IMMUNIZATION BY MEANS OF THE BACTERIOPHAGE 263 



Six days after the completion of the lysis the toxicity of the 

 culture was markedly diminished, as the following tests show: 



Rabbit no. 5. Two cubic centimeters of a Shiga bacillus culture which 

 had been lysed for six days were injected intravenously on August 10. 

 The animal lived. 



Rabbit no. 6. Three cubic centimeters of the Shiga culture which had 

 been lysed for six days were injected subcutaneously on August 10. This 

 rabbit also lived. 



Rabbit no. 7. Five cubic centimeters of the Shiga culture which had 

 been lysed for six days were injected intravenously on August 10. The 

 rabbit died on August 21. 



When the tests were done with a Shiga culture which had been 

 lysed for a month the toxicity had disappeared, as is shown by 

 the following. 



Rabbit no. 8. Fifteen cubic centimeters of Shiga culture which had been 

 lysed for one month were injected subcutaneously. The rabbit lived. 

 The injection was given on August 10. 



Rabbit no. 9. Ten cubic centimeters of this same culture were injected 

 intravenously on August 10. This rabbit lived. 



The following protocol illustrates an immunization experiment. 



On August 23, eight rabbits received a subcutaneous injection of 0.25 

 cc. of a culture of the anti-Shiga bacteriophage, two months after the lysis 

 was completed. These animals were tested by the injection of 3 cc. of a 

 twenty-four hour bouillon culture of Shiga bacilli. For the strain 

 employed this represented two surely fatal doses. The strain of Shiga 

 used in the test differed from that used to prepare the suspension lysed by 

 the bacteriophage. 



Rabbit no. 10; tested after twenty-eight hours. Died six days later. 



Rabbit no. 11 ; tested after four days. Died five days later. 



Rabbit no. 12; tested after six days. Lived. 



Rabbit no. 13; tested after eight days. Lived. 



Rabbit no. 14; tested after ten days. Lived. 



Rabbit no. 15; tested after one month. Lived. 



Rabbit no. 16; tested after two months. Lived. 



Rabbit no. 17; tested after three months. Lived. 



All the control rabbits inoculated with half the dose, that is, with 1.5 

 cc. of the Shiga culture, died in from four to seven days. 



The rabbit is therefore, immunized against two surely fatal 

 doses of B. dysenteriae Shiga culture by the injection of a quarter 



