IMMUNIZATION BY MEANS OF THE BACTERIOPHAGE 253 



dose inoculated. With a small dose the first surpasses the second 

 which disappears quickly; with a large dose, on the contrary, 

 the inhibitive action persists for a very long time — about sixty 

 days for an injection of 20 cc. As we have seen in the rabbit the 

 sensitization dominates and persists if the injections of the bac- 

 teriophage are repeated. 4 



The experiments further show that the immunity conferred 

 by the injection of cultures of the bacteriophage is absolute when 

 once established, and is negative during the period of incubation. 

 There is no intermediary state. The animals, young or old, 

 which receive the test inoculation during the period of incubation 

 die, with very few exceptions, in the same time as the controls, 

 even if this inoculation is made at a time very close to that where 

 all the immunized animals resist. On the other hand, all those 

 which are tested after the incubation period resist without pre- 

 senting any apparent malaise, whatever the test dose may be. 

 It seems indeed, as a result of these findings, that after an incuba- 

 tion time, more or less protracted according to the amount of 

 bacteriophage culture injected, a period during which the animal 

 remains as sensitive as a normal animal, the immunity increases 

 very rapidly once its manifestation has commenced. In a word, 

 the release of immunity is abrupt. 



Effect of the age of the animals on the acquisition of immunity 



We have seen that thirty-two animals, steers, young buffaloes, 

 or adult buffaloes of less than twelve years, have all acquired 

 an immunity that approaches the refractory condition within 

 twenty hours of the injection of 0.25 cc. of the bacteriophage cul- 

 ture. We wished to see how this would compare with the results 

 obtained in old animals. 



Three buffaloes between fourteen and sixteen years and five 

 very old animals no longer working and certainly more than 



4 Anaphylaxis shows a phenomenon of the same order. The smaller 

 the sensitizing dose, the shorter the period of time before the animal 

 is sensitized. For example, with a dose of 0.001 cc. of serum the guinea pig 

 is sensitized after about fourteen days, with 5 cc. sensitization is present 

 only after several months. 



