Dr. quence of a certain organization*. But while no fingle hypothesis respecting the vital principle prevailed generally, two theories appeared, which engaged attention by the eminence of their authors, as well as by their own nature. Monro accounts for the commencement of the involuntary motions, and fome other phænomena, on the fuppofition of a living principle, pervading the universet; fimilar, I apprehend, to the plaftic nature of the Platonifts. Mr. Hunter attributes to the blood, a power of forming and renewing parts, by its proper efforts, apparently carried, in fome cafes, almoft to a degree of rationality. It is fufficient to prove the great differences among modern phyfiologists, on this fubject, to obferve, that while Dr. Hoffman has distinguished, in very ftrong terms, between the fenfitive and rational fouls, Dr. Cullen allows, that Hoffman, T. I p. 18. Buffon, Hiftoire Naturelle Since this Effay was written, Dr. Fordyce has attempted to account for mufcular motion on the theory of a peculiar attraction, which he terms the attraction of life. But, as I had occafion to obferve elsewhere, there is too much defign in mufcular action to be mechanically explained, nor would our perplexity be at all diminished, by receiving an explanation which is fully as obfcure as the caufe of the phænomena to which it relates. + Obferv. on the Nervous System, p. ult. Med. Commentaries, vol. II. p. 198. Magna utriufque eft differentia, et diverfa plane ratio; ideoque deoque ambo non pro uno eodemque habenda... fed probé that this diftinction is only nominal, or, as Sennertus expreffes it, a differentia in anima*. Two general reflections occur, on this imperfect view of the progrefs of opinions refpecting a vital principle; that the chief difficulty confifted, in the perfuafion that matter is totally inert, and infufceptible of fenfitive life, by any organization, which Hoffman juftly calls infeli ciffimum dogmat; and that fyftematic diftinctions, in this, as in other cafes, have been mistaken for effential differences. Accordingly, inconfiftences are to be found in feveral of these opinions; thus Dr. Haller affigns two diftinct powers, the vis nervea, and vis infita, for producing the simple action of one muscle; and though the nervous fyftem is generally allowed to be the medium of fenfation and voluntary motion, yet Dr. Gaubius has contrived to exclude this vehicle of the living power from the title of the vital folids; Vis vitalis folidi eft, qua id ad contactum irritamenti fe contrabit, crifpat. It is well known that the nerves have no power of contraction. Gaubius muft have fuppofed the existence of a nervous fluid to be granted, in forming this definition, for it does not appear, probé ratione diverfarum operationum, quæ difcrepantem etiam effentiam produnt, funt diftinguenda. T. I. p. 88. *Inftit. of Med. fe&t. XCVII. + Proleg. cap. III. from from other parts of his Pathology, that he meant to exclude the nervous fyftem. Dr. Haller's theory of the vis infita was formed from a variety of experiments on living animals, by which he found the irritability of muscles to remain, long after their connection with the brain was deftroyed. But the experiments of Dr. Monro†, Dr. Whytt‡, and Dr. Smith ||, prove that there is no real diftinction between the vis infita and the nervous energy. This difpute is fo well known, that a particular account of the arguments and experiments is unneceffary; and fome of the strongest will be produced in the course of our inquiry. Galen, from fimilar obfervations with Dr. Haller, had drawn the fame conclufion with respect to the motion of the heart §. Dr. Whytt, with an inaccuracy surprizing in fo acute a phyfiologift, fupposes the foul to be present in different parts of the brain at the fame time, while he confiders the foul as immaterial and unextended¶. Nay, he afferts that when contraction takes place, on the irritation of a separated muscle, the action happens from the influence of part of the foul contained in the feparated part**. Yet he complains that Dr. Phyfiolog. T. I. p. 426 to 466. Id. T. IV. p. 516. + Obf. on the Nerv. Syft. ↑ Obf. on Irritab. and Senfib. p. 310, (of the Quarto Differt. Inaugural. edit.) § Van Swieten Comment. T. I. p. 3, 4. ** Ib. Haller Haller charges him with making the foul divifible. Dr. Whytt admits, alfo, contrary to experiments, the Stahlian doctrine of univerfal fenfation; a doctrine clearly difproved, by the effect of ligatures, or divifion of nerves, in the living animal. While he combats the vis infita, he produces fome facts which contradict his own. theory of the involuntary motions, and feem to fhew, that the motions of those organs may be explained from the ftimulus of the contained fluids. Thus, the power of ftimuli applied to any muscular part, even to a voluntary múscle, is greater than the power of the will over that part†, and the peristaltic motion of the inteftines fometimes continues, after the action of the heart has ceased, from the ftimulus of their contents. And Dr. Whytt is obliged to confefs, that the mind has no concern, as a rational agent, with the coalefcence of the ductus arteriofus & ductus venofus after birth§; for the mind is not even conscious that fuch parts have ever existed, and their circumstances are only known by anatomical investigation. Dr. Monro explains his opinion of the intelletus agens, in the human body, in thefe few Ib. p. 192. Dr. Haller fays, Vox (vis vitalis) non perinde placet, cum vis noftra vitæ aliquantum fupervivat. Phyfiolog. T. IV. p. 464. VOL. III. Vit. and Inv. Mot. p. 169. words; words; "that the power which created all things, "which gave life to animals, and motion to the heavenly bodies, continues to act upon, and to "maintain all, by the unceafing influence of a living principle pervading the universe, the "nature of which our faculties are incapable of duly comprehending." But this theory feems liable to the fame objection with the notion of a plaftic power; that neither of them affords a fatisfactory explanation of the phenomena of sense and motion. For the plaftic power, or living principle, must be either material or immaterial: if it be material, then it must be allowed that matter, as matter, is fufceptible of life; now as the existence of the plaftic power is merely affumed, we have a right, in this case, to suppose that the body acquires vitality by a certain degree of organization, as a preferable hypothefis. But if the plastic power be declared immaterial, its action on matter is as difficult to be conceived, as the action of an immaterial mind on the body, and confequently nothing is gained but a term by the fuppofition. If the living power be supposed to be an immediate act of the Deity, an opinion which has been held by many philofopherst, this is liable to ftill ftronger ob * Conclufion of Obf. on the Nervous System. + Sennert. Epitom. Phyf. p. 82. P. 530. Alfted. Encyclop. jections; |