VIRULENCE OF THE BACTERIOPHAGE 171 



All of those investigators who have studied the bacteriophage, with 

 the exception of Bail and of Wagemans/^^ have confirmed the fact that a 

 given race of the bacteriophage may show multiple virulences, and this 

 conclusion is reached whatever may be the individual opinion as regards 

 the nature of the bacteriophage itself. The two authors mentioned 

 above as exceptions have advanced the suggestion that when a bacterio- 

 phage filtrate causes bacteriophagy with different bacterial species the 

 phenomenon is due to the fact that the material contains a mixture of 

 several races of the bacteriophage. The experiments which will be 

 detailed in the following paragraphs show that such a conclusion is in- 

 admissible, simply because it is contrary to demonstrated experimental 

 facts. Foreseeing this objection I had refuted it before it was ad- 

 vanced*^^ but the authors named above have not even mentioned the 

 experiments which I had reported as bearing upon this point. 



9. PERSISTENCE OF VIRULENCE 



A race of the bacteriophage possesses the faculty of regaining its 

 virulence for a given bacterium, and this capacity persists throughout 

 a great many passages effected in vitro with a bacterium belonging to 

 another species. In 1916 I isolated a bacteriophage extremely active 

 for B. dysenteriae Shiga. At that time, as it was derived from the 

 body it also showed a moderate virulence for one strain of B. coli and 

 a low virulence for different strains of B. typhosus and the paratyphoids 

 A and B. This bacteriophage was used in many experiments through- 

 out the years 1916, 1917, 1918, and 1919, and during this time was sub- 

 jected to a very great many passages, always at the expense of B. dysen- 

 teriae Shiga. As a matter of fact the number of passages somewhat 

 exceeded 1200. Early in 1920 I showed that, without a preliminary 

 adaptation, it still possessed a moderate virulence for the strain of B. 

 coli and a slight virulence for the strain of B. typhosus toward which it 

 was active 4 years earHer. By means of passages with these bacteria 

 the virulence was increased, up to the point where it caused complete 

 dissolution. ^^^ 



Having preserved this race of Shiga-bacteriophage I carried out, in 

 1923, three successive purifications by the method of selection described 

 above, without causing a loss in the virulences for B. coli and B. typhosus. 

 This experiment has been repeated at different times with several races 

 of the bacteriophage, the result being that the multiple virulences per- 

 sisted after three successive isolations. Inasmuch as the suspension 



