Page:The third Huxley lecture.pdf/36

32 lining membrane. A more efficient mechanism for their constriction could hardly be conceived.

As regards the regulation of the arterial contractions, Bernard's classical experiment of inducing turgescence of the vessels of the ear by section of the sympathetic in the neck, and Wallers converse observation that galvanic stimulation of the distal end of the divided nerve made the distended vessels shrink and the ear assume unwonted pallor, had demonstrated the great fact of nervous control over the local circulation; but it was still a subject of discussion what part of the nervous centres exercised the function.

In entering on the inquiry, I first divided the sciatic nerve, a proceeding which had been stated on high authority to cause relaxation of the arteries of the web. The immediate effect of its division was, indeed, some enlargement of their channels, but this very soon passed off. I then resorted to operations on the roots of the spinal nerves and on the medulla. And, not to weary you too much with details, I may say that removal of all that part of the spinal cord which gives off branches for the hind legs, caused the arteries of the web to relax completely and to remain permanently of about the same calibre as the veins. But if any portion that furnished nerves to the posterior extremi-