APPENDIX.

A.

THE learned Archdeacon Paley speaks of the tongue thus. The variety, quickness, and precision, of which muscular motion is capable, are seen, I think in no part, so remarkably as in the tongue. It is worth any man's while to watch the agility of his tongue; the wonderful promptitude with which it executes changes of position, and the perfect exactness. Each syllable of articulated sound requires for its utterance a specification of the tongue, and of the parts adjacent to it. The disposition and configuration of the mouth, appertaining to every letter and word, is not only peculiar, but if nicely and accurately attended to, perceptible to the sight, insomuch that curious persons have availed themselves of this circumstance to teach the deaf to speak and to understand what is said by others; in the same person, and after his habit of speaking is formed, one and only ore, position of the parts will produce a given articulate sound correctly. How instantaneously are these positions assumed and dismissed, how numerous are the permutations, how various, yet how infallible! The muscles of the tongue are so numerous and so implicated with one another, that they cannot be traced by the nicest dissection; nevertheless, which is a great perfection of the organ, neither the number, nor the complexity, nor what might seem the entanglement of its fibres, in any wise impede its motion, or render the determination or success of its efforts uncertain."

B.

On the circulation of the blood he observes, 'This system presents itself under two views: first the disposition of the blood vessels, i. e. the laying of the pipes; and, secondly, the construction of the engine at the centre, viz. the heart, for driving the blood through them.

1. The disposition of the blood vessels, as far as regards the supply of the body, is like that of water-pipes in a city, viz. large, and main trunks branching off by smaller pipes, and these again by still narrower tubes, in every direction, and towards

every part in which the fluid, which they convey, can be wanted. -So far, the water pipes, which serve a town, may represent the vessels which carry the blood from the heart. But there is another thing necessary to the blood, which is not wanted for the water, and that is, the carrying of it back again to its source; for this office a reserved system of vessels is prepared, which uniting at their extremities, with the extremities of the first system, collects the divided and subdivided streamlets, first by capillary ramifications into larger branches, secondly by these branches into trunks, and thus returns the blood, (almost exactly inverting the order in which it went out,) to the fountain whence its motion proceeded.

The body, therefore, contains two systems of blood vessels, arteries and veins. Between the constitution of the systems, there are also two differences suited to the functions which the systems have to execute. The blood in going out, passing always from wider into narrower tubes, and in coming back from narrower into wider, it is evident that the impulse and pressure upon the sides of the blood vessels will be much greater in one case than the other. Accordingly the arteries, which carry out the blood, are formed with much tougher and stronger coats than the veins which bring it back. That is one difference; the other is still more artificial, or, if I may so speak, indicates still more clearly the care and anxiety of the artificer. Forasmuch as in

the arteries, by reason of the greater force with which the blood is urged along them, a wound or rupture would be more dangerous than in the veins, these vessels are defended from injury not only by the texture, but by their situation, and by every advantage of situation which can be given them; they are buried in sinuses, or they creep along groves made for them in the bones : for instance the under edge of the ribs is sloped and furrowed solely for the passage of these vessels. Sometimes they proceed in channels, protected by stout parapets on each side, which last is remarkable in the bones of the fingers, these being hollowed out on the under side like a scoop, and with such a concavity that the finger may be cut across to the bone, without hurting the artery which runs along it; at other times the arteries pass in canals wrought in the substance, and in the very middle of the substance of the bone; this takes place in the lower jaw, and is found where there would, otherwise, be danger of compression from sudden curvature. All this care is wonderful, yet not more than

what the nature of the case required. Because of its importance this system lies deep under the integuments, whereas the veins in which the mischief that ensues from injuring the coats is much less, lie in general above the arteries; come nearer to the surface; are more exposed.

2. The next thing to be considered is the engine which works this machinery, viz. the heart. Whatever be the cause, there is a something which causes, in the heart, reciprocal contraction and relaxation. This is the power we have to work with, and the inquiry is, how this power is applied to the instance before us. There is provided in the central part of the body, a hollow muscle, invested with spiral fibres, running in both directions, the layers intersecting one another; by the contraction of these fibres the sides of the muscular cavities are necessarily squeezed together, so as to force out from them any fluid which they may at that time contain; by the relaxation of the same fibres the cavities are in their turn dilated, and, of course, prepared to admit every fluid which may be poured into them. Into these cavities are inserted the great trunks, both of the arteries which carry out the blood, and of the veins which bring it back. This is a general account of the apparatus, and the simplest idea of its action is, that by each contraction a portion of blood is forced into the arteries, and at each dilation an equal portion is received from the veins, this produces at each pulse, a motion and change in the mass of blood, to the amount of what the cavity contains, which in a full grown human heart, I understand, is about an ounce or two table-spoons full. How quickly these changes succeed one another, and by this succession how sufficient they are to support a stream or circulation throughout the system, may be understood by the following computation, abridged from Keill's Anatomy: 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 passes through the heart, every hour, four thousand ounces, or three hundred and fifty pounds of blood. Now the whole mass of blood is said to be about twenty-five pounds, so that a quantity of blood equal to the whole mass of blood passes through the heart fourteen times in one hour; which is about once every four minutes. Consider 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 the water-works at London-bridge; and the water roaring in its

passage through that pipe is inferior, in impetus and velocity, to the blood gushing from the whale's heart.' Hear Dr. Hunter's account of the dissection of a whale. The aorta measured a foot diameter. Ten or fifteen gallons of blood is 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.'But, continues our author on the circulation of the blood in human beings.-'As soon as the blood is received by the heart from the veins of the body, and before that it is sent out again into its arteries, it is carried, by the force of the contraction of the heart, and by means of a separate and supplementary artery, to the luugs, (viz. to be purified by the action of the atmospheric air,) and made to enter the blood vessels of the lungs, from which, concocted and prepared, it is brought back by a large vein once more to the heart, to be from thence distributed anew through the system.This assigns to the heart a double office, for which four cavities become necessary, and four are accordingly provided; two called ventricles, which send out the blood, viz.; one into the lungs, in the first instance; the other into the mass, after it has returned from the lungs; two others also, called auricles, which receive the blood from the veins, viz. one as it comes immediately from the body, the other as the same blood comes a second time after its circulation through the lungs. So that there are two receiving cavities, and two forcing cavities. The structure of the heart has reference to the lungs, for without the lungs one of each would have been sufficient. The translation of the blood in the heart itself, is after this manner. The receiving cavities respectively communicate with the forcing cavities, and, by their contraction, unload the received blood into them. The forcing cavities, when it is their turn to contract, compel the same blood into the mouths of the arteries.'

But further, from the accouut which has been given of the mechanism of the heart, it is evident that it must require the interposition of valves; that the success, indeed, of its action must depend upon these, for, when any one of its cavities contracts, the necessary tendency of the force will be to drive the enclosed blood, not only into the mouth of the artery where it ought to go, but also back again into the mouth of the vein from whence it flowed. In like manner, when by the relaxation of the fibres the same cavity is dilated, the blood would not only run into it from the vein, which was the course intended, but back from the artery