The pulse is the wave-like movement which traverses the arteries with each beat of the heart, and which is perceived when a vessel is slightly compressed with the fingers against an unyielding surface. The arteries, in health, are always distended with blood, as shown by the spurt which takes place when one is divided, and when a fresh quantity is injected into it by the heart.
The Contractility Of the Arteries, unlike the property of elasticity, is feebly marked in the larger trunks and their primary branches, whilst it becomes more conspicuous in the smaller vessels. It is the means by which the supply of blood to the several organs is regulated in accordance with their condition of activity or repose. To take an example amongst many that might be given, the stomach during fasting receives a supply of blood sufficient to minister to the nutrition of the tissues of which its walls are composed. The vessels in this condition are contracted, and the colour of the organ is a pale pink; but after a hearty meal, when the process of digestion is in course of active performance, when gastric juice is being poured forth and absorption is proceeding, a much larger supply of blood is needed. Under the influence of certain (dilatator) nerves, by means of which the muscular tissue of the wall of the vessels is caused to relax, their calibre enlarges, a freer current of blood passes through them, and the whole organ becomes congested and of a deep rose-red hue. When the digestive process is completed, and the blood-supply is no longer required, the contractility of the vascular walls comes into play again under the influence of another set of nerves (constrictor), chiefly proceeding from the sympathetic system. The vessels now contract, the mucous membrane becomes pallid, secretion and absorption cease, and the organ resumes its normal condition in the fasting state. A similar succession of events may be observed in every organ of the body that undergoes variations in functional activity, as in the brain during mental effort, and in the muscles during exercise.