LIFE HISTORY OF TWO RARE CILIATES 



379 



If rejuvenescence mean a renewal of the vital activities of 

 the organisms, this process cannot be said to have taken place 

 in Spathidium. In every case artificial stimulation was fol- 

 lowed by a slight reaction on the part of the protoplasm, this 

 effect lasting for a short time only, when the protoplasm either 

 lapsed into its original condition or showed a somewhat lower 



Diagram 1 Complete history of Spathidium spathula, Culture A, from start 

 (February 24, 1911) to finish (July 7, 1911) in the 218th generation. The rate 

 of division is averaged for ten-day periods. The ordinates represent the average 

 daily rate of division for three individuals. The abscissae represent the number 

 of ten-day periods. 



vitality than before. This response must be interpreted, not 

 as rejuvenescence, in the sense indicated above, but as a tem- 

 porary response to stimulation, the chemical acting as a spur 

 to the waning activity of the cell. If however we define re- 

 juvenescence as a certain power given to protoplasm by means 

 of which its activitie-^ are sustained for a longer period of time 



