IF we consider the Useful­ness of Muscu­lar Motion, The Useful­ness of Mus­cular Motion, as it tends to the main­tenance of life. with respect to an In­dividual; and that, either as it tendeth [Page 2] to the maintenance of Life, or the perfection of Man, that is, with respect to the Soul, and the Animal Functions; it is the very spring upon which all our Actions, both Natural, Vi­tal and Animal wholly depend. By the Assistance of Muscular Motion, all the parts of our Body perform their particular Offices: Our Food is prepared by Mastication, and conveyed to the Stomach; the concocted Chymus is thence expelled into the Intestines, where the purest Chyle is separated from the im­purer Faeces; every peculiar Liquor circulates through its distinct and proper Vessels The Chyle through its Lacteals and the Lympha through its Ducts; and the Mass of Blood [Page 3] is disributed through the Ar­teries, that all the Parts of the Body, both Principal and Sub­subservient, Noble and Ignoble, may receive their proper Li­quors: In a word, it is by this very Action of Muscular Mo­tion, that [...].

If we respect the Animal Functions, With respect to the Soul and its Functions. they so much depend upon Muscular Motion, that when the Heart ceaseth to move, all the Facul­ties of the Soul are presently extinguish'd. The Faculties of the Soul are not only depen­dent on Involuntary, but also Voluntary Motion; without which, both our Eyes and Ears would be unfit to receive ex­ternal [Page 4] Objects; and Man would be endowed with a Sensitive and Rational Soul to no pur­pose. Our outward Senses would in vain receive external Objects, unless we had an In­telligent Faculty; in vain should we Understand, unless we had Reason to distinguish good from evil, that we might desire the one, and contemn the o­ther: In vain also would be the Dictates of our Reason, if we had not a Loco-Motive Faculty, to pursue those things we de­sire, and to flee from those things which we are willing to avoid. But by Muscular Motion, the Dictates of our Reason, accor­dingly as they are byassed by our Appetites, are put into Action, and the intimate results [Page 5] of all our Faculties are brought to light. Muscular Motion is the very Index Animi, by which the Temper and Disposition of the Animal Faculties are made evident; it's the Ultimate Re­sult of our most secret Thoughts and of our Will; so that if we weigh but the mutual depen­dance of all the Parts of a Man's Body, A Muscle is a Noble part. there is no Reason, that a Muscle should be termed an Ignoble part; since by the loss of a single one, either the Natural, Vital, or Animal Faculties are in some measure vitiated.

The Stomach, the Liver, the Spleen, the Lungs, &c. are all subordinate and subservient to the Principle Faculties of the [Page 6] Soul; in as much as they by their mutual Symbolums, pre­pare the Pabulum of the Ani­mal Spirits. But the Muscles designed for Motion, especially Voluntary (in as much as the most perfect and refined Actions of the Soul, are performed and expressed by Muscular Mo­tion,) are of a more noble use, the perfection of Man consist­ing more immediately on the energy and execution of the Principal Faculties of the Soul, than in the subordinate and subservient Faculties, both Na­tural and Vital.

For as much as the Life and Perfection of Man, so much depend on Muscular Motion, I [Page 7] shall enquire into the Efficient Causes of it: But before I pro­pose my own Hypothesis, it is necessary that I first confute what has hitherto been said on this subject; nevertheless, be­cause it would be too tedious to examine the Opinions of so many Authors, I will only shew the Errors of Two or Three of the latest and most considerable.

The most Learned and Fa­mous Dr. Willis Conjectures, Dr. Willis's O­pinion examin'd. that the Spirits are con­veyed to the Tendons of a Muscle, and are there plentiful­ly laid up as in a convenient Store-house; which Spirits be­ing [Page 8] of an Agile and Elastick Nature, as far as they are able, and are permitted, always en­deavour to expand themselves; and that when an Instinct to perform Muscular Motion, is carried from the Brain or Cere­bell, to this common Store-house, they presently leap out of the Tendinous, into the fleshy Fibers, where they meet with active Principles of ano­ther Nature, supplied by the Mass of Blood; which two strongly & mutually fermenting, stuff up and tumifie the Fleshy Fibers; whence proceeds the Contraction of a Muscle. When the Contraction ceaseth, he thinks that most of the purest Spirits that remain, return into the Tendons, the other more [Page 9] impure Particles remaining a­mongst the Fleshy Fibers; he fancies, that the Fibers of the outward Membrane contract­ing, promote the Retrocession of the Spirits into the Ten­dons; and that for a continual supply of these Liquors, the one is always stored up in the Tendons, through the Nerves; and the other in the Carnous Fibers, from the Mass of Blood.

This Conjecture as it seems ingenious, No Elastick Spirits laid up in the Tendons. and at the first view very mysterious, yet upon a more strict Examina­tion, it appears altogether as im­probable. For to suppose that these Elastick Spirits are laid up, and stored in the Tendi­nous [Page 10] Fibers, is contradictory to Reason, as well as the Laws of Circulation; for since in e­very Systole of the Brain, a fresh supply of Animal Spirits is sent into all the Branches of the Nerves, those Animal Spirits in the Tendinous Fibers, must needs by a succession of new matter, be pressed forwards in­to the Fleshy Fibres; and con­sequently Accidental Contra­ctions must follow: for as much as there are no Valves to hinder their immediate Pas­sage. And that there are no Valves, nor any thing else to stop the continual Passage of these Spirits, may be argued hence; because whatever would stop the protrusion of these Spi­rits, when pressed by the Sy­stole [Page 11] of the Brain, would also hinder 'em from rushing out of their Store-house, though stirred up by an Instinct, and so the Muscle would be depri­ved of Motion.

But supposing that it were possible for these Elastick Spi­rits, to be stored up in the Ten­dinous Fibers, and that neither their agility, and continual En­deavours to explosion, nor the force of succeeding Spirits would drive 'em out; yet when a Muscle ceaseth from Motion, perhaps a Day or Two; the Tendon would be so filled and stuffed up, that being no longer capable of receiving more Spi­rits, either they must be forced forth into the Carnous Fibers, and cause violent and Involun­tary [Page 12] Contractions; or regur­gitating and flowing back upon the Brain, would there cause a Vertigo, or some other more fa­tal Disease; and besides the Spirits by stagnating so long, would be chilled and coagula­ted, and thereby render'd unapt for Motion.

It is not only absurd to ima­gine, Nor instinct sent from the Brain, because that the Ten­dons, are Store-houses for Spirits; but also that they, the Instinct being given, should cush out of the Carnous Fi­bers; one might as well think, that the Contents of the Sto­mach, the Gall in the Vesica Bilaria, or the Urine in the Bladder, might be excluded by instinct, meerly without the [Page 13] help of Muscular Coats; or that the Circulation of the Blood might be carried on, with­out the Systole and Diastole of the Heart.

Moreover, Either it im­plies, that the Spirits are In­telligent, to allow, that those Elastick Spi­rits do after this manner rush into the Carnous Fibers, when the Instinct is given from the Brain, or to speak more properly, ad imperium animae, either implies, that those Spi­rits, which Dr. Willis calls Ma­teriam subtilem, are intelligent Matter; that they are able to understand the Dictates and Commands of the Soul; and to put them in Execution, pro­prio motu; or that some Spirits [Page 14] of a Different Na­ture, Or that Spi­rits of a Diffe­rent Nature are sent from it. are at the command of the Soul, sent from the Brain, which cause the Spirits in the Tendons to be uneasie, and by exagitation to expand themselves more powerfully, and consequently to leap forth. But if neither the texture of those Spirits, which as Dr. Wil­lis says, give the Instinct, be changed, and different from those in the Tendons, nor the Subtile Matter be Intelligent, there would be no Explosion, or leaping forth of the Spirits out of the Tendons, either by in­stinct, or the accession of new Matter from the Nerves; ex­cept, as I noted before, the Spi­rits which filled the Tendinous [Page 15] Fibers, were driven, and suc­cessively forced out by a fresh supply of Spirits, sent in by e­very Systole of the Brain; and so, Muscular Motion would not be Voluntary, but Acci­dental.

That this Matter is not In­telligent, is proved sufficiently; The Matter is not Intelligent. be­cause to allow that this acts as it re­ceives Instinct from the Brain, is to allow a subordinate Soul which acts proprià facultate in every Tendon; which is false; for an Intelligent Faculty in a Tendon, which must act accor­ding to the Dictates of the Principal Soul, cannot be sup­posed to be a Faculty of that Soul, no more than the Soul [Page 16] of a Disciple, Juratus in Verba Magistri, and who exactly fol­lows the Dictates of his Ma­ster, can be said to be a part or faculty of his Master's Soul.

That no Spirits of a different Nature from those he supposes to be in the Tendons, No Spirits of a different Na­ture are sent from the Brain. can be transmitted from the Brain, is evident. For since the same Spirits are distributed through all the Nevervous Chan­nels, from the same Fountains, the Brain, or the Spinal Mar­row, whatever causes the Spi­rits to leap out of one Tendon, would cause the same Effects in all, and all the Muscles must be contracted at the same Instinct.

[Page 17] Having thus confuted the Grounds and Foundation of his Hypothesis, it's not irrational to expect, that the whole Superstructure should fall: I shall only further take no­tice,

First, No active Principles heap­ed up in the Fleshy Fibers. That if Active Princi­ples of another Na­ture were heaped up in the Fleshy Fibers, by degrees they would be so stuffed and swelled up, that there would be no room for the entrance of Elastick Spirits from the Ten­dons; but they themselves would rather, by reason of their quantity, be forced into the Tendinous Fibers.

[Page 18] Secondly, That it would be absurd to imagine, Nor retroces­sion of subtile Matter into the Tendons. how these Two Spi­rits after so intimate a commixture, as would be produced by a strong Fermentation, can be so easily separated, that the one should suddenly run back into the Tendons, leaving the other be­hind in the Fleshy Fibers: For when Two Liquors of a diffe­rent Nature, and whose Mi­nute and Subtile Particles have a different Motion, are mixed together; by a mutual Fermen­tation is produced so intimate a mixture, that it is impossible to separate the one from the other sincere; because by a mutu­al collision of different Particles, both must needs in some measure [Page 19] be altered, and degenerate from their Pristine State, so that if the purest part of these Spirits remaining should run back into the Tendons, they would be dis­agreeable to, and different from those purer Spirits sent from the Brain; and would infect the Store-houses with such a fermen­tative taint, that as new supplys were laid down by the Nerves, fresh Explosions and Contracti­ons of the Muscles must fol­low.

Thirdly, To help the Retro­cession of these Spirits into the Tendinous Fibers; Dr. Willis would have the Fibers of the in­vesting Membrance to contract: But I should rather think, that they would contract at the same time with the Muscle, if the In­stinct [Page 20] were carried through the same Nervous Channels with the Spirits; because, as he says, they are first laid down in the Membrane, and thence con­veighed to the Tendon?

Mr. Cowper, in the Introdu­ction to his Myoto­mia Reformata, Mr. Cowper's opinion exami­ned. sus­pects; that the Blood is a Pondus, by which the action of a Muscle is per­formed: The grounds of this suspition are cheifly taken from two Experiments: The first is a Ligature on the descending ttunk of the Aorta, whereby all the inferior Parts, became desti­tute of Motion, which they re­covered again when that Liga­ture was loosed: The second, is [Page 21] to be taken for a more surprizing Argument, because after a ces­sation of Motion, the Muscles of the Legs renued their Con­tractions, by an Injection of Water into the Crural Arterie.

But that there is no Reason to assert, that the Blood acts as a Pondus from these Experiments, will hereafter sufficiently appear, by giving other Reasons for these Phenomena.

In the mean time to evince, The Blood does not act as a Pon­dus. that the Blood as a Pondus does in no wise help the Con­traction of a Muscle, but does on the contrary, much inter­rupt and resist the Intumescence of the Musculous Fibers, The First Ar­gument. by which the Contra­ction of a Muscle is performed, let any [Page 22] one hold his hands before a Fire, with his Arms perpendicular, continuing 'em in that posture till he feels the Musculous Parts well filled with Blood; then lift­ing up both his Hands, let him hold 'em up as high as he can, till the Pondus of the Blood be drained, and the Veins which before were full and tumid be­come flaccid and empty, and he'l move his Fingers much more easily and swifter, when the Mus­cles are eased of the Pondus of Blood, than he did whilst his Hands were dependent; yet certainly there was a greater Pondus of Blood upon the Mus­cles in the former posture, whilst they were tumid, than in the latter when emptied of superflu­ous blood.

[Page 23] Another Argument to prove, A Second. That the Pondus of the Blood doth not at all promote the Contraction of a Muscle; may be taken from the Observation of Cacochy­mick Bodies, who are far more dull and unapt for Motion than healthful people, whose Veins and Arteries are moderately fil­led with Blood, which is not so thick and heavy; for in Caco­chymick Bodies, there is a grea­ter Pondus of Blood, but because it doth not yeild matter for to swell the Carnous Fibers, as plentifully as blood of a more healthful constitution, Motion is not so brisk and strong; where­as if the Pondus of the Blood did any ways contribute to the performance of Muscular Moti­on, [Page 24] they would be far more strong; for the thicker the Blood is, the greater is the Pondus.

In the Muscles of the Legs and Thighs there is always, A Third. when the Body is erect, a greater weight of Blood, than on the Muscles belonging to the Hands and Arms; and yet the latter, are far more agile and nimble in Mo­tion.

Again, if we but make a Li­gature two or three fingers breadth above the Cubit, so as to hinder the Reflux, but not the Influx of the Blood; when the Sanguiferous Vessels are swelled, and the Muscles well filled, they are rendered much more unapt for Motion: Which evidently shews that the more the Sangui­ferous [Page 25] Vessels are distended, the more the Motion of a Muscle is hindered; because when the Vessels are dilated they resist the Intumescence of the Car­nous Fibers, and consequently the Contraction of a Muscle.

Furthermore, That the Con­traction of a Muscle is not per­form'd by the Pondus of the Blood, is apparently evident in the following Experiment: A Fifth. Viz. Make a Ligature two or three fingers breadth above the Cubit, so strong as to stop the Circulati­on of the Blood; then open the largest Vein with the common Instrument, and the Blood which more than usually swelled up the Sanguiferous Vessels will leap forth; but presently for want of [Page 26] subsequent Matter, and due Cir­culation, the Vein falls and the Blood ceases to run; yet by a Contraction of the Muscles to which that Vein leads, forth­with part of the Blood, which lay in the Muscle, is forced out: which plainly shews there is less Blood in a contracted Muscle, than before Contraction.

The same appears also in Run­ing, A Sixth. or any other violent Exercise, in which most of the Muscles are Contracted; for presently the Blood flows more than usually upon the tender Lungs, and cau­ses an Intollerable shortness of Breath: Because by an Intumes­cence of the fleshy Fibers, the Muscles are not only made in­capable of receiving so much Ar­terial [Page 27] Blood as before Contracti­on; but also, because the Blood which lay in the Veinous Ducts is driven out more forcibly upon the Heart, and the Heart being overwhelmed, drives it out up­on the Lungs. Whence proceeds that Palpiration of the Heart upon violent Motion, not di­rectly as Dr. Croone supposeth, because an Instinct is sent from the Brain to raise stronger Pul­sations, that the Blood may for­cibly be driven into the Mus­cles, and thereby cause Contra­ctions; for then why doth it not at the first instinct thus op­press the Lungs with its quanta­ty? but this strong Palpitation is Accidental; for when the Blood is more than usually dri­ven upon the Heart, and not so [Page 28] plentifully received by the Mus­cles; by degrees it oppresses the Heart with it's quantity, and the Animal powers being sensi­ble of the oppression, raise stron­ger Systoles to drive it out which presently is received and heaped up in the Lungs as a Part less able to resist its vio­lent Incursion. Nay many times, when the Vessels are well filled with Blood, by violent and fre­quent Exagitations, betwixt the Contraction of the Heart and of the Muscles, its texture is so loosened; that it ferments and boyles up so that the Lungs are not only swelled up and almost stifled, being rendered uncapable of receiving Air, but it is also more strongly & forcibly driven into the Muscles themselves, and [Page 29] there distending the Sanguife­rous Vessels hinders the Intu­mescence of the Fibers, and thereby the Contractions of the Muscles So that I have not once, trying this Experiment, found such an Oppression on my whole Thorax; and such con­trary and in some measure pain­ful endeavours, betwixt the San­guiferous Vessels tumified and the Carnous Fibers striving to swell; that I was forced to lay me down, to the end that the Carnous Fibers being flaccid might give way to the incourse of the Blood; and by receiving it more plentifully might case both my Thorax of its Oppres­sions; and that the Carnous Fi­bers yeilding to the Sanguife­rous Vessels might put an end [Page 30] to that uneasie contention. Thus much I think is sufficient to prove, that the Blood as a Pondus hinders the Contracti­on of a Muscle.

Dr. Ridley supposes, Dr. Ridley's Opinion exami­ned. That the Nervous and Carnous Fibers are only a Congeries of Fluids contained in certain Vessels; and that by Reason of a Plenitude in the aforesaid Vessels, the whole Machine is in a constant AEquilibrium, so that it will follow, upon the common Postulatum, viz. That the Sensitive or Rational Soul can command the Animal Spirits into a primus impetus; and that part of that Liquor, whenever a Muscle is Contracted, is trans­mitted [Page 31] through the Vessels from the Brain to its Carnous Fibers, and causes the Intumescence of a Muscle; the same Liquor at the same time being driven back with an equal speed from the An­tagonist Muscle, into the room of the former, which was trans­mitted from the Brain to the Contracted Muscle, to avoid a Vacuum.

That the Nervous Ducts as well as Carnous Fi­bers are always Wa­tered with a Fluid; The common Postulatum is not to be allow­ed. and that the Ner­vous Liquor equally flows into the Branches of all the Nerves, according to their Proportion, is beyond Contradiction; but if we allow the common Postu­latum, we must also conclude, [Page 32] That the Animal Fluid is Intel­ligent, and there will follow the same Difficulties as were before mentioned, about the leaping forth of Spirits out of Dr. Willis his Tendinous Receptacles; where I have given sufficient Reasons to reject this Postulatum as Im­possible.

Moreover if it were Possible, There is no Retrocession of a Fluid from the Autagonist. for so much of this Animal Fluid as is requisite to distend the Car­nous Fibers, to be conveiged in so short a time as Muscular Motion follows our Appetite through the small Branches of the Nerves; yet it would be altogether unconceivable, how it should flow back from the Antagonist, thus contrary to [Page 33] the Course of Circulation; but the Reason he gives is partly this, to avoid a Vacu­um: This is a most Stupen­dious sort of a Motion; at the same time that the Liquid is forced into the one Muscle, it runs directly opposite from the Antagonist; which is very irre­gular and unlikely.

Besides, I cannot understand how it comes to pass, Nor is it forced out so as to cause a Va­cuum. that the Animal Fluid is so much forced out of the Branches of the Nerves leading, to the Muscles to be contracted as to leave a Vacuum for the Re­ception of Liquids from the An­tagonist; but if an Emptiness or Vacuum could be so made, the Fluids would as soon be drawn [Page 34] back again, out of the Muscles into which our Appetite di­rected them, to fill that empty Space, as out of the Antago­nist.

To prevent an Objection a­gainst his Supposition, that the fluid runs back again from the Antagonist, he thinks he has answered it already, but very insufficiently: He says, if it be said, that the Reflux is oppo­sed by the constant direct Mo­tion, it's easie to reply, that it's slow direct Motion, is easily repelled, by the violent im­pulse of the forcibly relaxed Muscle. I must confess, it's no piece of difficulty to make such an Answer; but the Reply seems not so easily to give sa­tisfaction; I would fain know [Page 35] how the Antagonist comes to be so forcibly relaxed, as by a violent impulse to overpower the direct Motion: For the di­rect Motion cannot be so weak, as to be easily overcome; and since the Animal Fluid, as he calls it, is continually driven by the Pulsation of the Heart, through the Brain or Spinal Marrow into the Nerves, what­ever repells the direct Motion, must be of equal, if not greater, force than the Systole of the Heart.

He begs leave to ask, how when another bends his Arm against his Will, the Muscles become tumid, as when volun­tary contracted. This Question doth not at all confirm his Hypothesis, but on the contrary [Page 36] pleads against it. It doth not confirm it, because he doth not account for the Phaenomenon, nor give a Reason agreeable to his Opinion, but leaves the thing barely without explana­tion; it pleads against him, be­cause according to his Opinion, the Muscle instead of growing tumid, ought violently to relax, at least to endeavour a relaxa­tion, and not contrary to the Appetite, to run into a Muscle against our Will: For he says at the same time, that the Muscles to be contracted, grow tumid; the Antagonists by a violent relaxation, drive out the fluid contained in them: So that it will follow, that at the same time we endeavour to keep our Arm unbent, by [Page 37] striving to keep the one Muscle contracted, at the same time we ought to endeavour a relaxa­tion of the Antagonist; and though that force which bends our Arm, doth resist the Vo­luntary Contraction of the Muscle, yet there would no­thing hinder the voluntary Re­laxation of that Muscle, which is the Antagonist, but the slow direct Motion, as he calls it.

But here I humbly take leave to ask, whether there is not a great deal of difference, betwixt a Muscle that is thus tumid, and one that is Contracted? For al­tho a Muscle cannot but be tu­mid, when contracted, yet it may be tumid though not contracted: I mean, as it is in [Page 38] Muscular motion. I have in­deed oft taken notice, that when my Arm has been bent against my Will, the Muscles become tumid, but not as in Muscular Motion; for when a Muscle is Voluntarily contracted, it's hard and tumid; but when my Arm is bent against my Will, it's far more soft; and though tumid, yet very little contracted. Since the Reason why the Muscles grow thus tumid, cannot be accounted for by this Hypothesis, I shall explain it hereafter.

Having thus examined, and I hope confuted the aforemen­tioned Opinions, I shall in the next place briefly consider the Fabrick of a Muscle, the im­mediate [Page 39] Instrument of Mo­tion.

Anatomists, describing the Fabrick of the Muscles of the Body, divide 'em into Simple, Compound, and more Com­pound; as also every Muscle into Three Parts, the Head, the Belly, and the Tail; they acquaint you how the Belly is composed of several Fasciculi of Fleshy Fibers, which lie parallel to each other, &c. of which e­nough may be seen, with a full Description of each sort of Muscles in the Original Authors: I shall omit the Re­petition here, and only take Notice of it's Fabrick, as far as relates to my Hypothesis.

[Page 40] Every Muscle is endowed with opposite Ten­dons, Of the Stru­cture of a Muscle. which are composed of seve­ral Fasciculi of Fibers, lying parallel to each other.

These Fibers being strictly joyned together, compose a strong, tenacious and firm Ten­don; but being separated one from another, are more fragile, and subject to be easily broke, and pulled in pieces; they are continued from each Tendon to it's opposite.

The Interstices of the Fibers thus separated, are filled with the Branches and Extremities of Vessels, the major part of which are Sanguiferous; so that the Fibers continued through the Belly of a Muscle, being [Page 41] obscured by the colour of the Blood, seem to degenerate from the Tendinous Fibers, and therefore are called Fleshy.

These Fibers as they are continued from each opposite Tendon, so also there is a continued Cavity from one end of Every Fiber to the other; which being partitioned by se­veral transverse and perforated Membranes, every Fiber, ac­cording to Dr. Croone, re­sembles a continued Series of Bladders opening one into an­other.

By an Intumescence of these Fibers, they are con­tracted in length; The formal cause of the con­traction of a Muscle. and by a Contra­ction of their Lon­gitude, each Tendon is drawn [Page 42] nearer to its opposite; which is the formal cause of Muscular Motion, as far as can be made evident by Autopsie: This is so unanimously assented to, and so apparent to the naked Eye, that it requires no further proof.

As for the Efficient Causes of Muscular Motion; before they can be sufficiently shewn, we must enquire how many sorts of Vessels are implanted into each Muscle, which according to Anatomists are Four, Nerves, Arteries, Veins and Lymphaeducts; Vessels im­planted into a Muscle. the Nerves and Arteries furnish the Muscles with Spirits and Blood; the Veins and Lymphaeducts, carry [Page 43] back the superfluity of Blood and Lympha.

The Branches of all these Vessels are mi­nutely distributed through the whole Muscle, Their distri­bution. and by an intermixture and texture of the most Minute and Subtile Branches of the same, is formed that Substance, which fills up the Interstices of the Fibers, and which denomi­nates the whole Belly of a Muscle Fleshy. The colour of these Vessels, as of all others, is without doubt White, but by the Contents of the Sanguiferous Vessels, the whole Belly of a Muscle is coloured Red.

The Terminations of these Vessels are so minute and small, so brittle, and subject to be [Page 44] broke, that it's as difficult to trace, and find their Termina­tions, and Insertions, as to divide a Hair into an Hundred Parts; and though many things are made visible by the help of Mi­croscopes, which are otherwise too subtile to be discerned and discovered by the naked Eye; yet I am not without Reason perswaded, that the terminations of these Vessels, cannot be perceived by the help of a Microscope.

Some indeed, whatever they think is probable, lest it should not be credited, presently strenu­ously affirm, they saw it with their Microscopes; and so easily impose on those that less inquire after truth themselves, but take it on trust from others; and [Page 45] perhaps prevent those not so exquisitely skill'd in Micro­scopes, from making any further search after truth. I shall not here say, that what I propose concerning the Terminations of these Vessels, was seen with any Microscope, but shall declare my Opinion in this Matter, too subtile for any Microscope but Reason.

It being impossible for any one to understand the true Reason of Muscular Motion, And termi­nations in small Glands. unless first acquainted with the distribution of these Vessels, and their Contents; first, I conceive, that as the Nerves, Arteries and Veins, are all di­stributed through a Muscle, so it is but Reasonable to conclude, [Page 46] that their minute and subtile twigs are all, before they ter­minate, interwoven and mixed with one another: And if so, it will not be absurd to imagine, that they all end, as it were, in small and Diminutive Glands: And if the ends of the Vessels be so small, that their termina­tions cannot be perceived by a Microscope, these Glandules com­posed of the Invisible ends of the aforesaid Vessels, must needs be very small and fine, and consequently may not be per­ceived by the help of extraor­dinary Microscopes.

From these Glandules thus formed, are derived short Ducts or Passages, for the conveyance of a subtile Liquor, out of the aforesaid Glandules, into the [Page 47] Cavities of the Carnous Fibers. This Passage very likely, may be composed of the external Arterial Coat. Into the Cavity of the Carnous Fibers, besides these Ducts, the twigs of the Lymphaeducts are also inserted, to carry back a superfluous Lym­pha.

If any one thinks it improper or absurd to assert, Proved. that these Vessels do thus terminate, as if it were in small Glandules; let him but consider what a Gland is, and how it is composed, and he will not think the Conclusion irra­tional.

For a Gland is nothing else, What a Gland is. but a Composition of an Infinite Num­ber of small and di­minutive [Page 48] Vessels, several, and most of which, have Commu­nication one with another; which Gland so composed, is as a Store-house to receive and contain a certain Liquor, till necessity requires, or its quan­tity causes an exclusion of it: And this seems plainly to be favour'd by Dr. Ridley, when he says, that the whole Body is a continuity of Vessels, ad infinitum. Now, if a Gland consists of an infinite Number of small Vessels; and if the Branches of Nerves, Veins and Arteries be divided before they terminate, into an innu­merable number of most invi­sible twigs, as is most certain; when from one twig of each sort, is derived a vast number, [Page 49] and all these so derived, are mix­ed and interwoven one with another; why may we not say, at least Metaphorically, since they in their Distributions imi­tate the Composition of Glands, that they terminate in small Glandules.

Some perhaps will ask, how must we discover these Glands Malpigius hath observed the Liver to be composed of Clu­sters of Glands, hanging at the Extremities of the larger Ves­sels, like so many Bunches of Grapes; and the Glands in o­ther parts are apparent; but in a Muscle we can discern no such things; for it, especially when boiled, parts into distinct Car­nous Fibers.

[Page 50] To which I Answer, Why they can­not be discerned. That those Glands are nothing else but a Composition of the ends of importing and export­ing Vessels; and the Reason why we cannot discern the same in a Muscle is this, because the Ex­tremities of the Vessels are so fine, and consequently so brittle, and are contained in the Intersti­ces of so strong and firm Fibers; that whenever we endeavour a separation of the Fibers, the Glandules are torn away from the Vessels from which they are derived; whereas the Fibers which run transverse the Li­ver easily crumble away, being much more weak and less Nu­merous.

[Page 51] The Reason why the Muscu­lar Fibers are so much stronger, than those that run through the Liver, is apparent enough, Viz. because the former are the In­struments of Motion, and con­sequently there lies a greater stress of them, than on the latter, which serve to make the Part a little more compact, and to keep the outward Coat from be­ing loose upon it's Circumfe­rence.

Now because it is impossible to separate and remove these Muscular Fibers, so as to leave the Sanguiferous Vessels as en­tire as would be requisite for the exact and certain discovery of their Terminations; and be­cause it is certain, that these Vessels are divided, and subdi­vided [Page 52] ad minimum; that they are interwoven one with another, and that a Gland is nothing else, but a Composition of Vessels; we may rationally conclude they all Terminate in Diminu­tive Glands.

The Nerves, Veins and Ar­teries, composing and ending in these Glands; I shall next Enquire, to what end they do all thus meet together.

The Use of the Nerves in these is the same as in other Parts, The Use of the Nerves. Viz. to conveigh a Spirituo-saline Liquor from the Brain: Which Spirits being Volatile and apt to Ferment, when mixed with a Liquor of a contrary Nature, are conti­nually sent by the Systole of [Page 53] the Brain into all the Muscles of the Body, and being laid down forcibly in the aforesaid Diminu­tive Glands, And Arteries inserted in the Glands. do there meet with Arterious Blood dri­ven in by every Contraction of the Heart: Which two Liquors strongly fermenting together, the Animal Spirits do by an Attrition Subtilise, Attenuate, and Rarifie those Particles of the Succus Nu­tritius supplyed from the Mass of Blood; by which Means their own are much dulled, and become less Active for the fu­ture; and by a Mixture of these Animal Spirits, with the rarified Succus Nutritius, results a Li­quor Different from, To prepare a Liquor different from the Spirits or Succus. and of a middle State betwixt, the [Page 54] Animal Spirits, and the said un­fermented Succus Nutritius; which Liquor thus compounded and prepared, is driven by a Suc­cession of Matter through its proper Passages, into the Cavi­ties of the Fibrous Cells, the remaining and more crude Part of the Succus Nutritius being received together with the Blood, and carried back to the Heart.

This Liquor after this man­ner conveighed to the Cavities of the Fibers, The Use of it. does as it passeth, and is thrust through according to the continual Laws of Circu­lation, give nourishment to the Parts, and is thence received by the Lymphaeducts.

[Page 55] Thus I conceive it is conti­nually prepared in the Glandu­les, and Circulates through the Carnous Fibers of all the parts of the Body, whilst Motion ceaseth in a moderate quantity; so that the Lymphaeducts are ca­pable of receiving it, and there­by prevent the Praeternatural Repletion of the Fibers.

To prove what I have hither­to said, besides the Verisimili­tude the thing carries with it, I could bring many Arguments to illustrate, and to make it appear more Plausible and Evi­dent; but for Brevities sake, and to prevent unnecessary Repeti­tion, I shall omit 'em here, be­cause they are to be Mentioned hereafter.

[Page 56] I have given a breif Account of the Structure of a Muscle, as far as relates to my Hypo­thesis, and the Use of the Parts, as they serve to Nutrition. I now proceed to the Efficient Causes of Muscular Motion, both Voluntary, and Involun­tary; and first of the Reason of Voluntary Motion.

That Voluntary Motion does depend upon the Dictates of the Soul, and is the Result of it's Faculties, but more imme­diately of our Appetite, is suf­ficiently Evinced; because it's instantly perform'd according to our Will. Where the Soul is lodged; how, and after what Manner, it Operates; and what it is) is most difficult to deter­mine [Page 57] and is not designed for our present enquiry: But as it comes under the Consideration of the Brain, and it's appenda­ges; I shall defer my Thoughts of that, till I have a further Opportunity.

In the mean time, That nei­ther the Soul, nor any of it's Faculties are the immediate Causes of Muscular Motion, but Operate by the Mediation of the Animal Spirits, will ap­pear from what follows con­cerning the Reason of Volun­tary Motion: And that the Office of the Will, is only to open and shut the Pores of the Brain, by an Organical Motion, as necessity requires, what this Motion is, and how it is per­formed, and after what manner [Page 58] the Dictates of the Soul and of its Faculties are put in Action, is reserved for its proper Seat.

After what manner soever the Soul exerts it's Faculties, and directs that Subtile Matter the Animal Spirits (which is sent through the Branches of the Nerves, in greater or less quati­ties according to our Appetite) to this or that Part: it is al­lowed, that when our Body ceaseth from Motion, and all our Voluntary Faculties are at quiet, the Pores and Passages of the Brain leading to the Instru­ments of Voluntary Motion are locked or closed up: And then I suppose, that the Spirits mo­derately flowing into each Muscle, do prepare so much of the Subtile Liquor aforemention'd [Page 59] as is sufficient to Nourish the Parts as it passeth through 'em.

But when the Pores of the Brain are opened, The Reason of Tonick Motion and unlocked, the Animals Spirits forced by a continual Succession of Matter, flow into all the Branches of the Nerves more plentifully, and being laid down in the Glandu­les, raise a stronger Fermenta­tion; by which means a grea­ter quantity of the Subtile Li­quor is prepared, and forced into the fleshy Fibers more co­piously and rather faster that it can be received and evacuated by the Lymphaeducts; so that the Fibers being all equally swelled with its quantity, conse­quently Contract the Muscles; [Page 60] which is the Cause of a Tonick Motion.

When these Animal Spirits, are by a pressure and Systole of the Brain and succeeding Spirits, sent yet more plentifully into the Nervous Channels leading to the Muscles to be Contracted, than into those which are in Motu Tonico, or into the Anta­gonists (the Passages and Pores leading to those Nerves being yet more expanded and opened) there is a greater quantity of the Subtile Liquor prepared in the Glandules, and thrust out into the Carnous Fibers; and their Cells being more swelled and dilated, consequently there fol­lows stronger and more violent Contractions of the Muscles; [Page 61] whence proceeds Local Moti­on.

By the Systole of the Brain I don't mean any other Motion than what proceeds from the Pulsation of the Arteries distri­buted through that Part. That this motion only proceeds from the Pulsation of the Arteries im­plies, that it is stronger, & drives the Spirits through the Brain in­to the Nerves with greater force than if it were really the Motion of the Brain it self; the Heart from whence the Pulsation of the Ar­teries proceeds, being a stronger and more compact Part as to its Substance, than the Brain.

If it be asked, why this Sub­tile Liquor is not more easily forced into the Venous Ducts, than into those that lead to the [Page 62] Fibrous Cells, because the for­mer are larger?

I Answer, That the Venous Ducts are so proportioned, that they might not be capable of re­ceiving all that is laid down by the Nerves and Arteries; on purpose, that some Subtile Parts might be continually driven into the Fibrous Cells; and when by a more copious Influx of A­nimal Spirits, a stronger Fer­mention is raised in the Glandu­les; presently the Contents swell up and are expanded; so that the Veins being not able to receive them as before, more of that Liquor is not only subtilized, but forced into the Fibers.

As soon as, according to our Appetite, the Pores of the Brain, which conveigh Spirits to the [Page 63] Nerves leading to the Contra­cted Muscles, are shut more closely up again, and leave of to be dilated; the Animal Spirits cease to flow more into the Mus­culous Glandules, than are re­quired to Subtilize, and pre­pare a sufficient quantity of Nou­rishment for the Fibers (as in the Antagonist,) then presently the Contraction ceaseth to be carried on, and the Superfluous Liquor heaped up in the Fibers, is eva­cuated by the Lymphaeducts.

Here perhaps, because I said in the foregoing Pa­ragraph; Objections An­swered. the Liquor heaped up in the Fibers is Eva­cuated by the Lymphaeducts; it may be a Question whether this Liquor does all the time a Muscle is Contracted, constant­ly [Page 64] flow through these Cells into the Lymphaeducts; or whether it remains in the Cells till Mo­tion is to cease, and is not eva­cuated by the said Ducts till then.

I say it does continually run of by the Lymphaeducts, con­stantly all the time a Muscle is Contracted: Otherwise since as long as Spirits are directed, in a competent quantity, to the Con­tracted Muscles, to keep up the Dilation of the Fibers; they would presently be incapable of receiving it, and it must needs Regurgitate as it was prepared, and in a great Measure disturb Circulation. But to prevent ma­ny absurd Consequences, if it should remain in the Cells so long; I affirm, that it is con­stantly [Page 65] forced forward, by a Suc­cession of Matter; and as it is forced into, and Circulates through, these Cells, in greater or less quantities, so Contracti­ons are stronger or weaker or not at all, the Fibrous Cells be­ing accordingly Distended, Di­lated and Contracted in Longi­tude; and when according to our Appetite, this Liquor ceaseth to flow into the Fibers in so great a quantity as to Contract the Muscle; that matter which be­fore dilated the Fibers, is Eva­cuated, as being Superfluous Nourishment, so that for the future it runs through in a mo­derate quantity as before Con­traction, till their Repletion is again renued to Reiterate Mo­tion.

[Page 66] If it be asked, why this Li­quor is not as easily forced back­wards out of the Fibrous Cells into the Glandules from whence it came, as into the Lymphae­ducts; and so think there would be no need for Lym­phaeducts.

I answer, That if there be no Valve at the inward Orifice of every Duct, to hinder its re­flux; (which would be no ab­surdity to conclude; for we see always upon the like occa­sion, Nature hath furnish'd such Places with Valves;) yet I say, if there were none, the direct Motion of subsequent Matter from the Glandules, would suffi­ciently hinder the reflux of it; and since its reflux is opposed, by new matter forced successive­ly [Page 67] after it; and since according to the course of Circulation, the Matter driven into the Lymphaeducts before it, will give way for its expulsion, it would be more reasonable to imagine, that the matter con­tained in the Fibers is evacuated qua datur porta, rather than qua non datur; for when we design the Relaxation of a Muscle, though the Liquor successively sent from the Glands, does not press forwards altogether as for­cibly, and in as great Quanti­ties, as whilst Contraction is continued; yet it follows mo­derately, so as to oppose the Retrocession of any thing; I mean moderately, as to its quantity; for the continual vio­lent concourse of the Animal [Page 68] Spirits, and Arterial Blood, drive it then into the Fibers, almost as violently as when the Muscle is contracted.

That these Lymphaeducts do thus receive this Subtile Liquor; The Use of the Lymphaeducts. and that for that end they are inserted into the Fi­brous Cells, I am perswaded; because it cannot otherwise be understood, how the Matter that stuffs them up, and causes Contraction, could be drawn out again, without a Retroces­sion through the same Chan­nels by which it was brought in: And though the most Learned and Famous Dr. Willis, Dr. Ridley and others, do allow a Retrocession, yet since it con­tradicts the course of Circula­tion, [Page 69] we must either deny Cir­culation, or reject their Opi­nions.

Besides, I cannot conceive, what other occasion there is for Lymphaeducts in a Muscle; since whatever is brought by the Arteries, might as well be returned by the Veins, as by two sorts of Vessels: But for as much as Nature hath made nothing in vain, and since there is so great necessity, that they should be inserted into the Cells, I think it not irrational nor ab­surd, to conclude they were designed for the afore-mentioned end.

That we may understand a little better the Nature of this Liquor, The Nature of the Liquor con­sider'd, and the manner of its preparation. [Page 70] which we have so often men­tioned; let us consider a little more fully, how that Fermen­tation is carried on in the said Glandules. It's commonly known, that when a Ferment is put to a Mass, whether Liquid, or of a solid consistence, whatever is the nature of the Ferment, it, according to its power, always endeavours to render whatever comes within the Sphaere of its Activity, as like it as possible. By Fermenta­tion. So in these Glandules, the Animal Spirits fermenting with the Arterial Juice, and the Na­ture of 'em being, according to Dr. Willis and Diemerbroeck, Spi­rituo-Saline, composed of Vo­litile Salt and Sulphur, they by Reason of their absolute [Page 71] Quality, more readily mix with the crude Sulphureo-saline Par­ticles of the Nutricious Arterial Juice; and as they are more or less in quantity, so they exalt and carry forth into a Flux, more or less of that Crude Sul­phureo-saline Mass; which, be­ing by Fermentation subtilized, is diluted with a sufficient quan­tity of Lympha, or the watry part of the Serum of the Blood, and the Liquor resulting from that Composition, is thrust out into the Fibrous Cells.

That this Lympha might be thin enough to dilute the said Liquor sufficiently, it is much attenuated in that Fermenta­tion.

[Page 72] That there is such a Fermen­tation, Proved. that the Nerves are inserted into the Glandules, and lay down Ani­mal Spirits, as the Principal Cause of that Fermentation; that the Arteries lay down Blood together, with the afore­mention'd Juice, and that in those Glands, a subtile Liquor is prepared, being composed of Animal Spirits, and the most? rarified parts of the said Succus; that neither the Arterial Juice, nor the Animal Spirits simply can cause the Contraction of a Muscle; but furthermore, that it is necessary that this Subtile Liquor should be so prepared and composed, as being capable to enter into the Fibers, and to contract the Muscle, is suffi­ciently [Page 73] apparent from what hath been said, and will more clearly be evinced by what follows.

And first, if there be a Com­munication of these Vessels, as certainly there is; then it must needs follow, that there is a com­mixture of their Contents; if there be a commixture of their Con­tents, then there is a Fermentation, and in that Fermentation it must needs follow, that the Animal Spirits will according to their Energie and Activity Subtilize and Attenuate the Crudest Parts of the Arterial juice: By a mu­tual Fermentation there must needs be implyed an intimate Commixture, and the Re­sult of that Commixture must needs be different from the Ani­mal Spirits, or Arterial juice [Page 74] simply before they are mixed; so that the Liquor, resulting from the Mixture of 'em, may be properly called a Subtile Li­quor: And accordingly as the Animal Spirits are more or less in quantity, to mix with the Arterial juice, more or less will be prepared and thrust out into the Fibrous Cells, and conse­quently the Fibrous Cells must be more or less Tumified, and the Muscle Contracted, as more or less Spirits are laid down in the Glandules. So that all I have to Prove is, That neither the Arterial juice, nor the Animal Spirits can cause the Contraction of a Muscle, and then it will follow consequently, that there is a Communication of these Vessels, and for that end, in the aforesaid Glandules.

[Page 75] It hath often been found, that an Atrophea of the Parts will follow the Relaxation; The Arterial juice simply can­not cause the Contraction of a Muscle. & a Palsie the Abscis­sion, or Ligature of the Nerves leading to those Parts: Which sufficiently shews, that the Ar­terial juice it self, cannot cause the Contraction of a Muscle, without the assistance of the A­nimal Spirits; because when the Animal Spirits cease to flow in­to the Glandules, for want of a dew Fermentation, to Subtilize and Prepare a sufficient quantity of the Arterial juice, the Carnous Fibers are not only deprived of necessary Recruits, and Alimen­tal refreshment, so that they must needs waste away and grow Languid, but also for want of a [Page 76] sufficient quantity of the Sub­tile Liquor, to distend the Fibrous Cells, they become destitute of Motion.

That the Animal Spirits sim­ply, Nor the Ani­mal Spirits. cannot cause the Contraction of a Muscle is proved; because by a Ligature on the Descending Trunk of the Aorta, the In­ferior Parts become destitute of Motion: For tho' the Influx of the Animal Spirits, be not hin­dered; yet for want of Arterial juice, the matter requisite for the Composition of this Subtile Liquor, is not laid down in the Glandules; and the Muscles, the Instruments of Motion, cannot Contract without an Efficient cause.

[Page 77] From what is contained in these two Paragraphs, it appears; that neither the Animal Spirits, nor the Arterial juice, simply can cause the Contraction of a Muscle; because when the Animal Spirits are hindered to flow into the Glandules, to Subtilize and prepare the Arterial juice, it is not thin enough to be driven out into the Fibers: And tho' when the Influx of the Arterial juice is hindered, the Spirits are permitted to flow in; yet by Reason of the small quantity of 'em, they run through the Fibers without distending 'em.

That this Arterial juice ought not, Because the Arterial juice cannot pass into the Fibers till prepar'd by the Spirits. nay cannot, pass into the Fibrous Cells, till subtili­zed and prepared [Page 78] by the Fermentation in the Glandules, is Plain; because if it could, they wou'd be stuffed up with the quantity of it, driven in by the continual course of Cir­culation, so as to Contract the Muscle against our Will; which is otherwise.

Now since the Arterial juice cannot pass into the Fibers till Subtilized; and since the Ani­mal Spirits are not enough in quantity; moreover since neither of 'em, simply are capable of Contracting the Fibers, and if ei­ther be obstructed the Action is abolished; I say since it is an Action, that depends upon the mutual Assistance of each; it is apparent. That it must be per­formed by a Liquor resulting from a Mixture of both.

[Page 79] And then we must of Neces­sity allow a Communication of these Vessels; else there could be no mixture of their contents; and the Arterial juice must be prepared before it can be forced into the Fibers, for the Reasons beforementioned: to which end it will be necessary that the Vessels terminate in the Glan­dules, That their Contents may be mixed, and that this Subtile Liquor (resulting from a Mutual conflict of the Animal Spirits subtilizing the cruder Arterial juice by Fermentation, in grea­ter or less quantities accordingly as the Spirits are laid down by the Nerves) may be prepared and made ready to be driven into the Fibers.

[Page 80] To promote the Fermentati­on, and the Preparation of this Subtile Liquor, the forcible influx of the Animal Spirits, and of the Arterial Blood much con­duce: For be the Temper of the Arterial juice and of the Animal Spirits never so good, unless they are driven violently one a­gainst another, there would be required a longer time before they could be so mixed and, fermented as they ought, but the succession of new Matter admitting no long delay, it is requisite that they should be thus forcibly driven in together; to the end that the Spirits might be diffused through the whole Mass sooner, and that their Minute Particles, striking more violently against the fixed and [Page 81] compacted Particles of the Blood, might more immediately break and separate the strict Union of its Parts; and by a violent Fer­mentation, sufficiently dissolve and volatilize 'em, in so short a time as the Continual Pulsati­ons of succeeding Humors ad­mit.

The violent concourse of the Blood and Spirits, do not only promote this Fermentation, and the separation of the Subtile Li­quor, but also successively force the Matter prepared and separa­ted into the fleshy Fibers: This is so highly Probable, that it needs no Arguments to make it more Evident; it being the un­avoidable consequence of a con­tinual Circulation.

[Page 82] Now I have given the Rea­sons of Voluntary Motion, and the Efficient Causes of the Contraction of a Muscle; it will be easie to unfould the Rea­son of Involuntary Motion. That Voluntary Motion de­pends upon the Will is manifest; and that Involuntary Motion is not at all Subject to it, but is per­formed not only without the Dictates of our Appetite but a­gainst 'em, is so evident, that it would be superfluous and use­less to dispute it: I shall only shew how it is performed, which is indeed a little more ob­scure.

As Voluntary Motion is per­form'd, The Reason of Involuntary Mo­tion. for as much as the Pores of the [Page 83] Brain are dilated according to our Appetite, so that the Ani­mal Spirits flow more plentifully into the Glandules, and prepare a sufficient quantity of the Sub­tile Liquor to distend the Fibers as it passes through 'em; so those Pores, which lead to the Nerves serving to Involuntary Motion, are proportioned in such a manner, that they conti­nually conveigh Animal Spirits in a sufficient quantity to cause a perpetual Motion.

These Pores being so propor­tioned, there is no need that they shou'd have such an Or­ganick Motion as those serving to the Instruments of Voluntary Motion; because since they are proportioned so, as to carry Spirits in a competent quantity, there [Page 84] is no necessity that they should be either Dilated or Contract­ed.

To Prove that these Pores do lay down a com­petent Quantity of Spirits to be carried to the Glands, Proved. I need not bring many Arguments; for its plain and evident to all Practitioners in Physick, that when the Spirits are too much carried forth, and exalted, as in a Diary Fever, the Pulse is strong and vehe­ment, and by a too great exa­gitation of them, it becomes more quick and frequent; it is also Evident, that when the A­nimal Spirits are depressed, the Pulse is Weak, Slow and Rare, as most commonly in Women, subject to Hysterick Fits; and [Page 85] when the Spirits by an Acute or Cronick Distemper are worn out, and almost spent, the Pulse is either Vermiculans, Formicans or Tremens; which are signs that Nature is almost spent, and ready to yield to the Distemper. I say this is evident enough; it is then beyond Contradiction, that a healthful Pulse depends upon a moderate Quantity of Animal Spirits, and that they continually flow into those Nerves leading to the Instru­ments of Involuntary Motion; and as their Quantity varies, so more or less of the Subtile Li­quor is prepared to distend the Fibers of those Muscles.

When the Spirits are weak, or almost spent, there must needs flow a less quantity into [Page 86] the Glandules; and when they are exalted, a greater; and if Extremes either frustrate Natu­ral, or cause Preternatural Ef­fects, we may not only con­clude, that Natural Actions are performed by a moderate Quantity, but from hence we may bring good Arguments for a further proof and confirma­tion of my Hypothesis about Voluntary Motion.

Since I have said, that the Spirits, How it comes to pass, that the Systole of the Heart, is inter­rupted with such frequent Dia­stoles. by Reason of a particular Pro­portion of the Pores, flow continually in a just Quantity; and that these Pores are not subject to be Dilated or Contracted according to our Appetite; it remains, that I [Page 87] should shew how it comes to pass, that the Systole of the Heart is interrupted with such constant Diastoles; whereas, when the Pores serving to Vo­luntary Contractions are open, so as to convey a sufficient quantity of Spirits, the Motion is continual and without Inter­mission.

The Reason of the Difference will easily appear, if we do but take Notice, how when a Vein is opened, the Blood runs out continually, without ceasing or intermission; but if an Artery be opened, it gushes out with Intermissions answerable to the Diastoles of the Heart: because the Veins are always as a com­mon Cistern, distended with Blood; and before they can be [Page 88] emptied with a small Orifice, they are filled by the Extre­mities; but the Blood being continually received by the Ex­tremities of the Veins, and those Extremities being furnish­ed with Valves, to hinder it from Regurgitation; the Arteries are always kept more lank and empty, and are not as the Veins distended with Superfluous Blood: So that it only flows out of them, when they are distended upon violent Systoles of the Heart.

In like manner, that part of the Brain that furnishes the Nerves serving to Voluntary Motion with Spirits, is like a common Cistern full of Spirits; and when Vent is given (the Pores being opened according [Page 89] to our Appetite,) the Spirits are thrust forth in one constant course: But the Muscles serving to Involuntary Motion, being in continual Action, do so drain their Store-house, as to keep it more flaccid and empty; so that the Animal Spirits, as they are prepared, are continually wa­ved through their proper Pores; and as one Wave follows ano­ther, so one Contraction per­petually succeeds, the Subtile Liquor being according to the same Rules prepared in the Glands, and thrust out through the Fibers.

Some of the Muscles design­ed for Involuntary Motion, are, in some measure, subject to our Will, so that it lies in our power [Page 90] to retardate or quicken the suc­cession of their Contractions, but not totally to obstruct or hinder them; as the Muscles serving to Respiration: The Reason of which is this.

The Pores of the Brain lead­ing to the Nerves, which con­vey Spirits to these Muscles, Why the Muscles serving to Respiration, are subject in some measure to our Appetite. are so fra­med, that they car­ry Spirits to them, as to the other Muscles serving to Involuntary Motion, in a competent Quan­tity; but these Pores differ from those, for as much as these have such an Organick Mo­tion, as to contract or dilate according to our Appetite, we can by a constriction close up these, so as to deny a Passage [Page 91] for Animal Spirits, sufficient to prepare a quantity of the Subtile Liquor to cause due Contractions of the Muscles; till by degrees they increase to such a great Quantity, and di­stend their Receptacles so long, that those are no longer capable of receiving more; till that force which drives them violently in­to the Receptacles overcomes the constrictive Faculty of the Pores; and then the Spirits, a­gainst our Will, break forth, and flow violently into the Muscu­lous Glands.

It is easily noted, that after we have holden our Breath a long time, the first Contractions are as if Two or Three were joyned together without inter­mission: I mean so long conti­nued; [Page 92] which is sufficient to prove what I have said of the Muscles serving to Respira­tion.

For when by a Constriction of the Pores, the Spirits which ought to flow out, are kept in, and heaped up in their Re­ceptacle, and Two or Three Contractions are by that means hindered, that Receptacle be­comes like a common Cistern; and as soon as the Pores are forced open, the Spirits run­ning out, cause long continued Contractions, till that store is spent, and then they wave through, as before the Interrup­tion.

What I have hitherto said, might be sufficient to prove my Hypothesis reasonable; but to [Page 93] illustrate it a little more, I shall explain some of the Phaenomena about Muscular Motion, and give sufficient Reasons for them a­greeable to my Hypothesis.

Common Experience tells us, that Old People, Why old Peo­ple are subject to a trembling of their Head or Hands. whose Spirits are flat and weak, are most usually sub­ject to a Trembling of their Head or Hands; the Reason of which is this: The Fermentation in the Glandules is too low and weak, and doth not subtilize a sufficient Quan­tity of the said Liquor, to keep the Muscles in a constant Mo­tion: The Reason why a suffi­cient Quantity of Liquor is not prepared, is plain; for though [Page 94] their Appetite and Desire is strong enough, and endeavours to open and dilate the Pores of the Brain; yet when the Spi­rits are weak, it's a sign few are separated from the Blood; and if few be separated, they can­not flow plentifully into the Nerves, be the Pores never so wide.

This confirms the Reason I have given, why the Systole of the Heart is interrupted with constant Diastoles: For the Store-house which supplies it, is always kept empty, by reason of the constant efflux of Spi­rits; and in Old People, the Store-house which furnishes the Nerves serving to Voluntary Motion with Spirits, is kept empty; because few Spirits are [Page 95] separated from the Blood; and as they are separated, they are continually spent by a constant distribution of them, to pre­pare Nourishment in the Mus­culous Glands: So that when the Pores are opened wider for Voluntary Motion, for want of a sufficient Stock, they can­not flow out in a constant and equal proportion, but as they are separated, they wave through those Pores that are most ready to receive them. The Motion indeed is not interrupted with such perfect Intermissions, be­cause this Store-house is not so clearly drein'd; but there is a perfect Remission, because the Stock is not so copious as in Young and Lusty People to yield constant Supplies.

[Page 96] Moreover, when the Spi­rits are weak, its a sign that the Blood is much depaupe­rated, and declines from its Natural state; and then there is more need for strong Spi­rits to raise the Fermentation in the Glands, and to subti­lize the Liquor: Upon which account, when the Spirits are weak, the Disadvantage must needs be the greater.

Hence may be deduced a Reason, why when our Spirits are low, and almost spent, though our Appetite be strong, we cannot perform strong A­ctions.

From hence it may be proved; that there is something prepared in these Glands by the Animal Spirits, which is incapable of [Page 97] entring into the Fibers till pre­pared: For whether the Spirits be weak or strong, there is a sufficient quantity of Arterial juice laid down in the Glands, tho' its not made capable of passing into the Fibers, but as it is prepared, accordingly as the Spirits are more or less in quan­tity, stronger or weaker.

I have known Women, who seemed healthful, Another Phae­nomena Ex­plained. and of a Sanguine Complexion, whose Hands wou'd, when they were about any Moderate Exercise, Tremble as if Paralytick: For the Mass of Blood being a lit­tle more than usually depraved, and degenerated from its Balsa­mick and Sulphureous, into a more crude and Phlegmatick [Page 98] State, was unapt for Fermenta­tion; so that the Animal Spirits being not able easily to prepare a sufficient quantity of the afore­said Subtile Liquor, to keep the Muscle in a constant Motion, were forced to do it by an unequal Influx: just as an Horse, set to draw too great a Burthen, is forced by many reiterated draughts to get it forwards.

Mr. Cowper Mentions an Experiment, A Third. how by an Injection of Water into the Crural Arterie, the Muscles of the Legs renue their Contractions. From this he would infer, that Muscular Motion is performed by the Blood as a Pondus; but tho' his Myotomia Argues, it came from an Inquisitive Author, yet [Page 99] I rather an fully perswaded, that the Blood does not Act as a Pondus, because this Experi­ment pleads against it; but to avoid a long dispute, I shall on­ly give the Reason of the Phae­nomenon.

Before the injection of this Water, the Branches of the Ar­teries are full of Blood, and Ar­terial juice; and when by the mixture of the Water with this juice, it is attenuated and dri­ven into the Glands, faster than it can be received by the Venous Channels, the most Subtile Part is by the force of injection, strain­ed into the Fibers and distends 'em so as to Contract the Muscle.

Perhaps here it will be obje­cted that if the Water can thus pass through into the Fibers, [Page 100] what need is there that the Nerves should lay down their contents in the Glandules.

I answer, that the Water is thin and apter to pass through those Ducts than the Arterial juice, which is thick and viscid; wherefore it is necessary, that the Nerves should lay down their contents there, to Atte­nuate and Rarisie this Thick juice.

I have seen People inclining to a Dropsie, A Fourth. whose Blood and Serum was much diluted, could move much more nimbly, tho' more seebly, than some of a healthful Constitution, whose Blood and this Arterial juice was thicker and not so much diluted; which doth plainly [Page 101] shew, that the thinner the Blood is, and the more diluted the Nutritious juice, the less quantity of Spirits is required to subtilize it, and make it ca­pable of passing into the Fi­bers.

It may easily be observed, that those People whose Spirits are strong, A Fifth. and their Arterial juice very thin, are Nimble; but the Contractions of their Muscles are not so durable, as of those, whose Serum is of a thicker Consistence: For tho' in the former more of the Subtile Liquor is prepared, yet by Reason of its Tenuity it's sooner receiv'd, and carried off by the Lymphaeducts; which makes the Contraction shorter, [Page 102] Those whose Blood abounds with fixed Salts & Phlegmatick Hu­mours, A Sixth. which too much dull and resist the Activity of the Animal Spirits, are always slow and unapt for Motion; where­as, if the Blood Acted as a Pondus, they must be more nimble and strong; because the thicker the Blood is the heavier would be the Pon­dus.

As Muscular Motion is ma­ny ways vitiated, by the fault of the Arterial juice, or of the Spirits, and consequently by the Distemperature of this sub­tile Liquor; so it is very often depraved, and accordingly as the Mass of Blood degenerates [Page 103] from its genuine and proper Nature, are produced various Diseases or Symptoms of Di­seases: viz. Cramps, Convul­sions, Palpitation of the Heart, Leaping of the Tendons in Fe­vers, &c. for a farther illustra­tion of my Hypothesis, before I conclude, I will give the Reasons of these Phonomae­na.

When by an Abuse of Non-Naturals, the Fer­ments of the Visce­ra are perverted; The Reasons of Convulsions. and by the faults of the Pan­creatick juice and of the Spleen, an Acid or Austere Salt is car­ried forth into a flux; present­ly the Mass of Blood is viti­ated. The Animal Spirits [Page 104] meeting with this vitious Salt, and fermenting in the Glands, do there cause irregular Explo­sions of matter, into the Car­nous Fibers, subtilized in that Fermentation; whence follow irregular Contractions of the Muscles.

Why Convulsive Paroxysms come at uncertain times, will easily appear, if we do but consider the Procatartick Cau­ses; amongst which I shall on­ly mention two, viz. The Quantity of Morbisick matter irritating Nature to an Expul­sion of it; and sudden Passions of the Mind.

The Quantity of Morbisick matter is far greater in some Bodies than in others, before [Page 105] the Spirits are able to recover themselves, and to endeavour an Expulsion of it: In the former Case, Convulsions are Univer­sal and seise the whole Body; in the Latter Particular, the Morbisick matter being acci­dentally driven more on one Part than another. Again in some Bodies it is sooner hea­ped up, being generated in greater quantities.

The Matter heaped up, at the first is very crude and thick, and although it be cast forth into, and Circulates through, the Musculous parts, and con­tinually Ferments with the Spirits in the Glandules; yet because it is not sufficiently [Page 106] attenuated to be driven forth into the fleshy Fibers, till by frequent Circulations and Fer­mentations, it is exalted from it's state of sixedness to a more Volatile, no Convulsions suc­ceed. Moreover as long as it continues in its state of Cru­dity, the Animal Spirits are much dulled and their Acti­vity quashed by mixing with it, but it being at the length subtilized and rarified by fre­quent Circulations, the Ani­mal Spirits recovering 'em selves, and violently Fermenting with it in the Glands carry this Vi­tious juice explosively into the Fibers. The Reason why this Motion is Involuntary, is, be cause it is not produced by a [Page 107] greater quantity of Spirits flow­ing from the Brain, according­ly as the Pores are dilated by our Appetite, but by a mixture of Morbifick and Fermentitious Particles, which cause Preternatu­ral Fermentations & Expulsions of Matter Attenuated thereby.

Convulsive sits are sometimes brought on, before the Morbifick matter gradually arrives at this state of tenuity, when up­on sudden Passions of the Mind, the Animal Faculties quit their Stations, and being over­power'd by external Objects can no longer moderate the Ema­nations of the Animal Spirits. The Formal Cause of the Irre­gular Emanations of the Spirits in these Convulsions is this; the [Page 108] Pores of the Brain being shut up, to keep out external Objects, heap up the Spirits, till by Rea­son of their quantity, the Pores can no longer retain them; and then the Spirits rush out quà datur portà in a greater quan­tity, and violently setting upon the Crude juice, which they meet with in the Glandules, strongly Ferment Attenuate and carry it forth into the Fibers, of the Muscles wherein the Spirits are thus accidentally laid down: The Brain being thus emptied, the Pores are shut up again, till the quantity of Spirits make way a­gain; and so successively follow Convulsive Motions, in this or that Part where-ever the Spirits set upon the Crude Morbisick Matter.

[Page 109] The [...] of the Heart, as the [...] ­ed Dr. [...] has noted, [...] proceeds [...]. Con­vulsive Motion: The Reason why the Morbifick Matter on­ly shews it self in this part, and at the same time in no o­ther parts of the Body in this, The Mass of Blood [...] ­nated with a Morbifick [...] and whatever is the Nature of it, since it is [...] the whole Body, [...] Ra­tionally expect Universal Con­vulsions as well as [...]: But this Morbifick Matter be­ing as yet Crude, and not of a sufficient Quantity [...] [Page 110] Nature in all the Parts of the Body; these Effects are only produced in this Part, where a large Quantity of Spirits is continually laid down to ser­ment with it; by which means it is Subdued in this part, before it arrives at such a State of Activity of such a Quantity, as to cause irregular Fermenta­tions and Contractions in other Parts.

In a [...], The Muscles continue constantly contracted against our Appetite; [...]. these Distempers seize People, whose Blood is rather of a Vitriolick Tenacious Na­ture, [Page 111] and impregnated with more Fermentative Spirits; so that by reason of the Viscidity of the Matter violently forced into the Fibers, either the Lym­phaeducts are obstructed, or by reason of a continual Fermen­tation, Matter gradually suc­ceeds.

In the Cramp, the Fermen­tation is different from that which is Natural, Of the Cramp. or in o­ther Convulsive Motions; that which is Natural, being caused by the Animal Spirits preparing a Subtil and Homogenious Li­quor: In other Convulsions the Animal Spirits ferment with, [Page 112] and endeavour to subdue a Morbisick Humour brought and layed down by the Arteries, and the Matter thus attenua­ted, is accidentally forced into the Fibers: But these are caused by the continual Conflict of the Volatile Animal Spirits, strong­ly fermenting with Fermenta­tive and Elastick Particles of another Nature, supplied by the Mass of Blood; where both striving to subdue each other, the Elastick Particles of the Blood, more strongly op­pose the Motion of the Spi­rits, and the Spirits them, by a contrary agitation and intestine Motion of their Particles; and these Two being violently ex­ploded, and impetuously leap­ing [Page 113] into, and fermenting in the Fibers, cause most strong and painful Contractions.

The Subsultus Tendinum in Fevers are caused, Of the Sub­sultus Tendi­num in Fevers. when the Spirits being too much exalted, leap irre­gularly out of the Brain, and raise the Fermentation in the Glands so high, as to prepare and carry too much of the Subtile Liquor into the Fibers; which because it is so very thin, easily slips into the Lymphaeducts, and makes the Contraction short.

[Page 114] I shall add the Reason only of one other Phaeno­menon, Of a Spasmus Cynicus. which seems more evidently to prove, that Muscular Motion depends on the greater influx of Animal Spirits, viz. Why the Contraction of one Muscle followeth, when the Antagonist becomes Paralytick, as in Spas­mus Cynicus: The Branches of the Nerves being derived from the Brain, when the Influx of the Spirits into the Muscles of the one side are hindered, they regurgitate, and are driven presently in a greater quantity into the Antagonist; as by the Loss of one Eye, the other, by a greater Influx of Spirits, [Page 115] becomes more Acute: This is evident, and needs no further proof.

Thus I have laid down my Hypothesis of the Formal and Efficient Causes of Muscular Motion, and how it is vitiated or depraved; which I the more willingly commit to the Judg­ment of Learned and Compe­tent Judges, with due Submis­sion; because it seems to me to answer Natural Ends, and to account for the several Phae­nomena, without the Difficul­ties, Enormous Motions and Impossibilities, which usually attend Hypotheses on this Subject; not doubting, but it [Page 116] will give satisfaction, till one more probable and plausible shall succeed.