SUBSTANCES WHICH ACTIVATE COBRA VENOM. 447 



Under these circumstances, of course, we can no longer regard 

 the activating factor of guinea-pig serum and lecithin as being 

 identical. If lecithin and serum complement were identical, the 

 antilecithin should act also against the serum complement. In 

 guinea-pig serum, however, as is shown by its activating power, an 

 excess over any such inhibiting substances is surely present and this 

 excess, of course, persists even in quantities of the serum so small 

 as no longer to lead to haemolysis. A serum protection can there- 

 fore be exerted only against substances which are different from the 

 activating substance of the serum. 



Further confirmation of this difference was afforded by the fact 

 that we succeeded in demonstrating the existence of antilecithin 

 and anticomplement components in normal rabbit serum inactivated 

 by heating to 56 C. By the addition of lecithin we completely 

 neutralized the components which inhibit lecithin. 1 In fact we added 

 so much that there was a slight excess of free lecithin. Although this 

 mixture in large quantities was itself activating, in smaller quantities 

 it was able to markedly inhibit haemolysis with cobra venom + guinea-pig 

 serum. The anticomplement component of the rabbit serum had 

 been unaffected by the addition of lecithin, as can be seen from the 

 following experiment: 



20 cc. rabbit serum are mixed with 180 cc. absolute alcohol, the resulting 

 precipitate rapidly filtered, pressed out, and dissolved in 20 cc. salt solution 

 This solution protects against cobra venom haemolysis not only with lecithin 

 activation but also with that of guinea-pig serum. 



4cc. of the inhibiting solution are digested for three-quarters of an hour with 

 2 cc. of a 0.17% lecithin solution. In large amounts this mixture, through an 

 excess of lecithin, activates cobra venom; in small amounts it inhibits the 

 activation with guinea-pig serum. (See Table IV.) 



Besides this we have discovered that cholesterin markedly 

 inhibits, or even entirely prevents, the cobra-venom haBmolysis 

 brought about by lecithin. We shall return to this point later. In 

 contrast to the behavior of the lecithin we find that the serum com- 

 plement is practically unaffected by cholesterin, for only a very 

 slight inhibition is observed even with large amounts of choles- 

 terin, a phenomenon which may be due to absorption. Such an 

 experiment is reproduced in Table V. The solution of cholesterin 



1 In order to exclude the activating action of rabbit serum, which is due to 

 available lecithin, it is necessary to work with the alcoholic precipitate obtained 

 from rabbit serum This contains the inhibiting substances. 



