I. THE ORIGIN OF VIRUSES 135 



other strain of the same kind of bacteria, that is, a certain strain of 

 colon-bacteria or of staphylococci can be lysogenic to a strain of colon- 

 bacteria or of staphylococci, respectively. In this respect it may 

 appear impossible that the protoplasm of animal cells share a structure 

 which is in conformity with a structure in bacterial cells. Neverthe- 

 less, this must be the case in order that the combination between the 

 fragments or the particles of the protoplasm and the bacteria upon 

 which the fragments may act as a phage is established; and this seems 

 actually to be the case. Bacteria are commonly parasitic on some 

 animals, and since the correlation between bacteria and the animals is 

 considered to be analogous to that between a virus and the host cell, 

 there should likewise exist a structure in common between the bacteria 

 and the animals. 



If some bacteria combine with certain animal cells whose assimi- 

 lase action is weaker than that of the bacteria, then the animal cell 

 will be assimilized by the bacteria or, at least, will be disturbed in 

 their protoplasm structure, thereby the bacteria may be able to multi- 

 ply and the animal cells may fall into pathological conditions. In 

 order to avoid such a disturbance the animal cells should be stronger 

 than the bacteria in the protoplasm structure. If this were the case, 

 also the fragments or particles of the protoplasm of such animal 

 cells would also have a stronger assimilase action than the bacteria 

 and would be able to act upon the latter as a virus. Such particles 

 if excreted with feces would be called a phage. 



As is generally known, various animal organs produce an agent 

 known as lysozyme which can affect certain bacteria to lyse them. 

 Fleming (11) who found first this agent emphasized the similarity of 

 the agent to phage. There is, however, a striking difference between 

 these two agents. Namely, lysozyme cannot multiply unlike viruses. 

 Thus it seems possible that lysozyme can combine with some bacteria 

 and disturb the structure of the bacterial protoplasm to cause disin- 

 tegration or lysis as does phage, but without producing exact replica 

 and accordingly fail to multiply, presumably because of its structure 

 not fitted for acting as a template. Even phage, under some condi- 

 tions, only can cause lysis of bacteria without multiplying as pointed 

 out already. 



On the other hand, as mentioned above, if the bacteria are stronger 

 than some animal cells, the cells may be injured severely by the 

 bacteria. In such a case particles of the bacterial protoplasm may 

 likewise be able to affect the cells. Bacterial haemolysin may be re- 

 garded as one of such agents ; haemolysin is apparently protoplasm 

 particles of bacteria which can combine with red blood cells ; the 

 structure of the latter is disturbed by the particles (Part II, Chapter 



