460 BOTANICAL GAZETTE [December 



Certain of the by-products may be insignificant in their influence 

 upon the protoplast. Others will undoubtedly be toxic in their 

 effect, as many investigations upon auto-intoxication have gone 

 to show. Primitive excretory systems, developed primarily for 

 the disposal of waste materials, may remove a considerable part 

 of these by-products. Thorough cleansing of the protoplast by 

 this method, however, is impossible. Inevitably by-products 

 will accumulate with the age of the organism. In fact age itself, 

 in other than the purely chronological sense, is probably accounted 

 for by this very accumulation of by-products. The toxic influence 

 of these by-products will interfere with the efficient working of 

 the machinery of the protoplast, and metabolism will be slowed 

 down; hence "old age. " Rejuvenescence occurs with cell division, 

 because at cell division the protoplast is cleansed of many of these 

 toxic by-products. This cleansing probably involves both physical 

 and chemical forces. Physical reorganization at cell division will 

 explain the exposure of these by-products; chemical oxidation 

 will account for their removal (as toxins). 



Again, were the machinery of this cleansing process a perfect 

 one, rejuvenescence would be complete. Actually, however, the 

 cleansing of the protoplast at cell division is not (or is not 

 always) absolutely thorough. A few of the by-products pass 

 over to the daughter protoplasts. The daughters, therefore, start 

 life with a few by-products which the mother did not possess at 

 the beginning of her life. Since these by-products are toxic and 

 impair or retard metabolism, it is evident that the daughters are, 

 at birth, slightly "older" than was the mother. 



A series of repetitions of this performance through successive 

 generations will have a cumulative effect. As a consequence, not 

 only does the individual grow old through ontogeny, but, in a very 

 real sense, the whole race is gradually aging through phylogeny. 

 Evidence is not lacking that the higher organisms, cell for cell, 

 have a lower rate of metabolism than do the more primitive ones. 

 This is a statement of the quantitative effect of these by-products. 

 It is their qualitative effect, however, that casts light upon the 

 origin of the hereditary mechanism. 



