furrowed, to allow these important tubes to pass along in safety; and in the fingers, which are liable to so many casualties, the bones are hollowed out on the inside like a scoop. Along this channel the artery runs in such security, that you might cut your finger across to the bone, without doing it any injury"

"I am sure" said Harry, "that is a great proof of care, where care was very much wanted; for you must allow, papa, that people are apt to cut their fingers."

"Much more so than to dislocate their shoulders, I grant, Harry. But the care of the Artificer is not greater than the importance of these vessels requires. It has often been said of persons who venture their lives in a ship, that there is only an inch-board between them and death; but in our bodies, especially in the arterial system, there is, in many parts, only a membrane, a skin, a thread. The arteries are, therefore, deeply seated; while the veins, which may be wounded with much less danger, lie above the arteries, come nearer to the surface, and are more exposed. Here is a proof of care and contrivance, that cannot be disputed or denied."

"You have made it very plain to me, papa: I quite understand what you have said about veins and arteries."

"Well then," replied his father, "I will endeavour to give you some notion of the engine that works this curious machinery; that is, the heart."

"I can feel mine beating, and I have often seen

the hearts of different animals. We had a calf's heart for dinner yesterday."

"Then you probably observed that the heart is not a solid lump of flesh, but contains several cavities."

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I perfectly remember the appearance of the slice I had. There was a layer of flesh on the outside, and the hollow within was full of stuffing."

"Very well," replied Mr. Beaufoy: "it is on this hollowness of structure that the action of the heart depends. Like other muscles, it has the power of contracting; and when it contracts, the sides of its cavities are squeezed together, so as to press out any fluid the heart may at that moment contain. This purpose being effected, the fibres relax, the heart once more becomes hollow, and, as it dilates, the blood pours into the cavities from the large vein which brings it back to the heart. The next contraction forces the blood into the arteries; the quantity thus impelled being always equal to that which has just been received. And thus this wonderful organ goes on alternately contracting and dilating itself four thousand times in an hour! Month after month, year after year, it goes on without weariness or interruption, conveying renewed strength to every part of the body.

"I am sure I wonder that the heart is not tired it seems to work harder than any thing else."

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:

'Only think what this engine has to perform

in large animals! The opening through which the blood rushes from the heart into the arteries of a whale, is larger than the main pipe of the New River water-works at London; and the water roaring in that pipe, passes through it with less force and swiftness than the blood gushes from the whale's heart, which throws out ten or fifteen gallons of blood at every contraction, through a tube of a foot diameter !"

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"That is astonishing, indeed!" said Harry; "but I think it is more curious to see the same operation going on in the arteries of a tadpole. How very small its little heart must be; yet it performs its work as well as that of the whale." Certainly," replied his father; " and the skill of the Artist is equally admirable in both cases, because exactly adapted to the end in view. Some persons will be more struck by the grandeur of vast designs, others by the perfection of minute objects. But do you understand the account I have given you of the heart?"

"Not quite, papa: since the contraction of the heart squeezes the blood into the arteries, I do not see why, when it dilates again, the blood should not run back into the hollow."

"I have shown you the construction of a pump, and how, by the alternate opening and shutting of the valves, the water is enabled to rise, and prevented from running back again."

"Oh, yes! I remember those little doors, or valves, as you called them, in the pump; but has the heart any contrivance of that kind?"

"Yes; the heart can no more work without valves than the pump can. To prevent the inconvenience you have mentioned, valves are placed at the mouth of each of the great arteries which receive the blood from the heart. These valves, like flood-gates, leave the passage free while the stream flows forward, but close it whenever the blood, in consequence of the dilation of the heart, would attempt to run back. Can any contrivance be more strictly mechanical ?"

"No, papa and I see very plainly that after all, we must be content to call ourselves machines."

"And no disgrace to us either," replied his father: "surely we have abundant reason for gratitude, when we see our health and safety the objects of such minute and anxious care! The heart, on the unceasing action of which so much depends, has been guarded with peculiar solicitude it is not only placed within the shelter of the ribs, and defended by their bony arch from external injury; but it is enclosed in a tough, strong bag, which sits loosely and easily about it, guarding its substance without confining its motion, and containing a small quantity of water, just sufficient to keep the surface of the heart continually moist and supple. This bag answers no other purpose, and strikingly shows the care that has been taken of an organ so important.'

"I had not the smallest idea of this care, papa; and I wish I could know more about the circulation of the blood, it is so very curious."

"The account I have just given you," said Mr. Beaufoy, "is true so far as it goes, but it is imperfect. I have taken no notice of another important office which the heart has to perform; an office absolutely essential to the preservation of life."

"Is there more work still for the heart?" exclaimed Harry, with surprise: "I think what you have already told me is astonishing."

"So it is; but something yet remains to be effected. It is requisite for the blood to be continually brought into such a situation, as to receive, from the air, some quality or principle which is necessary to the support of animal life. This important office is also intrusted to the heart."

"How can that be, papa? Shut up, as it is, in the middle of the body, and secured in a tough bag that will hold water, how can the heart have any communication with the air?

"By means of the lungs; but as the lungs are themselves enclosed in the cavity of the chest, perhaps you may like to know how the air enters them. I dare say you perfectly recollect the uncomfortable sensation arising from a crumb, or a small quantity of drink, going the wrong way."

"Yes, I know that miserable feeling very well, and how it makes one cough; but I do not understand the reason of such a disturbance.'

"You must know, then, that two pipes go down our throats; one called the gullet, is intended to convey the food into the stomach; the other,