504 THE BACTERIOPHAGE AND ITS BEHAVIOR 



individuals have been secured and examined. According to the physi- 

 cians treating the cases the material was collected on the sixth and the 

 eleventh days after the beginning of convalescence. Examination 

 showed, in the first case, bacteriophage of average virulence (++) 

 and in the second case, one of feeble virulence (+) for B. pestis. The 

 virulence of the first of these strains has been enhanced in vitro and the 

 bacteriophage has been maintained in culture. 



An attempt was made to find a bacteriophage active against this 

 bacillus in the feces of twenty-two natives living in regions free of plague, 

 but in no case could a strain be isolated. However, in view of the par- 

 ticular mode of infection in bubonic plague the study of its propagation 

 in man offers only a matter of secondary interest, at least from the epi- 

 demiological point of view. We know that an epidemic of plague in 

 man is always consequent to an epizootic among rats. That which it is 

 interesting to study is, therefore, the epizootic, the primary cause of the 

 epidemic. In order to attain a correct interpretation of results it is 

 essential to follow the natural order of things. From the point of view 

 of man the epidemic is obviously the important fact; from the point of 

 view of nature this is but a secondary incident, for if we were able to 

 suppress the epizootic the epidemic would cease spontaneously. 



From what we actually know about the epidemiology of plague, it 

 results that all of the rats living in a city where there has been a case of 

 plague in man are the animals which have resisted the contagion, either 

 because they were infected and recovered, or because they remained 

 unaffected. I have then, investigated the virulence of the intestinal 

 bacteriophage of the rat toward B. pestis. 



First. Twenty-one specimens of the excrement of rats taken from 

 towns in Indo-China free of plague were examined. The intestinal 

 bacteriophage was found, active against one or another of the intesti- 

 nal bacteria, but it never showed any virulence whatever for B. pestis. 



Second. A small epidemic of plague (eleven fatal cases) occurred in 

 the village of Bac Lieu, in the eastern part of Indo-China, during July, 

 1920. On the following 6th of November I procured in this town four 

 specimens of the excreta of rats, each specimen composed of some 

 dozens of particles, and certainly derived from several individuals. 

 The tests for virulence against B. pestis gave the following results : 

 Specimen derived from a granary + + 

 Specimen derived from the embarkment quay + + + 

 Specimen derived from a decorticating mill + + + 

 Specimen procured in the house of a native + + + + 



