Page:The Harveian Oration,1902.djvu/30

 sometimes retard, sometimes incite the course of the blood according to the needs of the lower Viscera."

The tightening or relaxation of the grip of the vaso-motor nerves on the blood-vessels, imagined by Willis, was shown by the discovery of Henle, in 1840, of the muscular nature of the middle coat of the arteries to be a contraction or relaxation of the walls of the blood-vessels themselves. But the actual proof of the action of the vaso-motor nerves was first given in 1851 by Claude Bernard, in the well-known dilatation of the vessels of the rabbit's ear on section of the cervical sympathetic, followed almost immediately by the demonstration of the converse results on electrical stimulation of the distal end of the cut nerve by Bernard himself, Brown-Sequard, and Waller. Similar phenomena were speedily proved to obtain in reference to the vessels of the abdomen, the limbs, and most of the organs of the body. The blood-vessels are normally in a state of tone or semi-contrac-