SENESCENCE IN HIGHER ANIMALS AND MAN 289 



the substratum necessary for their continued function. But even 

 though the final stage of senescence, which terminates in death, 

 may be regarded as a wearing out and a breaking down of the 

 physiological mechanism at some point, it must not be forgotten 

 that this stage is merely the final stage of progressive development 

 and that the factors which determine it act from the beginning of 

 development on. 



CONCLUSION 



So far as the facts go, the process of senescence appears to be 

 essentially the same in the higher and lower organisms; the chief 

 difference is that with the absence of reproduction and the greater 

 degree of individuation and differentiation the later atrophic stages 

 of senescence are conspicuous and characteristic features of the 

 life history in the higher forms, while in the lower they either do 

 not appear or else occur in only a few cells at any given time. From 

 the lowest forms to man senescence is simply one aspect of the 

 developmental process, and we may expect to find it occurring 

 wherever the progressive changes are not balanced or overbalanced 

 by regression. 



The apparent continuity and irregressibility of senescence in 

 man and the higher forms is responsible for the very general belief 

 that the process is irregressible everywhere, but the plants and lower 

 animals show us clearly enough that this is not the case. Viewed in 

 the light of what we have learned from the lower forms, senescence 

 in the higher animals and man is merely a less frequently inter- 

 rupted process of the same kind as that which occurs in all pro- 

 gressive stages of the life cycle in the plants and the lower animals. 



REFERENCES 



ARON, H. 



1911. "Wachstum und Ernahrung," Biochem. Zeitschr., XXX. 



1912. "Weitere Untersuchungen liber die Beeinflussung des Wachstums 

 durch die Ernahrung," V erhandlungen d. Gesell. f. Kinder heil- 

 kunde. 



1913. Biochemie des Wachstums. Erweiterte Sonderausgabe aus dem 

 Handbuch d. Biochemie. Erganzungsbd. Jena. 



BECHHOLD, H. 



1912. Die Kolloide in Biologie und M edezin. Dresden. 



