Изображения страниц
PDF
EPUB

the author has happily applied to the illustration of this recondite subject. As he observes from dr. Hale's experiments, that the blood, in every circulation, loses te of the momentum communicated to it by the left ventricle of the heart, there must be therefore, he fays, in every animal a cause generative of motion to repair this great loss of it; which matter, in its inert nature, is incapable of. The human body, he adds, in which there is no mover that can properly be called FIRST, is a system far above the power of mechanism ; the contraction of the heart and fecretion of the spirits acting in a circle, and being mutually to be considered as cause and effect: from whence it becomes incumbent on thofe, who ascribe the motion of the heart to mechanical principles only, to demonstrate the poffibility of a perpetuum mobile, which an animal, while living, really is. But as the ablest philosophers have concluded this above the powers of mechanism, as it muft suppose the absurdity of a weight heavier, or an elasticity more elastic than itself, it follows, that the contraction of the heart, the propulsion of the blood, and the consequent continuance of life, are not owing to mechanical, or even material causes alone ; but to the energy of a living principle capable of generating motion. For though he fup >poses it formerly proved, that the alternate contractions of the heart are owing to the stimulation of the refluent blood, he affirms them no otherwise owing to it, than as the mind is excited By it to determine the nervous inAuence more copiously into its fibres. And this doctrine he very rationally extends to the other vital and involuntary motions.

He next proposes to invalidate fome objections that may be made to this opinion; and first, in answer to that which objects,--that, while we ascribe the vital motions to the mind, we attribute them to a power, whose nature and manner of action we are really ignorant of, he fays, it may be hoped, there are few philosophers so minute at present, as to deny the union of a sentient principle with animal bodies, which is the cause of voluntary motion : and, if it be not thought absurd to ascribe that to the energy of the mind, why should it be reckoned fo to derive the involuntary from the same source, when a variety of phanomena, and the strongest analogy support it? He observes, that no one doubts of gravity, tho' its cause be unknown: and if philosophers justly and continually use it to explain the phænomena of nature, why should it be thought unreasonable to have recourse to the energy of the mind, ever mani

festly

festly present with the body, and operative on it in numberless instances, tho' its nature is unknown.

The doctor being naturally led, by this part of his subject, to mention the anima and animus, or fentient and rational soul of the ancients, is inclined to think them but one principle acting in different capacities, which certainly appears the most simple and intelligible supposition, and is strongly sustained in the sequel of this section. In a'note here, which gives an abstract of dr. Nichol's elegant prælection de animâ meilicâ, he says, with a genteel ftri&ture, it scarcely seems to demand a serious answer. Many fubsequent pages are employed in rendering it highly probable, that the mind, in producing vital motion, does not act as a rational but fentient principle, contrary to the opi. nion of Stahl and his followers. They abound with me taphysical reflections, but such as unusually illustrate, instead of obscuring, the subject; and he finishes this part of the section, by acknowledging his furprize, that Descartes and his followers should seriously believe, that even the perfecter brutes were utterly, machines wound

up

and set agoing; when the animal principle in them is plainly intelligent as well as sentient, and evinces that strength of memory, with reflection, and even some degrees of reafon; this he attributes, among other causes, to an overfondness of reasoning in physics, from mechanical principles ; adding, it is not less strange, that the generality of theological writers should not, till very lately,, discover, that, from admitting all the actions of the more perfect brutes to result from

meer mechanism, the afcribing every thing in man to no higher a principle would be a natural and easy consequence.

To a second objection, which alledges the vital motions cannot be owing to a stimulus affecting the mind, since we are not conscious of it, he answers,, - this may be owing to the gentleness of the irritation, or to our having been long accustomed to it, perhaps from the very commencer ent of life.' Having rendered these points highly probable from many examples in familiar life, and from several occurrences in the animal economy, which, from this writer's very agreeable manner, entertain while they inform, he proceeds to consider a third objection, viz. That though we are insensible of the stimuli affecting the organs of vital mo. tion, yet we ought to be conscious of the exertion of the mind's power in causing these motions. To this he replies,

that generally the intervention of the mind in severa animal motions, which are unaccountable on any other system,

is

[ocr errors]

is no ways adverted to while we exert it. Thus we, as it were unconsciously, contract the palpebre on duft or insects passing near our eyes. The copious excretion of spittle in the mouth of an hungry person, on the sight of grateful food; and the effusion of milk from a nurse's breast, only · on a child's approach to it, with many other phænomena in animal motion, are manifestly exerted at an instigation of the mind, without our consciousness of it. But this objection our author thinks fundamentally destroyed from an observation, which every one may recollect; that even many voluntary motions are often performed, when we are insensible of the mental power's being exerted in their production: and the true reason of our ignorance of those things transacted within the sphere of our own body seems this, that we not only acquire, thro' long habit, a faculty of performing certain motions with unwonted ease, but, in proportion to this greater facility, we become less sensible of the share the mind has in them. He concludes his answer to this objection, by exposing the weakness of that opinion, which denies the faculties of the mind to be equal even to the functions of voluntary motion ; and proceeds to the fourth, which supposes,—that if the vital motions were owing to the mind, they should be under its dominion or controul, to suspend or vary them at pleasure. To which he answers, in effect, that though man is evidently free to embrace or abstain from actions which are the objects of deliberation, yet there are others not determined by reason, where the mind is a necessary agent, in the strongest sense, and that the involuntary motions of muscles from a stimulus are of this kind. As we cannot therefore hinder ourselves from seeing every object painted at the bottom of the eye, so neither can the mind suspend its power of moving a muscle, whose fibres are strongly stimulated. Yet while no one denies that the mind hears and sees, because on the presence of such objects no mere effort of our will can prevent our seeing or hearing, it must be unreasonable to pretend the involuntary motions cannot arise from the energy of the mind, because the will has no immediate power over them. And as they are not performed in consequence of any ratiocination of the mind, as an intelligent principle ; so neither do they flow from custom, since infants breathe immediately from the birth, as well as the most experienced: whence it remains, that our motions from irritation are owing to our original frame, and the law of union established by the all-wise Creator between the soul

and

and body; whereby the former, without reasoning, endeavours, in the most effectual manner, to extinguish every disagreeable sensation conveyed to it from whatever annoys the latter. Many of the phænomena in the animal oeconomy, specified in corroboration of this, are the very fame with those he has formerly instanced to support fome of his other arguments ; but as they are, without the least torturing, as strongly applicable here, their very general coincidence with the various divisions of his system seem no inconfiderable proof of its truth, and even demonstrate the great verisimilitude of the whole.

In answer to the fifth objection–That the mind can perceive distinctly but one idea at once, and therefore must be incapable of attending to, and governing all the vital and involuntary motions which are so numerous-he observes, it is chiefly levelled against the opinion of the mind's regulating the vital motions, as a rational agent, and does not affect his theory: for whether it can distinctly apprehend more than one idea at once or no, it certainly perceives different sentations in different bodily parts at the same time, and we know it can move many of the voluntary muscles in the same instant. But further, to the direct invalidation of the objection, dr. Whytt alks, When the famous Turkish equilibrist stands with one foot on the slack wire, tossing and catching alternately fix or seven balls in the air, is he not attentive to more than one thing at once? -Possibly some very tenacious disputant might reply to him here, that the extremely minute divisibility of time might warrant the affertion, that the equilibrist was, in the same strictly indivisible punctum of it, but attentive to one thing, the present toffing, or quickly successive catching a different ball; which, however, would appear so rapid to the spectators and himself too, as to be commonly considered for one and the same instant; tho', in a rigid analysis of time, it certainly was not : and he might, from long habit, have acquired such a facility of disposing his body into a proper poize on the wire, as should engage his mind very little more than standing in a common posture on the ground: or that, fupposing the attention of his mind sometimes necessary to his posture, the supputable divisibility of time might allow even for that. -But it is evident our author, in mentioning the same time here, only intends that portion of it, which generally appears instantaneous to human sense; and has no reference to such a minute and scarcely conceivable brevity of it, as that

in which light may be supposed, merely for argument's fake, to move an inch, or any division of one; which is perhaps more instantaneous than the energy of spirits, at least of those who are clogg'd with, and who act thro', material organs.-- Dr. Whytt obferves further, that a man can hear a found and perceive a particular colour at the fame time; yet, how attentive foever to these, if a fly runs along his face, he will certainly drive it off ; as the mind, however employed on its own thoughts or external objects, is always ready to perceive the various stimuli on the vital orgars, and thence to continue their motions. In the AuTHOR of nature, however, (says this writer, with a very feasonable reverence) who has framed both the soul and ·body, and thus adapted them to each other, we ought, as

upon many other accounts, so also upon this, to acknowledge a wisdom that is infinite and unsearchable !

The remainder of this section is chiefly employed in some ingenious remarks on the striking analogy between various animal motions; and after a brief recapitulation of the progress hitherto made in his theory, he concludes it in the following most sensible and modest terms :

• But what way the mind puts the muscles into motion; what is the material cause in the brain, nerves, and muscular fibres, which it employs as its instrument for this purpose ; what the intimate structure of a muscular fibre, or the precise manner in which the nervous influence acts upon it, when it produces its contraction; these are questions we have wholly avoided, being persuaded that whatever has been hitherto said on these subjects, is mere speculation; and that to offer any new conjectures on matters so greaily involved in darkness, and where we have neither clata nor phænomena to support us, is to load a science, already labouring under hypotheses, with a new burden.'

The 12th section enquires into the reasons of the continuance of the vital motions in sleep; or why the vital organs should not, like the organs of sense, and the muscles of voluntary motion, be rendered less qualified to perform their functions in that state. Sleep, lays our author, seems to be owing to some change produced in what anatomists, diftinguishing it from the cerebellum, call the brain. And there have been plain instances, where people, having loft part of their scull, were immediately seized with sleep, on a gentle compression of the brain; but death, or at least a Syr.cope, is the effect of a like compression of the cerebellum.

Now,

« ПредыдущаяПродолжить »