ANTI-ENZYME IMMUNITY 293 



an area of hyperemia and edema. These local reactions are common 

 to crotalidic venoms and the evolution of the lesion is essentially the 

 same with all the venoms studied. 



The neutralizing effect of antivenom serum was tested by mixing a 

 fixed volume of antivenom serum with varying doses of venom and 

 injecting after a reaction period of two hours at room temperature. 

 The local effect of the venom developed so rapidly that no beneficial 

 result could be obtained from antivenin given after the venom had 

 been injected. In a subcutaneous test, Q.5 ml. of crotalidic immune 

 globulin prevented the necrotic action of each of the venoms in doses 

 of 1 to 2 mg. The neutralizing effect of antivenin was also marked in 

 the intradermal tests. As the result of comparative tests Githens found 

 that quantitatively, the neutralizing power of antivenin is equal to, 

 or greater than, that on the neurotoxic factor of the same venoms. 



The mechanism of the clotting of blood plasma in vitro has already 

 been discussed in the preceding pages. Eagle and others had shown 

 that some venoms act as thrombin causing clotting of solutions of 

 fibrinogen, while others merely activate prothrombin. The failure of 

 certain lots of snake venoms was interpreted as due to either the ab- 

 sence of the clotting factor or to the preponderant action of proteolytic 

 constituents. In the latter case, it was stated that clotting may result 

 with small amounts of venom, but fail to appear with larger amounts. 



In a typical clot-forming test with fer-de-lance venom, Githens re- 

 ported the following results on the clotting of 1 ml. of horse blood 

 plasma. 



(a) 0.001 mg. of venom caused the beginning of a clot in 8 min- 

 utes; the clot was soft in fourteen, and firm in 30 minutes. 



(b) 0.000,03 mg. of venom caused the beginning of a clot in 10 

 minutes; the clot was soft in 35 minutes, and did not become firm. 



(c) 0.000,01 mg. of venom caused the beginning of a clot in 60 

 minutes; did not become soft. 



The time required for the formation of soft clot being more con- 

 stant was selected as a standard. The minimal effective dose was de- 

 fined as that which induced formation of a soft clot within 30 minutes. 

 Fifty lots of venom were tested, representing 26 species of pit viper, two 

 species of true viper and one elapine snake. Of these, seven caused no 

 clotting in any concentration. Seven others induced clotting irregu- 

 larly with 0.01 mg. per ml. of plasma, but never with higher or lower 



