XI. THE SUMMARY OF PART III 211 



Even when the structure can be retained in the particles, it will 

 soon be destroyed if it is labile, whereas stable and firm structure 

 may continue to exist, imparting the stable pattern to the host proto- 

 plasm, thus the virus with the strong and firm structure can multiply 

 far from becoming extinct. The more stable and the stronger is the 

 structure of a virus, the longer periods it will exist and the more 

 abundantly it will multiply. 



Viruses may affect certain cells because they are stronger in the 

 assimilase action than the protoplasm of the cells ; in other words, 

 in order to multiply in the prototoplasm viruses must beat the proto- 

 plasm in the competition for assimilase action. The protoplasm on its 

 part, however, may be making a continual effort to assimilize the 

 virus. Accordingly, if a virus sticks to the same kind of cells for 

 prolonged periods, it will gradually be assimilized until at last becomes 

 identical with protoplasm, resulting in the complete disappearance of 

 its action. Viruses with unstable structures will be soon assimilized 

 and cancelled, whereas the ones with strong structures may resist 

 the action of the protoplasm to continue their existence. 



Organisms once affected by a virus may acquire the resistance 

 to the virus, and become immune to it. Since the protoplasm struc- 

 ture of the organisms is to become identical in its structural pattern 

 with the virus following the infection, it may only be a natural 

 result that the organisms will become indifferent to the virus which 

 shares the structural pattern in common with the organism. Such an 

 immunity should last as long as the virus structure remains in the or- 

 ganisms. Strong viruses can remain long periods, so that immunity 

 induced by a strong virus is of a long duration, whereas weak viruses 

 may cause only transient immunities. 



In many virus diseases, such as measles, mumps, and yellow fever, 

 the immunity persists for prolonged periods, usually for life, while 

 in some other diseases, such as poliomyelitis and influenza, it is 

 only transient. It may be supposed therefore that the viruses of the 

 former diseases are highly advanced and are endowed with strong 

 structures, whereas the viruses of the latter diseases are probably 

 newly developed and unstable. 



