V. SUMMARY OF PART I. 33 



This may partially account for the fact that viruses exist commonly in 

 particles having sizes larger than a certain value ; if their particle 

 size are too small, viruses may be unable to exist as such because of 

 their extremely unstable property. 



Virus particles are immunologically distinct from the normal parti- 

 cles isolated from the healthy cells. The antibody against a virus can 

 specifically react with the virus particles, whereas the antibody against 

 the protoplasm protein isolated from the normal host cells usually 

 exhibit no action upon the virus particles isolated from the correspond- 

 ing cells. Thus there seems no doubt that a virus is provided with a 

 chemical group or groups capable of acting as an antigen different from 

 the normal protoplasm protein of the host cells. Actually, certain 

 differences are occasionally proved between them even in the amino acid 

 composition. 



Viruses appear to provide to the protoplams protein of the cell they 

 affected, in changing the property of the protoplasm, with a chemical 

 group or groups which are present in their own configuration. Hence, 

 viruses can be regarded as a kind of denaturase, or more adequately 

 "transnaturase", of the protoplasm protein. When the protoplasm 

 protein of host cells is furnished with such chemical groups through 

 "transnaturation" by a virus, the protein may acquire the ability to 

 act as the virus. 



Protein denaturation is considered, in general, to be infectious to a 

 certain extent, that is, a denaturating change occurring in a protein 

 molecule tends to infect other intact molecules, and thus the denatura- 

 tion spreads as a chain reaction. Such an infection seems to occur 

 always strikingly in the protoplasm. Denaturation or coagulation arising 

 in a portion of the protoplasm can spread promptly to the total proto- 

 plasm and occasionally even to that of surrounding cells. 



Similar chain reaction may occur also in the protoplasm of the 

 host cells infected with a virus resulting in the appearance of a chemical 

 group or groups specific to the virus ; thus the virus may multiply. 



The probable manner in which a virus structure is replicated in 

 the protoplasm protein and the mechanism by which the replicated 

 structure is transmitted successively in the protoplasm will be described 

 in detail in the next Part. 



