Proposition That the proper Action of the heart is the Constriction of its Ventricles and the consequent compression and expression of the bloud contein'd in them not by a Contorsion of its Spiral Fibres but by an inflation and corrugation of them Here some perhaps may be willing to propose to me this question If it be true that in the Systole or act of Pulsation neither the exterior Superfice of the heart is augmented nor the Cone of it drawn up toward the Basis both which we have asserted how then comes it that in every Systole the Cone of the heart knocks against the left side of the breast Which may be thus Answer'd Because the heart is hung in the middle of the Breast by strong Ligaments and yet in every Systole is brought to touch and strike the inside of the Breast therefore it is necessary that this be done either by a dilatation of the heart or by local motion and translation of it or by erection of the whole or by flexion and incurvation of the Cone thereof And as our observation and experience rejects the three former causes of this Phaenomenon so it obliges us to embrace and acquiesce in the last Wherefore it remains only that we investigate the Mechanic reason of this effect Which seems to depend first upon the disposition of the Fibres of the heart For we see that a crooked gut tied about with a thred and not wholly fill'd with water is by the weight of the water extended directly or in a strait line but if the water be impelled toward either end by compression then the gut becomes crooked again as the nature of it exacts and the other pendulous extremity will be erected and strike against your hand held a little over it This plainly follows from the curve figure of the membrane of the gut which is longer in the convex part and shorter in the concave So in the left part of the Ventricle of the heart the left wall is shorter less fleshy and less crooked than the two walls that make the right Ventricle Wherefore in the Systole of the heart the Cone of it ought to be erected toward the left side of the breast and to strike against it more or less strongly according to the degree of violence with which it is erected This may be somewhat helped also partly by the erection of the heart lying obliquely partly by the situation and disposition of the Fibres which are wound about obliquely and spirally from the right side of the Basis of the heart toward the left side of the Cone whence in the act of Pulsation when the Fibres are shortned the Cone may be a little distorted and erected by the fasciculus or combination of Fibres forwards toward the left side and so the Percussion may be made Seneca as ye may remember in epist. 57. most elegantly describes first the inevitable horror that invaded him while he was passing through the dust and darkness a darkness so thick as even to be seen of the Crypta Neapolitana now named the Grot of Pausilype in the way between Naples and Putzole and then the chearfulness he calls it alacritatem incogitatam injussam that returned to his mind upon the first sight of the restored light The same surprising alacrity methink I now feel within my self after my passage through the no less darkness in which Nature had through a long Series of ages involved her great secret of the Motion of the Heart made more obscure by the dust of mens various opinions and my arriving at the light of knowledge both what is the proper Action of the Heart and by what Mechanic necessity that Action is performed In the ardor of this alacrity I proceed to the use and action of the Ears of the Heart and of its Valves The end of the Vena Cava which is conjoyned to the heart is as hath been said before in greater Animals Musculose round about that the trunk of it may be constringed as Sphincters are closed by virtue of their circular Fibres But the end of the Vena Pulmonaris wants the like fulciment and therefore cannot constringe itself Then both these Veins end into the Musculose Ears which are hollow like little bags affixed to the sides of the heart and whose structure much resembles that by which the left Ventricle of the heart is contexed in the hollow part of it For the Ears also consist of fleshy Fibres intersecting each other like a St. Andrews Cross which within are bound together into many little Cylindrical Columns and trenches connecting the sides of the bags To these Ears succede three membranes in the right Ventricle and two in the left which are of a very strong contexture of a triangular figure the bases of which are closely affixed to the whole Circuit of the Tendon of the Orifice of the heart Then the areae or middle spaces of these little membranes are branched within the Ventricles of the heart into many little Tendinose Strings or cords which are fastned to the tops of the papillae or teats that stand pointing upwards placed on the opposite side Now this admirable structure being known let us enquire the design or use of it First the extreme part of the Vena Cava seems not to be made Musculose for strength lest it should be broken by the current of the bloud rushing in but rather by its constriction to protrude the bloud into the oblique Sinus of the right Ear and to render the same turgid Which action is helped by the peristaltic constriction of the whole trunk of the Vena Cava and by the compression of the Muscles and Viscera of the whole body as was yesterday demonstrated when we considered the motion of the Bloud Hence it comes that the bloud impelled through the open aperture of the Ear fills the cavity of it and then runs into the right Ventricle and by the like necessity the bloud flows out of the Vena pulmonaris into the left Ear and thence into the left Ventricle of the Heart No sooner are the Ears filled and distended with bloud but they both at the same time constringe themselves by a contractive and compressive action common to all Muscles resembling that of a Press in this order that first by shutting their apertures they hinder the regress of the bloud into the same Veins out of which it came in then by the great force of compression they squeez it into the Ventricles of the heart until they be filled and made turgid To this action of the Ears immediately succedes the compression of the press of the Heart itself by which the bloud itself by reason of its abundance inflating and distending the triangular and mitral valves exactly shuts the Orifices or mouths of the Veins and so prevents its own recoiling into them Whence it is of absolute necessity that the same bloud be expressed into the Pulmonary Artery or Vena Arterialis and into the aorta These are the
carry on the resemblance a little farther I soon discovered the disparities to be so many and so great that it was impossible to reconcile them into a just Analogy Whereupon condemning the extravagance of my fancy I soberly concluded that the Heart of an Animal is an Engine never to be imitated by human art and I found my self more inclined to applaud the judgment of that prodigy of Mathematical knowledge Archimedes of Syracuse for never attempting to counterfeit the motions of the heart than to admire his wit shewn in making a Sphear of Glass Athan. Kircher denies that any part of it was Glass but only the out-side that men might discern the wheels and motions within which represented the perfect order and motions of the Celestial Bodies and which Claudian describes in one of his Epigrams Now if we desire clearly to understand this inimitable Excellency of the Machine of the Heart and in what Proprieties of it the same doth chiefly consist we shall be obliged well to consider two things neither of which hath yet been explicated by us and without a due explication of both which all that we have hitherto said concerning the motion of the Heart will be maimed and unsatisfactory These are the Mighty and incredible Motive force of the Heart by which it expresseth the bloud out of the Ventricles and the Efficient Causes of its Motion Things so worthy to be known that I need not deprecate your impatience most Candid and accomplished Auditors if I detain you a few minutes longer while I enquire into them As to the FIRST therefore viz. The admirable Motive force of the Heart Since the round and Conical Figure of the Heart doth not permit us to attempt the measuring of its Motive power by the same way by which the most Learned Alphonsus Borellus hath with singular sagacity measured the forces of very many other Muscles of Mans body namely by weights suspended by them and since therefore in this disquisition we cannot from the effect procede to the knowledge of the cause we are compelled from some other Sign to raise a probable conjecture whence we may investigate the greatness of the effect And this Sign shall be the Similitude and Analogy which the Muscule of the heart seems to hold to other Muscles of the same Animal Let us then with the same excellent Mathematician Borellus in whose footsteps I now again tread suppose that all even the least Fibres or little Machines of the same or divers Muscules in the same Animal are equally strong and exercise an equal motive force in the same time in the state of health And because equal bulks of two Muscles contein equal multitudes of the least Fibres it follows that if we have foreknown the total motive power of one of the two equal Muscles we shall be able thence to conjecture what is the total power motive also of the other Therefore the fleshy bulk of the heart being of almost equal magnitude to the bulks of one of the Temporal muscles and of one of the Masseters and Borellus having demonstrated to us the total motive force of those two muscles we may probably infer that the motive force of the heart is equal to that which those two muscles shutting the mandible exercise Now because no intire Fibre of these two muscles is less than two inches long taking all the Fibres one with another that the excesses of the longer may compensate the defects of the shorter and because in an inches space of every single Fibre we may imagine more than twenty little Machines or Rhomboid Pores contained like the links of a chain in a Watch or the Meshes of a Net in a row one above another let us notwithstanding suppose no more than ten smallest Fibres to be conteined in that space therefore in the length of every one of the Fibres that compose the said two Muscles there will be conteined more than twenty of those most minute Machines And since the weight of 150 pounds may be suspended by one single Stratum or Layer of these small Machines of the same Muscles therefore that we may have the whole force that Nature exerciseth in those Muscles the force of that one Layer viz. that which is able to sustain 150 pounds ought to be twenty times multiplied Wherefore the whole force that Nature exercises to dilate all the Rhomboid meshes or pores of the said two Muscles when they act is greater than the force of 3000 pound weight and would if applied to the opposite end of the beam of a balance preponderate If then every most minute Fibre of the Heart exerciseth in the Systole of it a force equal to that which every Rhomboidal Machine of the Temporal or Masseter muscle makes when they act as most certainly it doth the motive power of all Fibres of the Muscles in the same Animal in the state of health being equal and if the multitude of least Fibres contein'd in those two Muscles be equal to the multitude of most minute Fibres contein'd in the Muscle of the Heart as the visible equality of their magnitudes warrants us to suppose it to be we may thence deduce this conclusion that the force which all the most minute Fibres of the heart when they are swell'd exercise to constringe the Ventricles i. e. when they act all together exceeds the force of 3000 pound weight and would preponderate if it were applied to the contrary end of the beam of a just balance Quod erat demonstrandum And thus have I given you a summary of what Borellus hath from a long chain of most ingeniose Propositions and Theorems in fine inferred I come therefore to the. SECOND and last considerable proposed to be inquired viz. the Efficient Causes of this so wonderful Motive force of the Heart These seem to be no more than two of which one is immediate the other mediate As to the the former viz. the immediate cause of the hearts Motive Power we are not to expect to learn either what it is or whence it procedes from the doctrine of the Ancients For they having observed that the heart was not as all the other Muscles of the body are moved ad arbitrium voluntatis at the command of the Will not only named the motion of those Voluntary and the motion of this Natural as they had good reason to do but also conceived and taught the cause of the motion of the heart to be divers from the cause of the motion of the rest of the Muscles and accordingly constituted and assign'd to the heart a certain blind and unintelligible Pulsifick Faculty whereto alone they ascribed as well the diastole as the Systole thereof which they had no just reason to do To evince this their palpable error I will assert this PROPOSITION That the immediate Motive cause of the heart is the very same with that by which the Muscles of the Limbs are moved Voluntarily First it is most evident to sense that
teach us that some influence whatever it be derived from the Brain to the Heart is absolutely necessary to the incitement and perpetuation of the Motion of the Heart For the Brain is in a great part perfected before the heart though those two Members ob communem officii necessitudinem be almost congenite And I have good cause to believe that the exordium of the Brain is that Colliquamentum which is first seen in an Egg after the first days Incubation of the Hen and which by the same warmth continued doth in a short time concrete and is condensed into a thicker substance that is soon invested as every viscid humor is wont to be with a thin film or membrane and shoots forth from itself little Nerves as branches every way From the observation of which that incomparable man Sir George Ent doubted not publickly to declare himself to be of this opinion that not the Heart but the Brain is the fountain of life His words are these Cor enim uti arbitror non est fons vitae qui cerebro peculiaris est sed rivulus duntaâ—at accessorius Which yet is no new opinion but ascribed by Galen to Erasistratus who said Omnium quae in corpore sunt principium esse Cerebrum apparet and asserted by Hippon whom Censorinus introduceth rightly teaching Caput primò fieri Now what can we with equal probability conceive to be the reason why Nature finishes the Brain before the Heart as this I have here given viz. because the Heart even from the beginning hath need of some influence to be transmitted from the Brain to it for the incitement and continuation of its motion as well as for the Nutrition of its substance the latter of which benefits is common to the heart with all other parts of the body Secondly It is highly probable that the Brain is not only the Laboratory but also the common Promptuary of the true Succus nutritius and that the Nerves are the Canes or Filtres through whose long and narrow Pores the same roscid Nutritive liquor is gently distributed to all parts for their nourishment both which Propositions have been formerly with many considerable arguments drawn as well from experiments Anatomical as from reason asserted by Sir George Ent Dr. Glisson and if it be lawful for me to put my self into the same period with such excellent men my self This therefore being supposed it is not unreasonable to think that this roscid balsamic and spirituose liquor by many called Succus Nervosus being for the most part in sufficient plenty in the Brain doth at all times touch and soak into the open Pores of all the Nerves thence elonged but more copiously into the Nerves that extend themselves into the Fibrose substance of the Heart because the Heart is furnished with many more and larger Nerves than any other Muscle of the whole body And because the extremely narrow cavities of the Nerves are full of a spongy medullary substance and continually wet with the same roscid liquor creeping through them therefore the liquor cannot flow out of the lower ends of them into the Fibres of the heart otherwise than guttatim drop after drop as all liquors chiefly such as have any thing of viscidity slowly creep along the threds of Filtres and when they at length arrive at the end fall down in equal drops with equal pauses betwixt the precedent and the succeding drops Farther because the distillation of each drop is almost momentaneous not persevering thence it seems to come that the constriction of the heart is performed and finished in a moment and a pause succedes in the next moment till a second drop comes to cause a second constriction and so forward And since in the Brain or fountain of this roscid liquor there is alway plenty to maintain a perpetual succession of drops and the liquor it self is in the state of health always of the same temper and consistence and the narrow Canales in the Nerves always equally retard its descent and efflux therefore it seems necessary that the times of quiet or the pauses intervenient betwixt the drops should be equal so long as the liquor retains the same degree of fluxility or is not hindred by greater violence But if it happens that the liquor is become either more thin and fluxible than is fit as commonly it doth upon debauches with Wine or other strong drinks or Saline Acrimonious Acid or of any other vitious and irritating quality as often it is vitiated in many maladies chiefly in Scorbuto inveterato or fall into a Fermentation which I have reason to conjecture it always doth in Fevers and more eminently in the Small Pox the matter of which seems to be not the bloud but the Succus nutritius in a peculiar manner corrupted and critically transmitted from the Brain through the Nerves into the habit of the body or be agitated by any swift motion as in the more violent passions of the mind and chiefly in anger it is in all these cases the motion and distilling of it into the Fibres of the heart must be accelerated proportionately and consequently the Systoles of the heart will be more frequently repeted and the pauses intercedent betwixt them will be as those intervenient betwixt the drops shorter And here a fair occasion offers itself to me of expatiating into the various and numerose differences of Pulses of the heart and endeavouring to solve them rationally by this Hypothesis which alone is capable to do it but the shortness of the time appointed for my sitting in this place forbids me to make use of the occasion Of this Stillicidium or guttulation of the Succus Nervosus out of the ends of the Cardiac nerves we have various familiar examples We see that Sponges Filtres and even Glass tubes of very small bores though they be continually replete with water or any other liquor yet the liquor doth not flow out of their lower ends or orifices in a continued course as water gushes out of a fountain or out of the cock of a Cistern but by drops with aequitemporaneous stops or pauses betwixt the drops The true cause of which effect seems to be this the great narrowness of the Canales which impedes the free permeation of the liquor the little particles or moleculae of the liquor being not exactly smooth but villose and viscose and therefore they are forced to creep along with a slow pace through the cavities of the tubes whose superfices within are equally full of little asperities too so that they must as they pass along be put into a vertiginose motion and interrupt their course and consequently fall out of the lower end of the Sponge Filtre or Tube guttatim Now since the Nerves are like Indian Canes composed of Filaments running their whole length in direct lines a medullary and spongy substance and many little interstices interjacent betwixt the Filaments with a thin coat investing them and since the superfices of their
of the Muscles of the Guts Stomach Tendons Membranes and the like Fibrose parts naturally resist distraction and have a power of contracting themselves after extension Yea more we see that all Fibres even in their natural posture are somewhat upon the stretch for when they are cut they instantly shorten themselves toward both ends which would not happen if they had been constituted in a middle state betwixt laxity and extension as a Bow unbent is quiet suffering neither contraction nor distraction of its parts Now if all Fibres even in their natural state suffer some degree of stretching certainly when the Arteries are replenisht with bloud their cavity must be dilated and in the dilatation of their cavity their transverse or circular Fibres must suffer much more stretching than they did before And because to this dilatation of the Arteries a constriction immediately succeeds which is not possible to be effected without an abbreviation of the circular Fibres of the Arteries and because that abbreviation or contraction is connatural to the Fibres themselves therefore it is impossible that the Arteries after that violent stretching caused by their repletion and turgency should not exercise by natural necessity that mechanic power they have of contracting themselves by vertue of their circular Fibres girding them inward and equally impossible that the Arteries should so contract themselves without expelling at the same time out of their Orifices the bloud that dilated them Whence it appears beyond dispute that the spontaneous constriction of the distended Arteries is the cause of the expulsion of the bloud out of them into the substance of the parts contrary to their opinion who ascribe this expulsion only to the Systole of the heart ¶ ⸪ The natural method of acquiring Science ye know is to begin from things more known and then to advance to things less known to procede from effects to their causes Seeing therefore that we are now certain that the bloud in Animals is carried by a perpetual circular motion through all parts of the body our next business is to enquire what are the Causes of this admirable motion as well the final as the efficient I begin from the final it being a question worthy our consideration why or to what end Nature all whose counsels and actions are ordained by an infinite wisdom hath instituted this rapid Circulation of the bloud Constant it is even from common experience that whenever the bloud is quiet or ceases from motion whether within or without the body of an Animal the red and grumose part of it soon curdles and is separated from the serose or albumen and so the constitution or contexture of it is dissolved and corrupted whereas on the contrary while the bloud continues in perpetual motion within its vessels in the body of a living Animal so long the ordinate mixture of its elements due temper and vital constitution of it is conserved for mechanical reasons in our ensuing discourse to be explained It seems then that such a mixture of the constituent parts of the bloud upon which the vitality of it doth necessarily depend cannot be otherwise conserved than by a continual agitation and concussion made in the vessels first by the heart with strong force impelling the bloud through the Arteries then that impulsive force languishing by filtration in the spaces intermediate betwixt the Arteries and Veins next in the Veins by the constriction of their circular Fibres by the compression of the Muscles and the Viscera and the inspired air All which compressions would not suffice were not Valves placed commodiously within the Veins by which the motion of the bloud is accelerated and a farther conquassation of it made And here we meet with a fair occasion to reflect upon the mutual Anastomôses of the Capillary Veins and the infrequent distribution of Valves in one and the same Vein for both these contribute also their proportions toward the end now under our disquisition For the texture of the Veins being indeed lax and soft yet such as may by virtue of their circular Fibres be constringed and contracted hence it is that by the bloud regurgitating in those tracts of the Veins that have no Valves by the great quantity and force of its regurgitation or recoiling the lowest part of the Vein is much dilated and on the contrary the highest part is contracted So that the bloud being by this reflux though inobservable agitated and conquassated may revive its due commistion and conserve its vital constitution It appears then the defect of Valves also hath its use Within the cavities of the Arteries as I said before no Valves are placed because the grand force by which the bloud is impell'd through them is more than sufficient to conquassate and commix it by wedging in as it were the more fluid albugineous particles among the red grumose particles that from both sorts comixt per minimas moleculas as they say and yet mutually reluctant the Vital Mication or Oscillatory intestine motion of the bloud may be continued So then here is neither need of nor place for a Fermentation Now from the consideration of these things premised I conclude that the Circulation of the Bloud was instituted for the conservation of its requisite temper and vital constitution Which was to be inquired and which leads us to The admirable effects and benefits arising to the Animal Oeconomy from the same Velocity of the Circulation of the Bloud Which being certainly so great that the whole mass of bloud runs its circular race in the twentieth part of an hour or thereabouts even in a sedentary and sedate man as hath by many been demonstrated from the quantity of bloud commonly contein'd in the body from the number of Pulses made in an hour and from the quantity of bloud exprest by every pulse of the heart and we having already seen what advantage redounds to the bloud it self from this velocity our curiosity spurs us on to enquire also what other scopes or ends Nature may probably be conceived to have proposed to herself when she instituted this so rapid motion or what emoluments and benefits from thence redound to the Oeconomy of the whole body Of these the first seems to be this that in every pulsation of the heart a great quantity of bloud is effused and protruded out of the Capillary Arteries into the habit of the parts for their refocillation by influent life of which I have formerly discoursed copiosely in this place For by how much swifter the motion of any liquor or other fluid through a pipe or canale is so much a greater quantity of it is in equal time effused at the Orifice thereof as hath been ingeniously demonstrated by B. Castellus and therefore the bloud is like a full and rapid torrent impelled into the Pores of the flesh and Viscera The second is the energy of the stroke with which the bloud projected by the heart dashes against the same extreme parts which energy is
little Canales within must therefore be full of small asperities it is necessary that the Succus Nervosus whose consistence is not much thinner than the white of an Egg well beaten should pass through them with a slow and interrupted course and at length fall out of their lower ends in drops with equal pauses between the drops Where we find a parility of Causes we may rightly expect a similitude of effects Here I see two formidable Difficulties standing like Romantick Giants in my way to deterr me from proceeding and I cannot without shame and infamy decline to encounter them One is That after the Cardiac Nerves are cut off and the heart itself taken out of the body the Pulsation of it continues for some time To remove this therefore I say that the cavities of the Nerves annext to the heart may remain still full of and turgid with the roscid Succus Nervosus which being hindred from regress by their spontaneous contraction toward the heart and kept in a state of fluxility by the yet lasting warmth of the heart may for some time be instilled into the Fibres of it and by swelling of them cause them to constringe the Ventricles as before Then the heart being irritated by the prick of a needle or some sharp and pungent liquor may be able by its peristaltic constriction to squeez out the few remaining drops of the roscid liquor Which being done the Pulsation ceaseth for ever To the bloud this effect ought not to be ascribed for after all reliques of it have been with warm water and a Syringe washed out of the Ventricles and squeez'd out of the Vessels the Pulsation notwithstanding will continue for sometime Nor can it be with more reason ascribed to Convulsions of the heart because all convulsions are disorderly and unequal both in the times of their girds and in those of their intermissions whereas in this case the Pulsations are regular and isochronical with equal pauses Nor to the Heat communicated by the bloud to the heart before it was exsected and not yet quite extinct because that borrowed heat soon vanishes and no external heat will revive the languishing Pulsation after all the roscid juice hath been exprest out of the ends of the Nerves left in the heart Nothing then remains to solve this Phaenomenon but the instillation of a few drops of our roscid liquor into the Fibres of the heart to swell them and so urge them to constriction of the Ventricles The other Difficulty is this Why is there not a Pulsation after the same manner also in all the Muscles of the Limbs since their Fibres are of the same nature in all things their disposition and direction only excepted since the Orifices of the Nerves perteining to them are in the Brain as open to admit and imbibe the Succus Nervosus there elaborate and provided for them and since the same Nerves are equally spongy and permeable in their constitution and so apt to transfer that liquor as the Orifices of the Cardiac Nerves are to receive or their Canales to transfer it If the whole apparatus be the same on both parts whence comes it that the same effect is not produced in both At this Goliah I have in my Scrip three Pebbles to throw and though my arm be weak I will not despair of hitting him in the forehead First therefore I say that it is not yet certainly known to any mortal man by what mediate cause the Muscles of the Limbs are moved at the command of the Will whether by simple contraction of the Originals of the Nerves inserted into them or by the immission of the Succus Nervosus more copiosely and swiftly at the time of their being put into action though the Mechanism of their Fibres make it more probable that they are moved by immission of some liquor from the Brain by which the rhomboid meshes or pores of their Fibres being all at the same time swell'd and dilated a contraction of the whole Muscle must in the same moment be effected and therefore I prefer this opinion to the former and have followed it in many places of this rude Discourse But yet this opinion hath not led me to a discovery of the Cause of the difference this present difficulty compells me to hunt after Should I imagine Valves affixt by Nature to the Orifices of the Nerves of the Muscles as Mons Des Cartes did in the bodies of them though such an artifice be not impossible yet beside that no such Valves have hitherto been found in the Brain I should still be to seek for a Cause to open and shut them ad arbitrium voluntatis and so should be put to a stand in my disquisition Which to avoid some other Organical contrivement such as may be not only possible but probable also and facile and fit to untie this Gordian knot must be excogitated Let it then be supposed that in the Brain the Orifices of the Nerves thence elonged to the Muscles of the Limbs and their Canales are in such a peculiar manner formed as at no time to take in and convey into the Muscles more of the roscid liquor than what is sufficient to nourish them and recruit their vigor unless when at the command of the Will under whose jurisdiction they properly are the Nerves being twitched up or convelled at their Originals both their Orifices are dilated to receive and their Canales rendred more pervious to transmit in a moment into the Fibres of the Muscles to be used a greater portion of the same invigorating liquor viz. so much as is requisite to swell them up by replenishing their pores and force them to contraction which is the common action of all Muscles On the other part let it be supposed that in the Brain Nature hath framed the Originals of the Cardiac Nerves by a different Artifice namely such as that not only their Orifices may always be open to imbibe but also their Canales so easily pervious to transmit the roscid liquor as that without any Vellication without any Convulsive motion the same liquor may merely by the plenitude of the Canales themselves be effused guttulatim into the Fibres of the heart to cause the alternate constriction or Pulsation of it And it is the more lawful for me to suppose this difference of structure in Nerves ordained for different uses because it is above all doubt that the Optick Nerves have a peculiar fabric and contexture wherein they differ from the Auditory and all other Nerves inservient to the rest of the external senses and that the Organ of every sense hath its nerve of a peculiar constitution accommodate to the nature of its proper object though those differences consist in such minute and subtle artifices as have hitherto eluded our most curiose researches though assisted by the best sort of Microscopes Why then may it not be thought that Nature hath given to the Cardiac Nerves also a constitution divers from that of all