IMMUNIZATION BY MEANS OF THE BACTERIOPHAGE 255 



lysed by the bacteriophage one month before use. In March, 

 1922, all of the animals were tested, along with nine controls, 

 by the inoculation of 0.1 cc. of a virulent culture of the bacterium 

 of barbone. The virulence of this culture was such that in 

 amounts of 0.002 cc. it regularly killed steers in less than thirty-six 

 hours. Of the animals thus infected all of the controls died in 

 from seventeen to twenty-three hours after the injection, while of 

 the vaccinated animals ten resisted without any evident reaction 

 and five died in from two to five days after inoculation. 



This experiment shows that fourteen months after vaccination 

 two-thirds of the animals possessed an immunity sufficiently 

 strong to enable them to withstand a massive dose of the patho- 

 genic bacterium. 



The immunizing principle 



Under the conditions of the experiment, that is to say, in a 

 non-contaminated area, what, in the culture of the bacteriophage, 

 is the principle which brings about the immunization? 



A culture of the bacteriophage contains, as we know: 



1. The bacteriophagous ultramicrobes, and 



2. The soluble substances contained in the culture medium. 

 These are the soluble substances derived from the bacterial 

 bodies at the expense of which the bacteriophage has developed, 

 the lysins secreted by these ultramicrobes and which remain in 

 the medium once lysis has ended, and finally, somewhat later, 

 the anti-lysins of defense secreted by the bacteria. 



The course of the phenomenon alone, has shown us already 

 that the immunizing principle must be different according as 

 the immunity is developed in a contaminated area, as was the 

 case in the experiments made on typhosis, or in a non-contaminated 

 area, as in those on barbone. In the first, the immunity is 

 acquired immediately; in the second, it becomes effective only 

 after an incubation period. However, direct experiment allows 

 us to confirm this idea. 



1. If one injects steers, by the subcutaneous route, with from 

 5 to 20 cc. of anti-barbone bacteriophage culture it is possible 

 to isolate the active ultramicrobe from the blood throughout the 

 first twenty-four hours after the injection. After this period 



