Theories of Rejuvenescence 149 



processes that lie at the foundation of life, it is difficult 

 to believe that mere relations of proportionate quantity of 

 two things so complex as nucleus and cytoplasm, both having 

 the power of assimilation and growth, is at the bottom of 

 these matters of life, death and reproduction. As Dobell 

 (1909) expresses it, one would almost "as soon argue that 

 grey hairs are the cause of old age in man" as to hold 

 that increase in size of the nuclei is the cause of degeneration 

 and death in cells. Furthermore, this theory gives absolutely 

 no ground for the chief feature of mating, the fact that it 

 is a mating of two nuclei, not a mere reorganization. And 

 like the other theories of rejuvenescence, its validity depends 

 finally on whether mating actually does restore vigor, vital- 

 ity and reproductive power to depressed organisms. Most 

 of such theories have proceeded on the ground that if one 

 can show that degeneration occurs without conjugation, then 

 it must follow that mating remedies the degeneration. The 

 real test lies in observing whether mating actually does rem- 

 edy the degeneration. If it does not, the probability be- 

 comes strong that the degeneration is simply a pathological 

 result of bad conditions. The evidence is becoming over- 

 whelming that this is the case ; that to avoid degeneration, 

 it is merely necessary to avoid the bad conditions. The work 

 of Woodruff, set forth in our first lecture, goes far to dem- 

 onstrate this. 



Hertwig's own test of the matter in Paramecium was, as 

 we have seen, opposed to the idea that mating increases 

 the vigor of reproduction ; Maupas' extensive work gave the 

 same result, and my own still more extensive experiments 

 led to the same conclusion. Only Calkins' experiments with 

 Uroleptus stand in the way of asserting this to be the general 

 rule in infusoria. 



Certainly no clear case has been made out for rejuvenes- 



