I. THE THEORY OF MEMORY 345 



will be prevented by the host change or in general by environmental 

 changes. The host change as well as the sexual reproduction may be 

 effective for the rejuvenation, as the individual is able to come into 

 contact with other individuals by these processes, whereby the internal 

 structures which are becoming fixed are unloosened and unfolded, and 

 in addition the intermixing of the structural component of another 

 individual can contribute to prevent the fixation. 



As already stated, according to the writer's view, the cytoplasm 

 is rejuvenated, presumably at every cell division, by the template 

 action of the gene. The cells, however, must become senescent as 

 above considered, a fact which seems to contradict with this view. 

 But it should be realized that the gene itself gradually grows old. 

 The cytoplasm recovers its proper form by the template action of the 

 gene, but the template itself has to become aged with which the 

 cytoplasm also must grow old, as the cytoplasm is to be endowed with 

 the gradually aging pattern of the gene. 



Individuals are thus bound to become old. As the aging is the 

 general fate of the elastic substances composed of thread-like constitu- 

 ents, the senescence is the unavoidable fate -of livings. Elastic sub- 

 stances such as gum, just like the living protoplasm, exhibits the 

 phenomenon of memory and forgetting ; at the same time they can 

 adapt themselves to the environments until finally undergo senescence. 



On the other hand, senescence makes a great contribution to the 

 evolution of organisms ; the evolution might be even impossible with- 

 out senescence. In order to remove the old-patterned individuals for 

 the promotion of more-advanced juniors, senescence is of course indis- 

 pensable. But in addition, senescence of a proper degree plays an im- 

 portant part in the evolution. Since rigid structure was necessary for 

 the continuance of the existence of the organisms, in order to achieve 

 the evolution, to become rigid in their structural pattern would be 

 required for viruses and primitive organisms including even primeval 

 protein molecules. The writer considered previously that this rigidness 

 might generally be acquired through the struggle for existence ; but 

 without this they would surely be able to become stronger in their 

 structure, for the protein is provided with the nature in itself to be- 

 come thus rigid in its structure. 



Newly generated viruses are as a rule weak, but they may be able 

 to be stabilized gradually without the struggle for existence owing to 

 this nature. Thus, viruses and primeval organisms can acquire auto- 

 nomically the rigid structure necessary for acting as strong assimilase ; 

 the rigid structure is raised without even increasing the amount of 

 nucleic acid, the stabilizing agent of the protein. 



Organisms can achieve the evolution thanks to this character of 



