IMMUNIZATION WITH BACTERIOPHAGE SUSPENSIONS 539 



result of some reaction on the part of the body of the animal, the stim- 

 ulus being provided by the products of bacterial dissolution as contained 

 in the bacteriophage suspension. These bacterial products, produced 

 through bacteriophagy, appear to be in a distinctive and pecuHar 

 physical state, one particularly suited to causing a reaction of immunity 

 by the body of the animal (d'Herelle32i,349)_ The extensive immuniza- 

 tion experiments made under natural conditions of exposure to infection 

 have confirmed those made in the laboratory (Le Louet^°^). 



In an epidemic environment, the experiments made on natural ty- 

 phosis show that the immunity conferred by the administration of 

 bacteriophage suspensions is acquired immediately. It begins at the 

 moment of the inoculation, and is lasting. Experiment shows clearly 

 that the immunizing agent is the bacteriophage, — as a living parasite 

 of bacteria. Under the conditions of an infected environment the 

 bacteriophage maintains itself because of the frequently occurring re- 

 infections which permit the corpuscles to multiply and perpetuate 

 themselves within the body of the animal. After an incubation period 

 this lasting exogenous immunity is followed by an endogenous immun- 

 ity, resulting, as in the previous case, from a reaction of the body to the 

 bacterial substances present in the suspension of bacteriophage protobes 

 inoculated (d'Herelle^-^). 



In brief, the mechanism is always the same; the only difference being 

 that immediately acquired exogenous immunity is transitory in an un- 

 contaminated environment; permanent in a contaminated environment. 



The antitoxic immunity which develops after the injection of bacterio- 

 phage suspensions is also endogenous in origin, due to the inoculation 

 of the bacterial products present in the suspension. These products 

 seem here to be found in a physical state particularly adapted to exciting 

 an antitoxic reaction response on the part of the animal body 

 (d'Herelle^^i). 



