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CHAPTER VII.

OF THE MECHANICAL AND IMMECHANICAL PARTS AND FUNCTIONS OF ANIMALS AND VEGETABLES.

IT

T is not that every part of an animal or vegetable has not proceeded from a contriving mind; or that every part is not constructed with a view to its proper end and purpose, according to the laws belonging to, and governing, the fubftance or the action made use of in that part; or that each part is not fo constructed, as to effectuate its purpose whilst it operates according to these laws: but it is, because these laws themselves are not in all cafes equally understood; or, what amounts to nearly the fame thing, are not equally exemplified in more fimple proceffes, and more fimple machines; that we lay down the diftinction, here propofed, between the mechanical parts, and other parts, of animals and vegetables.

For inftance; the principle of muscular motion, viz. upon what cause the swelling of the belly of the mufcle, and confequent

contraction

contraction of its tendons, either by an act of the will or by involuntary irritation, depends, is wholly unknown to us. The fubftance employed, whether it be fluid, gafeous, elastic, electrical, or none of these, or nothing resembling thefe, is also unknown to us of course the laws belonging to that fubftance, and which regulate its action, are unknown to us. We fee nothing fimilar to this contraction in any machine which we can make, or any procefs which we can execute. So far (it is confeffed) we are in ignorance: but no further. This power and principle, from whatever cause it proceeds, being affumed, the collocation of the fibres to receive the principle, the difpofition of the muscles for the use and application of the power, is mechanical; and is as intelligible as the adjustment of the wires and ftrings by which a puppet is moved. We fee therefore, as far as refpects the subject before us, what is not mechanical in the animal frame, and what is. The nervous influence (for we are often obliged to give names to things which we know little about)-I fay the nervous influence, by which the belly or middle of the muscle is fwelled, is not mechanical. The utility of the effect we perceive; G 3 the

the means, or the preparation of means, by which it is produced, we do not. But obfcurity as to the origin of mufcular motion. brings no doubtfulness into our obfervations upon the fequel of the procefs. Which observations relate, 1ft, to the constitution of the mufcle; in confequence of which conftitution, the fwelling of the belly or middle part is neceffarily and mechanically followed by a contraction of the tendons: 2dly, to the number and variety of the muscles, and the corresponding number and variety of useful powers which they supply to the animal; which is aftonishingly great: 3dly, to the judicious (if we may be permitted to use that term, in fpeaking of the author, or of the works, of nature), to the wife and well contrived difpofition of each muscle for its specific purpose; for moving the joint this way, and that way, and the other way; for pulling and drawing the part, to which it is attached, in a determinate and particular direction; which is a mechanical operation, exemplified in a multitude of inftances. To mention only one; the tendon of the trochlear mufcle of the eye, to the end that it may draw in the line required, is paffed through a cartilaginous ring, at which

it is reverted, exactly in the fame manner as a rope in a fhip is carried over a block or round a stay, in order to make it pull in the direction which is wanted. All this, as we have faid, is mechanical; and is as acceffible to inspection, as capable of being afcertained, as the mechanifm of the automaton in the Strand. Suppose the automaton to be put in motion by a magnet (which is probable), it will fupply us with a comparison very apt for our prefent purpose. Of the magnetic effluvium we know perhaps as little as we do of the nervous fluid. But magnetic attraction being affumed (it fignifies nothing from what cause it proceeds), we can trace, or there can be pointed out to us, with perfect clearness and certainty, the mechanism, viz. the steel bars, the wheels, the joints, the wires, by which the motion fo much admired is communicated to the fingers of the image: and to make any obfcurity or difficulty, or contraverfy in the doctrine of magnetisin, an objection to our knowledge or our certainty concerning the contrivance, or the marks of contrivance, difplayed in the automaton, would be exactly the fame thing, as it is to make our ignorance (which we acknowledge) of the caufe

G 4

cause of nervous agency, or even of the subftance and ftructure of the nerves themselves, a ground of question or fufpicion as to the reafoning which we inftitute concerning the mechanical part of our frame. That an animal is a machine, is a propofition neither correctly true, nor wholly falfe. The distinction which we have been difcuffing will serve to fhew how far the comparison, which this expreffion implies, holds; and wherein it fails. And, whether the diftinction be thought of importance or not, it is certainly of importance to remember, that there is neither truth nor justice in endeavouring to bring a cloud over our understandings, or a distrust into our reafonings upon this subject, by suggesting that we know nothing of voluntary motion, of irritability, of the principle of life, of sensation, of animal heat, upon all which the animal functions depend; for our ignorance of thefe parts of the animal frame concerns not at all our knowledge of the mechanical parts of the fame frame. I contend, therefore, that there is mechanism in animals; that this mechanifm is as properly fuch, as it is in machines made by art; that this mechanifm is intelligible and certain; that it is not the lefs fo

because

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