I. THE ORIGIN OF VIRUSES 133 



action than the former. All the particles, however, may not always be 

 able to act as the phage, for it is expected that sometimes certain 

 particles only, whose structure is especially stable and strong, can 

 exert the template action. Virus particles produced by healthy cells, 

 therefore, also should have an intimate connection with nucleic acids. 



In this connection it should be noted the important fact that dis- 

 ruption of lysogenic bacteria does not liberate infectious particle (6), that 

 is, lysogenic bacteria seem to contain no virus, but that if the bacteria 

 are treated with certain chemical or physical agents, such as ultraviolet 

 ray, phage liberation will occur (7). This may result from the need 

 of a certain slight modification in the healthy protoplasm protein struc- 

 ture for the exhibition of the virus action. As detailed later, in the 

 bacteria and animal cells the protoplasm protein threads appear nor- 

 mally to be present in a partially folded state and the particles consis- 

 ting of such partially folded peptide chains cannot act as the template. 

 Accordingly, for the virus liberation, healthy cell protoplasm proteins 

 have to unfold the chains under appropriate conditions. Ultraviolet ray 

 may lead the chains to unfold. As we shall have many occasions to 

 consider in detail of this important problem later, for the time being it 

 may be wise to put aside this problem and make a further advance on 

 the question we are now facing. 



Now, another reasoning led by the above theory is that the suscep- 

 tible bacteria will become lysogenic when the bacteria are affected by 

 the phage produced by lysogenic bacteria, since the structure of the 

 susceptible bacteria is to be changed to become similar to that of the 

 lysogenic bacteria through the infection, whereby the protoplasm of the 

 susceptible bacteria is endowed with the strong structure able to act 

 as a strong assimilase. 



As is well known this is actually the case. Bacteria infected with 

 a phage derived from a certain lysogenic strain are changed into the 

 lysogenic strain which produces in turn the phage by which they have 

 affected. Freeman (8) has isolated virulent strain of C. diphtheriae from 

 avirulent strain cultures by incubating with a specific phage ; the bac- 

 teria were found to become resistant to the phage, and even lysogenic. 



Freeman was unable to find any immunological difference between 

 the original avirulent and derived virulent strains, but since the aviru- 

 lent strains got possession of the faculty to produce toxin besides be- 

 coming both lysogenic and phage resistant when inoculated with the 

 phage, it is evident that the general property of the bacteria was al- 

 tered, although the difference failed to be detected immunologically. 



The manner in which phage-susceptible bacteria are changed into 

 lysogenic is illustrated diagrammatically in Fig. 16. The faculty to induce 

 such a change must be, of course, present also in the intact protoplasm 



