254 THE BACTERIOPHAGE 



twenty years old 5 received 0.25 cc. of the culture of bacteriophage. 

 All eight were tested forty-three days later by the inoculation of 

 1000 surely fatal doses of bacterium barbone culture at the same 

 time as a normal control animal. This last died in seventeen 

 hours. One of the three youngest buffaloes showed no reaction 

 other than a transitory edema at the site of the inoculation, the 

 other two showed a voluminous edema and were obviously sick, 

 but all three recovered and could be considered normal six days 

 after the test inoculation. The five very old buffaloes suc- 

 cumbed after 48, 53, 54, 60, and 142 hours; that is, after a time 

 considerably longer than the control. Fifteen young animals 

 immunized and tested at the same time failed to show any reac- 

 tion to the test injection. 



It is evident that although the test dose was enormous, that 

 did not alter the fact that in the old animals the acquisition of 

 immunity was much more difficult, somewhat in proportion to 

 the age. The relative immunity against an extremely severe 

 experimental test is observed only in these old animals; with the 

 young or with adults in the prime of life, the immunity, as we 

 have seen, is absent during the incubation period and complete 

 once it has appeared at all. 



The duration of the immunity 



After my departure from Indo-China, my collaborator M. 

 Le Louet, continued the experiments with a view to ascertaining 

 the duration of the immunity produced by the inoculation of a 

 culture of the bacteriophage. In January, 1921, he injected 15 

 steers, aged about one year, with a cubic centimeter of a culture 

 of the bacteriophage that was about one month old, that is, a 

 bouillon culture of the bacterium of barbone which had been 



6 The buffalo usually lives about twenty-five or thirty years. The 

 Annamite never kills a buffalo; old and no longer able to work, it is fed and 

 cared for as well as are the younger animals. The attachment of the 

 natives for these buffaloes is such that it is difficult to find a person who 

 will sell one of these animals. Those which served in the experiments were 

 procured, some through the agency of the Governor of Cochin-China, 

 M. le Gallen; others by M. Priv6, Director of the plantations of An Loc and 

 Suzannah, without considering the possible loss. I offer them my sincere 

 thanks. 



