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Books in the running brooks,
this, perhaps, might be the part of creation which we could best select in proof of the wisdom of the Creator.
It was formerly too much the custom to regard the animal frame as a mere mechanical machine; whence, in that spirit of absurdity with which the wisest of mankind are occasionally afflicted, Descartes affected to believe that brutes are as destitute of consciousness as a block of wood, and that it is exactly the same sort of necessity which drives a dog forward in pursuit of a hare, that compels the different pipes of an organ to give forth different tones upon a pressure of the fingers against its different keys. It is not every one, however, in modern times who has adopted the mechanical theory that has carried it to this extremity of absurdity ; but all of them are still carrying it too far who reason concerning the principal motions of the body as mere mechanical motions, and the powers which the muscles exert as mere mechanical powers; in which the bones are the levers, the joints the fulcra, and the muscles the moving cords; for it so happens that all the effects for which the whole of this complicated machinery is absolutely necessary out of the body, are in many instances performed by a single part of it within the body, namely, by the moving cords or muscles alone, without either bones or joints, levers or fulcra. I do not mean to contend that there is no kind of resemblance or conformity of principle between the laws of animate and inanimate mechanics, for I well know that in a variety of points the two systems very closely concur; but I am obliged to contend that they are still two distinct systems, and that in the one case the living power exercises an influence which finds no sort of similitude in the other.
It is, indeed, curious to observe the difference of result which has flowed from the calculations of the different promoters of this theory; and which alone, were there nothing else to oppose them, would be sufficient to prove the fallacy of their reasoning. Among those who have adopted this mode of explanation, and have pursued it with most acuteness, and may be regarded as the fathers of the school, I may be allowed to mention Borelli and Keil; but while the former, in order to account for the circulation of the blood in man, calculated the force with which the heart contracts to be equal to not less than a hundred and eighty thousand pounds weight at every contraction, the latter could not estimate it at more than eight ounces.
In like manner Borelli, in applying the same theory to the power with which the human stomach triturates, or, as we now call it, digests its food, calculated it, in conjunction with the assistance it receives from the auxiliary muscles, which he conceived to divide the labour about equally with itself, as equal to two hundred and sixty-one thousand one hundred and eighty-six pounds; and Pitcairn has made it very little less, since he estimates the moiety contributed by the stomach alone at one hundred and seventeen thousand and eighty-eight pounds; which gives to these organs jointly a force more than equal to that of twenty mill-stones ! “ Had he,” says Dr. Munro, assigned five ounces as the weight of the stomach, he had been nearer the
The fallacy of this theory, however, and especially as it applies to the stomach, has been completely exposed in our own day, by the well-ascertained fact, that though the muscular coat of the stomach in most animals bears some part in the process of digestion, this important operation is almost entirely performed by a powerful chemical solvent secreted by the stomach itself for this very purpose, and hence denominated the gastric juice; and which answers all the purposes of the most violent muscular pressure we can conceive, and with a curious simplicity of contrivance.
The laws of physical force will certainly better apply to the action of the heart and arteries than to that of the stomach, and in some measure assist us
* Comp. Anat. prer. p. viii. note.
in accounting for the circulation of the blood; but the moment we reflect that one-half of this very circulation, that I mean which depends upon the veins, and which has for the most part to contend against the attraction of gravitation, instead of being able to avail itself of its assistance, is produced with. out any muscular propulsion that we are able to discover, and that even the arteries do not, when uninfluenced by pressure, appear to change their diameter in a state of health,* we are necessarily driven to the conclusion, that there is in animal statics, as well as in animal mechanics, a something distinct and independent, and which the laws of physical force are altogether incompetent to explain. Dr. Young, in his excellent Croonian lecture, read before the Royal Society in 1809,f has endeavoured to revive the mechanical theory; but he is still compelled to admit a variety of phenomena in the ani. mal machine, and especially in the circulatory system, which are altogether unaccountable upon any of the known principles of common hydraulics, and which can never fail to reduce us to the same result.
So far, therefore, as we at present know, the circulation of the blood is performed by a double projectile power; one moiety being dependent on the action of the living principle in the heart, and perhaps the arteries; and the other moiety on the common law of hydraulics, or the vacuum produced in the heart by that very contraction or systole which has just propelled the blood returned from the lungs into the arterial system. Whence the heart itself becomes alternately a forcing and a suction pump; being the former in respect to the arteries, and the latter in respect to the veins. I
Upon a moderate estimate, the common labourer may be said to employ a force capable of raising a weight of ten pounds to the height of ten feet in a second, and continued for ten hours a day. A moderate horizontal weight for a strong porter, walking at the rate of three miles an hour, is 200 pounds: the chairman walks four miles an hour, and carries 150 pounds. The daily work of a horse is equal to that of five or six men upon a plane ; but from his horizontal figure in drawing up a steep ascent, it does not exceed the power of three or four inen. In working windmills, twenty-five square feet of the sails is equivalent to the work of a single labourer; whence a full-sized mill, provided it could be made to work eight hours a day, would be equivalent to the daily labour of thirty-four men. A steam engine of the best construction, with a thirty inch cylinder, has the force of forty horses; and as it acts without intermission, will perform the work of 120 horses, or of 600 men; every square inch of the piston being equivalent to the power of a labourer.
There are many muscles given to us which the common customs and habits of life seldom render it necessary to exert, and which in consequence grow stiff and immoveable. Tumblers and buffoons are well aware of this fact; and it is principally by a cultivation of these neglected muscles that they are able to assume those outrageous postores and grimaces, and exhibit those feats of agility, which so often amuse or surprise us.
The same muscles of different persons, however, though of the same length and thickness, and, so far as we are able to trace, composed of the same number of fibres, are by no means uniformly possessed of the same degree of power; and we here meet with an express deviation from the law of physical mechanics; as we do also in the curious fact, that whatever be the power they possess, they grow stronger in proportion to their being used, provided they are well used, and not exhausted by violence or over-exertion.
I have calculated the average weight carried by a stout porter in this metropolis at 200 pounds; but we are told there are porters in Turkey, who by accustoming themselves to this kind of burden from an early period, are able to carry from 700 to 900 pounds, though they walk at a slower rate, and only carry the burden a short distance. « The weakest man can lift with his hands about 125 pounds, a strong man 400. Topham, a carpenter, men
* See Lect. vin p. 91, as also the Author's Study of Medicine, vol. ii. p. 16. Edit. 21, 1825. 1 On the Functions
of the Heart and Arteries, Phil. Trans. 1809, p. 1. See Study of Med. vol. ü. p. 19. Ed. 20.
tioned by Desaguliers, could lift 800 pounds. He rolled up a strong pewter dish with his fingers. He lifted with his teeth and knees a table six feet long, with a half hundred weight at the end. He bent a poker, three inches in circumference, to a right angle, by striking it upon his left forearm; another he bent and unbent about his neck, and snapped a hempen rope two inches in circumference. A few years ago there was a person at Oxford who could hold his arm extended for half a minute, with half a hundred weight hanging on his little finger." We are also told by Desaguliers of a man who, by bending his body into an arch, and having a harness fitted to his hips, was capable of sustaining a cannon weighing two or three thousand pounds. And not many winters ago, the celebrated Belzoni, when first entering on public life, exhibited himself to the theatres of this metropolis, and by a similar kind of harnessing was capable of supporting, even in an upright position, a pyramid of ten or twelve men surmounted by two or three children, whose aggregate weight could not be much less than 2000 pounds; with which weight he walked repeatedly towards the front of the stage.
The prodigious powers thus exerted by human muscles will lead us to behold with less surprise the proofs of far superior powers exerted by the muscles of other animals, though it will by no means lead us to the means of accounting for such facts.
The elephant, which may be contemplated as a huge concentration of animal excellencies, is capable of carrying with ease a burden of between three and four thousand pounds. With its stupendous trunk (which has been calculated by Cuvier to consist of upwards of thirty thousand distinct muscles) it snaps off the stoutest branches from the stoutest trees, and tears up the trees themselves with its tusks. How accumulated the power that is lodged in the muscles of the lion! With a single stroke of his paw he breaks the backbone of a horse, and runs off with a buffalo in his jaws at full speed: he crushes the bones between his teeth, and swallows them as a part of his food.
Nor is it necessary, in the mystery of the animal economy, that the muscles should always have the benefit of a bony lever. The tail of the whale is merely muscular and ligamentous; and yet this is the instrument of its chief and most powerful attack; and, possessed of this instrument, to adopt the language of an old and accurate observer,t“ a long-boat he valueth no more than dust, for he can beat it all in shatters at a blow.” The skeleton of the shark is entirely cartilaginous, and totally destitute of proper bone; yet is it the most dreadful tyrant of the ocean: it devours with its cartilaginous jaws whatever falls in its way; and in one of its species, the squalus carcharias, or white shark, which is often found thirty feet long, and of not less than four thousand pounds weight, has been known to swallow a man whole at a mouthful.
The sepia octopodia, or eight-armed cuttlefish—the polypus of Aristotle is found occasionally of an enormous size in the Mediterranean and Indian seas, its arms being at times nine fathoms in length, and so prodigious in their muscular power, that when lashed round a man, or even a Newfoundland dog, there is great difficulty in extricating themselves; and hence the Indians never venture out without hatchets in their boats, to cut off the animal's holders, should he attempt to fasten on them, and drag them under water.
But this subject would require a large volume, instead of occupying the close of a single lecture. Let us turn from the great to the diminutive. How confounding to the skill of man is the muscular arrangement of the insect class ! Minute as is their form, there are innumerable tribes that unite in themselves all the powers of motion that characterize the whole of the other classes; and are able, as their own will directs, to walk, run, leap, swim, or fly, with as much facility as quadrupeds, birds, and fishes exercise these faculties separately. But such a combination of functions demands a more complicated combination of motive powers; and what
Young's Loct. on Nat. Phil. i. 120.
† Frederiek Martens. See Shaw, II. II. 482
it demands it receives. In the mere larve or caterpillar of a cossus, or insect approaching to the butterfly, Lyonet has detected not less than four thousand and sixty-one distinct muscles, which is about ten times the number that belong to the whole human body; and yet it is probable that these do not constitute any thing like the number that appertain to the same insect in its perfect state. The elator noctilucus, or phosphorescent springer, is a winged insect; but it has also a set of elastic muscles, which enable it, when laid on its back, to spring up nearly half a foot at a bound, in order to recover its position. This insect is also entitled to notice in consequence of its secreting a light, which is so much beyond that of our own glow-worm, that a person may see to read the smallest print by it at midnight. The cicada spumaria, or spumous grasshopper, is in like manner endowed with a double power of motion; and when attempted to be caught will either fly completely off, at its option, or bound away at the distance of two or three yards at every leap. This insect is indigenous to our own country, and is one of those which in their larve and pupe states discharge, from the numerous pores about the tail, that frothy material upon plants which is commonly known by the name of cuckow-spit.
Crabs and spiders have a strong muscular power of throwing off an entire limb whenever seized by it, in order to extricate themselves from confine. ment; and most of them throw off also, once a year, their skin or crustaceous covering, and secrete a new one. The muscular elasticity of the young spider gives it, moreover, the power of wings; whence it is often seen, in the autumn, ascending to a considerable elevation, wasted about by the breeze, and filling the atmosphere with its fine threads. The land-crab (cancer ruricola) inhabits the woods and mountains of a country; but its muscular structure enables it to travel once a year to the seacoast to wash off its spawn in the waters. The spawn or eggs thus deposited sink into the sands at the bottom of the sea, and are soon hatched; after which millions of little crabs are seen quitting their native element for a new and untried one, and roving instinctively towards the woodlands.
The hinge of the common oyster is a single muscle; and it is no more than a single muscle in the chama gigas, or great clamp-fish, an animal of the oyster form, but the largest testaceous worm we are acquainted with. It has been taken in the Indian Ocean of a weight not less than 532 pounds; the fish, or inhabitant, being large enough to furnish 120 men with a meal, and strong enough to lop off a hand with ease, and to cut asunder the cable of a large ship.
Nor is the muscular power allotted to the worm tribes less wonderful than that of insects, or its variety less striking and appropriate. The leech and other sucker-worms are as well acquainted with the nature of a vacuum as Torricelli; and move from place to place by alternately converting the muscular disks of their head and tail into air-pumps.
The sucker of the cyclopterus, a genus of fishes denominated suckers from their wonderfully adhesive property, is perhaps the most powerful, for the size of the fish, of any we are acquainted with; and is formed at will, by merely uniting the peculiar muscles of its ventral fins into an oval concavity. In this state, if pulled by the tail, it will raise a pailful of water rather than resign its hold.
The teredo navalis, or ship-worm, is seldom six inches in length, but the muscles and armour with which its head is provided enables it to penetrate readily into the stoutest oak planks of a vessel, committing dreadful havoc among her timbers, and chiefly producing the necessity for her being copperbottomed. This animal is a native of India; it is gregarious, and always commences its attack in innumerable multitudes; every worm, in labouring, confining itself to its own cell, which is divided from that of the next by a partition not thicker than a piece of writing-paper. The seaman, as he beholds the ruin before him, vents his spleen against the little tribes that have produced it, and denounces them as the most mischievous vermin in the ocean. But a tornado arises—the strength of the whirlwind is abroad—the clouds
pour down a deluge over the mountains—and whole forests fall prostrate before its fury. Down rolls the gathering wreck towards the deep, and blocks up the mouth of that very creek the seaman has entered, and where he now finds himself in a state of captivity. How shall he extricate himself from his imprisonment ?-an imprisonment as rigid as that of the Baltic in the winter season. But the hosts of the teredo are in motion :--thousands of little augurs are applied to the floating barrier, and attack it in every direction. It is perforated, it is lightened, it becomes weak; it is dispersed, or precipitated to the bottom; and what man could not effect, is the work of a worm. Thus it is that nothing is made in vain ; and that in physics, as well as in morals, although evil is intermingled with good, the good ever maintains a predominancy.
THE BONES, CARTILAGES, TEETH, ARTICULATION, INTEGUMENTATION, HAIR, WOOL, SILK, FEATHERS, AND OTHER HARD OR SOLID PARTS OF THE ANIMAL FRAME.
In a former lecture we took a general survey of the characteristic features that distinguish the unorganized from the organized world, and the vege. table kingdom from the animal: we examined into the nice structure of plants, and the resemblances which they bear to the animated form. In our last lecture we proceeded to an inquiry into the nature of the living principle, took a glance at a few of the theories that have been invented to explain its essence and mode of operation, and contemplated the origin and powers of the muscular fibre, which may be denominated its grand executive organ.
The muscles of an animal, however, are not the only instruments of animal motion; the bones, cartilages, and ligaments contribute very largely to the action, and the skin is not unfrequently a substitute for the muscle itself. These, therefore, as well as a variety of other bodies minutely connected with them, or evincing a similarity of construction,-as the teeth, hair, nails, horns, shells, and membranes, -are now to pass under our review, and are entitled to our closest attention; and I may add, that their diversity of uses and operations, and the curious phenomena to which they give rise, are calculated to afford not less amusement than instruction.
I had occasion to remark lately,* that lime is a substance absolutely necese sary to the growth of man. It is, in truth, absolutely necessary to the growth of almost ail animals; even soft-bodied or molluscous worms, except in a few instances, are not free from it; nay, even infusory animals, so minute as to be only discerned by the microscope, still afford a trace of it in the calcareous speck which constitutes their snout; but it is in the bones and shells of animals that lime is chiefly to be found ; and hence those animals possess most of it in whom these organs are most abundant.
Bone, shell, cartilage, and membrane, however, in their nascent state, are all the same substance, and originate from a viscid fluid, usually supposed to be the coagulable lymph, or more liquid part of the blood; which, secreted in one manner, constitutes jelly, or gelatine, a material characterized by its solubility in warm water, heated to about half the boiling point; and secreted in another manner, forms albumen, or the material of the white of the egg, characterized by its coagulating instead of dissolving in about the same heat: the difference, however, between the two, consisting merely, perhaps, in the different proportion of oxygen they contain. Membrane, is gelatin, with a small proportion of albumen to give it a certain degree of solidity; cartilage
* Series 1. Lect. vi. On Geology, p. 73, and passim; and Lect. viii. On Organized Bodies, and the Structure of Plants compared to that of Animals, p. 81.