In doses less than 1 milligramme for 1 c.c. of plasma, these venoms by themselves never produce coagulation as do those of Lachesis or Vipera russellii. They are thus sharply differentiated in this respect.
If fresh blood issuing from the arteries of an animal be received in a vessel containing a sufficient quantity of Colubrine-venom (that of the Cobra for example), and steps be immediately taken to ensure the perfect mixture of the venom and the blood, we find that the latter has entirely lost its coagulability, just as though it had been mixed with peptone or extract of leeches’ heads.
Again, if a mixture be made in vitro of coagulant venoms, such as that of the Lachesis, with anticoagulant venoms such as that of the Cobra or of Ancistrodon, it is found that these mixtures, when properly effected, become neutral, so that the respective effects of the component venoms are entirely destroyed. Assuming, for instance, that 1 milligramme of Lachesis-venom coagulates in two minutes 1 c.c. of 1 per cent. citrate rabbit-plasma, if we add to the plasma firstly 1 milligramme of Ancistrodon-, or 1 milligramme of Cobra-venom, and then 1 milligramme of Lachesis-venom, the plasma remains non-coagulated, yet coagulates perfectly on the subsequent addition of 1 c.c. of a ½ per cent. solution of chloride of calcium.
There is, therefore, a real antagonism between the actively coagulant substance contained in certain Viperine venoms and the anticoagulant substance comprised in the venoms of certain other Viperidæ (Ancistrodon), belonging to the subfamily Crotalinæ, and in those of all the Colubridæ.
The conclusion to be deduced from the foregoing facts is that the venoms of Colubridæ and those of certain Viperidæ are decidedly anticoagulant, while the majority of the venoms of Viperidæ, on the contrary, possess strong coagulant properties, even when mixed with blood in infinitesimal doses.
The question therefore arises why these coagulant Viperine venoms suppress the coagulability of the blood when mixed with it in vitro in strong doses (for example, in doses beginning from 4 milligrammes of Lachesis-venom, or 7 milligrammes of the venom of Vipera russellii for 1 c.c. of 1 per cent. citrate rabbit-plasma).
The explanation of this apparently contradictory phenomenon is furnished by the intense proteolysis that these Viperine venoms exert upon fibrin, in solution or coagulated. This proteolysis actually manifests itself with weak coagulant doses, for the compact clots formed at the outset soon become soft and then dissolve, like a cube of egg-albumen in an experiment in artificial digestion by trypsin. We shall revert to the subject later on.
III.—Mechanism of the Anticoagulant Action of Venoms on the Blood.
The anticoagulant action of the venoms of Colubridæ and of Ancistrodon upon the blood appears to take effect in the first place upon the fibrin-ferment, and afterwards upon the fibrin by proteolysis. The action on the fibrin-ferment seems manifest when we experiment with anticoagulant venoms which are feebly proteolytic, like the venom of the Cobra.
I have already stated that a mixture of fresh blood with a sufficient dose of Cobra-venom is non-coagulable, as though the blood on issuing from the animal had been mixed with peptone or leech-extract. But, while blood when peptonised or mixed with leech-extract coagulates readily on the subsequent addition of fibrin-ferment, blood mixed with venom remains positively non-coagulable. It is the same with citrate- or oxalate-plasmas, which no longer coagulate when chloride of calcium is added to them, and with 4 per cent. saline plasma on the addition of distilled water.