A TREATISE OF THE REASON OF Muscular Motion Or the Efficient Causes of the Contraction of a Muscle WHEREIN Most of the Phaenomena about Muscular Motion are explained By RICHARD BOVLTON of the City of Chester Medicin Proficiens 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 LONDON Printed by A. and J. Churchill at the Black Swan in Pater-Noster-Row 1697. TRactatum hunc cui Titulus A Treatise of the Reason of Muscular Motion c. dignum Censemus quî Imprimatur Samuel Collins Praeses Thomas Burwell Sen. Richard Torless William Dawes Thomas Gill Censor Datum in Comitiis Censoriis ex Aedibus Collegii nostri Sept. 11. 1696. TO THE MOST LEARNED AND EVER HONOURED Dr. Collins President Dr. Thomas Burwell Dr. Richard Torlesse Dr. William Dawes Dr. Thomas Gill. CENSORS OF THE Colledge of Physicians This Treatise is Humbly Dedicated By Your Most Faithful And Obedient Servant R. BOULTON TO THE READER I Have examined this Treatise with the strictest Reason that I am Master of and it appears to me Reasonable in every Particular But I am altogether desirous of Truth and would not out of any fond Opinion of my own Hypothesis receive it sooner than another Man's I am most inclined to suspect whatever is a Faetus of my own Brain If it may be any ways servicable to others I have my Desire THE CONTENTS THE Usefulness of Muscular Motion as it tends to the Maintenance of Life Page 1 With respect to the Soul and the Animal Functions p. 3 Dr. Willis's Opinion examined p. 7 Mr. Cowper's Opinion examined p. 20 Dr. Ridley's Opinion examined p. 30 The Structure of a Muscle p. 40 The Formal Cause of the Contraction of a Muscle p. 41 Vessels implanted into a Muscle p. 42 Their Distributions p. 43 And Terminations in Small Glandules p. 45 What a Gland is p. 47 The Use of the Nerves p. 52 And Arteries inserted in the Glands p. 53 To prepare a Subtile Liquor ibid. The Use of it p. 54 The Reason of Tonick Motion p. 59 Of Local Motion p. 60 The Use of the Lymphaeducts p. 68 The Nature of the Liquor and the Manner of its Preparation p. 69 By Fermentation p. 70 Proved p. 72 The Reason of Involuntary Motion p. 82 Why the Systole of the Heart is interrupted with frequent Diastoles p. 86 Why the Muscles serving to Respiration are in some Measure Subject to our Appetite p. 90 Some Phaenomena about Muscular Motion Explained p. 93 The Reason of Convulsions p. 103 of the Palpitation of the Heart p. 109 of the Cramp p. 111 Of the Subsultus Tendinum in Fevers p. 113 Of Spasmus Lynicus p. 114 OF THE REASON OF Muscular Motion OR The Efficient Causes of the Contraction of a Muscle c. IF we consider the Usefulness of Muscular Motion with respect to an Individual and that either as it tendeth 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 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 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 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 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 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 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 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 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 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
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 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 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 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 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 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 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 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 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 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 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 Moreover when the Spirits are weak it s 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 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' it s 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 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 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
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 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 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 by which the Contraction of a Muscle is performed let any 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 Another Argument to prove 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 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 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 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 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 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 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 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 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 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 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 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 through the Vessels from the Brain to its Carnous Fibers and causes the Intumescence of a Muscle the same Liquor at
to get it forwards Mr. Cowper Mentions an Experiment 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 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 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 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 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 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 Those whose Blood abounds with fixed Salts Phlegmatick Humours 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 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 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 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 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 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 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 over-power'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 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 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 〈◊〉 〈◊〉 Nature in all the Parts of the Body these Effects are only produced in this Part where a large Quantity of Spirits is
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 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 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 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 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 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 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 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 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 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 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 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 Every Muscle is endowed with opposite Tendons 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 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 and by a Contraction of their Longitude each Tendon is drawn 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
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 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 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 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 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 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 as is sufficient to Nourish the Parts as it passeth through ' em But when the Pores of the Brain are opened 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 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 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 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 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 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 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 forced forward by a Succession of Matter and as it is forced into
they become destitute of Motion That the Animal Spirits simply 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 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 nay cannot pass into the Fibrous Cells till subtilized and prepared 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 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 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 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 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 for as much as the Pores of the 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 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 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 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 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 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 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