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on the Globule of Air, they will hinder its efcape from be- Again, if a Weight of a determined Bigncfs e*n be rais'd
tween them. But the Force whereby they endeavour to to a certain Height by a Bladder, or one String of Blad-
come together being vaitly greater than that of Gravity, ders, to which the Weight is tied ; twice that Weight may
the Globule of Air mult be considerably condenfed ; but be rais'd by two fuch Bladders, or Strings ; thrice by three
the Force of Ehiticiry being proportional to that of its 2?c and, consequently, the Weight a Mufcle can raife, will
Condenfation, the Force wherewith the airy Globule en- be always as the Number of its Fibres, i. e. as its Thick-
deavours to expand itfelf, will likewife be vaitly great ; fo nefs, fappofing the Diflenfion of the Veficles equal, and the
that if the Ntfus of the Particles of the Fluid to come to- abfolute Strength of one Mufcle to that of another, as their
gether Jhould be taken off, the Air between 'em would Bulks.
expand itfelf with a confiderable Force. Now, if upon Dr. Boerhaave finding all the Requires before laid
the mixing of another Fluid, the Particles of the firfl Fluid down, for the A&ion ot the Mufcles in the nervous Juice,
ihould be more Arongly attracted to the Particles of this or animal Spirits, and in no other Fluid in the Body, think'
ie another, their it needlefs to have recourfe to a Mixture of feveral Li
other Fluid, than they were before to one Nifus to one another would then ceafe, and give the in clofed Globule of Air liberty to expand itfelf; fo that the whole Fluid will take up a greater Space than it did be- fore : But when the Particles of the two Globules come to be united together, they will again inclofe the Globule of Air that lies between them, and, by their mutual At- traction, foon bring it to its former State of Condenfa- tion.
Now, that the Blood contains a great number of Globules of Air, is evident from the great Quantity it yields in the Air-Pump ; and that the Particles of the Blood have a Arong attractive Force, cannot well be deny'd. Upon the meeting, then, of thefe two Fluids in the Veficles of the Fi- bres, the Nervous Juice, confining of fmaller Particles thf-
--veral Li- quors where one will do ; and therefore makes no fcrupie to attribute the whole Bufip -Ss to it alone. The manner of Action he conceives thus.
Suppofe the Spirit, from any Caufe, to be moved more fwiftly from the Origin of fome one Nerve, than thro the relt ; the influx will here be greaterinto the Mufcular Fibre open to this Nerve than into another: This will therefore be more dilated ; and the other Phenomena, mentioned a- bove, will fucceed. The fame Caufe continuing, the Effect will be increafed, fo that in a Moment of 'Lime the whole will be fwell'd up ; and while the fame Deter- mination lalls, will remain contracted : And this obtain- ing in an infinite number of FibrilU at once, the whole Mufcle will be inflated. Hence it neceffarily follows, that
the Blood, mull, from what Sir /. Nezvton has proved of asthe Celerity is increafed in one Nerve, the Motion will the Rays of Light, attract the Particles whereof tht^y are be lefs in another ; this therefore being relax'd, the Ef- compofed more iirongly than thofc do one another; and fort m contraction will be the Wronger. For which Rea-, confequently the Ntfus of thofe Particles to one another cea- ion, all the turgid Fibres of a Mufcle will comprefs the fine, the condenfed Globule of Air will expand itfelf with intermediate Spaces and Blood with a great Force ; whence a confiderable Force; whereby each Veiicle of the Fibre the Veins will be emptied, and the Arteries bein" corn- will be dillended, and confequently, therefore, fhorten'd ; prefled, will repel the groffer, that 'is, the red parts of i.e. the whole Mufcle will be contracted : but when rhe the Blood, but will drive the more fubtile parts by the Particles of the Globule of Blood are well mixed with the Force of the Heart and their own, into the moll minute Nervous Fluid, they will both together inclofe the Glo- Canals; and thus the Cruor being expell'd, the whole Body buleof Air again, and comprefs it into as fmall a Space as of the Mufcle will be found to aft by a fubtile Humour it was before; And thus the Contraction of the "Mufcle mull concurring from the Nerves and Arteries. immediately ceafe, till frefli Blood and Spirits, Hill fuc- Thus are* all the Phenomena accounted for ; without ceeding one another, continue the Inflation of the Veficles. any other Affum prion than an accelerating Force in the But when a Ms/rfe has been flrongly attracted for fome Origin of the Nerves ; which is common to all Hypothefes time, the Quantity of Spirits fpent being more than can and which can't be traced any further, be prepared in the Space of Time by the Glands which All other Hypothefes, therefore, Boerhaave abfolutely fupply its Nerves, the Inflation of the Veficles mufi fall, rejects 5 nor makes theleaft account of Galen's incorporeal and the Mufcle grow feeble and weak. And thus that Power inflating the Mufcles; the nitrous Spirit of the ingenious Author conceives the Veficles to be diflended Nerves mixing with theOil of the Blood, and fo rarifyins without any Ebullition or Effervefcence ; and their Diften- it ; the acid parts of the nervous Juice mixing with the fion to ceafe without any Precipitation, or flying-off of the alcalious ones of the Blood ; the Ebullition of the Air Aerial Globules thro' the Pores of the Mufcles. and the arterious Juice ; and the increafe or diminution ot"
He proceeds to fhew how artfully the Mechanifm of attractive Force of the minute Corpufcles of the Humours the Fibres is contrived for Contraction. 'Tis a known Ex- as repugnant to Senfe, Experience, the Laws of Matter* periment, that a Bladder blown up and diflended as to and of Mixture, and to the Phenomena of the Mufcles. its Capacity, but contracted as to Length, will raife a Dr. Jjiruc has gone a good way towards proving the "Weight to fome determined Height. Two Bladders, there- nervous Juice alone concern 'd in Mufcular Motion ■ and that fore, thus blown up, and communicating with each other, the Bloud hasno /hare in it ; by the followin" Experiment he argues, will raife the Weight double the Height, and which he tried feveral times with the fame fuccefs. three Bladders thrice the Height, &c. So that if there Cutting open the Ahd'imen of 'a live Do? and removing were a String of Bladders join'd together, of equal Bulk, the Inteltines out of the way, he hound up^ the Aorta where and like Figures, the Space thro' which the Weight would it divaricates into the Iliac Arteries, with a Thread fa as to rife, would be proportionable to the Number of Bladders, conflringc each Iliac and the Hypogaftric Artery vcry'clofelv ' i. e. to the Length of the String. Now each Fibre of a then fewing up the Epigaftric Mufcles, he found the Senla- Mufde confiiling of an infinite Number of fmall Veficles, tion and Motion ftill as brisk and vivid in the Dog's Polie- refembles a String of Bladders ; Co that the Contraction of riors t as before. So that when once fct at liberty he flood the Mufcle is always proportionable to the Length of its on all four, and walk'd with his ufual Eafe and Firmnefs- Fibres. " tho it is certain there could not be one drop of Blood con- Farther, the Veficles whereof the Fibres confift being vey'd to thole hind parts. very fmall, tho' one large Bladder might raife a Weight as Ajiritc, however, differs from Boerhaave in the manner high as feveral fmall ones, yet the Quantity of elaiHc Fluid wherein this nervous Juice acts ; nor will allow that Celerity ufed in the Inflation will in that cafe be much greater wherewiih the Mufcles act at the Command of the Will to than where the Weight is rais'd by a String of fmall be owing to the Velocity of the Juice fent thro the Nerve ones. but toantmpreflion given to one extremity of the Thread! For, luppoting two Bladders ot fimilar figures, but the and communicated thro all the intermediate Parts to the Diameter of the one triple that of the other ; then will the other Extremity ; fuppofi^g the Nerves in their natural one require twemy-feven times the Quantity of elailic State to be turgid, and full of Spirits : lb that -if the Ex- Fluid to expand it that the other does, and will alfo expand tremity in the Senfory be ever fo little prefs'd by the to twenty-feven times the Space ; and yet three of the lefs Accefljon of any new Spirit, as much will be inflantly ex- Bladders join'd together, (he goes on) will raife the Weight pell'd at the other Extreme, and -vice vcrfa ; a fmall Im- to the fame Height that the bigger one does ; but with preflion given to the outer Extremity of the Nerve will nine times lefs Expence of elaflic Fluid, and take up immediately move theother Extreme open totheSenfory but a ninth part of the Space. By diminifbing, therefore, fo that part of it will drop out : Which accounts for theBignefsof the Veficles, and increafing their Number, Senfation, as well as Mufcular Motion, the Force required to diflend them, and the Diilenfion it- Laflly, Dr. Lozvera.nd Mr. Cozuoer, and after them Dr felf, may be diminifhed in any given proportion, and come Morgan, the latefl Writer on the Subject, fetriqg afide all at laft to be infenfible. Suppofe a Bladder, v. g. of a de- adventitious Fluids, account for Mufcular Moticn from the terminate Bignefs, can raife a Weight a Foot; a hundred intrinfic Elaflicity of rhe nervous FibrHU contracting and Bladders, whofe Diameters are each a hundredth Part of refloring themfelves againfl the ftretching Force of the the former, being blown up, will raife the Weight to the Circulating Blood.
fame Height ; but the Force required to inflate them, and This Syftem, Morgan endeavours to evince from the fol-
the Swelling of all put together, will be ten thoufand lowing Confiderations : times lefs than the large one. , a 11
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