2C)2 C. M. CHILD. 



stage while other members of the same original generation have 

 given rise to twelve generations of descendants. As a matter of 

 fact the animals have not actually remained at exactly the same 

 stage during this time but their life has consisted of alternating 

 progressions and regressions of slight extent as periods of feeding 

 and starvation have alternated. 



IV. CONCLUSION. 



This partial starvation experiment affords an interesting 

 contrast to the experiment in asexual breeding. The latter 

 demonstrates that the animals may undergo senescence and 

 rejuvenescence for generation after generation of asexual repro- 

 duction without any indications as yet of progressive senescence 

 of the stock. The former, on the other hand, demonstrates 

 that senescence may be prevented by partial starvation for at 

 least a length of time equal to twelve generations and judging 

 from the present indications both experiments may be continued 

 indefinitely, although the partial starvation experiment will 

 finally be terminated by accidental losses, since there is of course 

 no increase in the number of animals such as occurs in the 

 breeding experiment. 



Senescence in these animals is evidently associated with growth 

 and rejuvenescence with reduction and reconstitution and neither 

 has any necessary relation to sexual reproduction. In papers 

 referred to above the writer has advanced the view that senescence 

 in its simplest terms consists in a decrease in rate of metabolism 

 resulting from the proportional decrease in amount of the meta- 

 bolic substratum and from changes in the substratum which 

 retard to the chemical reactions of metabolism. Rejuvenescence 

 on the other hand is an increase in rate of metabolism resulting 

 from the removal of inactive or less active substance and from 

 changes in the substratum which permit a higher rate of reaction. 

 Growth and differentiation bring about senescence and reduction 

 and reconstitution bring about rejuvenescence. The facts of 

 the present paper constitute further evidence in support of this 

 view and show not only that the rejuvenescence of old animals is 

 possible without reproduction of any kind but also that senescence 

 can be prevented or at least retarded so as to be inappreciable 



