142 THE BACTERIOPHAGE 



Here is another instance of the same order. Recently investi- 

 gating a bacteriophage active for the streptococcus of gourme of 

 horses, Doctor Forgeot sent me three different strains of Strep- 

 tococcus equi, taken from the culture collection of the Central 

 Veterinary Laboratory. Of these three strains, only one was 

 pure. The two others were in reality mixed cultures of the 

 streptococcus and the bacteriophage. 



These two examples suffice to give an idea of the great num- 

 ber of mixed cultures which must actually exist among stock cul- 

 tures. Not only are the intestinal bacteria subject to contamina- 

 tion by the bacteriophage, but bacteria in general, for we will see 

 that the bacteriophage does not remain restricted to the intestinal 

 tract, but passes into the circulation and exercises its action in 

 the different organs. 



It is therefore quite essential before undertaking any experi- 

 mental work to ascertain if the bacterial culture involved is not 

 in reality a mixed culture, composed of a resistant bacterium and 

 a bacteriophage. One must be sure that the culture is not only 

 pure, but ultrapure. 



The mutations noted by different authors may most certainly 

 be attributed to the frequency of these mixed cultures. And 

 the confirmation of these reports has been lacking for the very 

 simple reason that the verification has been attempted, not with 

 strains contaminated by the bacteriophage, but with cultures 

 really pure. The experimental results have thus very naturally 

 differed. In this regard I might say that it is indeed singular, 

 in view of the unique character of certain conceptions concerning 

 the bacteriophage, that not a single author has yet traced to the 

 fact that bacterial cultures are frequently contaminated by the 

 bacteriophage, the conclusion that the bacteriophage takes origin 

 spontaneously in these cultures. In reality, as we see it, in con- 

 nection with the genesis of these cultures, each time that there 

 is a contamination by the bacteriophage, it is in the form of a 

 mixed culture. The bacteriophage exists in the culture from 

 the beginning, that is, from the time of isolation. 



In the experiments touching immunity, the contradictory 

 results may likewise well reside in the presence of a bacteriophage 

 in the cultures employed in the experiments. We will see in the 



