362 Harris M. Benedict 



when abundant oxygen is available. Some of these products might 

 be such as would merely interfere with cell activities by their 

 accumulation, while others might be toxic in their action. It is quite 

 possible that some of these changed products resulting from incomplete 

 permeability might act upon the protoplasm in such a way as to further 

 decrease its permeability. This would lead in turn to a more rapid pro- 

 duction of the injurious substances. The presence of a decrease in per- 

 meability with age seems to account in part for the retention of inert 

 accumulations, and possibly may be considered an important cause for 

 the production of the accumulating material. It is interesting to note 

 that this idea had occurred to Child (1912) in connection with senile 

 degeneration in sperm cells, although he did not consider it as a general 

 cause of senility. 



The objections which may be raised against the theory that senility 

 is due to the retention of toxic waste products owing to the lack of sufficient 

 excretory surfaces in old organisms, do not apply when the retention of 

 these substances is referred to a general decrease in permeability operating 

 in all cells of the organism. A decrease in permeability as age increases 

 accounts perfectly for every condition that the older theory claimed to 

 exist. The loss of efficiency in excretion will occur in small organisms 

 as certainly as in large ones, will characterize all cells and not simply a 

 localized fraction, and does not require any postulates regarding relations 

 between mass and surface, which are certainly untenable for the higher 

 plants and probably for the higher animals. Furthermore, increasing 

 permeability interferes with the inward movement of substances, and this 

 undoubtedly is also an important consideration and perhaps in plants 

 more important than difficulty of excretion. 



Lillie (1909) argues strongly that many stimuli act on cells by the pro- 

 duction of temporary increases in their permeability. It is also obvious 

 that a complete cessation from activity tends to aid in the elimination 

 of substances from the cells. Since the production of new metabolic 

 products ceases, the cell is able to get rid of a certain amount of accumulated 

 waste. Hunger, sleep, the division of the lower animals in regeneration 

 experiments, encystment, and asexual reproduction, would therefore, in 

 varying degrees according to method and organism and environment, 

 utilize both these methods for decreasing the accumulations. The 

 internal stimuli which are set in force in starvation effect katabolism 



