368 THE SNAKES OF SOUTH AFRICA. 
Cobra venom contains an anti-fibrin ferment, and prevents 
the coagulation of the blood. This is not, however, by any 
means the case with all Colubrine snakes. 
Cobra venom, when diluted one in ten million with water, is 
a heart stimulant if injected under the skin or into a vein. 
VIPERINE VENOM. 
The venom of Viperine snakes, of which our Puff Adder, 
Horned Adder, and Berg Adder are examples, differs considerably 
in its physiological action from that of the Cobra (Colubrine) 
family. The neurotoxins or nerve poisons in it are not nearly 
so potent in their action as is the case with the nerve poisons in 
Cobra venom. But, whereas Cobra venom causes increased 
action of the heart and consequent increased blood pressure, 
Viperine venom slows down the pulsation of the heart and 
circulation of the blood. This narcotic power of the venom 
extends to the general nervous system, bringing about a state of 
nerve depression more or less severe according to the amount of 
venom injected. 
Cobra venom acts powerfully upon the nerve centres con- 
trolling the breathing functions, and tends to stop the action of 
the lungs. Viperine venom, on the other hand, exerts no special 
effect upon these nerve centres. 
GENERAL TENDENCY OF VIPERINE VENOM. 
The tendency of Viperine venom is to produce a gradual and 
general paralysis of the nerve centres which causes a feeble action 
of all the vital functions. If the dose injected be a fatal one, 
this slowing-down action progresses steadily but surely until 
death takes place. The venom of Viperine snakes contains a 
powerful poison known as a fibrin-ferment causing the blood to 
clot. If the venom be injected direct into a vein in sufficient 
quantity in reptile, mammal or man, coagulation or clotting of 
the blood takes place, followed rapidly by death. 
However, when the venom is injected into the muscular 
tissues as is usually the case in bites from snakes, the poison is 
not absorbed with sufficient rapidity to cause coagulation until 
after death. 
