Action of the Venom q/" Sepedon haemachates of South Africa. 81 



Strong solutions slightly constrict the frog's blood-vessels when perfused 

 through them. 



In rabbits, the venom injected intravenously causes a slight fall of blood- 

 pressure. This is soon recovered from, and thereafter the blood-pressure 

 rises and remains high till the end of Life. The transient fall of blood-pressure 

 is probably mainly due to a weakening of the heart's contraction. When 

 pronounced embarrassment of the respiration comes on, the blood-pressure 

 rises above the normal level. This is mainly due to stimulation of the vaso- 

 motor centre by the venous condition of the blood, the heart being at the 

 same time slowed through stimulation of the vagus. The venom also slightly 

 slows the heart by a direct action on it, and the direct but slight constriction 

 of the vessels may be a contributing factor in maintaining the level of the 

 blood-pressure. 



In the course of poisoning in frogs, the lymph hearts are paralysed tardily, 

 but long before the blood heart. 



Sepedon venom has little action on the blood. It does not definitely affect 

 the coagulability, and neither haemorrhages nor intravascular clotting are found 

 post mortem. Haemolysis is not found in vivo. 



Eespiratory failure in mammals is due to paralysis of the respiratory 

 centre, the excitability of the phrenic nerve-ends being practically unim- 

 paired. 



Non-lethal doses of Sepedon venom cause a rise of temperature ; lethal 

 doses cause a fall of temperature, with sometimes an initial rise. 



VOL. lxxxi. — B. 



G 



