24 THE SNAKES OF SOUTH AFRICA. 



are longer than the rest, and more or less grooved. Such snakes 

 should always be regarded as venomous to a greater or lesser 

 degree. The Boomslang or Tree Snake {Dispholidus typus) is one 

 of these latter, and it was shown, on experimentation, to be 

 highly venomous. The poison fangs and other teeth when shed 

 or accidentally lost are replaced at short intervals. 



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 temperature of 

 the blood is the same as that of the surrounding air or heat 

 absorbed from the sun or hot surfaces. The temperature of the 

 blood is thus determined by external circumstances, and is not 

 fixed as in warm-blooded animals. 



The blood circulation 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 hve, 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 to 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 



