VIRULENCE OF THE BACTERIOPHAGE 109 



gray rats which were rendered experimentally resistant to the 

 disease caused by the ingestion of cultures of the bacillus. The 

 resistant bacilli are very virulent and can be used for the destruc- 

 tion of gray rats, a large proportion of which resist the action of 

 the ordinary virus. It is possible that human infection may be 

 feared because of this increased virulence. 



The transitory appearance of such a bacteriophage in the 

 blood of several infected white rats has been demonstrated. Such 

 rats were resistant to infection. 



B. proteus 



Two strains of bacteriophage very active for this bacillus have 

 been isolated from the stools of two infants having a gastro- 

 enteritis. The virulence of these strains was tested against a 

 dozen strains of B. proteus of different origins. Only three of 

 the strains tested were affected by these strains of the bacterio- 

 phage, the same three in both cases. The other nine proteus 

 strains were non-susceptible. Included in this last group were 

 two strains of B. proteus Xi*. 



The lysate secured through the interaction of a bacteriophage 

 on a proteus suspension, is, immediately after the lysis, extremely 

 toxic for rabbits. Indeed, they are killed within a few hours by 

 the subcutaneous injection of but half of a cubic centimeter. 

 After ten days the lysate loses its toxicity. 



B. gallinarum (Klein); B. gallinarum (Moore); B. paragallinarum 



Characterization of these bacilli will be reserved for the chapter 

 in which avian typhosis is discussed. With the exception of 

 pathogenicity for man B. gallinarum presents all the characteris- 

 tics of B. typhosus, including agglutinability to the titre of the 

 serum with an anti-typhoid serum. There are, as we will see, 

 at least three different species of paragallinarum organisms. 



The bacteriophage active for B. gallinarum is not effective 

 with all species of paragallinarum, nor is the anti-paragallinarum 

 bacteriophage active for the other races. B. gallinarum is a very 

 homogeneous species. The anti-gallinarum bacteriophage is 

 constantly present in the intestinal tracts of fowls which resist 



