VIKULENCE OF THE BACTERIOPHAGE 103 



It should be noted that the result was the same whether the 

 bacteriophage was preserved directly in feces or in the filtrate, 

 that is, in bouillon. Likewise, it is significant that the degree 

 of virulence has no influence on the preservation or the disappear- 

 ance of the virulence. It was strong for B. typhosus and became 

 negative, it was weak for B. paratyphosus B } yet this remained 

 intact. 



In the absence of passages, simply as an effect of old age, the 

 virulence of the bacteriophage varies then with time, and indeed 

 in a different manner for the diverse bacteria attacked. It be- 

 comes attenuated more quickly for some than for others, and for 

 this no general rule can be fixed. We have seen above, with 

 another strain, that after four years and in spite of passages in 

 contact with the dysentery bacillus, the virulence for B. typhosus 

 persisted. The last experiment cited is not only interesting then, 

 in that it shows an attenuation of virulence associated with the 

 lapse of time, but also in that it gives evidence that the loss does 

 not occur in equal degrees for all of the bacteria attacked by one 

 and the same bacteriophage. 



BACTERIAL SPECIES ATTACKED 



Let us now consider the different bacteria for which active 

 strains of the bacteriophage have up to the present been isolated. 3 

 For each of these only the peculiarities of the reaction as they are 



3 In certain cases the bacteriophage can serve for the identification of 

 bacteria, as the agglutination reaction is used. In order to apply the test 

 a bacteriophage must be employed which has been subjected to numerous 

 passages at the expense of a particular bacterial type so that the accessory 

 virulences may be attenuated as far as possible. For example, all strains 

 of bacteria which are lysed by a strain of bacteriophage that has been 

 cultivated together with Shiga bacilli, are certainly B. dysenteriae Shiga. 

 With certain species, B. pestis for example, for which the specificity of the 

 bacteriophage appears high, diagnosis by means of the bacteriophage is 

 particularly conclusive. In this last connection it may be said that since 

 the publication of the French edition of this text, a bacteriophage has been 

 encountered active for B. pestis and equally active for the bacillus found 

 in pseudotuberculosis of the guinea pig. Thus, it is necessary to recognize 

 the lack of an absolute specificity, limiting somewhat the value of the 

 reaction as applied to the identification of bacterial species. 



