XIII. A contribution to the study of the action of indian cobra venom

Abstract

At the suggestion of Sir Thomas Fraser, H. M. Secretary of State for India very kindly placed me on special duty for Snake Venom research in the Pharmacological Laboratory of the University of Edinburgh. Professor Fraser, under whose superintendence I was directed to work, suggested that I should carefully study the pharmacology of Indian Cobra venom, and the work herein set forth is the outcome of that suggestion. Professor Schäfer also very kindly placed his laboratory at my disposal, and both to him and to Sir Thomas Fraser I owe my most cordial acknowledgments for their unvarying kindness and for their very valuable and always ready assistance. Some of the earliest work done on the pharmacological action of Cobra venom was that by Lauder Brunton and Fayrer, published about thirty years ago. They considered that Cobra venom selected the cerebro-spinal nerve centres for its seat of action; it paralysed these, and in large doses it acted also on the ganglia of the heart, causing arrest of cardiac action. They laid little stress on the rôle played by circulatory failure, and in support of their views they quoted a number of experiments in which cardiac pulsations continued after the apparent death of the animal. In volume 22 they go on to discuss the subject still further. With the facts at their disposal they were unable to come to any definite conclusion as to the exact influence of the venom on the heart, but they thought that the heart’s arrest in systole, which they at times observed was due to “some action on the cardiac ganglia.” They drew attention to the great difference observed in the effect of venom according as it was applied to the surface or to the interior of the heart. In this connection they quote an experiment in which they perfused the frog-heart with a solution of Cobra venom, and obtained arrest of it in a position midway between systole and diastole. The strength of solution used is not stated and details are wanting, but the experiment is of great interest, as it is the only record I can find in any writer’s works of an attempt to perfuse an isolated part with Cobra venom. They thought the action was due to an influence on the cardiac ganglia. They found that in large doses Cobra venom destroyed the inhibitory power of the vagus, which it did not do in small doses. That the inhibitory branches of the vagus were sometimes affected they were confident, but they do not seem to have been able to differentiate clearly between a direct action of the venom on the vagal system, and the indirect effects brought about by means of interference with respiration. In dealing with the last-named subject, they clearly observed the paralysis of the phrenic nerve ends, and divided the responsibility for respiratory failure between this and a direct interference with the centre in the medulla oblongata.