258 THE BACTERIOPHAGE 



bacteriophage culture is not destroyed but is sensibly weakened by 

 heating for a half hour at 56C. 



Although it is not yet possible to know with certainty the 

 nature of the process which controls the development of organic 

 immunity, we are at least able to recognize the result and to note 

 the property which distinguishes the animal immunized by an 

 injection of the bacteriophage from a normal animal. 



In the case of the immunity acquired as a result of an attack 

 of a contagious disease the blood possesses preventive properties. 

 The blood of immunized animals enjoys the same property, as 

 the following experiments show. 



I. Steer no. 54 received on November 5, 0.25 cc. of an anti-barbone bac- 

 teriophage culture. Fourteen days later 500 cc. of blood was taken into 

 a flask containing 25 cc. of a 10 per cent solution of sodium citrate. The 

 blood was immediately injected into the jugular vein of steer no. 43. This 

 last animal was tested twenty-three hours later by the injection of 1000 

 fatal doses of the bacterium of barbone culture. It failed to show the 

 least evidence of infection. A control died in twenty-three hours. Steer 

 no. 54 likewise resisted the inoculation of 1000 fatal doses, given on Decem- 

 ber 1st. 



II. The experiment given above was repeated. Steer no. 112 received 

 into the jugular vein 500 cc. of blood from steer no. 95. Both of them 

 resisted the test injections. 



III. Steer no. 104 received on December 29 a subcutaneous injection 

 of 0.04 cc. of a culture of the bacteriophage. Four days later 500 cc. 

 of blood were taken, as before, and this was transfused into steer no. 108. 

 The next day the two steers resisted the inoculation of five fatal doses, 

 which killed the control animal in thirty-two hours. 



IV. The above experiment (III) was repeated. The steer which received 

 the blood of the immunized animal was not tested by the inoculation of 50 

 fatal doses until forty-five days after the transfusion. It resisted, without 

 showing any apparent disturbance, as did also the steer which was immu- 

 nized directly. 



This last experiment does not, however, prove anything with 

 regard to the duration of passive immunity conferred by the blood 

 of an immunized animal, for it was performed with homologous 

 blood, and we know that an immunity thus produced is of much 

 longer duration than when produced with heterologous blood. 

 In all cases, the immunity thus conferred is extremely powerful 

 and these experiments open the way for further investigations 



