506 THE BACTERIOPHAGE AND ITS BEHAVIOR 



pathogenic bacillus. But observation and direct experimentation have 

 shown us that a bacteriophage is only possessed of a virulence for a 

 bacterium when the ingestions of this bacterium are frequent. The 

 permanence of the virulence of the intestinal bacteriophage of the rat 

 against the plague bacillus indicates the persistence of this bacillus in 

 the external world, at least for several months after the last human case 

 has taken place. Moreover, the revival of the epidemic each year in 

 certain localities, Bac Lieu for example, shows that it can not be other- 

 wise* (d'Herelle,^^')- 



4. BACILLARY DYSENTERY 



During the course of the epidemic of dysentery which occurred in the 

 region of Paris during the early autumn of 1918, an opportunity was 

 given to observe twenty-nine cases of benign diarrhea. In all of these 

 cases a bacteriophage of very high or extreme activity for the Shiga 

 bacillus was isolated from stools taken the day after the malaise. This 

 bacillus was the cause of all the severe cases studied at this same time. 



Living at this time in a locahty (Meulan) where several severe cases 

 of dysentery were noted together with a large number of cases of transi- 

 tory diarrhea, I examined the stools of nine persons who were healthy, 

 but who lived in contact with individuals who had had dysentery. 

 From these nine individuals a bacteriophage of average or high activity 

 for the Shiga bacillus was isolated. We have noted above that the same 



fact was observed in the institution where Germaine Mel had 



contracted dysentery. Individuals who are exposed to infection and 

 who resist show therefore in their intestine a bacteriophage virulent 

 for the causative pathogenic bacillus, exactly like the affected individuals 

 who recover. 



This would make it appear that in an epidemic period the simple cases 

 of diarrhea must in reality be cases of aborted bacillary dysentery, 



* Demonstration of the presence of a bacteriophage active for B. pestis in the 

 rats of a locality would in certain cases be very useful, for it would indicate the 

 j)resence of the bacillus in the exterior world and the possibility of a renewal of 

 the epidemic. Such a demonstration might also be useful in establishing a 

 retrospective or doubtful diagnosis. Suppose a few suspicious deaths have oc- 

 curred in a group some time previously. The presence in the rats of the neigh- 

 borhood of a bacteriophage showing a virulence for B. peslis would eliminate all 

 doubt; the deaths were due to plague. Or, the question of the nature of a epizoo- 

 tic among the rats may be in question. Was the mortality due to plague? The 

 demonstration of a bacteriophage active for B. pestis either in the dead rats or 

 in those that have survived provides the answer. 



