188 



Capt. K. H. Elliot. A Contribution to the [Jan. 18 r 



3. The stimulation of the vaso-motor centre, as a result cf the steadily 

 increasing venosity of the blood. 



The slight preliminary fall of blood pressure, which is sometimes seen,, 

 is due to cardiac inhibition, but this subject will be reserved for 

 discussion when dealing in the next section with the action of large 

 doses of the poison. 



The late fall in the rate of the heart beat is due to cardia inhibition... 

 the latter is clue to several factors. 



1. A gradually progressive asphyxiation is taking place throughout 

 such an experiment; this affects the vagal centre in common with 

 the rest of the nervous system ; the result is a stimulation of the 

 inhibitory mechanism, and a consequent slowing and weakening of the- 

 heart. 



2. The direct stimulating action of the venom on the vagal 

 inhibitory centre acts in the same direction as the asphyxiation of the 

 centre. 



3. There is distinct evidence that even when the influence of the vagal! 

 centres is removed, inhibition of the heart continues to progress,, 

 though in a lessened degree. The obvious inference is that the vagal 

 nerve-ends are stimulated by the circulating venom, and probably also- 

 as a result of deficient aeration of the blood. 



4. It is not improbable that a stage of exhaustion of the heart muscle- 

 follows the early stimulative action of the venom ; and 



5. Exhaustion of the heart is probably predisposed to by the strain 

 put upon the organ, in having to work for a long period against ai* 

 abnormally high blood pressure. 



We are now in a position to explain the sudden rapid fall of the 

 curves of heart-beat rate and of blood pressure, which usher in death 

 at the close of one of these long experiments. An over-strained and 

 weakened heart is suddenly and violently called upon to bear a 

 farther burden, for respiration has ceased and the medullary centres- 

 are acutely asphyxiated. As a consequence there is a violent excita- 

 tion of the cardio-inhibitory and vaso-motor mechanisms. The heart 

 is slowed and at the same time has to work against a suddenly 

 increased pressure, and it gives way. In fact we have the phenomena 

 of asphyxiation in their entirety. 



The vessels of the splanchnic area are affected pari passu with those- 

 of the body generally, and they in no wise act independently. The 

 vaso-motor mechanism remains active throughout, and is, as we have 

 seen, profoundly affected by changes in the venosity of the blood. 



6. Cobra venom, when injected in large doses and especially when 

 given intravenously, causes — 



(1) a sudden fall of blood pressure; 



(2) a subsequent rise, provided the dose has not been too large ; and 



(3) a final fall to zero. 



