250 THE BACTERIOPHAGE 



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 chronologi- 

 cal order of the experiments was somewhat different, since the 

 tests were first made with the injection of a dose arbitrarily fixed 

 at five cubic centimeters. In this experiment the animals all 

 died, when the test injection was given twenty days later. Think- 

 ing that the immunizing dose was inadequate it was increased 

 in the next test to twenty cubic centimeters. 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 bacterio- 

 phage cultures presents individual peculiarities. 



Determination of the immunizing dose 



I. Eight steers received 20 cc. of the bacteriophage culture subcutane- 

 ously. 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 repre- 

 senting 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 cul- 

 ture. 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 bacteri- 

 ophage culture. 



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

 the injection by the inoculation of virulent culture, representing, according 

 to the weight of the animal, from 5 to 1000 surely fatal doses. All died. 



B. Twelve steers and one buffalo were tested between the 13th and 20th 

 days, all by the inoculation of 1000 surely fatal doses of barbone culture. 

 Five resisted, the others succumbed. The experiment is given in detail: 



