530 THE BACTERIOPHAGE AND ITS BEHAVIOR 



IV. The above experiment (III) was repeated. The steer which 

 received the blood of the immunized animal was not tested by the 

 inoculation of 50 fatal doses until forty-five days after the transfusion. 

 It resisted, without showing any apparent disturbance, as did also the 

 steer which was immunized directly. 



This last experiment does not, however, prove anything with regard 

 to the duration of passive immunity conferred by the blood of an 

 immunized animal, for it was performed with homologous blood, and 

 we know that an immunity thus produced is of much longer duration 

 than that produced with heterologous blood. In any case, the im- 

 munity thus conferred is extremely powerful and these experiments 

 open the way for further investigations on the production of therapeutic 

 sera in animals immunized by a single injection of an active bacterio- 

 phage, not only for barbone, but for other diseases as well. 



One might conceive that the ''principle" which is contained in the 

 blood of the immunized animal and which confers the passive immunity 

 is nothing more than the suspension of the bacteriophage persisting in 

 the circulation. But this is impossible, for if the blood is taken at a 

 time sufficiently close to the immunizing injection of the bacteriophage, 

 it is in no way effective. That is, blood taken during the incubation 

 period confers no immunity to the transfused animal. 



Steers Nos. 89 and 90 received on December 19, 0.25 cc. of the 

 bacteriophage suspension subcutaneously. Sixteen days later 500 cc. 

 of blood were withdrawn from each animal and transfused into steers 

 Nos. 92 and 93. The four animals, tested the next day, died with no 

 greater delay than the controls. Steer No. 46 received on November 5, 

 20 cc. of the bacteriophage. On November 19, 500 cc. of blood were 

 taken and transfused into steer No. 42. These two animals died in 

 the same time as the control after a test injection. 



As is to be seen, the incubation period of immunity in animals which 

 receive the immunizing injection of bacteriophage suspension parallels 

 the appearance of the protective power in their blood. Immunity 

 develops abruptly; in the same way the protective power of the blood 

 manifests itself suddenly, and at the same moment. 



What then, is the immunizing principle which makes its sudden 

 appearance in the blood at the moment when immunity is established, 

 even in animals which have received only the minimal dose of a single 

 drop of the bacteriophage? Can it be an amboceptor? By no means, 

 for the complement fixation reaction shows that the sera of animals 

 immunized with suspensions of the bacteriophage do not contain a 



