208 THE BACTERIOPHAGE 



persistence of virulence depends solely upon the fact that the 

 pathogenic bacillus, distributed in profusion in the exterior en- 

 vironment, is frequently ingested by the animal and this maintains 

 the virulence of the intestinal bacteriophage since it is able to 

 grow at its expense. 



The feces of about one hundred chickens which had died of 

 avian typhosis were examined. In no case was there a bacterio- 

 phage active for B. gallinarum or for any of the bacillary agents 

 of the paratyphoses. Nevertheless the bacteriophage had been 

 present for it could be disclosed (91 times in 97 examinations) 

 because of the activity shown for one or several species of the 

 colon- typhoid-dysentery group. One sees clearly, then, that 

 the lack of defense is not due to the absence of the bacteriophage, 

 but .solely to the fact that the intestinal bacteriophage remained 

 passive because it failed to acquire a virulence for the pathogenic 

 bacillus. 



To summarize : as in dysentery and in typhoid fever in human 

 beings, the acquisition of virulence by the intestinal bacteriophage 

 for the pathogenic bacterium is the sine qua non of recovery. 



Role of the bacteriophage in the course of the epizootic 



Because of the dissemination and extent of the disease it was 

 possible to study the role of the bacteriophage in the course of the 

 epizootic as well as in the course of the disease in the individual 

 infected animal. 



Let us consider first a fact bearing on the territory involved in 

 the epizootic. During the last three years eighty-one examina- 

 tions have been made upon the feces of barn-yard animals, not 

 only in France but also in Indo-China, in regions where avian 

 typhosis had not occurred in epidemic form among the fowls for 

 several years. In each of these examinations a bacteriophage 

 active for one or several of the bacilli of the colon-typhoid-dysen- 

 tery group was isolated, but in no instance has the bacteriophage 

 shown any detectable activity for B. gallinarum. 



In contaminated regions the situation is quite different. As 

 an example, observations made on a farm located at Pougy-sur- 

 Aube may be cited, where the disease was followed very closely. 

 The disease appeared in 1917 in July. Within the period of a 



