214 III. THE EVOLUTION OF VIRUSES 



volved in a germ cell, the pattern will be rejuvenated together with 

 germ cell by the fertilization. The viruses, such as measles and 

 mumps, can probably be rejuvenated in this way without insect vec- 

 tors. Structural pattern of virus present in the germ cell, if ever 

 present, possibly exists in an altered state, so that it may fail to act 

 as the virus itself, but when the germ cell develops into an adult 

 form after the fertilization, the pattern may also be developed into 

 its original form, thereby becoming capable of acting as the virus ; 

 thus the virus may appear in the progeny only when germ cells have 

 developed to a certain extent. As will fully be discussed in Part V, 

 such is not a phenomenon restricted to virus pattern but may occur 

 generally in various, normal patterns which may develop to produce 

 adult forms. 



Virus demonstration is commonly impossible in larvae hatched 

 from the eggs deposited by an infected insect, but as they develop 

 into adult forms the demonstration may become possible. In like 

 manner, measles virus may not be demonstrated in a newly born 

 baby, but the full pattern of the virus will develop as the baby grows, 

 and thus the baby or the child will suffer from measles by the virus 

 •developed in its body. 



The structural pattern of a virus will naturally be spread to the 

 germ cells, when the structure of the virus becomes strong, and 

 thereby the virus can acquire by itself the means of rejuvenescence. 

 This must be the general course of the virus evolution. Thus, the 

 virus possessing insect vector can be rejuvenated by both the host 

 change and sexual reproduction of the host. Such an intimate corre- 

 lation of a virus with the host results in the excretion of the virus 

 from apparently normal organisms. In such a case the virus may be 

 called "latent," but to distinguish latent viruses from newly generated 

 ones may be difficult. 



8 



The increase in the strength of virus structure answers not only 

 the purpose of self-preservation of the virus, but also that of race- 

 preservation as just pointed out. Therefore, as the virus structure 

 becomes the stronger the virus may become the fitter to continue to 

 exist, and thus the property of self- or race-preservation will become 

 more marked until it can be called instinct. 



Both the strength of the virus action and the structural stability 

 of the virus seem to be directly proportional to some extent to the 

 polymerization degree of protein molecules, t. e., the size of virus par- 



