T

the author has happily applied to the illuftration of this recondite fubject. As he obferves from dr. Hale's experiments, that the blood, in every circulation, lofes 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 fyftem far above the power of mechanifm; the contraction of the heart and fecretion of the fpirits acting in a circle, and being mutually to be confidered as caufe and effect: from whence it becomes incumbent on thofe, who afcribe the motion of the heart to mechanical principles only, to demonftrate the poffibility of a perpetuum mobile, which an animal, while living, really is. But as the ableft philofophers have concluded this above the powers of mechanifm, as it must fuppofe the abfurdity of a weight heavier, or an elafticity more elaftic than itfelf, it follows, that the contraction of the heart, the propulfion of the blood, and the consequent continuance of life, are not owing to mechanical, or even material caufes alone; but to the energy of a living principle capable of generating motion. For though he fuppofes it formerly proved, that the alternate contractions of the heart are owing to the ftimulation of the refluent blood, he affirms them no other wife owing to it, than as the mind is excited by it to determine the nervous influence more copioufly 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 firft, in answer to that which objects,-that, while we afcribe the vital motions to the mind, we attribute them to a power, whofe nature and manner of action we are really ignorant of, he fays, it may be hoped, there are few philofophers fo minute at prefent, as to deny the union of a fentient principle with animal bodies, which is the cause of voluntary motion: and, if it be not thought abfurd to afcribe that to the energy of the mind, why fhould it be reckoned fo to derive the involuntary from the fame fource, when a variety of phænomena, and the strongest analogy fupport it? He obferves, that no one doubts of gravity, tho' its cause be unknown: and if philofophers juftly and continually use it to explain the phænomena of nature, why fhould it be thought unreafonable to have recourse to the energy of the mind, ever mani

feftly

feftly prefent with the body, and operative on it in numberless inftances, tho' its nature is unknown.

The doctor being naturally led, by this part of his fubject, to mention the anima and animus, or fentient and rational foul of the antients, is inclined to think them but. one principle acting in different capacities, which certainly appears the moft fimple and intelligible fuppofition, and is ftrongly fuftained in the fequel of this fection. In a note here, which gives an abftract of dr. Nichol's elegant prælection de animâ medicâ, he fays, with a genteel stricture, it fcarcely feems to demand a ferious anfwer. Many fubfequent 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 metaphysical reflections, but such as unusually illuftrate, inftead of obfcuring, the fubject; and he finishes this part of the fection, by acknowledging his furprize, that Defcartes and his followers fhould ferioufly believe, that even the perfecter brutes were utterly machines wound up and fet agoing; when the animal principle in them is plainly intelligent as well as fentient, and evinces that ftrength of memory, with reflection, and even fome degrees of reafon; this he attributes, among other caufes, to an overfondness of reasoning in phyfics, from mechanical principles; adding, it is not lefs ftrange, that the generality of theological writers fhould not, till very lately, discover, that, from admitting all the actions of the more perfect brutes to refult from meer mechanism, the afcribing every thing in man to no higher a principle would be a natural and eafy confequence.

To a fecond objection, which alledges the vital motions cannot be owing to a stimulus affecting the mind, fince 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 commencerment of life.' Having rendered these points highly probable from many examples in familiar life, and from feveral occurrences in the animal oeconomy, which, from this writer's very agreeable manner, entertain while they inform, he proceeds to confider a third objection, viz. That though we are infenfible of the stimuli affecting the organs of vital motion, yet we ought to be confcious of the exertion of the mind's power in causing these motions. To this he replies, that generally the intervention of the mind in fevera animal motions, which are unaccountable on any other system,

--

is no ways adverted to while we exert it. Thus we, as it were unconfcicufly, contract the palpebra on duft or infects paffing near our eyes. The copious excretion of spittle in the mouth of an hungry perfon, on the fight of grateful food; and the effufion of milk from a nurse's breast, only on a child's approach to it, with many other phænomena in animal motion, are manifeftly exerted at an inftigation of the mind, without our consciousness of it.' But this objection our author thinks fundamentally destroyed from an obfervation, which every one may recollect; that even many voluntary motions are often performed, when we are infenfible of the mental power's being exerted in their production: and the true reason of our ignorance of those things tranfacted within the sphere of our own body feems 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 lefs fenfible of the fhare the mind has in them. He concludes his anfwer to this objection, by expofing 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 fuppofes, that if the vital motions were owing to the mind, they fhould be under its dominion or controul, to fufpend or vary them at pleasure. To which he answers, in effect, that though man is evidently free to embrace or abftain from actions which are the objects of deliberation, yet there are others not determined by reafon, where the mind is a necessary agent, in the strongest sense, and that the involuntary motions of muscles from a ftimulus are of this kind. As we cannot therefore hinder ourfelves from seeing every object painted at the bottom of the eye, fo neither can the mind fufpend its power of moving a muscle, whofe fibres are ftrongly ftimulated. Yet while no one denies that the mind hears and fees, because on the prefence of fuch objects no mere effort of our will can prevent our feeing 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 confequence of any ratiocination of the mind, as an intelligent principle; fo neither do they flow from cuftom, fince 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-wife Creator between the foul

and

and body; whereby the former, without reasoning, endeavours, in the moft effectual manner, to extinguish every disagreeable sensation conveyed to it from whatever annoys the latter. Many of the phænomena in the animal œconomy, specified in corroboration of this, are the very fame with those he has formerly inftanced to fupport fome of his other arguments; but as they are, without the least torturing, as ftrongly applicable here, their very general coincidence with the various divifions of his fyftem feem no inconfiderable proof of its truth, and even demonftrate the great verifimilitude of the whole.

In answer to the fifth objection-That the mind can perceive diftinctly but one idea at once, and therefore must be incapable of attending to, and governing all the vital and involuntary motions which are fo numerous-he obferves, 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 fame time; and we know it can move many of the voluntary muscles in the fame inftant. But further, to the direct invalidation of the objection, dr. Whytt asks, When the famous Turkish equilibrift ftands with one foot on the flack wire, toffing and catching alternately fix or seven balls in the air, is he not attentive to more than one thing at once?--Poffibly fome very tenacious difputant might reply to him here, that the extremely minute divifibility of time might warrant the affertion, that the equilibrift was, in the fame ftrictly indivifible punctum of it, but attentive to one thing, the prefent toffing, or quickly fucceffive catching a different ball; which, however, would appear fo rapid to the fpectators and himself too, as to be commonly confidered for one and the fame inftant; tho', in a rigid analyfis of time, it certainly was not: and he might, from long habit, have acquired fuch a facility of difpofing 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, fuppofing the attention of his mind fometimes neceffary to his posture, the fupputable divifibility of time might allow even for that. -But it is evident our author, in mentioning the fame time here, only intends that portion of it, which generally appears inftantaneous to human fense; and has no reference to fuch a minute and scarcely conceivable brevity of it, as that

in

in which light may be fuppofed, merely for argument's fake, to move an inch, or any divifion of one; which is perhaps more inftantaneous than the energy of fpirits, at leaft 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 same 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 ftimuli on the vital organs, and thence to continue their motions. In the AuTHOR of nature, however, (fays this writer, with a very feasonable reverence) who has framed both the foul and · body, and thus adapted them to each other, we ought, as upon many other accounts, fo alfo upon this, to acknowledge a wifdom that is infinite and unfearchable!

The remainder of this fection is chiefly employed in fome ingenious remarks on the ftriking analogy between various animal motions; and after a brief recapitulation of the progrefs hitherto made in his theory, he concludes it in the following moft fenfible and modeft terms:

But what way the mind puts the muscles into motion; what is the material cause in the brain, nerves, and mufcular fibres, which it employs as its inftrument for this purpose; what the intimate ftructure of a mufcular fibre, or the precife manner in which the nervous influence acts upon it, when it produces its contraction; these are queftions we have wholly avoided, being perfuaded that whatever has been hitherto faid on thefe fubjects, is mere fpeculation; and that to offer any new conjectures on matters fo greatly involved in darkness, and where we have neither data nor phænomena to fupport us, is to load a fcience, already labouring under hypothefes, with a new

burden.'

The 12th fection enquires into the reafons of the continuance of the vital motions in fleep; or why the vital organs fhould not, like the organs of fenfe, and the mufcles of voluntary motion, be rendered lefs qualified to perform their functions in that state. Sleep, fays our author, seems to be owing to fome change produced in what anatomists, diftinguishing it from the cerebellum, call the brain. And there have been plain inftances, where people, having loft part of their fcull, were immediately seized with fleep, on a gentle compreffion of the brain; but death, or at least a fyncope, is the effect of a like compreffion of the cerebellum:

Now,