360 THE SNAKES OF SOUTH AFRICA. 
because their venom acts so rapidly on the nerve centres, often 
causing death or reducing the person bitten to a condition im- 
possible of recovery before there is time to apply any remedial 
measures. 
However, the venoms of all snakes of the Colubrine family do 
not act in this rapid way upon the nerve-centres in the brain 
and medulla. The venoms of many act primarily on the blood 
and secondarily on the nerve centres, as for instance in the case 
of the Boomslang, which is a member of the Colubrine family, 
although in classification it is placed in a sub-family with other 
back-fanged snakes. 
When a dose of viper venom is injected into a vein, even if 
the quantity be small, death rapidly results from clotting of the 
blood, chiefly in the pulmonary arteries. In animals, if a small 
fraction of a drop is injected direct into a vein, death quickly 
follows from clotting of the blood caused by a poisonous principle 
in the venom known as Fibrin-ferment. 
In these cases no remedial measures are of any avail. 
The venoms of the different species of snakes differ con- 
siderably in the blending of the nerve poisons (neurotoxins), 
blood poisons (hemorrhagins), and blood-clotting poison (Fibrin- 
ferment). This being so, the symptoms vary more or less 
widely. The venoms of two different species of snakes which 
apparently produce the same outward physiological effects are 
found, when examined, to be more or less dissimilar in their 
composition. However, when the victims are subjected to 
post-mortem it will be discovered that the venom of one snake 
has produced internal effects considerably different from the other. 
The venoms of the Colubrine (Cobra) family of snakes and 
the Viperine (Adder) family differ most widely in their nature 
and effects. Generally speaking, we can say that the venom 
of the typical Cobra family of snakes acts rapidly and chiefly on 
the nerve-centres, causing rapid paralysis and death ; while the 
venom of the Adders, although causing severe nerve depression, 
exerts a powerful poisonous influence on the blood and walls of 
blood vessels. 
Snake venom, when mixed with ammonium sulphate or 
absolute alcohol causes the poisonous substances (proteids) to 
be separated. These fall to the bottom but retain all their 
original poisonous properties. 
