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which is contrary to the nature of an elastic chord, that communicates its tremors equally to both ends from the point of percuffion. This is, in some measure, illustrated from the known experiment on the phrenic nerve, which being rubbed downwards, below the place of compression, renews the motions of the diaphragm, but rubbed upwards entirely stops it; whence it seems evident, the progress of the nervous Auid is urged by one motion, and intercepted by the other.' From thele and some other arguments he very rationally concludes it almost abfolutely certain, that the nervous fibres are hollow, and that they exercise their functions, not by their spring, but by the motion of their proper Auids. Nor is the extreme smallness of these canals, which no microscope can reach, an objection of any weight, with him, against the experiments above mentioned ; nor the absence of tumour in a nerve upon being tied, which he affirms, is not altogether true, nor other arguments of the like nature, which, he thinks, only prove the imperfection of our senses, but avail nothing against the actual presence of nervous fpirits.'
To these solid arguments, from this great physician, Dr. Flemyng ingeniously adds, that if the Hypothesis of the vibration of the nerves might be commodiously applied to explain senfation, it could no wise account for muscular motion, or action ; for what; faith he, hath trembling to do with traction or pulling ?'
Dr. Flemyng's assumption then, that the nerves are hol. low canals, the smallest in the body, which contain and transmit a peculiar Auid, being rendered so entirely probable, he proceeds to his first Lemma, viz. that the animal folids consist of phlegm or water, of oil, of a peculiar effential falt, and of earth, to which last their stability or firmness is owing.' He employs two or three pages to prove to his readers, in general, the certainty of those principles, which his medical and chemical ones will immediately allow him, And if he had added here, that the blood, that animal fluid, from which all the others are secreted, was constituted of the fame principles, tħo' differently proportioned, as the Lemma would have been equally admittable, perhaps it would have been more compréhensive, and not have had a less direct and immediate tendency to infer the principles of the nervous Auid fecreted from it. It might also have prevented ant unphyfical reader's misapprehending a passage in the 16th page of this performance, where Dr. Flemyng desires to ob
serve, that as the nerves are solid parts, that is, not fluid, they must be acknowledged to contain the same principles with the other solid parts of the animal structure. From whence, as the folids and fluids may secm mentioned here in fome contradiftinction to each other, fome readers might fuppose they consisted of different principles; which the doctor did not intend, having evinced the very reverse in the progress of his work. In f. 24, 25. he says, "the nerves are nourished principally by the nervous Auid; but that Auid cannot give to the nerves what it contains not itself.'
And p. 38. he asks, what can the most subtle Auid in tlie animal body consist of, but the fame principles which constitute the blood, out of which it is made ?" And that this fimilarity, or even identity, of the principles of the animal solids and fluids is not mere afertion, we know from chemical Analysis ; and particularly from a late accurate one of animal flesh, and of the human blood and urine, made by the worthy and indefatigable Dr. Langrish, in his valuable treatise of the * modern theory and practice of physic, where it appears, that the principles which the tendons and muscles of an ox, and the blood and urine of the healthy man were resolvable into, were the same, tho' in different proportions; with this only exception, that the solids afforded no fixt falt, as the fluids, and particularly the urine, did. Neither is it probable, that if sound human flesh were easily procurable for an Analysis, the principles would have been different ; tho' possibly their proportions might vary a little ; and perhaps the human Aelh might have afforded some fixt falt, which the quadrupeds did not, the fixt falt from the fluids exhibiting the usual Phanomena of sea-salt.
The doctor's second Lemma supposes,' that the nutrition of the smallest vessels in the animal body is supplied, at least in a considerable measure, if not principally, by the Auids or juices, which pervade their cavities.' This appears so rational in itself, and so obvious to every person, who is furnished with a tolerable idea of the animal economy, that we shall mention but two of the author's many argum'ents in support of it: the first is its analogy with the general manner of nutrition in the other animal vessels, as acknowledged by the best modern authors on that subject, who allow a plastic or nutritive quality in the fluids, which repairs 'the abrasions their friction has occasioned: the fecond is its not being agreeable to the simple procedure of Compare p. 53, 54. with 80, 81. and 92.
nature; to bring the greatest part of the nutrition from without, when the whole or greatest part of the Dispendium is made within.'
The Doctor probably observes this, in opposition to the sentiments of some, who supposed the nerves might be principally nourished by a vaporous moisture, surrounding their membranes, and pervading their substance : as he fupposes such moisture, if admitted, to be more applicable to the repair of their involving membranes, than to that of any abrafions in their containing cavities. In this he agrees with Mr. Monro, whom the Doctor, with great pleasure apprehends to have adopted this system of the nervous fluid, which he published above ten years past, though less explicitely than in his present pamphlet, in a Latin poem, entitled Neuropathia, a copy of which he then transmitted to that ingenious profeffor. And indeed it must be acknowledged, there is an essential agreement, or even fameness, in their sentiments of the nervous fuid, which is abundantly evinced by Dr.Flemyng's final proposition, that,
• The nervous fuid, or animal spirits, consists of phlegm or water, oil, animal salt and earth, all highly attenuated and fubtilized, and intimately mixed and incorporated together.'-- This, in short, infers no more, than that the nervous fuid, or animal spirits, consists of the same prin-. ciples with the circulating fluids from which it was derived, and with the nervous fibrills, it is intended to nourish and repair, which it is highly reasonable to infer. And indeed, in the Scholium, immediately subsequent to this proposition, the Doctor supposes it must appear strange, that an enquiry so seemingly abstruse, should terminate in fo great simplicity: but this he observes to be the case with many important truths:'
It is undoubtedly impossible to subject this nervous fluid, or animal spirits (if they be really the same) to such a chemical analysis, as the tangible animal fluids may ; have we ever heard of any such analysis even of the nerves. Mr. Monro affirms, that the whole Congeries of them in the human body would not form a rope of an inch diameter, the length of which, however, he does not mention. But as the nerves, as well as the feh and tendons of quadrupeds, may be subjected to this Examen, it might not be incurious to observe their different proportions of the common conftituent principles ; from whence possibly, some rational conjecture might be formed of the more par
ticular Crasis of the Auid contained in, and nutritive of them.
Hitherto our author feems, with sufficient force and perspicuity, to have deduced the principles of a fuid secreted in the brain, which permeates the cavities of the nerves, and repairs their solids. But whether this fluid, consisting solely of those principles, doth really constitute those animal spirits, that are indispensably requisite to voluntary and involuntary motion; to communicate the impressions of fenfation to the mind; and which, in this state, appear even necessary to a perceptible exertion of the faculties of the foul, is not so clearly determinable from the scope of this pamphlet. It must be confessed, however, that the author being well aware of those objections, becomes more diffident here, than in his title page, and very modestly says, p. 27. . I pretend not to prove, that there is nothing else in the nervous fuid, besides the principles I have enume, rated : but these principles, I affirm, it must consist of if the nerves are canals, and contain a fluid, There
may be in animal Auids in general, and that of the nerves in particular, some subtle Æther, fire or spirit, or whatever other name it may be called by, diffused through the ato mosphere, and perhaps over our whole system, acting by laws unknown to us, and in a particular manner in organized bodies : I say, there may be such a spirit necessary, to cause muscular motion, in co-operation with the proper fuid of the nerves, which is the product of the animal fabric and economy; and yet all my reasonings stand good. Be that as it will, certain it is, that the nervous , Huid I have described, if there is really a nervous Auid, is, at least, a Conditio fine quâ non of sensation and muscular motion.'
The promised demonstration then of the animal spirits. terminates either in this, that the nervous fluid, consisting of the common principles of the human mass, are the animal spirits themselves; or else, the indispensable vehicle of them, which last indeed seems the more probable :
may be fairly suggested, from what our author has supposed in the last cited paragraph, that he himself conceived something still more fubtle than those material principles, in their utmost attenuation, some Quintum quid, whose essence may be still very recondite, and whose operation is at once amazingly bland and active, involved in the nervous Auid he has demonstrated, as the exquisite and immediate agent betyveen mind and matter. If such there
be, it must probably remain the object of our contemplation only, and can never admit of a palpable, nor perhaps of an experimental demonstration. It may be asked also, . how far the nervous water, oyl, falt and earth, are capable of being fubtilized, and yet of continuing fo effentially fuch, as to deserve those appellations, by proving reducible to their own appearance and substance? We are sensible, the great lord Bacon suggests a commutation of the very elements, and particularly of water into air, which he says would be one of the Magnalia Nature. It is no injury, however, to the memory of that illustrious philosopher to affert, that phyfics have admitted of some improvements fince his time. But a pursuit of these subtilties might too easily lead us into a fruitless consideration of the amazing exility of matter, and the endless varieties of its formation: for fuch indeed is the natural curiosity of the human mind, and fuch the limitation of its powers, in this ftate, that it is no wonder if our researches are many, and our real acquisitions, comparatively, few.
Here then, consistently with the scope and purpose of the Revići, we might take leave of Dr. Flemyng's performiance; but there is something so distinct and entertaining in his reflexions on the seemingly instantaneous exertion of voluntary motion, that we chuse to conclude this article with a summary abstract of them ; which are not the less his own, for their being very obvious, or for their having probably occurred to many other discerning phyfiolőgifts.
< Time is infinitely divifible, as well as matter or extension. A musket bullet describes a certain line in a fecond, fuppofe one of a hundred yards, on a very moderate allowance, which containing 3600 inches, it describes an inch, taking its velocity at a Medium, in the 360oth part of a fecond; the roth of an inch in the roth of that time, and so on. Now every minutest part of this line of 100 yards must be got over, before the bullet can arrive at the next. Hence we fee that the divisibility of time keeps pace with that of a line, which mathematicians have demonstrated to be infinite, and which this single example is sufficient to convince us of.
- Motion is alternately measured by time, for length and shortness of time, and flowness and celerity of motion, are only relative and comparative terms.
In like manner no part of matter or extension is absolutely, but relatively, great or small. We can imagine no smaller part of time