446 



COLLECTED STUDIES IN IMMUNITY 



normal sera exert a considerable inhibition on cobra venom haemolysis 

 when serum is used as complement, and to a still greater degree when 

 lecithin is used. We observed no essential increase in the protective 

 action in the animals treated with guinea-pig serum. We therefore 

 next sought to distinguish anticomplement and antilecithin action 

 in normal serum. 



For this purpose guinea-pig serum itself seemed best suited; 

 inactivated by half an hour's heating to 56 C. it exerts a marked 

 inhibitory action on cobra venom + lecithin ha?molysis. This fact 

 by itself, however, in no way argues against the identity of lecithin 

 and the complementing substance of active guinea-pig serum. One 

 could assume, for instance, that, on heating, a substance is formed 

 which is capable of combining with the lecithin. In that case if an 

 excess of the substance were formed, this would be capable of com- 

 bining with lecithin subsequently added. This would explain the 

 apparently paradoxical phenomenon that the same serum when fresh 

 exhibits activating properties, but when heated to 56 C. is able to 

 bind lecithin. 



We therefore investigated the property of active fresh guinea- 

 pig serum to inhibit the action of lecithin and hoped that this prop- 

 erty would still be manifested in dilutions in which the serum was 

 no longer able to exert any activating influence on cobra venom. 

 As a matter of fact we succeded in proving that guinea-pig serum 

 still exerts an inhibiting influence on the lecithin, even in very small 

 amounts which no longer activate. This is shown by the example 

 in Table III. 



TABLE III. 



1 cc. 5% Ox BLOOD +0.001 cc. 1% COBRA VENOM + 0.075 cc. 0.025% 



LECITHIN. 



The lecithin and guinea-pig serum are digested for half an hour previous to 

 adding the ox blood and cobra venom. 



