BEHAVIOR OF BACTERIOPHAGE IN EPIDEMICS 505 



Those rats which have survived an epizootic, therefore, harbor in 

 their intestine a bacteriophage possessed of a high virulence for B. 



Plague has existed in the sporadic form in the region of Phantiet, in 

 southern Annam, for about twenty years. I obtained specimens of 

 the excrement of rats in the infected villages, each specimen being com- 

 posed 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 



ThieuDuc + + 

 Hung Long + 

 Due Hang + + + 

 DucThang-|- + 

 TriLong + + 

 PhuTay + + + 

 Cu Long -f 



The results are thus identical with those secured at Bac Lieu, although 

 the virulence seems to be somewhat lower, but this can only be of rela- 

 tive importance since in the present case each specimen was composed 

 of the excreta taken from several rats; the results then, indicate only an 

 average. 



Is the bacteriophage present in all of the rats of an infected region or 

 only in a certain number? At Phantiet I collected the excrement of 

 six young rats, according to their weight, aged from three to four 

 weeks. Examination showed that four of the specimens contained a 

 bacteriophage active for B. pestis (+) while two did not. These last 

 two animals were therefore susceptible to plague. 



From the results given above one may conclude that, as for avian 

 typhosis and for barbone, the cause of the resistance against B. pestis 

 is the presence in the organism of a bacteriophage possessing a virulence 

 for this bacillus. 



How is the adaptation effected in the case of B. pestis? At different 

 times it has been noted that the bacillus has been found in the intestinal 

 contents of victims of plague. Thus, it is possible for them to be dis- 

 seminated by the feces throughout the external world where they may 

 again be ingested. The bodies of dead rats constitute another mode of 

 dissemination. These bodies are often devoured by the surviving rats 

 and this extends the infection. In those animals which resist and which 

 are infected the intestinal bacteriophage is maintained virulent for the 



