522 THE BACTERIOPHAGE AND ITS BEHAVIOR 



Egypt, Piot has been herds of cattle decimated to the same extent as 

 the herds of buffalo. According to our observations the buffalo may 

 be rather easier to immunize than cattle. 



Let us consider first the experiments conducted for the purpose of 

 determining what conditions control the development of the im- 

 munity resulting from the injection of a suspension of the bacterio- 

 phage. The size of the dose and the age of the animals are the two 

 principal factors whose variation has the greatest influence on the 

 result. To facilitate discussion, we may consider the effects of smaller 

 and smaller doses, although in reality the chronological order of the 

 experiments was somewhat different, since the tests were first made 

 with the injection of a dose arbitrarily fixed at 5 cc. In this experiment 

 the animals all died, when the test injection was given twenty days 

 later. Thinking that the immunizing dose was inadequate it was in- 

 creased in the next test to 20 cc. Here again, the results were the same. 

 It was only somewhat later, when smaller doses were employed, that 

 the treatment proved to be efficacious. We have seen already that 

 immunization by means of bacteriophage cultures presents individual 

 peculiarities. 



Determination of the immunizing dose 



I. Eight steers received 20 cc. of the bacteriophage suspension 

 subcutaneously. Six of these were tested after a lapse of time varying 

 from fifteen to forty days by the inoculation of a quantity of barbone 

 culture representing certainly 50 fatal doses. All died in the same 

 length of time as the control animals. The remaining 2 were tested 

 also with 50 fatal doses, sixty days after the immunizing injection. 

 They showed no obvious disturbance. The two controls died in 

 nineteen and twenty-two hours after the inoculation of virulent 

 material. 



II. Four steers received, subcutaneously, 5 cc. of the bacteriophage 

 suspension. Three were tested after thirteen, fifteen and twenty- 

 eight days by the inoculation of 50 lethal doses of virulent bacilli. 

 All died in the same length of time as the controls. The fourth was 

 tested on the fortieth day. It showed no reaction. The control died 

 in twenty-two hours. 



III. Forty-one animals; 25 steers, 4 buffaloes aged from one to 

 two years, and 12 adult buffaloes, received an injection of 0.25 cc. of 

 the bacteriophage suspension. 



A. Eight steers were tested between the third and twelfth days 



