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rnufcular Fibres; which whether or no theybeveficular, is fome quettion.
Now, there are Nerves propagated to every Mufcle, and tliitributed through the Body thereof; fo as there is no af- filiable Point wherein there is not fomewhat of a Nerve. Add, that all the Nerves here difappear; and that in other Farts of the Body, the Extremities of the Nerves are ex- panded into Membranes. 'Tis therefore probable, the rnuf- cular Fibres are only Continuations of the nervous ones. See Muscle.
The animal Fibres have different Properties; feme are foft, flexible, and a little elaftick: And thefe are either hollow, like fmall Pipes; or fpongious, and full of little Cells, as the nervous and flefhy Fibres above mentioned. See Flesh.
Others are more folid, flexible, and endowed with a ftrong Elaiticiry, or Spring; as the membranous and cartilaginous fibres. See Membrane, &c.
A third fort are hard, and inflexible, as the Fibres of the Bones. See Bone.
Now of all thefe, again, fome are very fenfible, and 0- thers destitute of all Senfe : Some fo very fmall, as not to be eafily perceived; and others on the contrary, fo big, as to be plainly feen; and molt of them, when examin'd with a Microfcope, appear to be compofed of ftill fmaller Fi- bres. Thefe Fibres firlt. conftitute the Subflance of the Bones, Cartilages, Ligaments, Membranes, Nerves, Veins, Arteries, and Mufcles. And again, by the various Text- ure, and different Combination of fome, or all of thefe Parts, the more compound Organs are framed; fuch as the Lungs, Stomachy Liver, Legs, and Arms, the Sum of all which make up the Body. See Body.
The great Property of Fibres, is Elafticity, or a Power of Contraction, after the diftractile Force is removed; upon which the Knowledge of the animal Mechanifm greatly depends. See Elasticity.
To understand this, it may be obferved, that any Mem- brane or YefTel may be divided into very fmall Fibres, or Threads; and that thefe Threads may be drawn out into a very considerable Length, without breaking; and that when fuch external Force is removed, they will again re- ftore themfelves to their proper Dimenfions. It is farther alfo manifeft, that this Property is preferved to them by a convenient Moifture; becaufe if one of thofe Threads be dried, it immediately loofes it; fo that upon the Applica- tion of any Force to Stretch it, it will break; as alfo will its lying foked in Liquor too much, render it flaccid, and deftroy all its Power of Reftitution, when diflended.
Now fome Hints of that Configuration of Parts, upon which this Property depends, may be had from the Con- trivance and Properties of a Syringe; with the Reafon, why it is fo difflcult to draw back the Embolus, when the Pipe is ftopp'd; and the Neceffity of any Liquors following it, wherein the Pipe is immerfed.
All that is neceffary hereto, is, that the Embolus be fo exactly adapted to the inner Surface of the Earrel, as to prevent any Air paffing between them, when it is drawn up : It matters not what Figure the Barrel is of, fo that the Embolus is well fitted to it. A Cafe of Syringes there- fore might be contrived, wherein every Barrel may alfo ferve as an Embolus to its exterior, which immediately in- cludes it.
In this manner it is not difficult to imagine a continued Series of Particles, fo put together, that they^ may be moved, and drawn upon one another, without fuftering the Air immediately to enter into the Interftices made by their Diffraction; whereupon as foon as that Force, which drew them, is removed, they will, for the very fame Reafon as the Embolus of a Syringe, rufh up again into their former Contacts.
As fuppofe A. #■ (Fig. 1.) two Particles touching one an- othe in c. f. and C 2>. two others, covering the oppo- firc Sides of their Contacts. It is alfo to be fuppofed, that on the other Sides they are covered with other Particles in the fame manner, as by CD. fo that the Places of their Contacts arc on all Sides covered from the Air, or the In- fmuation of any fluid Body.
If now A. C B. by an external Force, greater than that of their Cohefion be drawn from each other, as far at* G. J. and II K. ( i n -pig. «,) as foon as that Force is removed, they will again run into their former Contacts in e.f. (Fig.i.) thatjs, if 'they are not fo far as to bring their tranfvcrfe Surfaces to coincide with C. and D. for then the Air, or circum-ambient Fluid will interpofe and prevent their Re- gion; fo that by this Contrivance, fo much of A. and %.
as is inclofed by other furrounding Parrichs, is as the Em- bolus of a Syringe, and the Particle furrounding tbeiri as its Barrel. And therefore when A. and &. are diffracted; from their Contacts in e.f. it will be with fome Difficulty ■;
and when the diffracting Force is taken away; they will a- gain run up in their former Contacts;juft as the Embolus o£ a Syringe, and for the fame reafon. See Syringe.
It is not rigidly contended that this muft exactly be th'a Contexture oiaFibre h but only fome thing like this; where- by the Interftices of the interior Orders are covered by the exterior in fuch a manner, that when the Thread is dif- tended, that is, when its conflituent Parts are drawn from their tranfverfe Contacts, neither the Air, nor any other ex- ternal Fluid can get between them, fo as to hinder their- Re-union, as foon as fuch Force is withdrawn; that is, if their Diffraction, as was before faid, be not fo far as to bring their tranfverfe Surfaces to a Co-incidence with one another; for then the circum-ambient Fluid will interpofe/that is, the Thread will be broke.
But befides this peculiar Arrangement of a determinate Set of Particles to compofe the main Suftance of an animal Fibre, endowed with the Properties above-mentioned; it feems not at all unreafohablc to conjecture, that into their Compofltion alfo enters a common Capfula, or Covering, which affifis in the wrapping up, and holding together thole Fafckuli, or Series of Particles already defcribed; not much unlike the Periollium of the Bones; the Contexture of which covering, refembling that of a Net, cannot any ways hinder, either the tranfverfe, or longitudinal Diftrac- tions of the other Parts. , ,
Suppofing this, then, the Contexture of a Fibre, it will be neceffary to confider, what farther Requisites are need- ful to put them into that State, which they arc in, in a liv- ing Body; to fhew how they are maintained in continual Mo- tion; and what are the Confequences of it. . «
And i°, it is neceflary to take notice, that all the Fibres in a living Body are in a State of Diftcntion; that is, they are drawn out into a greater Length than they would be in, f if feparated from any Part, and taken out of the Body; which is demonfirable upon any Solutio Continui, as in the tranfverfe Divifion of a Nerve, or Artery; for immediately the divided Parts run up, and leave a great Diftance be- tween them; and the Fluids contained between them, upon' fuch Contraction are fqueczed out. This alfo mews, that their natural Diffractions are owing to fome Fluids being propelled into the Veffels which they compofe, with a Force greater than their Endeavours of Restitution, fo far as to' obtain a clofe Contact of all their tranfverfe Surfaces; but yet lefs than that which is neceffary to diffract them, fo as tp; bring them into a Coincidence; for then the Veffels would break.
2. , This State of Diffraction muft neceflarily leave Va- cuola between all the tranfverfe Surfaces; as betwen G. L and H. K. (in Fig. 2.) which may be reprefented by the fe- veral Series of Particles (Fig. 3.) which Vacuola will con- tinue as long, as the longitudinal Surfaces of its component Parts continue to clofe to one another, as to prevent the In- finuation of any foreign Matter, how fubtile foever between' therm
Fig. 3.
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For the fame Reafon therefore, as when the Embolus of a Syringe is drawn, and the Pipe is flopp'd, there muft be continually a Nifus reftitimidl, or an endeavour of Contrac- tion.
There is alfo this farther Keceffity of their being conti- nued in a State of Diffraction, becaufe if they were clofely to touch one another in all Parts, they could not be put. in- to, and continue in thofe undulatory Motions, which they are always in, in a living Body, without being altered in" their Figures and Contextures.
3 . It being manifeft; that all animal Fibres are conti- nued by the perpetual fucceffive Impulfe of the Fluids, in fuch undulatory Motions; befides this Necefltty of their Di- ffraction, they muft alfo be continually moiften'd with feme convenient Fluid; becaufe otherwife their continual Attritions againft one another, would wear them out, as well as render it difficult to move them : The Fluid alfo for this purpofe, muft be very foft and fubtile, becaule otherwife it cannot infinuate into all the Interftices of the Fibres, without fo far fcparating their Parts, as is incouflftent with that Contexture and Mechanifm here kid down,
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