402 STUDIES IN IMMUNITY. 



sis is complete in C in 12 minutes, and in A in 35 minutes. In D 

 hemolysis is complete in 1 hour. B is not hemolyzed. 



To what is the inhibiting effect of normal serum due? It may 

 easily be shown that the serum does not act by suppressing the sen- 

 sitization of the corpuscles. This has been demonstrated by our 

 predecessors by the following simple experiment : In a mixture of 

 moderately sensitized ox corpuscles, heated normal serum and 

 guinea-pig alexin there is no hemolysis owing to the antagonistic 

 power of the normal serum. On subsequent centrifugalization and 

 decantation, however, the addition of salt solution containing a 

 trace of alexin causes hemolysis, which shows that the corpuscles 

 have retained their sensitization. 



This result also shows that heated normal serum does not directly 

 render the corpuscles refractory to hemolysis. One might suppose 

 that such a serum contains " complementoids " that satisfy the 

 affinities of the sensitized corpuscle and hinder the subsequent 

 fixation of active alexin. The preceding experiment would, how- 

 ever, invalidate this supposition. 



The normal serum, in addition to having no effect on the sensiti- 

 zation of the corpuscle, has also no neutralizing effect on the alexin. 

 It does, however, oppose the fixation of the alexin on the sensitized 

 corpuscles, and this explains the lack of hemolysis. 



The proof that normal serum does not alter the alexin is given by 

 the fact that hemolysis can be produced in an inhibited mixture of nor- 

 mal serum, alexin and sensitized corpuscles by adding salt solution; 

 in other words, as already stated, the opposition to hemolysis depends 

 on the concentration of normal serum. Muir and Browning in study- 

 ing this fact have clearly shown that the alexin is not fixed on the 

 corpuscles during the first phase of the experiment, when the mixture 

 contains much serum and little salt solution, but is absorbed only 

 on the addition of the saline solution. Similar results are obtained 

 if, as we have performed the experiment, corpuscles before dilution 

 in salt solution are sufficiently sensitized to produce their dissolu- 

 tion. Such an hemolysis, to be sure, naturally brings about an 

 absorption of alexin, which, however, is only partial if suitable 

 amounts are used and the sensitization is not too great; such ab- 

 sorption always remains less than when salt solution is added. 



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