versally believed; and though a mola has sometimes been found in
the uterus totally destitute of heart, and in which the blood must
have circulated, in its usual course, through the arteries and veins, it
cannot be known that there was any alternate pulsation; and, even
if there was any pulsation, it must have arisen from preternatural
power in the arteries, and the resistance in the extreme vessels must
have been preternaturally small.
The service which the author imagines is performed by the runscular coats of arteries, is that of adapting their capacities to the varying quantity of the blood contained in them.
According to this statement, the qualities of the pulse, as discernible to the touch, are ascribed almost entirely to the action of the heart.
The duration from the natural state may consist either in a change of the heart or of the capacity of the. smaller arteries. The quantity of blood transmitted may also remain the same, or be diminished, or be increased. When it remains the same, the change cannot be very material, and is not likely to lead to any disease of the vital functions. When the quantity transmitted is smaller than in health, the arteries must become contracted, and the veins distended. The pulse must be small and weak, until the blood accumulated in the veins stimulates the heart to greater action. From the vigour acquired during the former remission of its exertion, the pulse becomes full and strong, a greater quantity of blood being transmitted than in health, as seems to occur in the hot fit of fevers.
A relaxation of the extreme arteries may, at the same time, suffer the blood to pass more easily into the veins; but such a relaxation may be carried to excess, and the arteries be thereby emptied; so that the pulse becomes small and weak, and the heart exhausted by fruitless efforts to restore the equilibrium, as appears to occur in typhus.
As general derangements of the circulation appear to be concerned in different kinds of fever, so partial ones have a similar relation to local inflammations. The most obvious changes arise from partial dilatations or contractions of the capillary arteries. Distension will be accompanied with redness, pain, and heat. But it is possible that another species of inflammation may also arise from an obstruction of the extreme capillary arteries; so that the small branches are subjected to a pressure many times greater than that which they are intended to withstand in their natural state, and the consequent distension will be accompanied with redness and pain.
Besides these general illustrations of the nature of fevers and inflammations, the author is of opinion that the same theory may be of use in explaining the operation of remedies employed for relieving them, more especially (in the different modes of letting blood), the more speedy and efi'ectual relief from opening an artery than a vein, and the great benefit often derived from the more practicable expedient of withdrawing a small quantity of blood from the immediate neighbourhood of the part affected, by cupping or by leeches.
