1904] 



Pharmacology of Indian Cobra Venom. 



187 



consequence thereof all the harmful results of slow asphyxiation are 

 produced. 



If life is prolonged beyond the usual term by artificial respiration, 

 and possibly also if the dose of venom is a very low lethal one which 

 takes many hours to kill, the phrenic and other motor nerve-ends may 

 become paralysed, but this is certainly not an essential feature of death 

 from lethal doses of Cobra venom, which kill within five hours. I hope 

 to make a farther communication on this subject later. 



The convulsions which precede death are purely asphyxial, and can 

 be at once stopped by artificial aeration of the blood. Each such 

 convulsion is followed by a phase of exhaustion of the respiratory 

 mechanism, which is almost certainly central. 



If the dose of Cobra venom administered be a large one, and especially ' 

 if it be given intravenously, the respiratory centre is quickly and 

 severely affected, and respiration may cease almost at once. This 

 cessation of breathing may be permanent, if artificial respiration be 

 not quickly started, but if the dose be a smaller one, the rhythmic 

 activity of the centre reasserts itself. At first there may be a number 

 of deep spasmodic gasps, and then the movements of respiration 

 re-begin, very gently at the commencement, and gaining force as time 

 goes on, till a normal rhythm is re-established, or even a stage of 

 stimulation is manifested. Soon, however, the centre fails again, and 

 all the phenomena of asphyxiation appear. 



By applying Cobra venom directly to the exposed medulla oblongata 

 of the rabbit, I have shown that the respiratory centre can be 

 paralysed without the phrenic nerve-ends or the heart being appre- 

 ciably affected. 



If very large doses of venom are injected, death may take place by 

 cardiac failure, before the respiratory mechanism has given way. We 

 have here to do with the direct action of the venom on the heart 

 muscle ; the beats become rapid, and shortened, and the heart passes 

 into a systolic phase, in which it dies tightly contracted. 



5. Cobra venom, when given in low lethal doses subcutaneously, 

 raises the general blood pressure. There may be a slight preliminary 

 fall before the rise, but often this is wanting. In the absence of farther 

 interference the blood pressure remains high till very near the end of 

 life. In the asphyxial convulsions which herald death, a farther steep 

 rise of blood pressure takes place ; this is soon followed by a sudden 

 and very rapid fall to death. 



The high level of blood pressure is due to — 



1. The direct action of the circulating venom on the muscular tissue 

 of the arterioles, causing a constriction of these vessels, and thus opposing 

 a barrier to the onward flow of the blood ; 



2. The increased force of the heart beat as the outcome of the direct 

 stimulating action of the venom on its muscular tissue, and 



