The clotting of a snake (Crotalus viridis Helleri) plasma and its interaction with various snake venoms.

The clotting of C. V. Helleri plasma is not accelerated by the factor X activator or thrombin-like enzymes from its own venom. Clotting of the plasma is accelerated by the factor Xactivator from Russell's viper venom, but not by the thrombin-like enzyme from Agkistrodon Rhodostoma venom ("Arvin"). The prothrombin activator from the Taipan venom clots C.V. Helleri plasma equally well as human plasma, but the thrombin which is produced has a marked specificity for its own fibrinogen, and clots bovine fibrinogen more slowly. C.V. Helleri plasma contains an inhibitor which progressively inactivates bovine factor Xa and thrombin, but the inhibitor is not potentiated by heparin. The slow, protracted clotting of the snake plasma either alone or when mixed with human plasma or bovine fibrinogen suggests that this inhibitor may interfere with the polymerisation of fibrin monomer.