BEHAVIOR OF BACTERIOPHAGE IN EPIDEMICS 497 



In contaminated regions the animal in which the intestinal bacterio- 

 phage does not enjoy any activity for B. gallinarum quickly contracts 

 the disease. It may resist and recover, but this is the exception, occur- 

 ring only when the intestinal bacteriophage quickly acquires a viru- 

 lence for the infecting bacillus. In the contrary, and usual, case the 

 animal succumbs. 



In a chicken which recovers, the intestinal bacteriophage acquires a 

 considerable virulence against the pathogenic bacterium and maintains 

 this for a very long time ; in fact, as long as the exterior environment 

 remains infected. This persistence of virulence is maintained by the 

 frequent ingestion of pathogenic organisms, which allow the bacterio- 

 phage to multiply at the expense of the particular organism. The 

 resistant animal disseminates in its excreta the bacteriophage of 

 enhanced virulence; the animals which associate with it become "con- 

 taminated" and by this fact they enter the same class of resistant ani- 

 mals as those which have recovered. Recovery of one animal in a barn- 

 yard often marks the end of an epizootic, or its arrest for a few months. 



The study of an epidemic of avian typhosis shows, in a word, that the 

 history of the contagion reflects, in the last analysis, the story of the 

 struggle between the two agents — the pathogenic bacterium and the 

 bacteriophage protobe — and since this last is transmissible from individ- 

 ual to individual the immunity is contagious in the same sense as the 

 disease itself. The beginning of an epizootic is marked by a diffusion 

 of the bacteria, the end by a diffusion of bacteriophage virulent for 

 these bacteria. We will encounter the same facts in another disease; 

 in hemorrhagic septicemia in the buffalo (d'Herelle^^O • 



2. HEMORRHAGIC SEPTICEMIA OF THE BUFFALO (bARBONe) 



Barhone, the disease 



Unlike avian typhosis barbone does not present intestinal symptoms; 

 it is of the hemorrhagic septicemia type. The pathogenic organism is a 

 Pasteurella. Cultures of the organism in beef bouillon maintain their 

 virulence for a considerable time — at least eighteen months. The 

 inoculation of a buffalo or of a cow with 0.0002 cc. of a virulent culture 

 kills the animal in between thirty-six and forty hours with all the symp- 

 toms of the spontaneously acquired disease. At necropsy identical 

 lesions are found and the pathogenic bacterium swarms in the blood and 

 in the organs.* 



* In two different attempts I have proved that diluted blood or macerations 

 of organs (liver and lung) taken from animals dead of spontaneous infection, 

 filtered through a Chamberland filter (L^) and inoculated in large amounts into 

 the buffalo or into cattle do not cause the slightest disease symptoms. 



