CHAPTER V 

 SUMMARY OF PART I 



1 



There are a great number of infectious diseases caused by agents 

 evidently different from ordinary microorganisms. Such pathogens are 

 known as viruses. Viruses are usually of sizes much smaller than 

 ordinary pathogenic microbes and can pass through bacteria-proof 

 filters, and accordingly sometimes called "filtrable" viruses. Like usual 

 pathogenic microorganisms, viruses multiply in the body of organisms 

 they affected, but for their multiplication living cells are always neces- 

 sary. Generally, a virus tends to proliferate solely in the cells of a 

 certain kind of a certain organism. 



A virus which affects bacteria is named phage. Phage was formerly 

 regarded as a special type of viruses or a virus-like agent, but we 

 could not find any essential differences between phage and vaccinia 

 virus, one of the typical viruses. Our studies were made chiefly with 

 these two viruses, and a theory as regards the nature of viruses has 

 been put forwards. 



The activity of both phage and vaccinia virus is carried by parti- 

 culate protein which can be agglutinated at an isoelectric point of a 

 weak acid. Separation of the activity from the particles is impossible 

 and therefore the particles are regarded as viruses themselves. No 

 essential differences seem present between the particles prepared by our 

 isoelectric precipitation method and those isolated by other workers by 

 means of usual ultracentrifuge ; the latter particles appear in most 

 cases to be a portion of the former. Since we can prove that almost 

 all the phage particles isolated by our method occasionally exhibit the 

 virus action, it is unreasonable to regard our sample as having always 

 a great quantity of "impure" particles. 



Such particles are not peculiar to viruses, but can be isolated from 

 normal cells without any association with virus. In general, the pro- 

 toplasm appears to have the property to be coagulated or disintegrated 

 into minute particles by physical or chemical effects, but only those which 

 have been produced by a virus are endowed with the virus action. 



The yield of virus particles by our method is so great that almost 

 the total protoplasm of the cell affected by a virus is considered to 



