NATURE OF SNAKE VENOM. 355 



The difference in the constituents of venom is so great that 

 the venom of each species of snake differs in its action, even with 

 those belonging to the same genus. For instance, the serum of 

 an animal rendered immune to the bite of a Cape Cobra {Naia 

 flava) proved on experimentation to be an antidote to the bite 

 of this particular species of snake, but only had a partial 

 antidotal effect upon the venom of another species of Cobra, a 

 larger dose being necessary to neutralize the venom injected. 

 Tested on animals bitten by Puff Adders, or injected with fatal 

 doses of their venom, this serum had very little curative power. 



The poisonous substances in snake venom may be separated 

 into three main parts. 



(i) Neurotoxins, or nerve poisons. These combine with the 

 nerve cells and paralyse them. Neurotoxins are present in all 

 venoms, but are strongest in the poison of Cobras. 



The nerve poisons of some species of snakes will cause 

 paralysis of the nerve centres controlling the breathing, resulting 

 in collapse of the lungs. Each variety of nerve poison acts with 

 greater or lesser power upon the various groups of nerve centres, 

 according to its nature. The nerve poison in one species of 

 snake will cause complete paralysis of a certain set of nerve 

 centres, while the nerve poison of another kind of venom will 

 have little or no poisonous effect upon that particular nerve 

 centre, but will concentrate its benumbing power on a group of 

 nerve cells which the former venom has either not affected at 

 all, or only to a slight degree. 



In severe cases of Cobra poisoning, a certain amount of 

 structural change takes place in the nerve cells, numbers of them 

 being broken up and destroyed. However, death is not usually 

 caused by wholesale destruction of nerve cells, but by the para- 

 lysing action of the neurotoxin upon the cells. This neurotoxin 

 predominates in all Cobra venoms.* 



(2) H^MORRHAGiNS, or blood poisons. This portion of the 

 venom acts upon the endothelial cells, phagosytes, and red 

 corpuscles of the blood. The endothelial cells are the cells of 

 a membrane which lines the inside walls of blood vessels. The 

 cells are thin and flat. The venom alters their shape, changes 

 and expands their structure sufficiently to allow the altered 



* Adder venoms contain a comparatively small proportion of neurotoxin 

 or nerve poison. 



