344 



V. THE NATURE OF EVOLUTION 



change will be removed or rearranged to return to the original state; 

 as a result the change will come readily to occur. 



Environment A 



Environment B 



Fig. 33. Aging of protein molecule. 



On the other hand, further progress of the fixation due to the per- 

 sistent staying under the same environment will result in the es- 

 tablishment of the form a-i or b.. In such a state the polj'peptide 

 chain is folded very firmly by the mutual attraction of polar forces of 

 opposite signs, leading to a shrinkage accompanied by a deformation 

 and the loss of elasticity as well. This must be aging. 



It is a well known fact that young tissues are tender and elastic, 

 while old ones are hard and fragile. Similarly, as is generally recog- 

 nized, colloids tend to change into gel when become aged, thereby the 

 component particles becoming attached firmly and the contained water 

 is pressed out as known as syneresis, a phenomenon which is also well 

 acknowledged with living tissues. These phenomena may be expected 

 from this figure. Instead of the long thread of polypeptide in this 

 figure, many long colloidal particles may also be considered which are 

 attached to one another in a colloidal system. 



In the previous Part the writer has assumed that the senescence 

 of viruses or of primeval organims may be mainly attributed to the 

 effect of the assimilase action of the host or of the surrounding mas- 

 ses with which they are to be evolved. However, it has now become 

 clear that another important reason for the senescence is involved 

 in the nature of the protein itself. The senescence due to the 

 assimilase action of the host is brought about because the viruses are 

 persistent on the same host, that is, persistent on the same environ- 

 ment. Thus, it may be said that in both cases senescence, whatever 

 the cause may be, results from the persistent staying under the same 

 environment. 



The senescence therefore, whether it be raised by the adaptive 

 nature of the protein itself or by the assimilase action of the host 



