Since these minor fluctuations occurred during 



