The venom of VIPERIDÆ, on the contrary, especially that of _Lachesis_, is characterised by the almost total absence of _neurotoxin_, while its richness in _hæmorrhagin_ is considerable. Consequently, heating for a few minutes at + 75° C. renders it almost entirely inactive, since _hæmorrhagin_ 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 COLUBRIDÆ or VIPERIDÆ, by determining its richness in _neurotoxin_ resistant to heating at + 85° C. Certain VIPERINE 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 greatly in amount according to the species--of _neurotoxin_, and a much larger proportion of _hæmorrhagin_. 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 _Bungarus cæruleus_, which are very rich in _neurotoxin_, contain a quantity of hæmorrhagin 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 COLUBRIDÆ (_Hoplocephalus_, _Pseudechis_) form a special group, which is richer in _hæmorrhagin_ than are those of the COLUBRIDÆ of the Old World.[99] On studying, in the case of these various venoms, the action _in vitro_ and _in vivo_ of a purely _antineurotoxic_ antivenomous serum, such as, for example, that of an animal vaccinated against cobra-venom heated to + 75° C., it is found that this serum has a very decided effect upon cobra-venom, and likewise upon that of snakes belonging to allied species (_Naja bungarus_, _Naja haje_), and that its action upon the other venoms is less in proportion as they contain less _neurotoxin_. It prevents hæmolysis _in vitro_, and suppresses the effects of intoxication on the nervous system, but does not modify in any way the phenomena of coagulation or of proteolysis. If this serum be made to act _in vitro_ on those VIPERINE venoms that, when heated to + 75° C. and deprived of their hæmorrhagin, remain neurotoxic, like the venom of the common viper, it is found that it renders them entirely innocuous. Therefore, in the case of all species of poisonous snakes, and perhaps also in that of other poisonous animals (such as scorpions), it appears that the _neurotoxic_ substance is _one and the same_, and always neutralisable by an _antineurotoxic_ serum like that of animals vaccinated against cobra-venom.