4 I. INTRODUCTION TO VIRUSES 



tiply in the cells. 



To the belief of the writer, viruses are a kind of enzymes, and the 

 protoplasm protein of the cells is their substrate, and when the protein 

 is affected by a virus, an active structure or structures are produced 

 which can act as the virus ; this change of the protein is to spread 

 through the protoplasm as a chain reaction. The reason why the writer 

 has reached such a conclusion will be mentioned step by step. 



2. Bacterial Viruses 



The virus which affects bacteria is called phage. Since there are 

 numerous kinds of bacteria and, moreover, since a certain strain of 

 bacteria is generally affected by a number of different viruses, the kind 

 of phage should be very numerous. Phage has formerly been regarded 

 by many workers as a special kind of viruses or virus-like agent, not 

 as a true virus, but now it has become evident that it is a typical virus 

 having no peculiar property dissimilar to the ordinary. As we could 

 ascertain this fact long ago, we chose phage as our object of virus 

 researches. Besides phage, our experiments were carried out with 

 vaccinia virus and the experimental results obtained with this virus 

 w^ere well consistent, without exception, with those obtained with phage, 

 and vice versa. 



Since viruses affect living cells only, it is a rather difficult task to 

 investigate into their function. Phage, however, affects bacteria which 

 can easily be cultivated and handled in vitro, so that the employment 

 of phage as an experimental object offers a vast advantage. 



When bacterial cells are infected with a phage they will generally 

 be dissolved into minute particles and such particles carry the virus 

 activity ; the particles may, therfore, in turn affect other normal cells 

 causing the latter again to dissolve into minute particles. In such a 

 way phage may multiply. 



The chief reason for which viruses were regarded as a microorgan- 

 ism might be dependent on their multiplicability but, besides this, their 

 particulate nature might have a share with it. As will be mentioned 

 later, the fact that viruses exist in minute particles involves a striking 

 significance. 



A high speed centrifuge is commonly used to isolate virus, but as 

 we unfortunately had no such an apparatus we contrived a chemical 

 method for the isolation. Thus, we were able to make virus particles 

 sedimentable by an ordinary centrifuge by taking advantate of the fact 

 that the virus particles have the property to agglutinate at a weakly 

 acid pH (1). Although no fundamental differences seemed to exist in 

 their property between particles obtained by a high speed centrifuge 



