THE PROBLEM OF REJUVENESCENCE IN 



PROTOZOA* 



LORANDE LOSS WOODRUFF 



It is a pleasure to accept the invitation to present a summary of 

 the results derived from our genetic cultures of Paramcecium at 

 Yale, with special reference to the bearing of this and other work 

 on the problem of rejuvenescence in protozoa; for, it seems to me, 

 the problem has now passed successfully through the periods of 

 youth and adolescence, and is approaching that of maturity, when 

 we may confidently expect the production of some conclusions of 

 general significance. 



Although the problems of protoplasmic senescence and the func- 

 tion of conjugation have afforded the Stimulus for investigations 

 on the life history of infusoria since Ehrenberg, nearly a Century 

 ago, theorized on the potential ' immortality ' of those forms, we 

 may take, as the point of departure for our present brief review of 

 the subject, the classical experimental studies of Maupas. As is 

 well known Maupas' studies ajfforded a wealth of data, all of which 

 indicated that continued reproduction by division results in degen- 

 eration and death, and seemed to place the conclusion, that conju- 

 gation is a sine qua non for the life of infusoria, upon a firm em- 

 pirical basis. 



A series of important Investigations by Hertwig and Calkins 

 confirmed Maupas' general conclusion that infusoria, after a more 

 or less definite number of divisions, degenerate and finally die if con- 

 jugation is prevented. Calkins, however, made the significant dis- 

 covery that artificial Stimuli of different kinds may, for a time, be 

 substituted with success for conjugation since, by the opportune use 

 of artificial Stimulation, he was able to prolong the life of one cul- 

 ture of Paramcocium caudahim to the 742d generation. 



* Presented at the Symposium on protozoology. Amer. Ass'n. Adv. Science, 

 Berkeley, Cal., August 5, 1915. For a review of the earlier work on this subject, 

 at Yale, see Biochemical Bulletin, 1912, i, p. 396, 



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