IMMUNIZATION BY MEANS OP THE BACTEKIOPHAGE 247 



is indeed much larger than necessary, as we will see. Even in 

 mixing five or six different strains of bacteriophage, the quantity- 

 necessary to effect immunization is not more than a fraction of 

 a cubic centimeter. 



In the course of the experiments cited there has been no 

 selection. All of the animals of the poultry-yard, even though 

 they were moribund, received the immunizing injection. About 

 100 sick chickens have therefore been injected, and the mortality 

 among these has been 5 per cent. This is an appreciable reduc- 

 tion since the mortality among affected animals varies from one 

 hundred per cent at the beginning of the epizootic to 95 per cent, 

 when, after some weeks, the disease appears in only sporadic 

 cases. 



A culture of the bacteriophage, as we have shown in several 

 ways, is composed of bacteriophagous ultramicrobes suspended 

 in a medium containing the dissolved bacterial substance; the 

 bacteria which have been destroyed by the action of the lysins 

 secreted by the ultramicrobe. What, among these different 

 principles, is the one which plays the active role in the protec- 

 tion of the healthy animal or in the one already sick, under the 

 conditions of the experiment, that is, in a contaminated area? 

 Unquestionably it is the bacteriophagous germs themselves. The 

 immediate protection assured by the injection or even by the 

 ingestion of the bacteriophage culture suffices to demonstrate 

 this. An organic immunity necessarily requires a certain time 

 for its development. Other phenomena of immunity, organic 

 in nature, are produced only after an incubation period, as the 

 experiments on barbone will show. 



For the moment, let us conclude only that with sensitive 

 animals immunized by the injection of a culture of the bacterio- 

 phage active for the causative pathogenic bacterium, in a con- 

 taminated area, that is to say, in an area where frequent reinfec- 

 tions may take place as a result of the dissemination of the 

 pathogenic bacteria in the external environment, the principal 

 role of protection is played by the bacteriophage itself. The 

 other phenomena of immunity which may later develop, stimu- 

 lated by the other substances contained in the cultures injected, 

 play no role under such conditions, unless it be a very secondary 



