INFECTION AND IMMUNITY. 561 



a temperature of from 41° to 42° C. for three or four 

 days, or to 60° C. for from one to two hours, its intra- 

 venous injection was followed by complete immunity 

 in from three to four days ; whereas, if the unwarmed 

 material was used, immunity did not appear before 

 fourteen days, and then only after the employment of 

 relatively large amounts. Moreover, when the pre- 

 viously heated products are introduced into the circu- 

 lation of the animal the systemic reaction is of but 

 short duration; but if the unwarmed substance is 

 employed, immunity is manifest only after the onset 

 of considerable elevation of temperature, which lasts 

 for a long time. 



In explanation of these differences they suggested 

 that, in the latter case, the high fever that is seen to 

 occur in the animal may serve to replace the warming 

 to which the bacterial products had not previously been 

 subjected, and which is necessary before they are in a 

 position to bring about the condition of immunity. 

 They claimed that the bacterial products employed to 

 produce immunity in this case are not, in reality, the 

 immunity-affording substance, but that they are only 

 the agents that bring about in the tissues of the animal 

 alterations that result in the production of another body 

 that protects the animal. In support of this, their 

 argument was that several days are necessary for the 

 production of immunity by the introduction into the 

 animal of the bacterial products ; whereas, if the blood- 

 serum of this animal, which is now protected, be intro- 

 duced into the circulation of another animal, no such 

 delay is seen, but instead the animal is forthwith pro- 

 tected. In the former case the actual protecting body 

 had first to be manufactured by the tissues ; whereas 

 36 



