288 STUDIES IN IMMUNITY. 



by washing? To settle this question we add 0.1 of a cubic cen- 

 timeter of normal rabbit serum, 56 degrees.* On this addition 

 hemolysis soon appears. In control tubes we find that this 

 normal rabbit serum has in itself no power to sensitize ox 

 corpuscles. We must therefore conclude that the sensitizer has 

 remained with the corpuscles, that the antisensitizer has joined 

 with it, but has not expelled it, and that normal rabbit serum 

 contains a substance (normal sensitizer?) that is able to break up 

 the combination of specific sensitizer and antisensitizer by re- 

 placing the first in its union with the second substance. And if 

 normal rabbit serum under these conditions seems to sensitize, it 

 does so indirectly by liberating the specific sensitizer that has been 

 neutralized. 



We shall later return to this experiment in other connections, 

 particularly in considering the multiplicity of active substances 

 in a given immune serum. We may note simply, for the moment, 

 that this phenomenon, which may be designated as a suppression 

 by normal serum of a cure effected by antiserum, varies in rapidity 

 with the conditions of the experiment. We have already remarked 

 that the reappearance of sensitization on adding normal rabbit 

 serum becomes slower and more difficult in proportion to the time 

 of contact between the corpuscle and the antiserum before the 

 addition of the normal serum. In other words, it would seem, so 

 far as our experiments go, that the combination between specific 

 sensitizer and antisensitizer becomes more perfect in some way 

 with time and less apt to be affected by the sensitizers of normal 

 serum. The combination would also seem to be more stable when 

 the antiserum employed is very powerful. 



It is not surprising that normal rabbit serum should contain 

 substances with an affinity for the antisensitizer. We showed in 

 1899 that substances similar to sensitizers f may be detected in 

 normal sera, and Ehrlich and Morgenroth have furnished numerous 

 analogous examples. In consideration of the experiment we have 



* It may be remembered that our antiserum was obtained by injecting guinea- 

 pigs with normal rabbit serum. 



t Although these substances would seem to belong to the same category as 

 sensitizers, they are, with few exceptions, very inferior to them as regards their 

 affinity for the sensitive cells. They are, moreover, very little known, and we call 

 them "normal sensitizers," only with a certain reservation. 



