EFFECTS OF VENOM 239 



Snake-venoms are analogous with toxins and enzymes ; 

 they are of all degrees of potency and complexity, being 

 not quite alike even in snakes of closely related species. 

 In a general view their principal but not their only toxic 

 components may be classed, according to their action, 

 into (a) those which act upon the central nerve system 

 neurotoxins ; and (6) those which act upon the blood 

 and vascular system. In the latter, again, several kinds 

 are included, the chief of which are those which destroy 

 (a) the red blood cells (haemolysins), and (6) the cells of 

 the capillary walls (haemorrhagins), and thus diminish 

 both the coagulability of the blood and the continence 

 of the blood-vessels; (c) those which act upon the plasma 

 and increase the coagulability of the blood (fibrin 

 ferments) ; and (d) those which act directly upon the 

 heart and vaso-motor system. Of the neurotoxins it is 

 known that they show a selective affinity for the cells of 

 the respiratory centre in the medulla. 



It is generally agreed that neurotoxins (with a special 

 affinity for the breathing centre) preponderate in the 

 venom of Colubridce, and that toxins that act upon the 

 blood and circulatory system preponderate in the venom 

 of Viperidce, and that among the Australian Colubrines 

 venoms rich in both classes of toxins are not rare. 



It must be understood that the toxins mentioned in 

 this brief review are far from being the only toxins 

 known ; and, furthermore, that with any given venom 

 and especially with venoms that act chiefly on the blood 

 one toxic effect or another may be either emphasized 

 or masked, according to the amount of venom injected 

 and the rapidity with which it is absorbed. 



Effects of Venom upon Animals. It is obvious that these 

 must differ, not only with different kinds of venom, but 

 also with the condition of the venom at the moment, 

 with the amount of venom injected, and with the manner 

 of injection, whether intravascular (rapid) or subcutaneous 

 (slow). The matter cannot be treated quite concisely, 

 the simplest plan is to consider some typical examples of 

 the different kinds of venom. 



