THEORIES OF IMMUNITY. 



heat, occurring in the serum of an unimmunized 

 animal (complement). When the presence of 

 any one of these substances is suspected, it can 

 be traced by adding the other two, and observ- 

 ing whether hemolysis takes place. In the in- 

 vestigation, sheep's blood was taken next, fresh 

 goat's serum was added, the mixture centrifugal- 

 ized, and the fluid on the one hand and the de- 

 posit on the other investigated for complement. 

 JSTone was found in the deposit, but it was found 

 in the clear fluid, so that no combination had 

 taken place between it and the blood corpuscles. 

 Next it was found that there was a greater affin- 

 ity between the immune body and the blood 

 corpuscles than there was between it and the 

 complement. The proof was as follows: It 

 was observed that in a mixture of five cubic 

 centimeters of five per cent sheep's blood, one to 

 one and one-third cubic centimeters of heated 

 immune goat's serum, and one-half cubic centi- 

 meter of fresh goat's serum, there was just 

 enough of all the constituents to satisfy all the 

 affinities and leave none over. If all these sub- 

 stances were mixed at 0° C, and the mixture 

 centrifugalized as before, it was found that the 



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