IMMUNIZATION BY MEANS OF THE BACTERIOPHAGE 261 



In a non-infected region, and this was the case in the experi- 

 ments performed on barbone, the mechanism is not the same. 

 In the absence of reinfection the bacteriophage active for the 

 bacterium is eliminated very rapidly from the organism, since it 

 is not able to multiply at the expense of this bacterium. The 

 heterologous immunity disappears with it, that is to say, after 

 one or two days, and the animal then becomes susceptible. It 

 remains in this condition throughout the entire duration of the 

 incubation of the organic immunity, which develops under the 

 influence of the soluble products contained in the culture of the 

 bacteriophage. Once this organic immunity is established the 

 animal is refractory. 



We will see in connection with dysentery, that when a culture 

 of the bacteriophage is injected the organism responds by the 

 production of an antitoxin. It is probable that the same thing 

 takes place in barbone and that the protective principle present 

 in the blood, since it is neither an amboceptor nor an opsonin, 

 is likewise an antitoxin ; the response of the organism to the in- 

 jection of the modified substance of the lysed bacterial cells 

 contained in the culture of the bacteriophage. 



To summarize: the injection of the buffalo or of cattle, with 

 a culture of bacteriophage active for the bacterium of barbone 

 confers : 



1. An heterologous immunity, solely due to the presence in 

 the body of bacteriophagous ultramicrobes virulent for the bac- 

 terium of barbone, which assures the destruction of the bacteria 

 upon their introduction into the organism. This immunity 

 terminates just as soon as the ultramicrobes are eliminated from 

 the body. In the absence of frequent reinfections this elimina- 

 tion is very rapid, since the continued growth and the mainte- 

 nance of virulence can not persist. 



2. An homologous immunity, or organic and powerful immunity, 

 induced by a reaction of the organism of the animal to the soluble 

 principles contained in the culture of bacteriophage injected. 

 This organic immunity is characterized principally by the appear- 

 ance in the blood of an extremely potent immunizing substance 

 probably an antitoxin. The organic immunity establishes itself 

 abruptly after an incubation period, which varies with the dose in- 

 jected, being longer as the amount of injected culture is increased. 



