i go 



SENESCENCE AND REJUVENESCENCE 



This cycle of changes, which may occur within a few hours and 

 which may be repeated in a single cell, is, I believe, not funda- 

 mentally different from the age cycle in organisms. All the essen- 

 tial features of both senescence and rejuvenescence up to a certain 



FIGS. 66, 67. Pancreas cells of toad: Fig. 66, fully loaded and almost quiescent; 

 Fig. 67, partially discharged after stimulation. From preparations loaned by R. R. 

 Bensley. 



point are present. The cell probably does not return to the em- 

 bryonic condition at any point in the cycle, but it certainly does 

 undergo changes similar in character -to those of the age cycle, 

 though their period is short. At the same time the gland cell 

 may be undergoing senescence in the stricter sense, that is, more 



