EXERCISE. - Muscular exertion increases the frequency of the pulse more than any other cause, as will sufficiently appear by the following quotation from Bryan Robinson.* " The pulse, in a minute, of a man lying, •- sitting standing, or walking at the rate of two C miles in an hour, at the rate of four miles in an hour, or running as thst as he could, were 64, 68, 78, 100, 140, and 150 or more." Change of posture, as has just been proved, forms merely a particular case of muscular ' effort. The act of changing from one posture to another and the maintenance of different positions the action of the muscles, both occasion an increased frequency of the pulse ; so also does the stretching out of the arm or the holding of it in the same posture, the pulse rising rapidly with the continuance of the effort, and falling, as the writer has proved experimentally, on returning to a state of' rest, below the frequency which it had before the effort was made ; and the same obser vation applies to fatigue induced by long con tinued exertion, as in walking. The cause of the increased frequency of the pulse which attends muscular effort is partly mechanical, that is to say, depending on the rapid pro pulsion of the blood through the large veins, and partly due to the effort of the will which sets the muscles in action. It is probable,
however, that the first-named cause is by far the most influential. , Passive exercise, as in riding and the various forms of carriage conveyance, has also a marked effect on the pulse ; an effect partly due to the varying action of the muscles in supporting the different postures into which the body is being constantly thrown, and partly to a cause correctly pointed out by Dr. Ar nott in the following passage.
" In a long vein below the heart, when the body falls, the blood, by its inertia and the supporting action of the vessels, does not fall so fast, and therefore really rises in the vein ; and as there are valves in the veins preventim, return, the circulation is thus quickened with'. out any muscular exhaustion on the part of the individual. This helps to explain the effect of the movement of carriages, of vessels at sea, of swings, Sze., and the effect on the circulation of passive exercise generally, and leaves it less a mystery why these means are often so useful in certain states of weak health."*