REJUVENESCENCE 155 



which forms the framework of the chemico-physical 

 basis of life. Chemically regarded, living means the 

 co-ordination of characteristic chemical changes, 

 differing in nature and in rate in different creatures 

 and in different parts of the same creature; but as 

 these proceed they form a colloid framework in 

 which they work. As the complexity of the frame- 

 work increases, and the stability of the organism, 

 so, too, the effectiveness of its chemical reactions. 

 Thus the earthworm is more of an agent than the 

 amoeba, and the bird more than the earth\vorm. 

 But the nemesis is senescence the tax on stability, 

 and rejuvenescence is the attempt at evasion. 

 In the Protozoa, as Weismann and others have 

 pointed out, the recuperative processes are so perfect 

 that natural death need never occur; the stable 

 mortal parts of the colloidal substratum can be 

 reduced and restored piecemeal, and the creature 

 never grows old. It is probable that the same is 

 true of a simple animal like the freshwater Hydra, 

 which may also be credited with immortality. But 

 as life became more worth living, and the organism 

 more of an agent, it became more and more difficult 

 for the processes of rejuvenescence, which are 

 always going on, to keep pace with those of senes- 

 cence, which, to tell the truth, may begin before 

 birth! Then it became necessary to have special 

 periods for rejuvenescence, " spring-cleanings " of 

 the organism, and we see these in the de-differentia- 

 tions and new beginnings associated with budding 

 and the like, perhaps even in such striking phe- 



