24 THE SNAKES OF SOUTH AFRICA. 
of these latter, and it was shown, on experimentation, to be 
highly venomous. 
The study of the fangs of snakes clearly shows the operation 
of the great law of Evolution. 
THE CIRCULATION OF THE BLOOD. 
The heart of a snake has three cavities—one ventricle and two 
auricles, not two of each, as is the case with all warm-blooded 
creatures. The heart pumps the blood through blood-vessels in 
the ordinary way. The blood corpuscles are both red and white, 
as is the case with the higher animals. The red corpuscles are 
elliptical, flattened, and bi-convex. The circulation of the blood 
is very sluggish, and its temperature is much below that of the 
mammal class of animals. Hence the reason they are termed 
“cold-blooded.”’ Reptiles are all “ cold-blooded,” and mammals 
are without exception, “‘ warm-blooded.” 
The circulation of the blood of snakes being very sluggish, 
they do not require nearly so much oxygen as do animals of the 
warm-blooded class such as mammals and birds, hence the reason 
they are able to live and thrive in air charged with carbonic acid, 
gas, and other gaseous impurities given off by decaying vegeta- 
tion and stagnant water. Snakes, if entirely deprived of air, 
will continue to live, in many instances, for several hours. I 
have seen ordinary land snakes, such as the Puff Adder, sink 
themselves in a shallow pool and remain immovable at the 
bottom for nearly half an hour. I sat one day and watched a 
Python for one and a half hours lying coiled up at the bottom of 
a clear spring of water, without once raising its nostrils to the 
surface. If corked up in a bottle of water, a snake will die in 
one or two hours as a general rule. When swimming upon the 
surface of water, a snake inflates its lung, which makes it very 
buoyant. When swimming upon the surface they wriggle with 
a wave-like motion. I have watched snakes stretched out 
motionless upon water, apparently lying on it as lightly as a cork, 
sunning themselves in the hot rays of the midday sun. On being 
alarmed, they instantly sank out of sight without any apparent 
muscular effort. This is accomplished by expelling the air from 
the long, tube-like lung, whereupon the body sinks, being then 
denser than the water. 
