The phenomenon known as the arterial pulse or arterial pulsation is due to the distension of the arteries consequent upon the intermittent injection of blood into their trunks, and the subsequent contraction which results from the elasticity of their walls. It is perceptible to the touch in all excepting very minute arteries, and, in exposed positions, is visible to the eye. The pulse is usually examined at the radial artery at the wrist, the advantages of that position being that the artery is very superficial, and that it is easily compressed against the bone. It is usual and convenient, though not quite accurate, to include under the term the conditions observed between the beats, as well as those produced by them. The condition of the pulse depends mainly on two factors, each of which may vary independently of the other: first, the contraction of the, heart, which propels the stream of blood along the artery; and second, the resistance in the small arteries and capillaries, which controls the rate at which it leaves the artery.

The first determines the frequency and rhythm of the pulse and the force of the beats; but the tension of the artery between them and their apparent duration depend mainly upon the peripheral resistance. "Feeling the pulse," therefore, gives important information besides the rate of the heart's action, and implies much more than the mere counting of pulsations. Dr. Broadbent says, "A complete account of the pulse should specify (1) the frequency - i.e. the number of beats per minute, with a note of any irregularity or intermission or instability of the rhythm; (2) the size of the vessel; (3) the degree of distension of the artery between the beats; (4) the character of the pulsation - whether its access is sudden or gradual, its duration short or long, its subsidence abrupt or slow, note being taken of dicrotism when present; (5) the force or strength of both the constant and variable pressure within the artery, as measured by its compressibility; (6) the state of the arterial walls."

The frequency of the pulse varies with age, from 130 to 140 per minute at birth to 70 to 75 in adult males, and with sex, being six or eight beats more in adult females. In some individuals it deviates considerably from this standard, and may even be habitually below forty or above ninety without any signs of disease. It is increased by exertion or excitement, by food or stimulants, diminished in a lying posture or during sleep. In disease (acute hydrocephalus, for example) the pulse may reach 15 J or even 200 beats; or, on the other hand (as in apoplexy and in certain organic affections of the heart), it may be as slow as between thirty and twenty.

The normal regular rhythm of the pulse may be interfered with either by the occasional dropping of a beat (intermission), or by variations in the force of successive beats, and in the length of the intervals separating them (irregularity). These varieties often occur in the same person, but they may exist independently of each other. Irregularity of the pulse is natural to some persons; in others it is the mere result of debility; but it may be caused by the most serious disorders, as by disease of the brain, or by organic disease of the heart.

The other qualities of the pulse are much more difficult to recognize though of no less importance. The degree of tension or resistance to compression by the fingers varies greatly: in a soft or "low tension" pulse the artery may be almost imperceptible between the beats; in a hard or "high tension" pulse it may be almost incompressible. An unduly soft pulse is usually an indication of debility; an unduly hard one is most often characteristic of disease of the kidneys and gout. But the tension, like the frequency of the pulse, undergoes considerable variations in health from temporary causes, and may in certain individuals be habitually above or below the average without actual disease.

The force of the beats is a measure of the vigor and efficiency of the heart's action. A strong pulse is correctly regarded as a sign of a vigorous state of the system; it may, however, arise from hypertrophy of the left ventricle of the heart, and remain as a persistent symptom even when the general powers are failing. As strength of the pulse usually indicates vigor, so weakness of the pulse indicates debility. Various expressive adjectives have been attached to special conditions of the pulse, into the consideration of which our space will not permit us to enter. Thus, we read of the jerking pulse, the hobbling pulse, the corded pulse, the wiry pulse, the thrilling pulse, the rebounding pulse, etc. The full significance of changes of the pulse in disease can only be appreciated by considering them in connection with the other signs and symptoms of the case.