192 III. THE EVOLUTION OF VIRUSES 



agglutinated by the antiserum, probably because of the denaturation 

 of the surface protein of the corpuscle due to the antiserum, whereby 

 free polar groups causing the corpuscles to combine with one another 

 are set free. If an agent named complement is present in this process, 

 the phenomenon called complement fixation may occur, in which com- 

 plement is combined with blood corpuscles owing to the same polar 

 groups set free. Such a state of corpuscles to achieve agglutination 

 and complement fixation is actually known to be only transient, 

 showing that unfolding of the peptide chains is soon followed by the 

 refolding (12). 



Lesley et al. (101) have suggested that infection of bacteria by 

 phage stimulates some mechanism whereby phage adsorbed subse- 

 quently to the cell is broken down extensively at the cell surface. 

 This may be ascribed to the activation of the cell surface by the 

 preliminary combination with phage ; the activation resulting from the 

 liberation of polar forces may enable the cell surface to cause a 

 severe structural disturbance in the phage added at a later time. 



Some plant viruses can readily infect leaves by rubbing if the 

 leaves injured by carborundum, indicating that the protein in the sur- 

 face of the leaves is activated by the application of the agent to adsorb 

 the virus. In this case the activated state is likewise temporary, as 

 it is confirmed that the leaves regain their resistance to infection 

 within three hours of the procedure, though they remain permeable 

 to salts presumably because the cuticle is not repaired (102). 



Now we have to return to the problem concerning the transmis- 

 sion of plant viruses by insects in which no virus multiplication takes 

 place. The writer claims that also in this case viruses may acquire 

 the activated state in insect bodies. The agent causing such an 

 activation is presumably a protein, present in the alimentary tract of 

 the insect, which can combine specifically with the virus, like an anti- 

 body with the antigen. 



As already mentioned, some insects can be parasitic on certain 

 plants because of the presence of common structure between their 

 proteins, whereas the same relationship must be present between a 

 plant and a virus which can affect the former. Therefore, also be- 

 tween a virus and an insect living on the plant which the virus affects, 

 there must likewise be common structure, through which the protein 

 of an insect can combine specifically with virus. Thus, if the virus 

 is taken into the alimentary tract of the insect, some protein present 

 in the latter will combine with the virus. This combination should 

 be analogous to that between antigen and antibody, and hence a kind 

 of denaturation is to be raised in the virus, thereby the temporarily 

 activated state will result in the latter. 



