EFFECTS OF SNAKE VENOM ON COAGULABILITY OF THE BLOOD 139 



ANTICOAGULATING PROPERTY OF SNAKE VENOMS. 



From Fontana's time to the present it has been one of the most remarkable 

 features of venom poisoning that the blood of animals bitten by certain snakes, 

 or of those injected with the venoms of certain species of snakes, tempo- 

 rarily loses its coagulability totally or partially. As has been briefly mentioned 

 in the beginning of this chapter, Fontana determined the fluidity of the blood 

 of animals which died of viper poison; Weir Mitchell and Brainard observed 

 the same fluidity in subacute crotalus poisoning, Fayrer in daboia poisoning, 

 Wall in cobra venom toxication in case of man, and Halford found the same 

 with animals which had received an injection of some Australian snake 

 venoms. The occurrence of the fluidity of the blood of the animals accident- 

 ally or experimentally toxicated with these different venoms was nevertheless 

 so inconstant that its nature had been a great puzzle to most of these observers. 

 Weir Mitchell has shown by a direct test-tube experiment that the venom of 

 rattlesnake exerts an anticoagulating effect upon blood shed and allowed to 

 flow into a flask containing rather a large amount of the venom. Martin 

 demonstrated in vivo that an amount of the venoms of Notechis and Pseu- 

 dechis, insufficient to produce instantaneous thrombosis (positive phase), 

 diminishes or destroys coagulability of the blood for some time to follow 

 (negative phase). Martin's work as a whole received confirmation in the 

 careful investigations of Lamb with daboia venom, but the latter author 

 went into a deeper inquiry as to the nature of the negative phase produced 

 by these Australian as well as Indian snake venoms. The primary question 

 was to ascertain whether the incoagulability brought about by a small amount 

 of daboia venom in the animal body is identical in its mechanism with the 

 diminution of coagulability occasioned by the cobra- venom poisoning. 



Cunningham l found that if a sufficient quantity of cobra venom is mixed, 

 outside of the body, with shed blood, coagulation of the latter may be greatly 

 diminished or eventually suppressed in toto. 



Kanthack 2 followed and enlarged Cunningham's observations by his experi- 

 ments with the normal and immunized bloods. With the latter Kanthack 

 found no inhibitory action of cobra venom on coagulation with the dose 

 which just suffices to suppress clotting of the normal blood. It may be 

 added that the addition of sufficient quantity of antivenomous serum neu- 

 tralized the discoloring and anticoagulating effects of cobra venom upon 

 the blood in vitro. 



Stephens and Myers, 3 working under Kanthack, confirmed the anticoagu- 

 lating property of cobra venom on the blood, although they conducted the 

 blood direct from the artery to the test solution, and the results were observed 

 at intervals of varying lengths of time. Their results show that when more 

 than o.oi gm. of cobra venom is contained inVc.c. and mixed with i c.c. of 



i D. D. Cunningham. Sci. Mem. by Medical Officers in the Army of India, 1895, part 9, i. 

 a Kanthack. System of Medicine, edited by T. Clifford Allbutt, London, 1896, I, 570. 

 * Stephens and Myers. The action of cobra poison on the blood; a contribution to the study of passive 

 immunity. Jour, of Pathology and Bacteriology, 1898, V, 279. 



