434 THE BACTERIOPHAGE AND ITS BEHAVIOR 



had been preserved in a sealed ampoule during the period of the above 

 manipulation, and I made a series of 12 passages at the expense of 

 B. dysenteriae Shiga. Three plaques were selected and the race was 

 purified by isolations from the limiting dilution. Virulence deter- 

 minations on these three plaques showed : 



1 

 B. dysenteriae Shiga + + + + 



B. dysenteriae Flexner + + + + 

 B. dysenteriae Hiss + 



B. paratyphosus B 



B. coli + + 



This proves that there were, indeed, two races of the bacteriophage, 

 the one active for B. dysenteriae Shiga, the Hiss strain, and B. para- 

 tijphosus B, the other virulent for the three dysentery strains and for 

 B. coli. 



Ji. Bacteriophage from a dog {Alexandria) 



The original filtrate showed virulences for: 



B. dysenteriae Shiga + + + 

 B. dysenteriae Flexner + + 

 B. dysenteriae Hiss 

 B. paratyphosus B 

 B. suipestifer + + + + 

 B. coli + + + 

 Passages were made with B. suipestifer; purifications were made, 

 and the three plaques isolated showed virulences as follows : 



1 

 B. dysenteriae Shiga + 



B. dysenteriae Flexner + 



B. dysenteriae Hiss 



B. paratyphosus B 



B. suipestifer + + + + 



B.coli ' + + 



Obviously, this filtrate contained but a single race. 

 It may be concluded from these experiments that as a rule but a 

 single race of the bacteriophage can be found within the digestive tract 

 of an animal at a given time. This is the more strange in view of the 



