188 III. THE EVOLUTION OF VIRUSES 



one another either in size or in nucleic acid content. In such a case, 

 large particles rich in nucleic acid only may be able to act as a strong 

 virus, whilst small particles with little or no nucleic acid may be 

 extremely unstable, scarcely capable of acting as a virus, and may 

 therefore disappear immediately after the production. 



Moreover, the replica corresponding to the virus pattern may not 

 be uniformly produced in all the particles ; in some particles complete 

 replica may be formed but in others only incomplete replica. Particles 

 endowed with such incomplete replica may be unable to behave as a 

 virus. It can be said, therefore, that the demonstration of virus action 

 can scarcely be achieved with all the particles produced by infected 

 cells. However, the property to constantly produce similar large par- 

 ticles, rich in nucleic acid, having complete replica should be required 

 for a virus in order to evolve into a typical organism. 



