The History of a Mouthful of Bread Part 22

At the same time were we to review the birds in detail, as we have done the mammals, you would see that there are almost more modifications to be observed in this one single instrument than in our thirty-two teeth. All birds have a beak, but each has his own, organized expressly with reference to the kind of food needed by its owner. The eagle's beak, which mangles living prey, is pointed, bent, and hard as steel; the bill of the duck, which laps up water from ponds and puddles, in order to get worms and half-decomposed refuse out of it, is soft, and flattened like a shovel. The woodp.e.c.k.e.r's, which has to pierce the trunks of trees, is like a pickaxe; that of the humming-bird, which has to suck up the juice of flowers from the bottom of their corollas, is slender as a needle. The swallow feeds on flies, which it snaps up on the wing, and has a soft bill, which opens like a little oven. The stork picks up reptiles in the mud of the marshes; its beak is straight-pointed, cutting as a knife, and resembles a long pair of pincers. The sparrow feeds especially on hard grains, difficult to break; accordingly its beak is stumpy, short, and thick, and is arched on the upper side for still further solidity. But I should never end if I began to enumerate all the thousand varieties in the bills of birds. Each variety, too, corresponds with some peculiar sort of life, and consequently with a general conformation (easily ascertained) of the animal in which it appears. Give a naturalist the bill of a bird--only its bill remember--and he will tell you half its history without fear of being mistaken.

On the other hand, we must not deceive ourselves as to the real value of this complaisant bill. Let it transform itself as it pleases into all manner of forms for the better fulfilment of its task, it makes, at the best, but a very poor instrument for mastication; nay, to say the truth, it breaks, cuts, and tears, but it never masticates at all.

Thus the bird's mouthful is far from undergoing as perfect a preparation as ours does. It is no sooner taken in than it is swallowed, and the salivary glands, which are still to be found under the tongue, seem only to be there as a matter of form; what little saliva they produce is thick and sticky, and has none of the qualities necessary for making that liquid paste which our tongue sweeps up from every corner of the mouth. Besides, it must be owned that a bird's tongue would be a very awkward implement in such a task. Open a hen's bill and you will see therein a very inferior sort of porter. It is merely a dry hard lance, as it were, armed with p.r.i.c.kles at the point, as ill-qualified for tasting as for sweeping. So the hen does not waste her time in finding out the flavor of what is thrown to her. She picks up and swallows over and over again, without appearing to experience any other pleasure than that of satisfying her appet.i.te. Birds of prey, it is true, have rather more convenient tongues, capable, moreover, of tasting up to a certain point; and the parrot, who is a complete epicure, and chews his food philosophically, has a charming-little black one, thick, fleshy, and susceptible--a true porter, in fact-who enables Polly thoroughly to enjoy her breakfast. But certain birds who live on insects surpa.s.s even the hen in the dryness and hardness of their tongues.

That of the woodp.e.c.k.e.r, especially, is a model of the kind, and deserves a few words more than the others. Picture to yourselves a long pin, terminated by an iron point with barbs like those of fish-hooks. An ingenious mechanism enables the bird to dart it out with the rapidity of lightning, far beyond his bill, upon the insects to which he gives chase. The point pierces them, and the hooks retain them, without any need of a.s.sistance from the bill. I have just told you that this bill pierces the bark of trees; but it only plays the part of gamekeepers on grand sporting occasions, who beat the bushes to make the game rise.

The woodp.e.c.k.e.r's bill routs up the insects by destroying their shelter; but the real sportsman is the tongue. Good-bye to any notion of a cosy little chat in such a porter's lodge as that! What could a harpoon have to say for itself?

Do not, however, let this miserable entrance-hall alarm you, at the same time, for the fate of the mouthful thus presented half-dressed to the ?sophagus. You will find it only so much the better treated within. In the first place, the ?sophagus, when half-way down to the stomach, swells out suddenly and forms a pocket, which is generally particularly well developed in birds who feed on grain; this is called the _crop_ in English, in French _jabot_; whence comes the application of that word to those full s.h.i.+rt-frills which have sometimes been the fas.h.i.+on. It is the pigeon's _crop_ that gives him the rounded chest over which he bridles so prettily. The crop is a receptacle where the food makes a halt: it is something between the pouch of the monkey and the paunch of the ox; a preparatory stomach, which does not, it is true, send back the grain to the bill, for the bill could do it no good, but in which that grain lies until there is room for it further on.

Prom thence it resumes its journey; but, before reaching the true stomach, it pa.s.ses through a second enlargement of the oesophagus, whose walls are pitted with numberless little cavities, from which pour over it the juices destined to supply the place of the saliva that was wanting above.

It reaches its destination at last, but still hard, and generally whole. No matter, however. The stomach which receives it, and which is called the gizzard, is quite a different sort of thing from a useless membrane, thin and delicate like ours. It is a thick muscle of enormous power, lined inside with a kind of h.o.r.n.y skin, so tough that nothing can break through it. You may form some idea of the prodigious strength of this organ, when I tell you that turkey-fowls have been made to swallow hollow b.a.l.l.s of gla.s.s, so thick as not to break when dropped to the ground, and that at the end of a few days they have been found reduced almost to powder in the uninjured stomach. No fear of indigestion with such an apparatus as that. Though the grain may not have been masticated in the bill, what does it signify? There is a power here, as you see, quite equal to carrying the whole work through.

Thanks, indeed, to the invaluable horn which lines it, fowls which have no teeth of their own can safely present themselves with as many and as hard ones as they please. They swallow small pebbles, which rub against the grain, during the contractions of the gizzard, and act just as effectually as if they were fixed in the jawbone. Well, this terrible gizzard performs its crus.h.i.+ng work with such energy, that not only the grain but the pebbles themselves are ground down there, and end by being pounded into fine sand. When you rear fowls, do not forget, if you keep them shut up, to put within their reach a store of small pebbles, so that they may have teeth to run to in time of need.

You remember the _pylorus_--the porter down below, who keeps the door of egress from our stomach? He is as badly provided for here as his fellow-workmen up above; worse in fact. It is a gaping hole, and we cannot expect a very strict supervision from it. Birds who feed on fruits profit by this fact to carry vegetables from one country to another. With such an easy opening, seeds have a good many chances of pa.s.sing from the stomach unaltered; and then they drop from the clouds, as is supposed, hap-hazard, and germinate afterwards, when circ.u.mstances prove favorable, to grow up before the astonished eyes of the natives into plants of which they have never even heard. The French Acclimatization Society, which I spoke of lately, and which, though so modern, has correspondents all over the globe, is at this moment laboring to effect an exchange between all countries of the natural productions of their soil. But here you see that nature had thought of this before, and established her acclimatization society long ago.

To complete the internal work of digestion, so feebly begun in the bill, an extremely large liver pours torrents of bile into the duodenum, and the manufacture of chyle proceeds with that wild rapidity which characterizes all the living actions of birds. But speaking of this liver, I think I ought to give you an account of a celebrated dish, considered a great dainty by epicures, called _pates de foies gras_--_fat liver patties_, to translate it into its meaning.

Very likely you will not care to eat them after hearing my story; but that will be no great loss to you, for it is a very indigestible sort of food, and not at all good for children.

You remember my telling you about Englishmen going to India and coming back with a liver-complaint, from having eaten and drunk more than the climate allowed? By an imitation of this process, human ingenuity--occasionally so cruel--has created the _pates de foies gras_, the glory of Strasburg. I have been in the country, and can tell you how it is managed. They shut a goose up in a square box, where there is just room for his body. They open his bill at feeding-time, and cram down with the finger as much food as can be got in. This is throttling rather than feeding it. The poor beast, who can use no resistance, since it cannot move, and who is kept in the dark to prevent excitement; the poor beast is quite unable to burn all the ma.s.s of combustibles with which the blood soon finds itself loaded. This carries them to the liver to be turned into bile; but the liver is not equal to the work, becomes loaded in its turn by unemployed materials, and grows and grows, till at last, having filled up all the s.p.a.ce around it, it stops the play of the heart and lungs. When the animal is nearly suffocated they kill it; and this is how we come to have _pates de foies gras_ to eat! If they give us a fit of indigestion afterwards, it is a vengeance we richly deserve. At Toulouse, where the same trade is carried on on a large scale, they used formerly to go even beyond this. They fastened the goose by the feet before the fire-place, after having put out its eyes. The imitation of the Englishman's proceeding was still more perfect here, for the fire acted the part of the Indian sun to perfection. I do not know that part of the country well enough to tell you whether they have quite given up this piece of wicked ingenuity; all I can say is, I devoutly hope so.

The intestine of birds is much shorter than that of mammals. Here everything is done at full gallop, and the chyle has not to go far before it is absorbed. I have before me a book, in which I am told that the wagtails eaten in France can be fattened in twenty-four hours, if you only know how to set about it, and these birds are not rare; they belong to the same family as the red-b.r.e.a.s.t.s, the tomt.i.ts, and the nightingale. Thrushes and wheatears (ortolans) require, for the same purpose, four or five days in the same country, left to themselves to roam about, when the vine keeps open table for them.

This incredible quickness, not only in digesting, but, what is much more, in transforming food into fresh living material (_a.s.similating_ it, as it is called), has often a fatal result for the bird. He is prohibited from fasting; his life is a fire of straw, which must be replenished unceasingly, or it will die out in the twinkling of an eye. Our own little birds--children--eat oftener than grown-up people, and if by any accident they are kept waiting awhile, they soon cry out with hunger. You know this, do you not? Well, then, if any one should give you a bird to keep in a cage, remember that you have undertaken a great responsibility, and that it will not do to be careless with him. To neglect feeding him for one day is to run the risk of finding him starved to death next morning. With this warning, I will conclude my chapter on birds. I hope I have not spoken in vain in behalf of those poor little captive songsters, whose fragile lives are at the mercy of their young masters and mistresses.

LETTER x.x.xV.

REPTILIA. (_Reptiles_.)

Pa.s.sing from birds to reptiles is like falling from a torrent into still water. Life drags on as sluggishly with the second as it dashes furiously forward with the first.

I spoke to you just now about a fire of straw: now we have a fire such as Frenchwomen make in their _chaufferettes_, or foot-stoves. A handful of charcoal-dust, and a few live embers between two layers of ashes, is enough for the whole day; which is economical, is it not?

but then it throws out only just warmth enough to keep one's feet comfortable. And so it is with reptiles. They live at very small expense. If you feed them once a month they will not complain, for so slow a fire does not often need replenis.h.i.+ng with combustibles. It is even said that the experiment has been carried so far with tortoises that they have been made to fast for more than a year, and still the charcoal fire kept up its languid pace. Of course, on the other hand, there is not nearly so much oxygen consumed at once upon such a diet as this. Where a bird would perish twenty times over in five minutes for want of oxygen, a lizard can remain whole hours with impunity.

Moreover, the animal heat of reptiles is in proportion to their expenditure of it. Graceful as is the snake (that living jewel so often copied by bracelet-makers), you feel on touching it an instinctive horror, caused by the thrill of cold it produces. All the animals we have considered hitherto have warm blood, and bear within themselves the source of their heat, which is pretty nearly always the same. But reptiles are cold-blooded, and heat comes to them chiefly from without.

If, at the end of a cold winter, we go to some favorable corner to catch the first rays of spring suns.h.i.+ne, we feel ourselves almost re-born, as it were, as if a new life had come into us with the sunbeams. Look at the little lizard you see frisking on the white stones of the wall; upon him decidedly the sun is darting actual life from its rays. While the cold lasted he staid squatting in his hiding-place--not asleep, but annihilated--congealed, so to speak, like water caught by the frost; no longer digesting, and hardly breathing, he had ceased to live in reality: and it is no imaginary regeneration which the return of warmth brings to him. Like those helpless people who have not the power to carve out their own destinies, reptiles have within them only an insufficient source of animation; their life is at the mercy of the sun, and is high or low, according as that rises or sets in the heavens. At Martinique, where at noonday it darts its devouring rays perpendicularly upon the cane-fields, and every one flies into the shade to escape its scorching heat, the rattlesnake traverses the country, monarch of all he surveys; he strikes rapidly with a vigorous tail upon the calcined ground; and woe then to any one who receives his bite! All the fire of the atmosphere has pa.s.sed into his frame. Now go to the Zoological Gardens, and see him there: he crawls languidly under the coverings that shelter him; if by chance he bites any one, it is with an idle tooth that no longer knows how to kill; his life was left behind with the sun of the tropics, and it is little more than a corpse that you are looking at.

And so among ourselves, my dear child: we meet with people whose whole power comes from without, who are brilliant and haughty in the suns.h.i.+ne of good fortune, but crest-fallen, cowardly, and cringing in the cold days of adversity. Nevertheless, they are const.i.tuted originally like other people: they are neither greater fools as a general rule, nor less gifted than their neighbors; where they fail is in the heart, but that is enough to spoil everything. And so with reptiles: the heart is their weak point also. Like us, they have lungs into which the air pours without any difficulty, and a heart to send the blood to them; so it seems at first sight as if there could be nothing to prevent their resisting the changes of external temperature just as well as ourselves. There is only one small trifle wanting, and that is a part.i.tion in the middle of the heart; but this one defect is enough to disorder the whole machinery.

You know that, with us, the heart is divided into two compartments: the right ventricle, which receives the venous blood from the organs and sends it to the lungs; the left ventricle, which receives it (now become arterial) from the lungs and returns it to the organs. Hence the double system of veins and arteries, the one going from the heart to the lungs, the other from the heart to the organs. All this is found the same in reptiles: except that the part.i.tion, which separates our two ventricles from each other, does not exist in them; and the heart has only one common room, in which, therefore, arterial and venous blood become mixed together. It follows from this that, at each contraction of the heart, it is a mixture of arterial and venous blood which is sent in the two opposite directions at the same time, and that the organs receive some which has been used before, while the lungs have some returned to them which has been regenerated already.

Now, on the one hand, this mixed blood can only keep up an imperfect combustion in the body (like the live embers between two layers of ashes that we spoke of lately), and, on the other hand, the air in the lungs can only act upon a part of the blood it meets with there, the rest having already undergone the regenerating process. And this accounts for both the feeble animal heat and the small consumption of oxygen in reptiles.

Added to which the lungs of a reptile are coa.r.s.ely constructed, and composed of cells enormous in comparison with ours, so that the blood does not find nearly as many little chambers to rush into for a taste of air as with us. Moreover, you must understand that there is no such thing as a diaphragm here: the lungs float loosely in the form of elongated bags in the one only cavity of the body, and the slight movement of the ribs does not allow them to dilate sufficiently to take in much air at a time.

All these things, taken together, make the reptile a very poor stove, and render him incapable of any prolonged exertion. The serpent darts like an arrow upon his prey; but he could not pursue it for half a mile without stopping, not even over the burning soil of the equator.

The lizard is very nimble, is it not? and the quickness of its movements rather reminds one of the agility of a bird. But watch it, and you will see it only moves in jerks, and keeps stopping every minute; it cannot escape you if there is no hole near into which it can disappear.

In France there is a large green lizard that runs among the vine trees.

If you pursue him he is off like lightning for a second; then he stops suddenly short. You return to the charge, and he starts afresh, but only to stop again. At the fourth or fifth attack he is quite out of breath; you poke him with the stick with which you have been hunting him, but in vain; there he lies motionless, in spite of his alarm. A few steps have brought him to the end of his powers, like a man whose heart is diseased and who cannot go far. This, however, is a peculiarity common to all reptiles. Each of the three orders of which this third cla.s.s of Vertebrata is composed has its own particular history besides.

You must excuse my mentioning the barbarous names that have been given them, and allow me to call them _tortoises_, _lizards_, and _serpents_, like other people. The hard names mean no more than these; but they are Greek, which is always more imposing.

The slowness of the tortoise has pa.s.sed into a proverb, which is not to be wondered at; for they cannot inhale the air, because their ribs (which are a reptile's only resource for breathing) are condemned to absolute immobility. The _carapace_, or sh.e.l.l, which the tortoise carries on his back, and under which it retreats upon the least alarm, as under a s.h.i.+eld, is really formed of its ribs, each of which has widened itself so as to join on to its neighbor, like the boards of an inlaid floor, which run one into another. Of course there is no question of moving up and down with such ribs, and the poor bellows cannot work at all. How does the tortoise get out of this difficulty then, you will ask? I answer, it swallows air, as we should swallow a gla.s.s of water. You see its mouth open and then shut again, thereby taking in an actual mouthful of air, which the sides of the mouth, by contracting themselves, send straight to the lungs. These, which are very large, get filled in this way by degrees, and, when they are quite inflated, they expel the overplus by collapsing, like an over-stretched spring. You may imagine that this does not produce a very active respiration, and that a tortoise would be puzzled to run at even a moderate trot. To be sure, when he has once filled his great lungs with air, he has enough for a long time. Most tortoises are aquatic, and, as divers, leave the cetaceans far behind. Mery, an obscure French naturalist of the days of the Empire, pretended that he had kept in his house, _for a month_, some tortoises, whose breathing he had completely stopped. Only imagine from this how far their life must be below ours, although it is the result of similar actions, performed by organs which after all are copies (imperfect ones, it is true) of our own.

Some tortoises feed on vegetable substances, and some upon fish or small soft-bodied animals. Like birds, they mash their food with difficulty, by means of a real bill. Their jawbones are generally arched forward toward the front, and are furnished with sharp h.o.r.n.y plates, in which a fairly-marked denticulation or notching may sometimes be traced, as in the bills of birds of prey. Indeed there is one, the _caretta_, whose hooked and notched beak so completely recalls the warlike bill of a hawk, that it is usually known by the name of the "Hawk's-bill Turtle." You ought to know about this tortoise, for it is the one which furnishes tortoise-sh.e.l.l, that nice material which is so smooth to the touch, so pretty to look at, and so very fragile, that it seems only fit for the use of ladies' hands. I could hardly speak of tortoises without saying something of this one, out of whose back was carved the handle of your own pretty little penknife.

Behind this bill of the hawk's-bill there is a tongue, but of the character of a whale's tongue, and it is fastened underneath to the bottom of the mouth. At the base of it there is a sort of fleshy pad or cus.h.i.+on, which serves instead of a soft palate, that being another detail which is about to disappear from our history. We are now really entering upon the simplification of the digestive tube, which will, I forewarn you, end by being nothing more than a perfectly straight pipe, without any appendages whatever. In tortoises the intestine is still tolerably long, and is doubled up backwards and forwards many times in the abdomen; but it is already beginning to lose that variety of form which its different parts a.s.sumed in the higher animals. The large intestine can no longer be clearly distinguished from the smaller one, nor this from the stomach, which itself seems to be a continuation of the oesophagus, without any very distinct boundary line between them.

The porter, who with us keeps the door of the stomach, does his duty here so badly, that there are certain kinds of tortoises whose oesophagus is covered with spines, the points inclined backward, to prevent the food from rising up into the mouth whilst the oesophagus is driving it down by its contractions.

In the gray lizards of our walls we find teeth again, but very different from any that we have hitherto seen. In the first place, they are not content with their usual place on the edge of the jaws, but encroach upon the surface of the palate, where they stretch out in close lines.

Besides, they are even still less like teeth than the great nails in the jaws of the cetaceans. They are little ivory p.r.o.ngs, with the points turned inwards, a.n.a.logous to the thorns of the oesophagus in the tortoise, and serve the lizard solely to retain and bruise his prey.

He lives on insects, especially flies, which he seizes on the wing with the greatest skill, hastily catching and engulphing them in his open jaw; they pierce themselves on the little p.r.o.ngs, and are swallowed promiscuously. The tongue of the lizard has also a curious peculiarity, which is shared by that of the serpent: it is divided at the end into two threads, which dart in and out of its mouth, and by means of which it laps, like a dog, the few drops of water it requires to satisfy its thirst. I have seen lizards which had been tamed by children greedily sucking up the saliva from their lips by drawing across them those little forked tongues of theirs, which, after all, are very soft, and perfectly inoffensive.

The tongue of the chameleon, another species of lizard, is still more curious. You must know that the chameleon is a lumbering lazy animal, who feeds on flies and other swift insects, and who would, therefore, be constantly liable to go without his dinner but that his tongue serves him for a hunting weapon, like those of the wood-p.e.c.k.e.r and the ant-eater. When at rest, it is an oval spongy ma.s.s, lying comfortably in the mouth, with nothing formidable in its appearance; but let the prey come frisking round the chameleon, as if despising so helpless an enemy, and this great soft tongue is transformed into an active dart. It shoots forth like an arrow, and will sometimes seize the rash intruder at half a foot's distance, transferring it with equal rapidity to the motionless mouth. The blow is so soon struck, that it is very difficult to see how it all happens. Some say that the chameleon curves the tip of his tongue by a sudden effort, and then catches his flies with it, just as you would catch them with your hand. Others maintain (and this is the general opinion) that the tongue of the chameleon is terminated by a sort of sticky cus.h.i.+on, on which the flies are caught, like birds with birdlime. This singular dart is always out-jerked with such force that, if it strikes against a gla.s.s (the experiment has been tried with chameleons in captivity), it makes a sound as loud as that of a pea from a pea-shooter; so you may judge if it is not strong enough to stun a fly. Besides this, too, the chameleon (who is by-the-by, a hideous little beast) has given endless trouble to naturalists on another and very different point. It is he who is so celebrated for his faculty of changing color when any emotion agitates him; and ever since the days of Aristotle, who lived more than two thousand years ago, people have been trying to explain this, without any one being able to flatter himself that he has found out the exact answer to the riddle.

But there is a lizard more interesting still, and that is the crocodile.

He stands alone among reptiles. His heart has two ventricles, and you would think that he ought to be included in the cla.s.s of warm-blooded animals. But, no. The separation of the two kinds of blood takes place in the heart, it is true, and it is really true arterial blood which the aorta carries away from the left ventricle. But the right ventricle has two doors of exit. One communicates with the lungs, the other with the aorta; and the latter has hardly performed its distribution in the upper part of the body when it meets, as it descends, with a treacherous tube bringing to it a current of venous blood. In this way only half the blood that comes from the veins pa.s.ses on to be regenerated by contact with the air, and all the hinder part of the body receives nothing but the mixed blood common to reptiles, while the head and fore members enjoy the privilege of the superior orders. After this go and lay down your laws of cla.s.sification! Nature, while maintaining amongst all animals the same principle of life--the regeneration of the blood by oxygen--has in their construction followed many systems leading to the same result by different combinations, and which seem to permit the establishment of essential distinctions among them. Here is an animal who, if I may so express myself, is climbing up from one system to the other, and you would have to cut him in two before you could cla.s.sify him properly, since his fore-quarters have risen to the warm-blooded animals, while his hind ones are left behind among the cold-blooded reptiles!

But there is something which even outdoes this.

On dry land the crocodile is timid, faltering, a bad walker, incapable of regular combat, and a man can manage him with a stick. One feels that he is betrayed by the hinder half of his body, through which circulates the only half-oxygenized blood. But when once he has plunged into the water his whole behavior suddenly alters; he is a ferocious being, high-mettled, indomitable, a savage enemy, redoubling his exertions, as if the entire ma.s.s of his blood had suddenly become arterial. Geoffroy St. Hilaire, who followed Bonaparte as a scientific explorer when he set out for the conquest of Egypt, the country of crocodiles, was deeply struck by studying on the spot this double life, which seems in a way to maintain two beings in the same body. He afterwards gave an extremely curious explanation of it in his work on the crocodiles of Egypt. Here it is; but I forewarn you that you will not understand it:

"The crocodile, when it is under water, receives by two ca.n.a.ls into the cavity of the abdomen, a considerable quant.i.ty of water, which the animal can renew at will."

You are not much the wiser, are you? But wait a moment. We are soon coming to the fishes, and you will then see what an unlimited scope nature has allowed herself here. Not satisfied with two systems in one animal, she appears to have got hold of three.

If we continue the examination of this privileged reptile, we shall find many other infractions of the usual rules of his cla.s.s. His tongue, certainly, is fastened to his mouth like that of the tortoise, so much so that the ancient Egyptians told the Greeks he had not got one; but his set of teeth clearly approach those of the lower mammals. You have probably heard a great deal of the strength of the crocodile's formidable teeth. Travellers have given them this reputation; but we have nothing to do with that now. They stand in battle array, in a single line, along the whole length of the jaws, into which they are sunk with genuine fangs, whilst the p.r.o.ngs of our little lizard are merely fastened to the surface of the bones which support them. Indeed, in one way, the crocodile is even better provided than the mammals.

He possesses under each tooth one or two germs, the life of which lasts as long as that of the animal, and which are always there ready toreplace the previous one should it chance to fall out. There are many ladies, and (not to be rude) gentlemen as well, who would, I am sure, give a great deal to have as many teeth at their service. Indeed, they may possibly think Dame Nature very unjust to have selected this great villanous beast rather than us as the object of a gift which they would have been so well able to appreciate. But we must not blame nature too quickly: she had her reasons. We, during our infancy, have teeth in reserve. Now, a reptile may be considered as an imperfect rough draft of a mammal; and the crocodile gives one thoroughly the idea of a mammal half-finished and fixed for life in a state of childhood. I am sorry that I cannot enter into full details, that you might see how far the idea is a just one. Moreover, in his character of a perpetual child, he is always growing bigger all his life long, and never seems able to die but by accident, hardly ever, I may really say, from old age. By specimens kept in captivity, it has been ascertained that their growth is very slow. Well, imagine their being only from seven to eight inches long when they come out of the sh.e.l.l, and that full-grown crocodiles have been found thirty feet in length, and calculate accordingly. You will not account for it under a century; and I should like to know what would become of this venerable child of more than a hundred years old if kind Mother Nature had not left him our system of milk-teeth to the end?

A curious peculiarity of these persistent teeth is, that they are hollow inside, so much so, that the bowls of tobacco-pipes are said to be made from them in Europe. I mention the fact, although of no great interest to you, for the benefit of any pipe-merchants who have not yet thought of sending for such things to Cairo.

But let us return to the efforts perceptible in the organization of the crocodile to raise itself to a higher level. The soft palate, as we called it (Letter VII.), is wanting in other reptiles; but here there is one which completely closes the entrance of the windpipe (the larynx). I announced, too, the disappearance of the diaphragm; and we bewailed together the loss of that servant of the good old times, whose touching history you must, I am sure, remember. But I reckoned without this wretched crocodile, who seems determined to give the lie to all we have been saying. He has a diaphragm, and one which acts well enough in the main, although it is pierced right through the middle, as if it were rather ashamed of being there, and wished to make up for dividing the body into two compartments, against all proper reptile regulations, by opening a door of communication between them. What shall I tell you besides? The lungs, not to be behind the rest of this aristocratic reptile's organization, are hollowed into cells much more complicated than those of his fellows. You find here no end of nooks and corners, which multiply opportunities of contact between the air and the blood, and so give the crocodile almost the respiration of the mammals, as he has already got pretty nearly their system of circulation.

With serpents, again, we fall very low. When we were speaking of the tortoises I told you that, in proportion as we come down in the scale, the digestive tube has a tendency to get rid of its accessories, and to a.s.sume the appearance of a perfectly straight tube. If any one were to cut open a serpent before you, you would see this final condition almost reached already. In the first place, the soft palate is entirely suppressed, and the mouth extends straight into the oesophagus, whose tube seems to run through the whole length of the body without interruption, with just four or five doublings towards the base, in that part which represents the intestines. An imperceptible swelling indicates the place where the real stomach lies within; but in another sense one may call the oesophagus, and I might almost add the mouth itself, its stomach. You shall see how.

The jaws of serpents are even in a more unfinished state than those of other reptiles. Nature has not taken the time to weld the different parts of them together; but these begin by not being very firmly joined, remember, in young mammals. The bones of the head, which support the jaws, are themselves movable, and can be detached from the skull if necessary, so as to allow the throat to open extraordinarily wide; thus it is not uncommon to see a serpent swallow animals much larger than itself. You will be horrified when I tell you that the anaconda, one of the giants of the family, swallows large quadrupeds at a single mouthful. What are our mouthfuls in comparison with his? however, it must be confessed, that his often take several days to go down. When the animal has rolled up his prey in his terrible folds, he pounds and kneads it till it is reduced to a kind of long roll, which he moistens with a copious slaver to make it slip down more easily. Then, attacking it at one end, he fastens this very expansive jaw upon it, and the gigantic mouthful slowly begins its journey; what was left outside the mouth, advancing little by little, in proportion as the digestion reduces what has entered to pulp, and sends it farther down. This is on great occasions; but in the case of more modest prey--a rabbit, for instance--the mouthful goes in whole at one gulp and remains stationary, partly in the oesophagus, partly in the stomach, while the powerful juices distilled by the walls of the latter are dissolving it.

You can see that a soft palate would have been quite useless here, and that the serpent has not much need of teeth to chew his food.

Accordingly, his are nothing but simple p.r.o.ngs, like those of the lizard, and, like his, they extend over the palate, the more effectually to cut off the return of the swallowed ma.s.ses of food. About a hundred and twenty have been counted in the throat of the boa-constrictor; but their number varies considerably in the different species. They are not organs of the highest order, and nature is not very particular about the quant.i.ty.

There is only one tooth among serpents of which she takes any particular care, and that is the venomous tooth which she has bestowed on certain species, and which serves them for striking down, as it were, the animals on which they feed. Let us study it in the rattlesnake, the most celebrated of this odious race. On each side of the upper jaw you may see, isolated from the others, and exceeding them all in length, a very sharp fang pierced through by a tiny ca.n.a.l, which opens into a gland placed at the root of the tooth. The bone which supports this little apparatus is very flexible, and when at rest, the fang, falling back, hides itself in a fold of the gum. When the animal wishes to bite, it springs up again, and the gland, compressed by the action of biting, sends into the little ca.n.a.l a jet of poison, which runs through it into the wound. As far as can be ascertained, this poison paralyses the victim and disorders the blood, which at once loses its power, and no longer acts upon the organs as before; still it is only injurious when it has been carried by the current of circulation into the ma.s.s of the blood; if swallowed, it has no effect whatever on the stomach.

Now do not look at me with such incredulous eyes, as if it were quite impossible any one should think of swallowing such a thing. You have no idea what a scientific man is capable of when he comes to close quarters with nature, for the purpose of extracting one of her secrets.

He has his own fields of battle, where very often as much courage is displayed as on any other.

These two fangs, in which lie all the power of the animal, are of the greatest importance to him, and their want of solidity makes them liable to remain in the wounds which they have made. In consequence of this, they enjoy the same privilege as the teeth of the crocodile, and in a still greater degree even. Behind each poison fang lie in wait, not one nor two, but several sentinel germs, ready at the first alarm of a loss to set to work and re-supply the disarmed serpent with his venomous needle. So the serpent also lives in a state of perpetual childhood: he is always growing; and I could not tell you the exact natural limits of his life any more than of that of the crocodile.

They are gentlemen who do not allow themselves to be very closely studied in a state of freedom. But these also grow very slowly, and some have been met with whose size had extended quite enormously from their first start. I ought to tell you, once for all, that this indefinite growth, joined to extreme longevity, is found in many of the inferior species whom we have yet to consider. It seems the portion of these unfinished creatures, in which nature has only as it were sketched in her work, and who seem vowed to endless youth, in testimony of the state of childhood they represent, a state transitory among the superior animals, but permanent with them. It belonged of right, therefore, to the serpent, which is the most unfinished animal we have yet met with, and who, at the first glance, seems almost reduced to a mere digestive tube, lodged between a vertebral column and a series of small ribs, whose number sometimes reaches three hundred. The liver, which, with us, presents such a distinct and bulky ma.s.s, is here elongated into a thin cord, which runs the whole length of the oesophagus and intestine, to the walls of which it is, to some extent, attached.

It is the same with the lungs. There is rarely room for the full development of two in this narrow conduit, where everything has to follow the shape of the master of the house: one, therefore, is often merely indicated by a very slight protuberance; the other, presenting the appearance of a long tube, which extends nearly half-way down the body, and whose feeble action halts periodically at each of those monstrous repasts, after which the torpid animal becomes nothing but a huge digesting machine. We have now reached the extreme limits of that organization, the most perfect model of which we find in man, and which is no longer to be recognized in fishes.