The whole of the blood driven out by the left ventricle at each of its contractions, pa.s.ses into one large ca.n.a.l called the _aorta_. The _aorta_ as it goes away at first ascends; then bends back in a curve; and from this curve, which is called the _arch of the aorta_ (from its shape) diverge right and left, certain branch-pipes which carry the blood into the two arms and on each side of the head; and which are, in fact, the beginning, or upper end, of those whose pulsations we feel with our fingers in the two wrists and at the temples.

The supply to the upper part of the body being secured, the _aorta_ begins to descend. But now imagine of what importance it must be, that this head-artery--the foster-father of the whole body--should be sheltered from every accident. The _aorta_ once divided, death is inevitable; you might as well have your head cut off at once; and thus it 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 _vertebrae_. 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 una.s.sailable; 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 pa.s.sage 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 pa.s.s 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 occasion 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 p.r.i.c.k 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 ca.n.a.l filled with blood; for if there were such a one, there at any rate the needle would pa.s.s in without tearing the ca.n.a.l, 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 coa.r.s.e stake, and tears not one but a thousand of these little tubes in its pa.s.sage.

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 so 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 follows.

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 necessary, larger than they really are. With the microscope, therefore, as a matter of course, we can see a good many of those tiny ca.n.a.ls which elude our unaided sight. But, alas! we discover at the same time that these are by no means the last subdivisions. The ca.n.a.ls 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 ca.n.a.ls being torn by a needle in pa.s.sing 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 ca.n.a.ls 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 cables--and coa.r.s.e cables too, believe me, compared to the _capillary 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.

But what would happen, I should like to know, if the eye took to seizing upon the food of the nail, if the hairs stopped on the way what was intended for the muscles, if the tongue absorbed what ought to go to the teeth, and the teeth what ought to go to the tongue! Yet what prevents their doing so? Can you tell me? They all drink alike out of the same cup. The same blood goes to furnish them all. The substances that it brings to the eye are the same as those which it brings to the nail; and nevertheless the eye takes from it that which makes an eye, and the nail that which makes a nail.

How is this done, do you think? that is the question.

When the doctors reply to this, that each organ has its peculiar sensibility, which makes it recognize and imbibe from the blood one particular substance and no other, they are strangely mistaken if they flatter themselves that they have really answered anything. They have done nothing but reproduce the question in other words, for it is precisely that sensibility which requires explanation, and to tell us that it exists, does not explain much, you must own. If you were to ask why you had got a headache, and some one were to reply that it was because your head ached, you would not be much the wiser I fancy.

Each of our organs, then, may be considered as a distinct being, having its separate life, and its particular likings. These organs behave towards the blood like men who recognize some friend in a crowd, and proceed to seize him by the arm; and when I told you just now that they never made a mistake, I spoke of their regular course of action in ordinary circ.u.mstances. Like men, they also make mistakes sometimes, in certain cases; and take one substance for another, or do not recognize the one they are in need of; an unanswerable proof that at other times they exercise a sort of discernment, and do not act by a sort of fatality, as one might be tempted to believe. Look at the bones, for instance. They are composed of _gelatine_ (which cooks serve up under the name of meat-jelly, but which would be more properly called bone-jelly), and of phosphate of lime, a kind of stone of which we have spoken before, if I remember rightly, and from which they get all their solidity. Originally, the substance of the bone is entirely gelatinous, and the phosphate of lime deposits itself therein by degrees, as time goes on, and always in greater abundance as we advance in age.

Properly the bones borrow only gelatine and phosphate of lime from the blood. But when they come to be broken, their texture or _tissue_ inflames in the fractured place; and then it changes its tastes, if I may so express myself; and, lo and behold, extracts from the blood that which forms certain little fleshy shoots, which unite together from the two sides of the fracture, and so mend the broken bone. Here is one exception to the rule.

Again, in certain diseases, the bones suddenly quarrel with the phosphate of lime; they will not hear of it any longer, they will not accept a fresh supply; and as the old wears out by degrees, by reason of the continual destruction of which I spoke the other day, the bones become more and more enfeebled, and soon can no longer support the body. A second exception this.

Finally, when old age comes on, the bones end by being so much enc.u.mbered with phosphate of lime, that they have no room to admit the fresh supply which keeps coming to them in the blood. What becomes of it then? It goes to seek its fortune elsewhere; and there are charitable souls, who forgetting their instinctive antipathies, consent to give it hospitality, though much to the prejudice of the poor old man himself, who is no longer served so well as formerly, by the incautious servants who have allowed themselves to be thus fatally beguiled; but no one consults him. It is the arteries especially, and sometimes the muscles, which take this great liberty, and it is not unusual among old people to meet with these fairly _ossified_--that is to say, changed into bone, thanks to the phosphate of lime with which they have consented to burden themselves. This is a third exception, and I will spare you any others.

What may we infer from all this, my dear child? Well, two things.

First, that we know nothing at all about the whole affair; a fact which at once places us on a footing with the most learned philosophers in the world. Secondly, that our body is a perpetual miracle; a miracle which eats and drinks and walks, and which we must not look down upon for so doing: for G.o.d dwells therein. I should have to come back to this at every turn, if I wanted to fathom everything I have to tell you about. Each tip of hair which you grow, is an incomprehensible prodigy which would puzzle us for ever, if we did not call to our aid those eternal laws which have made us what we are, and to which it is very just our spirits should submit, since we could not exist for one second were they to cease from making themselves obeyed in our bodies.

Reflect on this, my dear little pupil. Young as you may be, you can already understand from it, that there is above you something which demands your respect. The good G.o.d, to whom your mother makes you pray every night, on your knees, with folded hands, is not so far off as you might perhaps suppose. He is not a being of the fancy, secluded in the depths of that unknown s.p.a.ce which men call Heaven, in order to give it a name. If His all-powerful hand reaches thus into the innermost recesses of your body, His voice speaks also in your heart, and to what it says you must listen.

LETTER XVI.

THE ORGANS.

Contrary to my custom, my dear child, I made use, in the last chapter, of a new word, without giving an explanation of it.

I spoke to you of _our organs_, and we have not yet ascertained what an _organ_ is.

You probably knew what I meant, because it is a word which is used in conversation and pretty well understood by everybody. But I am bent upon giving you a more exact idea of it, for the trouble will be well bestowed. If I did not do this at once it was because there is a good deal to tell about, and that would have carried me too far away from my subject.

_Organ_, comes from the Greek word _organon_, and means _instrument_. It was used particularly to signify instruments of music, so much so that our word "organ" comes from it. Our bodily organs then, are _instruments_, or _tools_ if you like it better, which have been given to us, wherewith to perform all the acts of life; and as there is not one part of the body which is not of use to us for some purpose or other, our body is, in point of fact, from head to foot a compound of _organs_. Thus the hand is the tool which we make use of to lay hold of anything--so an _organ_; the eye is the instrument of sight--so an _organ_; the heart is the machine which causes the blood to circulate--so an organ; the liver fabricates the bile--it is an organ therefore; the bones are the framework which support the weight of the body--so organs; the muscles are the power which sets the bones in movement--organs also, therefore; the skin is the armor which protects them--so an organ: in fact everything within us is an organ. If there was any corner of our body which was not an organ, it would be useless to us, and we should not, therefore, have received it, because G.o.d makes nothing without a use.

Here lies the secret of that great miracle which is called life. I do not know whether you will be able to understand me thoroughly, but open your ears, as if some one was going to explain addition to you; this is not more difficult.

Life is in reality the total of an addition sum. Each one of our organs is a distinct being which has its particular nature and special office; its separate life consequently; and our individual life is the sum total of all these lesser lives, independent one of the other, but which nevertheless blend together by a mysterious combination, into one common life, which is everywhere and nowhere at the same time. It follows from this, that the more organs a being has, the greater is the sum total; the more, consequently, is life developed in him.

Remember this when we begin to study life in the lower animals. In proportion as you find the number of _organs_ diminish, you will find life diminishing in power, until we arrive at beings who have, as it were, only one organ apparent, and whose life is so insignificant, that we have some difficulty in giving an account of it, and are saying the utmost that can be said in calling it life at all.

But this comparison of life to the total of an addition sum, is too dry; and, although it has its appropriate side, yet it might give you a false idea of life; which is what always happens when one tries to solve inscrutable questions and hidden mysteries by a matter-of-fact ill.u.s.tration.

Let us try for something more to the purpose.

I told you that the Greek word _organon_ was applied especially to instruments of music. Well, let us consider our organs as so many musical instruments. You have, probably, sometimes been at a concert.

Each of the instruments in the orchestra performs its own part, does it not? The little flute pipes through all its holes; the double-ba.s.s pours thunder from its chords: the violin sighs with his; the cymbals clash; the Chinese bells dance to their own tinkling; all go at it in their own fashion, each independently of the other. And yet, when the orchestra is in good tune together, and well played, you hear but one sound; and to you the result of all these various noises, each of which would have no meaning alone, is music composed by some great artist whom you do not see. It is no longer a flute, a double-ba.s.s, or a violin which you h.o.a.r; it is a symphony of Beethoven's, an oratorio of Haydn's, or Mozart's overture to _Don Juan_.

Life is just like this. All the instruments are playing together, and there is but one music; music written by G.o.d.

But wait! when I say _life is just like this_, let us come to an understanding. Life is _some_thing like it, that is all, for as to telling you what life is, I shall not attempt it. I know nothing about it, do you see, though that is a painful confession to have to make to a pupil; but in this case it does not distress me, and you are welcome to hunt the world through for a master, who in this matter does know anything. I could make a hundred other comparisons, but theywould all fail in some point or other. Shall I tell you where this one fails? In an orchestra there is always a musician by the side of the instrument. Now with us we see the instrument well enough, but we cannot see the musician.

You are inclined to ask me, perhaps, why I am wasting so much paper to-day in talking to you about organs, instead of going on tranquilly with our little history of the circulation. But I told you just now that the secret of life lies in the organs, and before entering upon the history of life, I ought to have begun with them. It is there all the books begin which treat of the subject we are studying together, and if you had one in your hands at this moment, it would teach you that all creatures whatsoever are divided into those which have organs and those which have none--that is, into _organic_ and _inorganic_ beings [Footnote: A lump of iron is the same throughout. Each of its parts has the same properties and the same uses. It has no organs, it is an _inorganic_ being. A rose tree has flowers, which are differently made from its leaves, and serve a different use: a root which sucks up the precious food of the earth; a bark which is of a different nature from the wood, and serves a different purpose. It has organs; it is an _organic being_: all animals and vegetables are _organic beings_.] (_in_ stands here for _not_, as _in_complete means not complete).

This is, in fact, the starting point for the study of nature, and there are many other things besides which I ought to have told you before I began. But we went straight ahead, without looking at what we were leaving behind, satisfied with turning aside from time to time to pay our debts.

And while I am making my confession, I ought to tell you all. You would probably only have listened to me with half an ear, if I had begun at the beginning. There is a proverb which says--"The appet.i.te comes with eating." I do not advise you to follow this proverb too closely at dinner, for it might mislead you sadly. But it is always true when applied to learning; it is what one knows already that gives one a taste for learning more. If I have been making you bite at the organs to-day, which is rather a tough morsel, it was because I fancied that your appet.i.te had begun to come. Was I wrong?

Let us now return to the blood which nourishes the organs.

LETTER XVII.