once; and thus has been fixed in the best--that is to say, the safest place. Of course you know what is meant by the backbone or spine, called also the vertebral column, in consequence of its being made like a sort of column composed of a series of small bones fastened together, which are named vertebra. Touch it and feel how solid it is, and how few dangers there can be for anything placed behind it. Well, that is the rampart which has been given to the Aorta. As this descends, it slips behind the heart and takes up its place in front of the vertebral column which it follows all the way down the back, just to the top of the loins. There it is, so to speak, almost unassailable; in fact hardly, any cases are known of the Aorta being wounded; to get at it, it would be necessary to bestow one of those blows which used to be given in the time of the Crusades, which cut the body in two. There was an end of the Aorta, as of every thing else then; it was unfortunately not worth talking about any longer!

The next time you see a fish on the table, ask to be shown the large central bone. It is the fish's vertebral column, and it will give you an idea of your own, for it is constructed on the same plan. You will perceive a blackish thread running all along it-that is the aorta.

As it descends, the aorta sends off on its passage a great number of arteries which carry the blood into all parts of the body. Arrived at the loins it forms a fork; dividing into two great branches, which continue their descent, one on each side the body, down to the very extremities of the two feet.

As you perceive, dear child, this is not very difficult to remember. A large fork, whose two points are at the tips of the feet, the handle of which curves at the top like the crook of a crozier; from this curve come four

branches, which pass into the two arms and to the two sides of the head-and this is the whole story. But of course, it would be another affair were I to enter into the detail of all the ramifications. Here it is that all engineers, past, present, and future, are baffled, defeated and outdone! Choose any place you please upon your body, and run the finest needle you can find into it what will issue from the puncture?

"Thanks for the proposal," you say; "I have no oc casion to try the experiment, to discover that blood will come out."

You say that very readily, young lady; but have you ever asked yourself, what is implied by your being so sure before hand that you can bring blood from any part of your body if you choose to prick it, though never so slightly? It implies that there is not on your whole frame a spot the size of a needle's point, which has not its own little canal filled with blood; for if there were such a one, there at any rate the needle would pass in without tearing the canal, and causing the blood to flow out. And now count the number of places from the top to the bottom of your dear little self, on which one could put the point of a needle, and even when you have counted them all, do not fancy you have arrived at the number of the tiny tubes of blood. Compared to these, your needle is a coarse stake, and tears not one but a thousand of these little tubes in its passage.

That seems to you rather a strong expression, does it not? But let me make good my boldness. A needle's point is very fine, I admit; but a person who could not see it without spectacles must have very poor sight. Whereas the last subdivisions of the blood-tubes are sc attenuated, that the best eyes in the world, your own included, cannot distinguish them. You are astonished

at this, and yet it is nothing compared to what fol lows.

No doubt you have heard of the microscope, that wonderful instrument by which you may see objects a thousand a hundred thousand, a million times, if neces sary, larger than they really are. With the microscope, therefore, as a matter of course, we can see a good many of those tiny canals which elude our unaided sight. But, alas! we discover at the same time that these are by no means the last subdivisions. The canals invisible to our naked eyes subdivide themselves again into others, and these into others again, and so it goes on, till at last—the man at the microscope can see no more, but the subdivisions still continue.

You were ready to exclaim, at my talking of thousands of canals being torn by a needle in passing through; but had I even said millions, it may be doubted whether I should have spoken the whole truth.

Besides, when you consider the office of the blood, you can easily understand that if there were a single atom of the body left unvisited by him, that atom could never be nourished. Do I say nourished? I have made here a supposition altogether inadmissible; it could have no existence at all, since it is the blood only which produces it.

These imperceptible canals of blood have been called capillaries, from the Latin word, capillus, which means a hair; because the old learned men, who had no suspicion of the wonders hereafter to be revealed by the microscope, could think of no better way of expressing their delicacy, than by comparing them to hairs. Very likely they thought even this a great compliment, but your delicate fair hairs, fine as they are, are absolute cablesand coarse cables too, believe me, compared to the ca

pillary vessels which extend to every portion of your body.

Observe further, that each of these arterial capillaries is necessarily composed (being the continuation of the large ones) of three coats enclosed one within the other, which can be perfectly distinguished in arteries of a tolerable size; add to this that within these coats there is blood, and in the blood some thirty substances we know of, not to speak of those we do not know; and then you will begin to form some notion of the marvels collected together in each poor little morsel of your body, however minute a one you may picture to yourself.

LETTER XV.

THE NOURISHMENT OF THE ORGANS.

WHEN I said formerly that our dear and wonderful steward the blood, was everywhere at once, you little suspected the prodigies involved in that everywhere. But you will have a glimpse of them now, when I tell you it is at the extremities of the capillary arteries that he carries on his distribution of goods, and accomplishes a mysterious act of nutrition; a wonder much greater even than that of which we have just spoken. Here, indeed, the question is no longer mechanical divisions, whose delicacy, surprising as it may be, is yet within our powers of comprehension. What is more surprising still, what moreover we cannot comprehend at all, is the delicate sensitiveness of tact-I would almost say of instinct-with which each one of the million millions of tiny atoms of which our body is composed, draws out of the blood-the common food of all-exactly that aliment which is necessary to it, leaving the rest to his neighbor, and this without ever making a mistake.

You have never thought about this; for children go on living at their ease, as if it was the simplest thing in the world to do; never suspecting even that their life is a continued miracle, and never, of course, therefore, feeling bound to be grateful to the Author of that miracle. And alas! how many hundreds of people live and die children in that respect.