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which is contrary to the nature of an elaftic chord, that communicates its tremors equally to both ends from the point of percuffion. This is, in fome measure, illuftrated from the known experiment on the phrenic nerve, which being rubbed downwards, below the place of compreffion, renews the motions of the diaphragm, but rubbed upwards entirely ftops it; whence it seems evident, the progrefs of the nervous fluid is urged by one motion, and intercepted by the other.' From these and fome other arguments he very rationally concludes it almoft abfolutely certain, that the nervous fibres are hollow, and that they exercife thèir functions, not by their fpring, but by the motion of their proper fluids. Nor is the extreme fmallness 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 fenses, but avail nothing against the actual presence of nervous fpirits.'
To thefe folid arguments, from this great phyfician, Dr. Flemyng ingeniously adds, that if the Hypothefts of the vibration of the nerves might be commodiously applied to explain fenfation, it could no wife account for mufcular motion, or action; for what, faith he, hath trembling to do with traction or pulling?'
Dr. Flemyng's affumption then, that the nerves are hollow canals, the smallest in the body, which contain and tranfmit a peculiar fluid, being rendered fo entirely probable, he proceeds to his first Lemma, viz. that the animal folids confift of phlegm or water, of oil, of a peculiar effential falt, and of earth, to which laft their stability or firmness is owing.' He employs two or three pages to prove to his readers, in general, the certainty of thofe 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 fecreted, was constituted of the fame principles, tho' differently proportioned, as the Lemma would have been equally admittable, perhaps it would have been more comprehenfive, and not have had a lefs direct and immediate tendency to infer the principles of the nervous fluid fecreted from it. It might alfo have prevented an unphysical reader's misapprehending a paffage in the 16th page of this performance, where Dr. Flemyng defires to ob
ferve, that as the nerves are folid parts, that is, not fluid, they must be acknowledged to contain the fame principles with the other folid parts of the animal ftructure.From whence, as the folids and fluids may feem mentioned here in fome contradiftinétion to each other, fome readers might fuppofe they confifted of different principles; which the doctor did not intend, having evinced the very reverse in the progrefs of his work. In p. 24, 25. he says, the nerves are nourished principally by the nervous fluid; but that fluid cannot give to the nerves what it contains not itself.' And p. 38. he afks, what can the moft fubtle fluid in the animal body confift 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 folids and fluids is not mere affertion, we know from chemical Analyfis; and particularly from a late accurate one of animal Hesh, and of the human blood and urine, made by the worthy and indefatigable Dr. Langrish, in his valuable treatife of the modern theory and practice of phyfic, where it appears, that the principles which the tendons and muscles of an ox, and the blood and urine of the healthy man were refolvable into, were the fame, tho' in different proportions; with this only exception, that the folids afforded no fixt falt, as the fluids, and particularly the urine, did. Neither is it probable, that if found human flesh were eafily procurable for an Analyfts, the principles would have been different; tho' poffibly their proportions might vary a little; and perhaps the human flesh might have afforded some fixt falt, which the quadrupeds did not, the fixt falt from the fluids exhibiting the ufual Phænomena of sea-salt.
The doctor's fecond Lemma fuppofes,' that the nutrition of the smallest veffels in the animal body is fupplied, at leaft in a confiderable measure, if not principally, by the fluids or juices, which pervade their cavities." This appears so rational in itself, and fo obvious to every perfon, who is furnished with a tolerable idea of the animal œconomy, that we fhall mention but two of the author's many arguments in fupport of it: the firft is its analogy with the general manner of nutrition in the other animal veffels, as acknowledged by the beft modern authors on that subject, who allow a plaftic or nutritive quality in the fluids, which repairs the abrasions their friction has occafioned: the fecond is its not being agreeable to the fimple 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 Difpendium is made within.'
The Doctor probably obferves this, in oppofition to the fentiments of fome, who fuppofed the nerves might be principally nourished by a vaporous moisture, furrounding their membranes, and pervading their fubftance as he fuppofes fuch moisture, if admitted, to be more applicable to the repair of their involving membranes, than to that of any abrasions in their containing cavities. In this he agrees with Mr. Monro, whom the Doctor, with great pleasure apprehends to have adopted this fyftem of the nervous fluid; which he publifhed above ten years past, though lefs explicitely than in his prefent pamphlet, in a Latin poem, entitled Neuropathia, a copy of which he then tranfmitted to that ingenious profeffor. And indeed it must be acknowledged, there is an effential agreement, or even fameness, in their fentiments of the nervous fluid, which is abundantly evinced by Dr. Flemyng's final propofition, that,
The nervous fluid, or animal fpirits, confifts of phlegm or water, oil, animal falt and earth, all highly attenuated and fubtilized, and intimately mixed and incorporated together.' This, in fhort, infers no more, than that the nervous fluid, or animal fpirits, confifts of the fame principles 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 fubfequent to this propofition, the Doctor fuppofes it must appear ftrange, that an enquiry fo feemingly abftrufe, fhould terminate in fo great fimplicity: but this he obferves to be the cafe with many important truths.'
It is undoubtedly impoffible to fubject this nervous fluid, or animal fpirits (if they be really the fame) to fuch a chemical analyfis, as the tangible animal fluids may; nor have we ever heard of any fuch analyfis 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 flesh and tendons of quadrupeds, may be fubjected to this Examen, it might not be incurious to obferve their different proportions of the common conftituent principles; from whence poffibly fome rational conjecture might be formed of the more par
ticular Crafts of the fluid contained in, and nutritive of them.
Hitherto our author feems, with fufficient force and perfpicuity, to have deduced the principles of a fluid fecreted in the brain, which permeates the cavities of the nerves, and repairs their folids. But whether this fluid, confifting folely of thofe principles, doth really conftitute thofe animal fpirits, that are indispensably requifite to voluntary and involuntary motion; to communicate the impreffions of fenfation to the mind; and which, in this ftate, appear even neceffary to a perceptible exertion of the faculties of the. foul, is not fo clearly determinable from the fcope of this pamphlet. It must be confeffed, however, that the author being well aware of thofe objections, becomes more diffi dent here, than in his title page, and very modeftly fays, p. 27. I pretend not to prove, that there is nothing elfe in the nervous fluid, befides the principles I have enume rated but these principles, I affirm, it must confist of if the nerves are canals, and contain a fluid. There may be in animal fluids in general, and that of the nerves in. particular, fome fubtle Ether, fire or fpirit, or whatever other name it may be called by, diffused through the atmosphere, and perhaps over our whole fyftem, acting by. laws unknown to us, and in a particular manner in organized bodies: I fay, there may be fuch a spirit necessary. to cause muscular motion, in co-operation with the proper fluid of the nerves, which is the product of the animal, fabric and economy; and yet all my reasonings ftand. good. Be that as it will, certain it is, that the nervous. fluid I have described, if there is really a nervous fluid, is, at least, a Conditio fine quâ non of sensation and muscular motion.'
The promised demonstration then of the animal fpirits. terminates either in this, that the nervous fluid, confifting of the common principles of the human mafs, are the animal fpirits themselves; or else, the indifpenfable vehicle of them, which laft indeed feems the more probable for it may be fairly fuggefted, from what our author has fuppofed in the laft cited paragraph, that he himself conceived fomething ftill more fubtle than those material principles, in their utmost attenuation, fome Quintum quid, whofe effence may be ftill very recondite, and whofe operation is at once amazingly bland and active, involved in the nervous fluid he has demonftrated, as the exquifite and immediate agent between mind and matter. If fuch 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 alfo,. how far the nervous water, oyl, falt and earth, are capable of being fubtilized, and yet of continuing fo effentially fuch, as to deserve thofe appellations, by proving reducible to their own appearance and fubftance? We are fenfible, the great lord Bacon fuggefts a commutation of the very elements, and particularly of water into air, which he fays would be one of the Magnalia Natura. It is no injury, however, to the memory of that illuftrious philofopher to affert, that phyfics have admitted of fome improvements fince his time. But a purfuit of these fubtilties might too eafily lead us into a fruitless confideration of the amazing exility of matter, and the endlefs varieties of its formation for fuch indeed is the natural curiofity 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 acquifitions, comparatively, few.
Here then, confiftently with the fcope and purpose of the Review, we might take leave of Dr. Flemyng's performance; but there is fomething fo diftinct and entertaining in his reflexions on the feemingly inftantaneous exertion of voluntary motion, that we chufe to conclude this article. with a fummary abftract of them; which are not the less his own, for their being very obvious, or for their having probably occurred to many other difcerning phyfiologifts.
• Time is infinitely divifible, as well as matter or extenfion. A mufket bullet describes a certain line in a fecond, fuppofe one of a hundred yards, on a very moderate allowance, which containing 3600 inches, it defcribes an inch, taking its velocity at a Medium, in the 3600th part of a fecond; the roth of an inch in the 10th of that time, and fo 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 divifibility of time keeps pace with that of a line, which mathematicians have demonftrated to be infinite, and which this fingle example is fufficient to convince us of.'
• Motion is alternately measured by time; for length and fhortness of time, and flowness and celerity of motion, are only relative and comparative terms. In like manner no part of matter or extenfion is abfolutely, but relatively, great or small. We can imagine no smaller part of time