BACTERIA SUSCEPTIBLE TO BACTERIOPHAGY 247 



high virulence but I have not yet found one of maximum virulence 

 (giving complete and always permanent bacteriophagy) . 



All of the races tested presented about the same virulence for the 

 different strains of bacteria isolated from the blood of buffaloes dead of 

 barbone (pasteurellosis of buffaloes) in Indo-China; as well as for a strain 

 found in Italy and tested after frequent passages through rabbits; for a 

 strain isolated from the mud of a water-hole frequented by buffaloes, 

 some of which contracted the disease shortly afterward.* On the 

 other hand in two instances I have isolated from the excreta of sick 

 buffaloes refractory strains of the bacterium, and it is of interest that 

 although presenting all of the morphological, cultural, and fermentative 

 characters of the bacterium they were inagglutinable by an antiserum. 

 These two strains were not normal, then, and the fact that they were 

 not attacked does not prove that Pasteurella bovis is not a homogeneous 

 species. 



Races of the bacteriophage virulent for Pasteurella hovis are to be 

 found, during an epizootic period, in the intestinal contents of buffaloes 

 who escape infection (d'Herelle^--). 



7. B. pestis {Pasteurella pestis) 



Two races of the bacteriophage virulent for B. pestis have proved to 

 be active for all strains of B. pestis with which they have been tested. 

 Of the plague bacillus two cultures were obtained in Indo-China, two in 

 France (Marseilles, 1919, and Paris, 1920), seven from the Dutch 

 Indies, and five from Egypt. B. pestis is certainly, then, a homogeneous 

 species as regards the bacteriophage. 



After about the thirtieth passage one of these two races proved to be 

 virulent for B. dysenteriae also and this virulence, at first weak, suddenly 

 increased at the 10th passage with B. dtjsenteriae and became very 

 strong. 



Races virulent for B. pestis are likewise virulent for the bacillus caus- 

 ing pseudo-tuberculosis in guinea-pigs. 



The colonies of B. pestis which are resistant to the bacteriophage 

 are very viscous, and are made up of polymorphous bacilli. Some of 

 the resistant colonies are composed of bacilli inagglutinable by an anti- 

 serum, and they are extremely virulent for the guinea-pig. 



Races of the bacteriophage virulent for B. pestis may be found in the 

 intestinal contents of rats which have survived a plague epizootic, 



* With barbone raging in the neighborhood, buffaloes which were sick had 

 undoubtedly frequented this previously. 



