294 IMMUNO-CATALYSIS 



concentrations. Three venoms caused clotting uncertainly over a wide 

 range of dose, but showed no consistent relation between concentra- 

 tion and clotting action. All other venoms showed a definite relation- 

 ship between the concentration and the speed and degree of clotting. 

 The venom of the fer-de-lance proved much richer in the clotting 

 factor than any other. One part in 100 million parts (1 : 100,000,000) 

 of plasma caused clotting. 



In testing the neutralizing effect of antivenin on the plasma clot- 

 ting property of venoms, 0.1 ml. of antivenin was added to the plasma 

 and was thoroughly mixed before adding the venom. In general, 

 Githens found the antivenins were slightly less effective against the 

 clotting factor than against the neurotoxic and necrotic factors of the 

 same venoms. In most tests 0.1 ml. of antivenin prevented clotting 

 with no more than 0.03 to 0. 1 mg. of venom. 



With regard to the specificity of antivenin action the following is 

 quoted from Githens' study: "In our tests, specificity is seen in better 

 neutralization of most of the rattlesnake venoms by crotalidic and 

 cascabel antivenins, while bothropic antivenin was most effective 

 against bothropic venoms. On the other hand, the cascabel antivenin 

 was not especially effective toward its specific venom." 



In studies on the antiproteolytic property of antivenins Githens 

 found that 0.3 ml. of antivenin prevented the proteolytic effect of as 

 much as 1 mg. of some snake venoms, and was entirely ineffective 

 and irregular with others. Both crotalidic and cascabel anti-venins 

 showed stronger action against the venoms of a true viper, the daboia, 

 and of an elapine snake, and the Australian tiger snake, than against 

 those of many pit vipers. 



The question as to whether the irregularity and the absence of a 

 more striking antiproteolytic neutralizing property of antivenins, as 

 shown in this study, is due to the absence of more suitable experi- 

 mental procedure, or to the weak antigenicity of the proteolytic 

 enzymes of venoms must be left open for the time being. 



The above experimental data show that the toxicity of snake 

 venoms is related to the activity of various enzymes all of which are 

 neutralized by antivenom immune sera. The physiological conse- 

 quences of the hemolytic enzyme, lecithinase, of snake venoms, and its 

 neutralization by antivenom sera will be discussed in a succeeding 

 section of this book. 



