REJUVENESCENCE IN UROLEPTUS MOBILIS 145 



amounted to 4.8 divisions in ten days. Finally, the J series 

 came from the same parent A series when the latter was in the 

 311th generation, i.e., the protoplasm was about 230 generations 

 by division older than it was at the time when the C series came 

 off. The discrepancy in division rates between the young J 

 series and the old parental A series now amounted to 17.6 di- 

 visions in ten days. This means that, if the protoplasm con- 

 tained in the two weakened cells of the parental A series had not 

 conjugated in the 311th generation, it might have divided during 

 the subsequent sixty days at the rate of twenty-five hundredths 

 of one division in ten days, but having conjugated, it actually 

 divided at the rate of 17.9 times in ten days. 



These results indicate that the protoplasm of Uroleptus under 

 these cultural conditions has a certain optimum capacity or 

 potential of metabolic activity which is gradually exhausted, but 

 which can be restored by conjugation. The greater the ex- 

 haustion, the more remarkable the restoration. As recharging 

 a storage battery restores its potential of active energy, so con- 

 jugation restores the potential of vital energy. If the battery is 

 recharged before the old charge has been drawn upon, its poten- 

 tial of activity would scarcely be affected. An analogous con- 

 dition is shown by the Uroleptus protoplasm after encystment, 

 and after conjugation occurring in an earlier period of the life 

 cycle (e.g., the A and C series, or the C and F series). If, how- 

 ever, the battery is nearly exhausted before it is recharged, the 

 difference in potential between the newly changed condition and 

 the exhausted condition would be marked. The analogue to this 

 is the J series and the parental A series. The restored potential 

 of vitality in Uroleptus protoplasm is a 'charge' of vital energy 

 which is capable of metabolic activities through a period of from 

 260 to 300 days, or vitality sufficient to produce individuals to 

 the number of 2 to the 300th -1- power. 



In regard to the second of the phenomena shown by table 5, 

 it is interesting to see that, as the protoplasm of a series grows 

 older, the potential of vitality is exhausted at an increasingly 

 rapid rate. Thus, the discrepancy between the division rates of 

 parental and filial series is greater during the second sixty-day 



