VACCINATION AGAINST SNAKE-VENOM 249 



The venom of Colubrid^ in general is characterised by the 

 constant predominence of neurotoxin, to which it owes its extreme 

 toxicity, which is especially intense in the case of cobra-venom. 

 Tt contains no, or scarcely any, hcemorrhagin ; for this reason the 

 local symptoms of poisoning hj Colubrine venom are almost nil. 

 This neurotoxin, as we have seen, shows itself very highly resistant 

 to heat. 



The venom of Viperid^, on the contrary, especially that of 

 Lachesis, is characterised by the almost total absence of neuro- 

 toxin, while its richness in hcemorrhagin is considerable. Con- 

 sequently, heating for a few minutes at + 75° C. renders it almost 

 entirely inactive, since hcemorrhagin is very sensitive to heat. 



Given venom of some kind or other, the origin of which is 

 unknown, it is therefore possible to ascertain whether the snake 

 from which it was extracted belonged to the C0LUBKID2E or 

 ViPERiD^, by determining its richness in neurotoxin resistant to 

 heating at + 85" C. 



Certain Vipehine venoms, such as those of the European Vipera 

 berus and Vipera aspis, the African Cerastes and American Crotalus 

 contain at the same time a small proportion — varying greatlj' in 

 amount according to the species — of neurotoxin, and a much larger 

 proportion of hcemorrhagin. It is for this reason that these venoms, 

 although greatly attenuated and deprived of their local action by 

 heating, still remain toxic when injected in large doses into animals 

 after having been heated to + 75° C. 



On the other hand, some Colubrine venoms, such as those of 

 Bungariis cceruleus, which are very rich in neurotoxin, contain a 

 quantity of hsemorrhagin sufficient to differentiate their effects in 

 appearance from those produced by cobra-venom, when they are 

 injected, not beneath the skin, but directly into the veins. In this 

 case their effects upon the blood are added to those of their 

 neurotoxin. 



It would seem, too, that the venoms of Australian ColtjbbiDjE 



