VACCINATION AGAINST SNAKE-VENOM 249 
The venom of CoLUBRIDÆ in general is characterised by the 
constant predominence of newrotoxin, to which it owes its extreme 
toxicity, which is especially intense in the case of cobra-venom. 
It contains no, or scarcely any, hemorrhagin ; for this reason the 
local symptoms of poisoning by COLUBRINE venom are almost mil. 
This newrotoxin, as we have seen, shows itself very highly resistant 
to heat. 
The venom of VIPERIDÆ, on the contrary, especially that of 
Lachesis, is characterised by the almost total absence of newro- 
toxin, while its richness in hemorrhagin is considerable. Con- 
sequently, heating for a few minutes at + 75° C. renders it almost 
entirely inactive, since hemorrhagin 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 hemorrhagin. 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 ceruleus, which are very rich in newrotoxin, 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 
