356 THE SNAKES OF SOUTH AFRICA. 



blood to escape through the walls of the blood vessels into the 

 surrounding tissues. The phagosytes are the white corpuscles 

 of the blood. They are altered, damaged, and often more or less 

 dissolved by the action of the haemorrhagin principle in snake 

 venom. The chief action, however, is upon the red corpuscles 

 of the blood. The haemorrhagin attacks these corpuscles, dis- 

 solving out their colouring matter and rendering them spherical 

 and sticky. This dissolved colouring matter then escapes 

 through the expanded walls of the blood vessels and finds its 

 way into the tissues, spreading out under the skin and causing 

 purple blotches more or less extensive. Red corpuscles, un- 

 changed, also escape through the expanded blood vessel walls. 

 The escape of blood into the tissues is greatest near the various 

 small arteries which branch off and terminate in a fine network 

 of capillaries. The reason is that, at these points, the pressure 

 of blood upon the capillaries is greatest. 



The brokcn-up blood also oozes out through the mucous or 

 lining membranes of the moutli, nose, lungs, stomach, bowels, 

 and bladder. This blood-destroying poison predominates in 

 Adder venom. Recent experiments, however, tend to show that 

 the venom of the Puff Adder acts chiefly if not entirely on the 

 endothelial cells, and not on the blood corpuscles. 



(3) Fibrin-ferments. These cause the fibrin of the blood 

 to solidify, which produces clotting. Fibrin ferments are usually 

 strongest in Viper venoms, although they are present in lesser 

 or greater degree in the poisons of all snakes. 



When human subjects are bitten by Vipers (Adders) the 

 fibrin-ferment does not cause coagulation of the blood, unless 

 injected in an unusually large quantity, or direct into a vein 

 (intravenously). In the latter cases, coagulation of the blood and 

 death may occur at any instant. When injected direct into a 

 vein even in small quantit}^ death occurs within a few moments. 



However, when the small animals on which snakes feed, such 

 as rats, mice, or birds, are bitten by Adders, the fibrin-ferment 

 in the venom almost instantly coagulates their blood, causing 

 rapid death. This is due to the relatively large dose of venom 

 injected. In the case of man or the larger mammals, sufficient 

 of the fibrin-ferment principle in the venom does not usually 

 enter the blood all at once to cause clotting, as is usual with small 

 creatures. In the case of Cobras, the neurotoxin or nerve poison 



