212 III. THE EVOLUTION OF VIRUSES 



The structural change of protein is liable to be reversible. This 

 reversibility is especially distinct in the protoplasm. Thus distorted 

 protoplasm can spring back like a spring to its original state when 

 an agent causing its distortion is removed ; that is, the protoplasm, 

 in remembering its former structure, is inclined to recover the struc- 

 ture it once possessed. 



The recovery from virus diseases may chiefly be achieved owing 

 to this reversibility of protoplasm. The reversibility tends to persist 

 even when the protein is freed from the protoplasm, resulting in the 

 fact that protein denaturation is generally reversible to some extent. 

 Thus inactivated viruses may sometimes be reactivated when the 

 inactivating agents are removed. A virus once subjected to a varia- 

 tion will tend to recover its original property if released from the 

 causative agent leading to the variation. 



The failure of virus demonstration in some inflammatory diseases, 

 such as allergic dermatitis, may be attributed to a high reversibility^ 

 of the distortion. On the other hand, the distortion induced by strong 

 viruses may be so intensive that the recovery of the original structure 

 is rendered impossible. Since such a distortion means a structural 

 change of the protoplasm, a distortion induced by a virus must involve 

 the structural patttern of the virus itself, and accordingly the irrever- 

 sible distortion is nothing but the multiplication of the strong irre- 

 versible virus. 



However strong and firm the structure of a virus may be, it will 

 gradually be assimilized and annihilated by the assimilase action of 

 the host protoplasm if the virus continues to multiply in the same 

 kind of host, thereby the virus structure becomes identical with the 

 protoplasm structure. In order to escape this fate virus has to change 

 the host. 



Host change enables a virus, which has already assimilized to 

 some extent by the host protoplasm, to come into contact with the 

 protoplasm of a new host having a structure different from the former 

 host. Through this contact the virus will recover the original, non- 

 assimilized structure, and at the same time structure of the new host 

 will be introduced into the virus ; thus the rejuvenescence of the 

 virus is established. 



