the body beneath it, which is of still greater importance: and that purpose is concealment. Were it possible to view through the skin the mechanism of our bodies, the sight would frighten us out of our wits. "Durst we make a single movement," asks a lively French writer, "or stir a step from the place we were in, if we saw our blood circulating, the tendons pulling, the lungs blowing, the humours filtrating, and all the incomprehensible assemblage of fibres, tubes, pumps, valves, currents, pivots, which sustain an existence at once so frail, and so presumptuous?"

V. Of animal bodies, considered as masses, there is another property, more curious than it is generally thought to be; which is the faculty of standing; and it is more remarkable in two-legged animals than in quadrupeds, and most of all, as being the tallest, and resting upon the smallest base, in man. There is more, I think, in the matter than we are aware of. The statue of a man, placed loosely upon its pedestal, would not be secure of standing half an hour. You are obliged to fix its feet to the block by bolts and solder; or the first shake, the first gust of wind, is sure to throw it down. Yet this statue shall express all the mechanical proportions of a living model. It is not therefore the mere figure, or merely placing the centre of gravity within the base, that is sufficient. Either the law of gravitation is suspended in favour of living substances, or something more is done for them, in order to enable them to uphold their posture. There is no reason whatever to doubt, but that their parts descend by gravitation in the same manner as those of dead matter. The gift therefore appears to me to consist in a faculty of perpetually shifting the centre of gravity, by a set of obscure, indeed, but of quick-balancing actions, so as to keep the line of direction, which is a line drawn from that centre to the ground, within its prescribed limits. Of these actions it may be observed, first, that they in part constitute what we call strength. The dead body drops down. The mere adjustment therefore of weight and pressure, which may be the same the moment after death as the moment before, does not support the column. In cases also of extreme weakness, the patient cannot stand upright. Secondly, that these actions are only in a small degree voluntary. A man is seldom conscious of his voluntary powers in keeping himself upon his legs. A child learning to walk is the greatest posturemaster in the world: but art, if it may be so called, sinks into habit; and he is soon able to poise himself in a great variety of attitudes, without being sensible either of caution or effort. But still there must be an aptitude of parts, upon which habit can thus attach; a previous capacity of motions which the animal is thus taught to exercise: and the facility with which this exercise is acquired, forms one object of our admiration. What parts are principally employed, or in what manner each contributes to its office, is, as hath already been confessed, difficult to explain. Perhaps the obscure motion of the bones of the feet may have their share in this effect. They are put in action by every slip or vacillation of the body, and seem to assist in restoring its balance. Certain it is, that this circumstance in the structure of the foot, viz. its being composed of many small bones, applied to and articulating with one another, by diversely shaped surfaces, instead of being made of one piece, like the last of a shoe, is very remarkable. I suppose also that it would be difficult to stand firmly upon stilts or wooden legs, though their base exactly imitated the figure and dimensions of the sole of the foot. The alternation of the joints, the knee-joint bending backward, the hip-joint forward: the flexibility, in every direction, of the spine, especially in the loins and neck, appear to be of great moment in preserving the equilibrium of the body. With respect to this last circumstance, it is observable, that the vertebræ are so confined by ligaments as to allow no more slipping upon their bases, than what is just sufficient to break the shock which any violent motion may occasion to the body. A certain degree also of tension of the sinews appears to be essential to an erect posture; for it is by the loss of this, that the dead or paralytic body drops down. The whole is a wonderful result of combined powers, and of very complicated operations. Indeed, that standing is not so simple a business as we imagine it to be, is evident from the strange gesticulations of a drunken man, who has lost the government of the centre of gravity.

We have said that this property is the most worthy of observation in the human body : but a bird resting upon its perch, or hopping upon a spray, affords no mean specimen of the same faculty. A chicken runs off as soon as it is hatched from the egg; yet a chicken, considered geometrically, and with relation to its centre of gravity, its line of direction,

and its equilibrium, is a very irregular solid. Is this gift, therefore, or instruction? May it not be said to be with great attention, that nature hath balanced the body upon its pivots ? I observe also in the same bird a piece of useful mechanism of this kind. In the trussing of a fowl, upon bending the legs and thighs up towards the body, the cook finds that the claws close of their own accord. Now let it be remembered, that this is the position of the limbs, in which the bird rests upon its perch. And in this position it sleeps in safety; for the claws do their office in keeping hold of the support, not by any exertion of voluntary power, which sleep might suspend, but by the traction of the tendons in consequence of the attitude which the legs and thighs take by the bird sitting down, and to which the mere weight of the body gives the force that is necessary.

VI. Regarding the human body as a mass; regarding the general conformations which obtain in it; regarding also particular parts in respect to those conformations; we shall be led to observe what I call "interrupted analogies." The following are examples of what I mean by these terms; and I do not know how such critical deviations can, by any possible hypothesis, be accounted for without design.

1. All the bones of the body are covered with a periosteum, except the teeth, where it ceases; and an enamel of ivory, which saws and files will hardly touch, comes into its place. No one can doubt of the use and propriety of this difference; of the " analogy" being thus "interrupted;" of the rule, which belongs to the formation of the bones, stopping where it does stop: for, had so exquisitely sensible a membrane as the periosteum invested the teeth, as it invests every other bone of the body, their action, necessary exposure, and irritation, would have subjected the animal to continual pain. General as it is, it was not the sort of integument which suited the teeth; what they stood in need of, was a strong, hard, insensible, defensive coat and exactly such a covering is given to them, in the ivory enamel which adheres to their surface.

2. The scarf-skin, which clothes all the rest of the body, gives way, at the extremities of the toes and fingers, to nails. A man has only to look at his hand, to observe with what nicety and precision that covering, which extends over every other part, is here superseded by a different substance, and a different texture. Now, if either the rule had been necessary, or the deviation from it accidental, this effect would not be seen. When I speak of the rule being necessary, I mean the formation of the skin upon the surface being produced by a set of causes constituted without design, and acting, as all ignorant causes must act, by a general operation. Were this the case, no account could be given of the operation being suspended at the fingers' ends, or on the back part of the fingers, and not on the fore part. On the other hand; if the deviation were accidental, an error, an anomalism; were it any thing else than settled by intention; we should meet with nails upon other parts of the body. They would be scattered over the surface, like warts or pimples.

I

3. All the great cavities of the body are enclosed by membranes, except the skull. Why should not the brain be content with the same covering as that which serves for the other principal organs of the body? The heart, the lungs, the liver, the stomach, the bowels, have all soft integuments, and nothing else. The muscular coats are all soft and membranous. can see a reason for this distinction in the final cause, but in no other. The importance of the brain to life (which experience proves to be immediate), and the extreme tenderness of its substance, make a solid case more necessary for it than for any other part: and such a case the hardness of the skull supplies. When the smallest portion of this natural casket is lost, how carefully, yet how imperfectly, is it replaced by a plate of metal! If an anatomist should say, that this bony protection is not confined to the brain, but is extended along the course of the spine, I answer, that he adds strength to the argument. If he remark, that the chest also is fortified by bones; I reply, that I should have alleged this instance myself, if the ribs had not appeared subservient to the purpose of motion as well as of defence. What distinguishes the skull from every other cavity is, that the bony covering completely surrounds its contents, and is calculated, not for motion, but solely for defence. Those hollows, likewise, and inequalities which we observe in the inside of the skull, and which exactly fit the folds of the brain, answer the important design of keeping the substance of the brain steady, and of guarding it against concussions.

CHAPTER XII.

cotton.

COMPARATIVE ANATOMY.

WHENEVER we find a general plan pursued, yet with such variations in it, as are, in each case, required by the particular exigency of the subject to which it is applied, we possess, in such a plan and such adaptation, the strongest evidence that can be afforded of intelligence and design; an evidence which the most completely excludes every other hypothesis. If the general plan proceeded from any fixed necessity in the nature of things, how could it accommodate itself to the various wants and uses which it had to serve under different circumstances, and on different occasions? Arkwright's mill was invented for the spinning of We see it employed for the spinning of wool, flax, and hemp, with such modifications of the original principle, such variety in the same plan, as the texture of those different materials rendered necessary. Of the machine's being put together with design, if it were possible to doubt, whilst we saw it only under one mode, and in one form; when we came to observe it in its different applications, with such changes of structure, such additions and supplements, as the special and particular use in each case demanded, we could not refuse any longer our assent to the proposition, "that intelligence, properly and strictly so called (including under that name, foresight, consideration, reference to utility), had been employed, as well in the primitive plan, as in the several changes and accommodations which it is made to undergo."

Very much of this reasoning is applicable to what has been called Comparative Anatomy. In their general economy, in the outlines of the plan, in the construction as well as offices of their principal parts, there exists between all large terrestrial animals a close resemblance. In all, life is sustained, and the body nourished, by nearly the same apparatus. The heart, the lungs, the stomach, the liver, the kidneys, are much alike in all. The same fluid (for no distinction of blood has been observed) circulates through their vessels, and nearly in the same order. The same cause, therefore, whatever that cause was, has been concerned in the origin, has governed the production, of these different animal forms.

When we pass on to smaller animals, or to the inhabitants of a different element, the resemblance becomes more distant and more obscure; but still the plan accompanies us. And, what we can never enough commend, and which it is our business at present to exemplify, the plan is attended, through all its varieties and deflections, by subserviences to special occasions and utilities.

1. The covering of different animals (though whether I am correct in classing this under their anatomy, I do not know) is the first thing which presents itself to our observation; and is, in truth, both for its variety and its suitableness to their several natures, as much to be admired as any part of their structure. We have bristles, hair, wool, furs, feathers, quills, prickles, scales; yet in this diversity both of material and form, we cannot change one animal's coat for another, without evidently changing it for the worse; taking care however to remark, that these coverings are, in many cases, armour as well as clothing; intended for protection as well as warmth.

The human animal is the only one which is naked, and the only one which can clothe itself. This is one of the properties which renders him an animal of all climates, and of all seasons. He can adapt the warmth or lightness of his covering to the temperature of his habitation. Had he been born with a fleece upon his back, although he might have been comforted by its warmth in high latitudes, it would have oppressed him by its weight and heat, as the species spread towards the equator.

What art, however, does for men, nature has, in many instances, done for those animals

which are incapable of art. Their clothing, of its own accord, changes with their necessities. This is particularly the case with that large tribe of quadrupeds, which are covered with furs. Every dealer in hare-skins and rabbit-skins, knows how much the fur is thickened by the approach of winter. It seems to be a part of the same constitution and the same design, that wool, in hot countries, degenerates, as it is called, but in truth (most happily for the animal's ease) passes into hair; whilst, on the contrary, that hair, in the dogs of the polar regions, is turned into wool, or something very like it. To which may be referred, what naturalists have remarked, that bears, wolves, foxes, hares, which do not take the water, have the fur much thicker on the back than the belly; whereas in the beaver it is the thickest upon the belly; as are the feathers in water-fowl. We know the final cause of all this; and we know no other.

The covering of birds cannot escape the most vulgar observation. Its lightness, its smoothness, its warmth ;-the disposition of the feathers all inclined backward, the down about their stem, the overlapping of their tips, their different configuration in different parts, not to mention the variety of their colours, constitute a vestment for the body, so beautiful, and so appropriate to the life which the animal is to lead, as that, I think, we should have had no conception of any thing equally perfect, if we had never seen it, or can now imagine any thing more so. Let us suppose (what is possible only in supposition) a person who had never seen a bird, to be presented with a plucked pheasant, and bid to set his wits to work, how to contrive for it a covering which shall unite the qualities of warmth, levity, and least resistance to the air, and the highest degree of each; giving it also as much of beauty and ornament as he could afford. He is the person to behold the work of the Deity, in this part of his creation, with the sentiments which are due to it *.

The commendation, which the general aspect of the feathered world seldom fails of exciting, will be increased by farther examination. It is one of those cases in which the philosopher has more to admire, than the common observer. Every feather is a mechanical wonder. If we look at the quill, we find properties not easily brought together-strength and lightness. I know few things more remarkable than the strength and lightness of the very pen with which I am writing. If we cast our eye to the upper part of the stem, we see a material, made for the purpose, used in no other class of animals, and in no other parts of birds; tough, light, pliant, elastic. The pith, also, which feeds the feather, is, amongst animal substances, sui generis; neither bone, flesh, membrane, nor tendon t.

But the artificial part of the feather is the beard, or, as it is sometimes, I believe, called, the vane. By the beards are meant, what are fastened on each side of the stem, and what constitute the breadth of the feather; what we usually strip off from one side or both, when we make a pen. The separate pieces or laminæ, of which the beard is composed, are called threads, sometimes filaments, or rays. Now the first thing which an attentive observer will remark is, how much stronger the beard of the feather shews itself to be, when pressed in a direction perpendicular to its plane, than when rubbed, either up or down, in the line of the stem; and he will soon discover the structure which occasions this difference, viz. that the lamina whereof these beards are composed, are flat, and placed with their flat sides towards each other; by which means, whilst they easily bend for the approaching of each other, as

Even the chemical composition of feathers marks an adaptation of means to an end. They are composed almost entirely of albumen (white of egg) and are consequently little affected by moisture. By the most long continued boiling, Mr. Hatchett was unable to dissolve them: hence the feathers of the water fowl are totally unaffected by the divings, and other habits of the bird. The very pen, with which I am writing, though it slightly softens, yet never dissolves in the ink. The effect of water upon hair, on the contrary, is much more decisive; in a continued and elevated temperature, as in a Papin's digester, it is entirely dissolved: every lady is aware of the considerable effect of a moist atmosphere upon her curls, however inoperative upon her ostrich feathers. Hair is composed principally of gelatine (isinglass, glue, &c.), and is rarely required to withstand that degree of moisture, so

requisite in the feathers of birds. It is remarkable that the composition of all descriptions of hair differs but very slightly in whatever form it appears. Bristles, hair, wool, and down, are not perceptibly different in composition; these not being the ordinary clothing of the inhabitants of the water, are not rendered insensible to moisture, it is only in the instance of feathers that the demand occurs, and the necessity is provided for by a change in composition.-Vauquelin. Nich. Jour., xv. p. 141; Berthollet. Ann. de Chim., v. 47, p. 267; Thomson, iv. p. 483.

The quill part of a feather is composed of circular and longitudinal fibres. In making a pen, you must scrape off the coat of circular fibres, or the quill will split in a ragged manner, making what boys call cat's teeth.

any one may perceive by drawing his finger ever so lightly upwards, they are much harder to bend out of their plane, which is the direction in which they have to encounter the impulse and pressure of the air, and in which their strength is wanted, and put to the trial.

state.

This is one particularity in the structure of a feather: a second is still more extraordinary. Whoever examines a feather, cannot help taking notice, that the threads or lamina of which we have been speaking, in their natural state unite; that their union is something more than the mere apposition of loose surfaces; that they are not parted asunder without some degree of force; that nevertheless there is no glutinous cohesion between them; that, therefore, by some mechanical means or other, they catch or clasp among themselves, thereby giving to the beard or vane its closeness and compactness of texture. Nor is this all when two laminæ, which have been separated by accident or force, are brought together again, they immediately reclasp the connexion, whatever it was, is perfectly recovered, and the beard of the feather becomes as smooth and firm as if nothing had happened to it. Draw your finger down the feather, which is against the grain, and you break, probably, the junction of some of the contiguous threads; draw your finger up the feather, and you restore all things to their former This is no common contrivance; and now for the mechanism by which it is effected. The threads or laminæ above mentioned are interlaced with one another; and the interlacing is performed by means of a vast number of fibres, or teeth, which the laminæ shoot forth on each side, which hook and grapple together. A friend of mine counted fifty of these fibres in one-twentieth of an inch. These fibres are crooked; but curved after a different manner : for those which proceed from the thread on the side towards the extremity of the feather, are longer, more flexible, and bent downward; whereas those which proceed from the side towards the beginning, or quill-end of the feather, are shorter, firmer, and turn upwards. The process then which takes place is as follows: when two lamina are pressed together, so that these long fibres are forced far enough over the short ones, their crooked parts fall into the cavity made by the crooked parts of the others; just as the latch that is fastened to a door, enters into the cavity of the catch fixed to the door-post, and there hooking itself, fastens the door; for it is properly in this manner, that one thread of a feather is fastened to the other.

This admirable structure of the feather, which it is easy to see with the microscope, succeeds perfectly for the use to which nature has designed it; which use was, not only that the laminæ might be united, but that when one thread or lamina has been separated from another by some external violence, it might be reclasped with sufficient facility and expedition *.

In the ostrich, this apparatus of crotchets and fibres, of hooks and teeth, is wanting; and we see the consequence of the want. The filaments hang loose and separate from one another, forming only a kind of down; which constitution of the feathers, however it may fit them for the flowing honours of a lady's head-dress, may be reckoned an imperfection in the bird, inasmuch as wings, composed of these feathers, although they may greatly assist it in running, do not serve for flight.

But under the present division of our subject, our business with feathers is, as they are the covering of the bird. And herein a singular circumstance occurs. In the small order of birds which winter with us, from a snipe downwards, let the external colour of the feathers be what it will, their Creator has universally given them a bed of black down next their bodies. Black, we know, is the warmest colour; and the purpose here is, to keep-in the heat, arising from the heart and circulation of the blood. It is farther likewise remarkable, that this is not found in larger birds; for which there is also a reason:- small birds are much more exposed to the cold than large ones; forasmuch as they present, in proportion to their bulk, a much larger surface to the air. If a turkey were divided into a number of wrens (supposing the shape of the turkey and the wren to be similar), the surface of all the wrens would exceed the surface of the turkey, in the proportion of the length, breadth (or of any homologous line), of a turkey to that of a wren; which would be, perhaps, a pro

The above account is taken from Memoirs for a Natural History of Animals, by the Royal Academy of Paris, published in 1701, p. 219.