THE BACTERIOPHAGE IN DISEASE 225 



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 intestinal bacteria, but it never showed any virulence what- 

 ever 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 speci- 

 men 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 ++ + + 



Those rats which have survived an epizootic, therefore, har- 

 bor in their intestine a bacteriophage possessed of a high viru- 

 lence for B. pestis. 



Plague has existed in the form of sporadic cases in the region 

 of Phantiet, in southern Annam, for about twenty years. I 

 obtained specimens of the excrement of rats in the infected vil- 

 lages, each specimen being composed of the feces derived from 

 several animals. The results of the tests for the virulence of 

 the intestinal bacteriophage in these specimens were: 



Village Virulence 



Thien Due + + 



Hung Long 



Due Hang + + + 



Due Thang + + 



Tri Long + + 



PhuTay + + + 



Cu Long 



