recalling to your recollection houses, in which water is carried up, by means of pumps and other machinery, to every room in the house, even to the highest story, and to the remotest chambers.

The truth here, as almost always happens, falls between the extremes. The heart really pushes the blood with considerable force; and the muscular capillaries, at the same time, act in some slight degree like little pumps. Then the vacuum I have spoken of has some influence; and there may be other causes in operation which I have not mentioned. The whole process of circulation is wonderful, and it requires a volume to illustrate and explain it fully.

Popular Summary of the Process of the Circulation of the Blood.—I will here insert an eloquent description of the circulation of the blood, extracted from that useful and popular periodical the Saturday Magazine, a work which blends sound instruction with forcible lessons of piety. Though this will involve a repetition of some parts of the same subject, yet its importance is so great, that the time bestowed on the perusal will be amply repaid.

'The heart, which is the principal organ of circulation, is placed within the breast, between the two lobes of the lungs. It is a fleshy substance, and has two cavities, which are separated from each other by a valve. From the left ventricle, a large blood-vessel, called the aorta, proceeds, and soon divides into several branches, which ascend and descend by innumerable ramifications, become smaller as they proceed, and penetrate every part of the body. When the right ventricle contracts, the blood is propelled into the arteries with so much force, that it reaches the

minutest extremities of their most remote ramifications. This motion is called the pulse, which is merely the effect of the pulsation of the heart, and is quicker or slower according to the frequency of its contractions.

'When the blood arrives at the extremities of the arteries distributed through the body, Nature employs it in the wisest manner. Certain vessels absorb the watery, oily, and saline parts. In some parts of the body, where the arteries are distributed, the secretion of milk, fat, and various fluids is performed: the remaining portion of blood flows into the extremities of the veins. These vessels gradually enlarge in size, till they form very large tubes, which return the blood back to the right ventricle of the heart. The blood is then propelled into the pulmonary artery, which disperses it through the lungs by innumerable small branches. It is there exposed to the action of the air, is afterwards received by the pulmonary veins, and by them is conveyed to the left auricle of the heart. This contracts, and sends it into the left ventricle, which, also contracting, pushes it into the aorta, whence it circulates through every part of the body.

'For this complicated function, four cavities, as we have seen, become necessary, and four are accordingly provided: two called ventricles, which send out the blood, (one into the lungs in the first instance, the other into the mass after it has returned from the lungs): two others, called auricles, which receive the blood from the veins (one as it comes immediately from the body, the other as the same blood comes a second time, after its circulation through the lungs,

for without the lungs one of each would have been sufficient).

'Such is the admirable circulation of the blood in man and most animals. But there is still much obscurity in this interesting subject. We meet with wonders here, that prove how incapable the human mind is of explaining this work of Divine wisdom. "The wisdom of the Creator," saith Hamburgher, "is in nothing seen more gloriously than the heart;" and how well doth it execute its office! An anatomist, who understood the structure of the heart, might say beforehand, that it would play; but he would expect, I think, from the complexity of its mechanism, and the delicacy of many of its parts, that it would always be liable to derangement, or that it would soon work itself out. Yet shall this wonderful machine go night and day for eighty years together, at the rate of one hundred thousand strokes every twenty-four hours, having at each stroke a great resistance to overcome; and shall continue this action for this length of time, without disorder and without weariness!

'From KEILL's Anatomy, we learn that each ventricle will contain at least one ounce of blood. The heart contracts four thousand times in one hour, from which it follows that there pass through the heart every hour, four thousand ounces, or three hundred and fifty pounds of blood. The entire weight of blood is said to be about twenty-five pounds, so that a quantity equal to the whole mass of blood passes through the heart fourteen times in one hour, which is about once in every four minutes.

""Consider," says PALEY, "what an affair this is, when we come to very large animals. The aorta of a

whale is larger in the bore than the main pipe of some waterworks, and the water roaring in its passage through a pipe of that description, is inferior, in impetus and velocity, to the blood gushing from the whale's heart." Dr. HUNTER, in his account of the dissection of a whale, says, "The aorta measured a foot diameter. Ten or fifteen gallons of blood are thrown out of the heart at a stroke, with an immense velocity, through a tube of a foot diameter. The whole idea fills the mind with wonder."

'The account here given will not convey to a reader ignorant of anatomy, anything like an accurate notion of the form, action, or uses of the organs concerned in the circulation of the blood (nor can any short and popular account do this): but it is abundantly sufficient to give him some idea of the wonderful mechanism bestowed on his frame, for the continuance of life, by the hand of a Being who is all-wise, all-powerful, and all-good, and whose bountiful care is equally extended to the preservation and happiness of the humblest creature in existence, which has been, equally with ourselves, called into life at his Divine behest, and for a wise and good purpose.'

We are no v prepared to enter upon another subject— the study of the process by which the purity of the blood is promoted, notwithstanding the many causes

M

· which are continually in operation, to render it unfitted

for its purpose. Purification of the Blood.-This is effected by the aid of atmospheric air. But how is air to be introduced into the human body? Can we eat it? Can we drink it? Can it enter by means of the eyes, or the ears, or the nose? Not exactly in either of these ways. It can, indeed, enter through the nose, but, without some other machinery, it would go no further than the throat, before it would return, or pass out at the mouth: a little, it is true, is swallowed, both in our food and in is very way our drink; but the quantity in this incon

siderable.

There is air, moreover, in almost every part of the body; all the great cavities—the chest, the abdomen, &c.-contain air; were it not thus, we should soon be crushed. The atmosphere in which we live presses upon the whole frame with a tremendous force, comeach square puted at about fifteen pounds' weight upon inch of the body; and its entire pressure on a middlingsized man is estimated at about thirty-two thousand pounds. But as there is air within us, in almost every part, both solids and fluids, which forces outwardly, while the atmosphere keeps up a pressure in the opposite direction, we are not sensible of its weight.

But when I said that the blood must be purified through the agency of the air, I meant in a manner much more rapid and effectual than could be done by its gradual introduction and circulation through the vessels. The manner in which this great change is effected I will now explain.

The Lungs.-The House I live in contains a curious apparatus, which may be compared to a great bellows