160 III. THE EVOLUTION OF VIRUSES 



2. The Variation of Newly Produced Viruses 



It may be not impossible to regard allergic dermatitis and cancers 

 as virus diseases, but, since the pathogenic factors of these diseases, 

 as a rule, fail to be carried by protoplasm particles, the pathogenic 

 agents or viruses share their fate with the organisms in which they 

 have been generated, and therefore become extinct without being 

 transmitted to other organisms. 



However, in the case of common cold, the virus of which may be 

 generated under the influence of environmental changes, the situation 

 is entirely different. If a man of the predisposition to the disease 

 was exposed to chilling under some peculiar conditions, some change 

 would result presumably in the cells of mucous membrane of the up- 

 per respiratory tracts, the change being able to spread successively in 

 the protoplasm of the cells, accompanied by inflammation, which 

 would in turn lead to the decomposition of the cells into fragments or 

 protoplasm particles, and if the newly formed structure generated by 

 the change remained intact in some of the particles, these latter, when 

 transferred to another man, say, by coughing, would transmit the 

 structure to cause common cold. It may be possible that further al- 

 terations would occur in the structure of the particles through some 

 environmental changes during the periods they would affect succes- 

 sively different persons, and thus the virus would be able to undergo 

 variations to become a more virulent virus entirely different from the 

 one generated at the start. 



This may also hold for viruses released from normal cells, /. e., 

 normal protoplasm particles, capable of acting as a virus upon proper 

 other cell. Thus, if a normal protoplasm particle of a certain organ- 

 ism capable of acting upon a man as a virus giving rise to symptoms 

 like those of influenza undergoes variations during the successive pas- 

 sages through man to increase in its virulence for the latter, then it 

 may be possible that the virus will acquire the properties entirely 

 similar to those of influenza, thus becoming a strain of influenza 

 virus itself. 



Presumably each virus particle shows each individuality. This 

 may be based upon the degree of precision in the replication which 

 may vary with particles, and perhaps also upon the degree of damage 

 which each particle may suffer during the course of the protoplasm 

 decomposition into the particles or after their liberation from the cells. 

 The difference in these degrees resulting from the dissimilarities in 

 the structure of particles may cause the divergence in variations. 



