THEORIES OF IMMUNITY. 



sheep's red-blood corpuscles. (It may be said that 

 a great number of similar hemolytic sera can be 

 obtained by treating one species of animal with 

 the blood of another species.) Ehrlich took four 

 cubic centimeters of five per cent defibrinated 

 sheep's blood in .75 per cent salt solution, 

 added one cubic centimeter of immune goat's 

 serum which had been heated half an hour to 

 55° C. (and which thus contained only immune 

 body), and placed the mixture for fifteen minutes 

 at 40° C. The question of where the immune 

 body was, he now investigated in the following 

 way: the mixture was centrifngalized until all 

 the corpuscles were deposited at the bottom of 

 the tube; the supernatant clear fluid was de- 

 canted, and there was added to it .2 cubic cen- 

 timeter of ordinary sheep's blood (containing, 

 therefore, susceptible red-blood corpuscles) and 

 .8 cubic centimeter of " fresh " goat's serum 

 (containing, therefore, goat's complement) ; 

 the mixture was placed at 37° C. for two hours 

 without any trace of hemolysis occurring. Now, 

 if the immune body had been left in the fluid 

 after centrifugalizing, the complement from the 

 fresh goat's serum ought by it to have been 



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