Part2d.Prop.67.Prop.73.Prop.76.
The AccurateBorellus, in hisOeconomia Animalis, computes theMotivePower of theMachineof the Heart to be equal to, or to surmount that of a Weight of 3000l.TheObstaclesto the Motion of the Blood thro' theArterieshe esteems equivalent to 180,000l.which is 60 times as much as he rates the Force of the Heart at. Then deducting 45,000l.for the adventitious Help of theMuscular Elastic Coatof theArteries, he leaves the Heart with a Force of 3,000l.to overcome a resistance of 135,000l.that is, with 1, to remove 45.
This stupendous Effect he contents himself to ascribe to theEnergyofPercussion. But, had he proceeded in his Calculation to the Veins, which he allows to contain constantly a quantity of Blood, quadruple to the Contents of the Arteries, and to which thisEnergyofPercussiondoes either not reach at all, or but very languidly, he might probably have seen a necessity for some other Expedient to remove so insuperable a Difficulty.
But not to insist rigorously on the Exactness of this Calculation, (though the great Abilities of the Author in this way, and his Ingenuity and Modesty, are a sufficient Warrant for the Accuracy of his Computations, and the Fidelity of his Accounts) we may allow a much greater Deduction, than would be justifiable, without lessening the Difficulty. But this AccountI have taken notice of purely for the sake of the Calculation, which may be of use in the Sequel; the account it self being in other respects more defective than Dr.Lower's, to which we will return.
The Doctor, notwithstanding his great Sagacity, appears (to me) to have overlook'd something of very great moment, and importance in the explication of the Action of the Heart. For, tho' it should be granted, that theMuscular Fibresof the Heart acted by the Nerves, are the immediate Instruments of itsConstrictionorSystole, yet it must not be denied, that theIntercostalMuscles andDiaphragmare of great service to aid and facilitate this Contraction, by opening a Passage for the Blood through the Lungs, which denied would be an invincible Obstacle.
Neither do they promote it that way only. The manner how they farther assist the Heart in its Contraction, will appear manifestly, if we consider the different Posture, Situation, and Capacity of the Blood-Vessels of the Lungs in the several times ofElevationandDepressionof theCostæ.
ThePulmonaryArtery rises from therightVentricle of the Heart, and runs in one Trunk, till it comes to theAspera Arteria, where it is divided, and sends a Branch along with each Division of theAspera Arteria, according to all the minutest Subdivisions, of which it is likewise subdivided, accompanying all theBronchi, in their whole progress through the Lungs.
ThePulmonaryVein, which empties itself into theLeftVentricle of the Heart, spreadsit self on theAspera ArteriaandBronchi, in the same manner that the Artery does.
The necessary confluence of this Disposition if, that this Artery and Vein being co-extended with, and fasten'd to theBronchi, must needs suffer such alteration ofSuperficialDimensions, as theBronchido in theElevationorDepressionof theCostæ.
While the Ribs are in a State ofDepression(whether before Commerce with the External Air or after) theAnnular Cartilagesof theBronchishrink one into another, and by that means theirDimensionsare exceedingly contracted. In conformity to this condition of theBronchi, thePulmonaryArtery and Vein must likewise, either by means of theirMuscularCoats, contract themselves to the sameDimensions, or lye inFoldsorCorrugations, which is less probable.
On the other hand, when the Ribs are elevated, and theDiaphragmbears downward, the Air rushing into the Lungs, shoots out theCartilaginousRings, anddivaricatesthe Branches of theTrachea, and by them extends and divaricates the several Divisions of thePulmonaryArtery and Veins, and thereby lengthens and enlarges their Cavities.
This enlargement of their Cavities is very considerable, not only upon the score of the addition, which they receive in length thereby, but also upon the account of theirDivarication. For whereas, when the Ribs are depress'd, and the Lungs subside, the Blood-vessels are not only contracted, (as I have already observ'd) but their Branches, which are exceeding numerous, approach one another,and lie injuxta-position, by which their Cavities are very much compress'd and streighten'd: When the Ribs are elevated, and the Lungs turgid with Air, not only the Fibres, by which their Coats in the opposite state were contracted, are extended; but those innumerable Vessels, which lying before in lines almost parallel upon one another, compress'd one another, making anacuteAngle at their Junctures, are divaricated and separated from each other, and make anobtuse, whereby their Channels are widened.
Thus a passage is open'd to the Blood, from theRightVentricle of the Heart to theLeft, through the Lungs, to which it could not otherwise pass; and the opposition, which the Blood contain'd in that Ventricle, must otherwise necessarily have made to its Constriction, is taken off, and theSystolethereby facilitated.
Nor is that all. For theDiastolebeing caus'd (as I shall in the Sequel shew) by the force of the Blood rushing into the Ventricles, this Ampliation and Extension of thePulmonaryArtery is a sort ofCheckorCounterpoiseto it, and prevents an endeavour towards two contrary Actions at once, which must necessarily frustrate both. For the Heart being aSpringy,CompressibleBody, whose proper Action, which is Contraction, depends on the influx of certain Fluids into its Fibers, or Substance; and containing besides a Fluid in itsVentricles, or great Cavities, in one of which is the Mouth of this Artery, the action of this Vessel must in great measure resemble that of aSyringe, whose extremity is immers'd in Water,the Enlargement or Expansion of the Chanels of the Artery answering the drawing of theEmbolum, as the constrictive motion of the Muscle of the Heart does the pressure of theAtmosphereupon theSurfaceof the Water, the one making way for the fluid, and the other forcing it to follow, where the resistance is least. In this Sense we may allow a sort of Attraction to thePulmonary-Artery, depending wholly upon the Action of theIntercostalMuscles andDiaphragm, which we must therefore confess to be very serviceable and instrumental in promoting theSystoleof the Heart.
But if the Learned Author be deficient in his Account of theSystole; that is, if he has not observ'd all the Mechanism and Contrivance of Nature for the Contraction of the Heart; much less sufficiently has he accounted for theDiastole, or Dilatation of it, which he ascribes to a motion ofRestitutionof the over-strain'd Fibres, which yet he confesses are made forConstrictiononly. 'Tis true, he immediately after joins theInfluxof theBloodas a concurrent Cause; but from the slight notice that he takes of it, 'tis plain, that he did not so much as dream of any great share it had in that Action. His Words are these:
De Corde,Pag. 75.
Quin & (ut obiter hoc moneam) omnis motus contractione perficiatur, & Cordis Fibræ ad constrictionem solum factæ sint, apparet quoque Cordis motumtotuminSystolepositum esse; cumque Fibræ ultra tonum suum in omni constrictione eius tendantur, idcirco ubi nixus iste absolvitur, motu quasirestitutionisCor iterum relaxatur, & sanguineà Venisinfluenterursus distenditur; ànulloenim cordis motu, nisitensionem suam remittente, & abirruentesanguineDiastoleejus libratis adeo viribus succedit.
I have transcrib'd the intire Paragraph, because it contains his wholeHypothesisof theDiastole, and all the notice that he takes of it through his whole Work. But how slender soever this may prove, it is the most substantial that I have any where met with, except a late one of Mr.Cowper, which is properly an Improvement of this, and shall be consider'd in the Sequel.
But if Contraction be the sole Action of these Fibres (as this Great Man confesses it to be) and as indeed it is of allMuscularFibres, I wonder how so judicious a Writer came to slip into such an Absurdity, as to call their Distention (vulgarly but improperly call'd Relaxation) a Motion ofRestitution. For from the Nature of those Fibres, and their disposition in the Structure of the Heart, the natural State of the Heart appears manifestly to beTonical, and its Dilatation a State of Violence; and consequently, the Constriction is thetruemotion ofRestitution, and the State to which it willspontaneouslyreturn, when the Force is taken off, which is the work of theIntercostalMuscles andDiaphragm.
Thus we are left still to seek for the true Cause of theDiastole, which seems to me to be the main and most difficultPhænomenon, relating to the Heart and the Circulation of the Blood. But in Mr.Cowper's ingeniousIntroductionto hisAnatomy of Humane Bodies, Ifind the Share which Dr.Lowerhints the Blood to have in that Action, further prosecuted, and improved into the main Instrument of the Dilatation of the Heart, wherein I agree intirely with him. But as to the manner, and reasons of its being so very instrumental, I can't be so perfectly of his mind.
The Heart (says this accurate Anatomist) of an Animal bears a great Analogy to the Pendulums of those Artificial Automata, Clocks and Watches, whilst its motion is performed like that of other Muscles, the Blood doing the Office of aPondus.
This Explication, being but a Simile without a distinct application to Particulars, is beside so very short, that I can at best but give a conjecture at the meaning; which if I mistake, I shall deserve to be excused, and expect to be better inform'd.
By theBloodsdoing the Office of aPondus, I suppose he means, that the Blood contributes in the same manner to the motion of the Heart, as theWeightsdo to that of thePendulumof aClock. If so, the Blood, according to him, must be the Instrument ofConstriction; andDilatationmust be theNaturalState, orSpontaneousMotion, to which it wou'd, when under no violence, return; the contrary of which, I presume, will appear e're I have done.
But if he means, that theBloodin its reflux, bygravitatingon theAuriclesandVentricles, dilates and expands 'em, acting therein as aCounterpoiseto its contractions as a Muscle, I cou'd wish his Design had not bound him upto so narrow a compass, and that he had given us an explication at large of so abstruse and so important aPhænomenon: Because theSpecifick Gravityof the Blood seems to me a cause by no means alone adequate to the effect, which it is here suppos'd to produce.
For, if the Blood acts only as aweightby meergravitation, then that part of it only which descends from the Parts above the Heart can be employ'd in that Action. This at the largest computation can't amount to Five pound weight, and must, according to the computation ofBorellus, force a Machine, that is able to overcome a resistance of 135,000l.I leave every Man to deduct what he shall upon examination find reasonably to be deducted, and yet shall rest secure, that it is not to be effected in the least with so small a Weight.
But neither does theRefluentBlood gravitate in any such proportion, as I have here assign'd. For to make a true estimate of itsGravitation, we must consider the Circumstances of the Liquor suppos'd to gravitate; in which it very much resembles Water inclos'd in a recurve Tube, of which, if the length of the two Legs be equal, it may be suspended in the Air full of Water, with the Extremities downwards, without losing a drop, although theDiameterof those Legs should be very unequal. The Case of the Arteries and Veins is pretty near a parallel to a Tube, so fill'd and inverted. For, if the Arteries and Veins be continued Tubes, (as by the Microscope they are made to appear) then supposing their contents to have no other determinationof motion, than their own weight wou'd give them, the contain'd Fluids must be Counterpoises to each other. For the Veins and Arteries being join'd at the smaller Extremities, and the larger of both terminating in the same parallel Line, it is impossible, according to the Laws ofHydrostaticks, that the contents of either shou'd overbalance t'other. How far then must it fall short of forcing the natural Power and Resistance of so strong a Muscle as the Heart, by meer Gravitation?
The Blood indeed has aProgressiveMotion through its Vessels, wherein it differs from Water, in a recurve Tube, in the Experiment above-stated. But, if the natural Gravitation of the Blood contributes nothing to the Dilatation of the Heart, this progressive Motion will not be found much more sufficient. For, as this Motion is deriv'd intirely from the Heart's Constriction (as all Accounts hitherto derive it) cou'd the Blood be suppos'd to re-act upon it by the Heart, with all the force first impress'd upon it by the Heart, it would be insufficient, unless we will suppose theForce communicatedto be superiour to thePower Communicant, which is absurd.
But when the just and necessary Deductions for the Impediments, which the Blood meets with in its Progress through the Vessels, shall be made, the remaining Force will be found so exceeding weak, that to prop the Blood through the Veins may be a task alone too great for so small a Power, without charging it with the additional difficulty of forcing the Muscle of the Heart.
Alphonsus Borellus, after a great deal of solemn pains taken to shew his Care and Exactness, and to possess his Reader of the Truth of his Calculations, casts up the force of the Heart, and theMuscularCoat of the Arteries, to be together equal to a weight of 3,750l.and allots them a Resistance equal to 180,000l.to overcome which is 45 to 1. To make up for a disproportion, by his own confession, incredible to those who have not consider'd the Matter as he had done, he flings into the Scale the additionalForce of Percussion, which he leavesindefinite, and thinks sufficient toforce any quiescent finite Resistance whatsoever.
But as this Account andHypothesisare part of a Posthumous Work (if a liberty of Conjecture may be allow'd in so uncertain a Matter,) I shou'd suspect, that these Papers were left unfinish'd byBorellus; or at least, that in many places the last Hand was never put to them. For neither in this Place, nor any other of this Work, does he account for any more than theSystoleof the Heart, and the resistance which is made to the progressive motion of the Blood in the Arteries only. This alone he found to exceed the Power of the Heart so prodigiously, that he seems to shuffle it off his Hands with a general and precarious Solution, as a difficulty that he was desirous to be rid of. For, having ascrib'd thisstupendous(as he himself calls it) effect to theEnergy of Percussion, he takes no care to satisfie his Reader any farther about it, or to refer him, or give him the expectation of Satisfaction any where else; although he has an express Treatise on theForce of Percussion, which was writtenpreparatory to this, and to which he frequently refers in other Places of this Work. But what confirms my suspicion, that this part was intended for a farther Revise by the Author, is, that he has left the Progress of the Blood through the Veins, and theDiastoleof the Heart, absolutely untouch'd, tho' they are Difficulties of a much greater magnitude than this, which he has attempted to account so slightly for: For, in these he is excluded the benefit ofPercussion, and has yet a greater resistance to overcome without it. Omissions of this kind are so unusual with this Author, where-ever he knows himself to go upon sure grounds, that it is to me an Argument, that he doubted the sufficience of hisPercussion, and reserv'd these importantPhænomenafor farther Consideration, without plunging himself into such an Absurdity, as to ascribe toPercussionany suchEnergyas to be able (so broken as it returns to the Heart) by its re-action to force that Power, from whence only it was at first deriv'd.
Dr.Lower, and Mr.Cowper, deliver their Opinions of the Cause of the Dilatation of the Heart so very short, and without any Arguments to support them, that by exposing them naked, they seem rather to discourse of it transiently, as Men oblig'd by the Nature of their Subjects to say something of it, than solicitous to give any full or satisfactory Account; and therefore I shall proceed no farther upon them here.
But though theHypothesisofBorellusmay, in this Case, be found precarious or insufficient(a Misfortune that has befallen him in divers other Particulars) hisTheoryholds still good. At least it ought to be allow'd, in justice to his great Abilities and Exactness, till some Body convicts him of some material Error in his Calculations, which has not as yet been done by any Body, that I know of.
Supposing then the force of the Heart, and of theMuscularCoat of the Arteries, as likewise of the resistance, which they must overcome, to be computed with any degree of accuracy, there remains yet such a prodigious disproportion to be accounted for, as requires some more powerful Agent, than any yet assign'd, to make up the deficiency.
What assistance the Heart receives from the action of theThoraxtowards the facilitating its Contraction, without which assistance there cou'd have been noSystole, has been already shewn. But neither theIntercostalMuscles, orDiaphragm, which are so instrumental in that part of its action, can contribute any thing to theDiastole; because they serve only to enlarge the Cavity of theThorax, and thereby to open a passage to the Blood from the Heart, and promote its Constriction.
Whatever therefore the force is, that dilates the Heart, and is the cause of theDiastole, it must be equal to that of the Heart, theIntercostalMuscles andDiaphragm; to all which it acts as an Antagonist. I take no notice of theSerratus Major Anticus, and other Muscles; which have an obscure share in theElevationof theCostæ, because as much may reasonably be deducted upon the account of theObliquus externus Abdominis, and other Muscles; which having their Insertions on some of the lowerRibsare as instrumentaltowards theDepressionof them, and so balance the Account. But the chief use of these is in violent Respiration: In ordinary Respiration their share is small.
Such a real Power (which may in the least be suspected of any share in this Action) is hard, perhaps impossible to be found in theMachineof anyAnimalBody; and yet without some such Antagonist, it is as impossible the Circulation of the Blood should be maintain'd. All the Engines yet discover'd within the Body, conspire towards theConstrictionof the Heart, which is theStateofQuiescence, to which it naturally tends. Yet we find it alternately in aStateofViolence, that is, ofDilatation; and this upon necessity, because upon thisAlternationdepends all Animal Life.
Some sufficient Cause External must therefore be found, to produce this greatPhænomenon; which Cause must be either in theAir, orAtmosphere, because we have no constant and immediate Commerce with any otherMediums.
Some great Physicians observing this, and that depriv'd by whatsoever means of Communication with theexternalAir, we became instantly extinct, have imagin'd, that in the Act of Inspiration certain purer parts of the Air, mixed with the Blood in the Lungs, and was convey'd with it to the Heart, where it nourish'd a sort ofVital Flame, which was the Cause of this reciprocalÆstusof the Heart. Others not quite so gross, rejecting anActual Flame, have fancied, that these fine Parts of Air mixing with the Blood in the Ventricles of the Heart, produc'd anEffervescencewhich dilated it. But these Fancies have been longsince exploded and condemn'd upon ample Conviction; and 'tis a Point yet undetermin'd, whether any Air does mix with the Blood at all in the Lungs, or not.
But supposing, that some Air may insinuate it self into thePulmonaryVein, it can no other way dilate the Heart than by an Effervescence in the Left Ventricle, which wou'd not dilate the Right. But this Opinion is contradicted byAutopsie, and too laboriously confuted by others, to be brought upon the Stage again here.
There remains therefore only thegross Bodyof theAtmosphereto be considered, which is undoubtedly thetrue Antagonistto all those Muscles, which serve for ordinary Inspiration, and the Constriction of the Heart. This will appear more evidently, if we consider not only the Power, but the Necessity of its Action uponAnimalBodies, as well as the want of other sufficient Agents.
The Heart is aSolitaryMuscle of very great strength, and theIntercostalMuscles and Diaphragm, which likewise have noAntagonists, are a vast additional Force, which must be balanc'd by the contrary Action of some equivalent Power or other. For, tho' the Action of theIntercostalMuscles be voluntary, that does not exempt them from the condition of all other Muscles serving forvoluntarymotion, which wou'd be in a State of perpetual Contraction, notwithstanding any Influence of the Will, were it not for the Libration ofAntagonistMuscles. This Libration between other Muscles, is answer'd by theWeightof the incumbentAtmosphere, which presses upon theThoraxand other parts of the Body. And,as in all other voluntary Motions the influence of the Will only gives a prevalence to one of its two Powers before equilibrated, so here it serves to enable those Muscles to lift up a weight too ponderous for their strength not so assisted; and therefore as soon as that assistance is withdrawn, theCostæare again depress'd by the meerGravitationof theAtmosphere, which wou'd otherwise remain elevated through the natural Tendency of those Muscles to Contraction.
This is evidently prov'd from theTorricellianExperiments, and those made upon Animals in Mr.Boyle's Engine; where, as soon as the Air is withdrawn, and thepressurethereby taken off, the Intercostal Muscles and Diaphragm are contracted, and the Ribs elevated in an instant, and can't by any Power of the Will be made to subside, till the Air is again let in to bear them forcibly down.
It were scarce worth while to take notice here of a Mistake of the Learned Dr.Willis, were it not for the great Authority of the Man, which is almost sufficient to keep Error in countenance.|De RespirationisOrganis & Usu.|The Doctor having observ'd, that the Fibres of theExternalandInternal IntercostalMuscles ran in a contrary order, as it were, decussating each other, takes occasion from thence to fansie, that there was an opposition in their Office; and that as theExternalserv'd to raise up the Ribs, theInternaldrew them down again, forgetting at that time, That, when a contractile Body is fasten'd at the several ends to Points unequally moveable, let the Contraction happen in what part or manner soever, the more moveable Pointmust be drawn towards the less moveable: By which Rule, whetherExternalorInternal Intercostalsbe contracted, the lower Ribs will be forc'd to approach the upper, that is, be rais'd up.
As in the Elevation of theCostæ, the Blood, by the passage that is open'd for it, is in a manner solicited into the Lungs; so in the Depression of them, by the subsidence of the Lungs, and the Contraction of the Blood-Vessels, both which are consequent thereof, the Blood is forcibly driven, as it were with anEmbolum, through the Pulmonary Vein into the Left Ventricle of the Heart. And this, together with thegeneral Compressionof theBodyby theweightof theAtmosphere, which surrounds and presses upon the whole Surface of it, is that Power which causes the Blood to mount in the Veins, after the force impress'd upon it by the Heart is broken and spent, and which is sufficient to force the Heart from its natural State to Dilatation.
He that is able to compute the weight of a Column of Air, equal to the Surface of the whole Body, will readily grant it a power sufficient for the Effects, which are here ascrib'd to it. And when he considers, that the Bodies of Animals are compressible Machines, he will find that it must of necessity affect them in the manner here laid down. But though our Bodies be entirely compos'd ofTubuli, or Vessels fill'd with Fluids; yet this pressure, how great soever, being equal, cou'd have no effect upon them, if the superficial Dimensions were not easily variable; because being compress'd on all parts with the same degree of Force, the contain'd Fluids cou'd not anywhere begin to recede, and make way for the rest to follow, but wou'd remain as fix'd and immoveable as if they were actually solid. But by the Dilatation of theThorax, room is made for the Fluids to move, and by the Coarctation of it, fresh motion is imprest, which is the main Spring whereby the Circulation is set and kept going.
This reciprocal Dilatation and Contraction of the superficial Dimensions of the Body, seems so necessary to Animal Life, that there is not any Animal so imperfect as to want it, at least none to the inward Structure, of which our Anatomical Discoveries have yet reach'd. For, tho' most kinds ofFishandInsects, want bothmoveableRibs and Lungs, and consequently have no dilatableThorax, yet that want is made up to 'em by anAnalogousMechanism, answering sufficiently the Necessities of their Life.
Those Fishes which have no Lungs, haveGills, which do theOfficeof Lungs, receiving and expelling alternately the Water, whereby theBlood-Vesselssuffer the same alteration of Dimensions, that they do in the Lungs of more perfect Animals.
The Lungs orAir-Vesselsof Insects, are yet exceedingly more different in Structure, Distribution, and Situation from those of perfect Animals, than those of Fishes are, and yet in their Use and Action agree perfectly with both; that is,receivingandexpellingthe Air, andvaryingtheDimensionsandCapacitiesof theBlood-Vessels. These having noThorax, or separate Cavity for the Heart and Air-Vessels, have the latter distributed through the whole Trunk of their Bodies, by which they communicatewith theExternalAir through severalSpiraculaorVent-holes, to which are fasten'd so many littleTracheæ, or Wind-pipes, which thence send their Branches to all the Muscles andViscera, and seem to accompany the Blood-Vessels all over the Body, as they do in the Lungs only of perfect Animals. By this disposition in everyInspiration, the whole Body of these little Animals is inflated, and in everyExpirationcompress'd; and consequently the Blood-Vessels must suffer aVicissitudeof Extension and Contraction, and a greater motion must thereby be impress'd upon the Fluids contain'd in them, than the Heart, which does not in those Creatures appear to be Muscular, seems capable of giving.
The only Animal that is exempted from this necessary condition ofBreathing, orreceivingandexpelling alternately some Fluidinto and out of the Body, is aFœtus. But this, while included in the Womb, has little more than avegetativeLife, and ought scarce to be reckon'd among the number ofAnimals. For, were it not for that small share ofMuscularMotion, which it exercises in the Womb, it might without absurdity be accounted for as a Graft upon, or Branch of the Mother.
Concerning the immediate Matter, and Means of Life, and Nutrition, Authors are not agreed, nor is it the business of this place to reconcile, or decide their Differences, but to account for the Motion of the Blood through the Vessels only. In order to this, it will be necessary to observe, that the Pulsation of the Heart in aFœtusis so very weak and obscure, and the Motion of the Blood so extream slowand languid, as to be scarce, if at all perceivable, as has been experienced in the Dissection of Puppies before Respiration had. To|Boyleof the Elasticity of Air. Pechlinus de Aeris & Alimenti defectu.|produce such a feeble Palpitation, and creeping Motion, no greater force seems to be required, than may be deriv'd from the Communication between the Vessels of the Mother andFœtusin thePlacenta. I am not ignorant, that divers very Learned Anatomists (whom the Crowd have implicitly follow'd) have absolutely rejected all Communication between these Vessels. But, with submission to Great Authorities, I think they have acted arbitrarily, and without sufficient Warrant from Reason or Experiment: For neither are the Arguments which they bring against it conclusive, nor the Office which they assign to the Umbilical Vessels in lieu of it, proper, or natural to those Vessels, or the reality of the Fact made out by any substantial Reasons. Those that reject this Communication usually do it in favour of one or both of these Opinions, that the Arteries of theUterusdo deposite a Nutritive Juice, or a Juice impregnatewith Airin thePlacenta, which is suck'd in by theUmbilicalVein, and convey'd to theFœtus, for the necessary Uses of Nutrition and Life. Now those that patronize either of these Opinions, lead Nature an unnecessary Dance. For if theMaternalBlood does really contain any suchNutritious, or any such necessaryAerial Particles, why shou'd they be separated and extravasated, to be with difficulty receiv'd into theUmbilicalVein, andagain mixt with the Blood, when they might more easily have been imparted by the plain simple way of Transfusion from the Arteries of theMotherto the Veins of theFœtus. And, that this is the course which Nature takes in this Case, I am perswaded from the easiness and simplicity of the Method, which readily performs what might be perhaps in vain expected from the other, and wou'd over and above find them, what they seem to grope so blindly about for, a first Mover of the Blood in aFœtus.
Those that contend for the conveyance of theNutriciousJuice, through theUmbilicalVein from thePlacenta, are forc'd upon two Difficulties next to Absurdities. For first they are oblig'd to make this Vein, which, as all other Veins, seems dedicated to the Re-conveyance of Blood only, the proper and immediate Chanel, thro' which a very different Liquour is to be carried; and next, to give a Power of Attraction or Suction to it; because theNutriciousJuice, which it is thus destin'd to carry, is both viscous and stagnant, and has neither force to drive, nor subtilty to penetrate, or insinuate it self into the Capillary Veins; and therefore must be drawn or suck'd asMilkis from theBreast, to which thePlacentaand itsNutriciousJuice are by the Favourers of them expresly compar'd. But if this were the sole use of thePlacenta, andUmbilical Vessels, why were the UmbilicalArteriessent along with the Vein? Their business is not to bring any thing back to theFœtus, nor can they contribute any thing to the benefit of theMother; for theUterineArteries bring all to thePlacenta, the Umbilical Vein carries it to theFœtus, and theUterineVeins conveyback again the Surcharge of theMother's Blood; the UmbilicalArteriesonly, have nothing to do, and are superfluous and impertinent, which is contrary to the constant Practice of Nature. Yet ifAutopsiedid in the least countenance this Hypothesis, some Defence might still be made; but we find in the UmbilicalVeinof aFœtusnothing butFloridBlood, such as in all probability it received immediately from theArteriesof theMotherwithout any mixture. And therefore I can't help concluding, that this Opinion engages its Favourers in some Absurdity, without Necessity and without Proof.
They that from thePlacentasupply the Body of theFœtuswithAir, are as much distress'd as t'other; for they are forc'd to beg the Question twice, which, even when granted, will not answer their Ends. First, they suppose, that an intimate mixture or confusion ofAirwith theBlood, is necessary for the support of Animal Life, aPostulatum, which perhaps the former part of this Discourse may have render'd unnecessary; and next, that theFœtusis supply'd withAirfrom, and itsBloodmix'd with it in thePlacenta.
But here again they fetch a Compass without necessity or proof. For if a mixture ofAirwere necessary to aFœtus, why should it be separated from theMother's Blood, and not rather both communicated together, since it is so much more easie and commodious? But neither does thePlacentaseem to be instructed and provided for the separation ofAir, but of a muchgrosser Fluid, destin'd to some other use, whichAutopsieconfirms: Yet, were both these Opinionstrue, they are however defective, and the Circular Motion of the Blood unprovided for.
By the way ofTransfusion, this great Phænomenon is naturally accounted for, and the Ends, for which the other two Hypotheses were devis'd, might both be answer'd with more ease. For theHysterickArteries transmitting their Blood immediately to theUmbilicalVein, may very easily transmit suchNutriciousJuices orAerìalParticles, as are contain'd in the Blood, along with it, without depositing them by the way. By this means so much of the Impulse of the Mother's Blood is preserv'd, as suffices to maintain that languid Circulation which aFœtusenjoys. For the Blood being driven through theArteriesof theUterusinto theUmbilical Vein, is convey'd directly to theSinusof thePorta, and thence by a short and direct Passage through theCavato the Heart; where passing through theForamen Ovaleto theLeftVentricle, and through theCanalis Arteriosusfrom theRightandPulmonaryArtery, it is all deliver'd without coming at theLungsto theAorta, and from thence again by theUmbilical Arteriesto theVeinsof theUterus, making a sort ofEpicycleto the main Circulation in the Mother.
As this Opinion is Favour'd by the Structure and Disposition of the Blood-Vessels on both Parts, so there is nothing in it difficult to be conceiv'd, or repugnant to Experience. Late Discoveries have made it appear, that the Arteries and Veins are continu'd Tubes, and that the latter contain nothing but what they receive from the former, and no Reason appears whywe shou'd think this Method to be varied in thePlacenta. On the other hand, if the Arteries of theUteruswere continued to the Veins of thesamepart, and those of theFœtusin like manner, without communicating with each other, their Confluence in thePlacentaseems to be altogether impertinent, and of no use, and theUmbilicalArteries and Vein fram'd for no other Service or Purpose, than to give the Blood room for an idle Sally.
Thus the Reasonableness of this old Opinion may be vindicated, but the Certainty of it rests upon stronger Proof. Mr.Cowper, to whose happy Industry we owe the Confirmation of many ancient Discoveries, and the Benefit of some new ones, has the Honour to re-establish this old, but long exploded Truth. For by pouringMercuryinto a Branch of theUterine Arterieof aCow, that went into one of theCotyledonesof theUterus, he fill'd those Branches of theUmbilicalVeins, which went from thatCotyledonto theNavelof theFœtus; which, with a part of theUterus, he keeps prepared by him.
It would be a weak Objection, to alledge, That the Observation and Experiment being made on theUterusof aCow, the Inference would not hold from thence to aWoman, the one beingGlanduliferous, and the otherPlacentiferous; since every one of theseCotyledones, orUterine Glandules, is in all respects a littlePlacenta, and all the difference between them is in number, name, and magnitude. WhyRuminantsdiffer in this Particular from otherViviparousAnimals, is beside the Subject of our present Enquiry. But the great Flux of Blood, which constantly follows upon drawing thePlacentafrom Women (which is frequently so great as to cost them their Lives) is as plain a demonstration to Reason of theContinuityof the Vessels, as Mr.Cowper's Experiments is to the Eye.
I have heard it objected by very Learned Men, that if there were such aContinuityof Vessels, and suchTransfusionof Blood, theFœtusmust necessarily perish through loss of Blood, upon the separation of thePlacentafrom theUterus; but that, on the contrary, no visible Flux of Blood does follow while theFœtuscontinues wrapt in the Membrane, in which Condition it may be kept alive some Hours. To this it may be answer'd, that the Circulation in theFœtus, being deriv'd from the Mother, may be suppos'd wholly to cease upon the cutting off the Communication between them, till it is again renew'd more forcibly byRespiration. But if we allow the motion already impress'd upon the Blood to be sufficient to keep it going a little while; yet it must needs be so exceeding languid, that the meer resistance of the External Air must be more than enough to hinder any Efflux of Blood from aFœtusbefore Respiration. How long Life may be preserv'd without anactualCirculation of the Blood, is a Question not of this place. But we have been convinc'd by many and notorious Observations and Experiments, that Life has been recover'd a long time after all tokens of Respiration, Circulation, or even Life it self, have disappear'd; so that we can't think the first Solution either impossible or improbable.
I expect to be told, that in the early Days ofGestationinViviparousAnimals, there is noPlacenta, or any Adhesion of theUmbilicalVessels to any part of theMother, and consequently no suchTransfusion; and that inOviparousthere is nocontinuity, orcommunicationof Vessels of any kind, during the whole time ofIncubation.
But these Objections carry neither the Weight nor Difficulty along with them, that they may be suppos'd to do; for in those Days there is neitherBloodorBlood-Vessels, and consequently there can be noCirculationof theBlood; and theEmbryo, of what Species soever, is no more than aVegetableat that time; nor does theFœtusof anyViviparousCreature enjoy anyCirculation, or shew any signs of Animal Life, till after those Vessels, as well as others requisite to the Circulation, are compleated.
It must be confess'd, thatOviparousAnimals are denied the benefit of this Communication; but that want is sufficiently compensated by a peculiar Mechanism, which directly answers the ends ofRespiration, and thepressureof theAtmosphereupon theFœtus. There is at theobtuseend of an Egg a small Cavity fill'd with Air, which is the succedaneous Instrument to theRespiratoryOrgans. For as soon as the Contents begin to be warm'd by theIncubationof the Hen, orany analogousHeat ofFurnaceorDunghill, the several Humours of the Egg require afermentativemotion, and theAircontain'd in theCavityorVesicle, at theobtuseend of the Egg, is rarefied, and the Vesicle extended and enlarg'd, and consequently the other Contentsare comprest; to which thefermentativemotion naturally resists. But both Bodies being as wellcompressibleasdilatable, and both having anexpansivemotion imprest upon them byIncubation, the Compression and Renitency will be mutual, but varied in degree, according as either, through the variation of Circumstances, shall prevail. By this means, an Alternation of Compression and Dilatation will be produc'd in both, answering therespiratorymotion, by which a motion will be communicated, which, as soon as the Organs by which it should be regulated are compleated, will in the Body of thePullusberegularandcirculatory.
FabriciusabAquapendente, and after him, our Great Dr.Harvey, have assign'd divers Uses to this Cavity or Air Vesicle, the Extravagance of which have perhaps deterr'd others from enquiring so much into the Use, as the Importance of it requir'd. But though I can't agree to thatPerspiration,Refrigeration, andRespiration, which they make it the Instrument of; yet perhaps theAir, that was inclos'd in thatCavity, may through the Augmentation of the Body of thePullus, and its ownRarefaction(which is at last so great as to occupy half the Shell) break theMembrane, which separated it from thePullus, and thereby give so muchRespirationas to form thechirping Voice, which is often heard before the breaking of the Shell, and with it give an addition of Strength to enable it to break the Shell. But how it should respire sooner, is to me inconceivable.
There are many Problems of great seeming Difficulty, the Solutions of which flow naturally from what has been laid down here: But intending to prosecute this Subject farther, and to treat of the Impediments of Respiration, and the Consequences of Respiration obstructed or intermitted, I shall reserve them for that Opportunity, and content my self here to attempt theHarveyanProblem only, which has given abundance of Authors so much perplexity.
That incomparable Philosopher enquires,Why aFœtus, taken out of theUteruswith theMembranesintire, shall live in Water some Hours without communication with theExternal Air; whereas if it be taken out and suffer'd once to breath, it can't afterwards survive a Moment without the benefit ofRespiration.
Granting the Fact to be as he has deliver'd it, which yet is not so in all Cases, the main Difficulty is grounded on a Mistake, which from the stating of the Question I find this Great Man to have slipt into. For he thinks, that aFœtusis sooner suffocated after having once breath'd, than if it had not breath'd at all, and that by breathing it had contracted something which render'd it more perishable.Idem tamen secundis exutus, (says he) si semelaeremintraPulmonesattraxerit, postea ne momentum quidem temporis absque eo durare possit, sed confestim moriatur.And presently after,Siquidem constat, fœtum, postquameum semelhauserit,citiussuffocari; quam cum abillo prorsusaccebatur.The Doctor observing aFœtusto live longer without Respiration, and to dispence better with the want of Air while included in the Membranes intire, than it cou'd afterwards; infers thence, that the Air does inthe first Act of Inspiration impress upon the Lungs some quality, which renders it ever after more indispensably necessary. But allowing his Observation, I must yet deny his Inference to be good: For deprive aFœtusof means of respiring, and then take it out of the Membranes, and it shall be as soon suffocated, as if it had respired before. This proves, that this necessity of intercourse with the Air, by way of the Lungs, is not the Offspring, but the Parent of Respiration, and that, that Learned Man was drawn into a Fallacy ofNon causa pro causa.
The Reason of this Necessity is the pressure of the External Air upon the Surface of the Body, from which it was defended by the Interposition of the Membranes, and the Humours contain'd, which are not so compressible as the Body of theFœtusit self. So soon therefore as theFœtusis excluded, and expos'd to the immediate contact of the ambient Atmosphere, the Vessels and all the Cavities of the Body must necessarily be so compress'd, that the Fluids can't have room for motion, and consequently theFœtuscould have no Life, if Nature had not contriv'd by the motion of theThoraxto remove and admit that pressure alternately, and thereby to impress a motion on the Fluids, which is the Spring of Life. But this motion of theThoraxbeing any way suppress'd, the equal pressure of the Atmosphere on all parts, occasions a total Cessation of motion, which is Death.
I shall prosecute this Subject no farther now, nor trouble the Reader with any Apology, for dissenting from those Great Men herein named;because, I hope, I have done it with Modesty, and all the Respect due to so great Authorities, and have assign'd nothing which is not Matter of Fact uncontroverted, or deduc'd from it by plain Mechanical Necessity.
THEAncientsgenerally intitled theEarthto the Production of theAnimals,Vegetables, andother Bodiesupon and about it; and that for that Reason 'twas, that they gave it so frequently the Epithets ofParentandMother[1]. They were of opinion, that it furnished forth theMatterwhereofthose Bodiesconsist; and receiv'd it all back again at their Dissolution for the Composure ofothers. Even those who assertedfour Elements, supposed that theEarthwas theMatterthatconstitutedthose Bodies; and thatWaterand therest, serv'd only for theConveyanceandDistributionof thatMatter, in order to theformingandcompositionof them. 'Tis true,Thales, a Philosopher of the first Rank in those early Ages, has been thought to have Sentiments very different from these; but that without just Grounds, as I think I have sufficiently prov'd in another Paper, which I am ready to produce.
But thoughAntiquitythus gave itsVoteforTerrestrial Matter, several of theModerns, and some of verygreat Nametoo, bothhereandabroad, have gone quite counter, and giventheirsin behalf ofWater. TheDignityof thePersonsthat have espoused it, as well as theirNumbers, renders this Doctrine very considerable, and well worth our enquiring into. The great Restorer ofPhilosophyin this last Age, my LordBacon, is of Opinion,That for Nourishment ofVegetables, the Water is almost all in all; and that the Earth doth but keep the Plant upright, and save it from over-heat, and over-cold[2]. Others there are who are still more express; and assert Water to be the only Principle or Ingredient of all Natural Things. They suppose that, I cannot tell by what Process of Nature, Water istransmutedintoStones, intoPlants, and in brief, all other Substances whatever.Helmont,[3]particularly, and hisFollowers, are very positive in this; and offer someExperimentsto render it credible. Nay, a veryExtraordinary Personof our ownNation[4]tries thoseExperimentsover again; and discovers a great Propensity to the same Thoughts and Opinion they had; declaring for thisTransmutation of WaterintoPlantsandother Bodies, though with great Modesty and Deference, which was his usual manner.
TheExperimentsthey insist upon are chieflytwo; thefirstis, thatMint, and severalotherPlantsprosper and thrive very greatly inWater. Theotheris this; they take a certain quantity ofEarth, andbakeit in anOven; then they weigh it, and put it into anEarthen Pot. Having well water'd thisEarth, they make choice of some fitPlant, which, being first carefullyweigh'd, theysetin it. There they let it grow, continuing towater itfor some time, till 'tis much advanced inbigness: Then they take it up; and though theBulkandWeightof thePlantbe much greater than whenfirst set, yet uponbakingtheEarth, andweighingit, as at first, they find it little or not at all diminished inweight; and therefore conclude, 'tis not theEarthbutWater, that nourishes and isturn'dinto the Substance of thePlant.
I must confess I cannot see howthis Experimentcan ever be made with thenicetyandjustnessthat is requisite, in order tobuildupon it somuchasthese Gentlemendo. 'Tis hard to weighEarthin thatquantity, orPlantsof thesizeof those they mention, with any greatexactness; or tobakethe Earth with thataccuracy, as to reduce ittwiceto just thesame Driness. But I may wave all this; for though theExperimentbe never so easily practicable, and all the Accidents of it exactly as they set forth, yet nothing like what theyinfercan possibly be concluded from it; unlessWater, which they so plentifully bestow upon thePlantinthis Experiment, bepure,homogeneous, and not charged with anyterrestrial Mixture; for if it be, the Plant after all may owe itsGrowthandEncreaseintirely tothat.
SomeWatersare indeed so veryclearandtransparent, that one would not easily suspect anyterrestrial Matterwere latent in them; but they may behighly saturatedwith suchMatter, though the Eye be not presently able to descry or discern it. 'Tis true,Earthis anOpake Body; but it may be so far dissolved, reduced to so extreme small Particles, and these sodiffusedthrough thewatry Mass, as not sensibly to impedeVision, or render the Water much the lessdiaphanous.Silveris anOpake, and indeed a verydense Body; and yet, if perfectlydissolvedinSpiritofNitre, orAqua Fortis, that isrectifiedand thorowlyfine, it does notdarkentheMenstruum, or render it lesspellucidthan before[5]. And other Instances there are, that oftentimesgreat quantitiesofOpake Matterare sustain'd inFluids, without considerably striking theEye, or being perceiv'd by it. So that were thereWaterany where found sopure, that the quickest Eye could discover in it noterrestrial Intermixture; that would be far short of aProof, that in reality there wasnone.
But after all, even theclearest Wateris very far from beingpureand whollydefecate, in any part of the World that I can learn. For ours here, I have had an Opportunity of examining it over a good part ofEngland; and cannot say I ever met with any, that, however fresh and newly taken out of the Spring, did not exhibit, even to the naked Eye, great numbersof exceeding small terrestrial Particles disseminated through all parts of it. Thicker and crasser Water exhibits them in still greater Plenty.
These are of two general kinds. The one a vegetable terrestrial Matter, consisting of very different Corpuscles; some whereof are proper for the formation and increment of one sort of Plant, and some of another; as also some for the Nourishment of one part of the same Plant, and some of another. The other kind of Particles sustain'd in Water are of a Mineral Nature. These likewise are of different sorts. In some Springs we find common Salt, in othersVitriol, in othersAlum,Nitre,Sparr,Ochre, &c. nay, frequently several of these, or other Minerals, all in the same Spring; the Water as it drains and passes thorough theStrataof Stone, Earth, and the like, taking up and bearing along such loose Mineral Corpuscles, as it meets with in the Pores and Interstices of thoseStrata, and bringing them on with it quite to the Spring. All Water whatever is much charg'd with the Vegetable Matter, this being fine, light, and easily moveable. For the Mineral, the Water of Springs contains more of it than that of Rivers, especially when at distance from their Sources; and that of Rivers more than the Water that falls in Rain. This I have learn'd from several Trials, which I must not give Account of here; my Drift in this place being only to evince the Existence of Terrestrial Matter in Water.
Any one who desires farther Satisfaction in this, may easily obtain it, if he only put Water into a clear Glass Viol, stopping it close, to keep Dust and other exterior Matter out, and letting it stand, without stirring it for some Days: He will then find a considerable Quantity of terrestrial Matter in the Water, however pure and free it might appear when first put into the Viol. He will in a very short time observe, as I have frequently done, the Corpuscles that were at first, while the Water was agitated and kept in motion, separate, and hardly visible[6], by degrees, as the Water permits, by its becoming more still and at rest, assembling and combining together; by that means forming somewhat larger and more conspicuousMoleculæ. Afterwards he may behold these joining and fixing each to other, by that means forming large thin Masses, appearing likeNubeculæ, or Clouds in the Water; which grow more thick and opake, by the continual appulse and accretion of fresh Matter. If the said Matter be chiefly of the Vegetable kind, it will be sustain'd in the Water; and discover at length a green Colour, becoming still more and more of that Colour, I mean an higher and more saturate Green, as the Matter thickens and encreases. That thisMatterinclines so much to thatColour, is the less strange, since we see so large a share of it, when constituting Vegetables wearing the same Colour in them. But if there be any considerable quantity of meer Mineral Matter in the Water, this, beingof a greater specifick Gravity than the Vegetable, as the Particles of it unite and combine in such Number, till they form aMolecula, the Impetus of whose Gravity surpasses that of the Resistance of the Water, subsides a great deal of it to thebottom. Nor does it only fall down it self, but frequently entangling with theVegetable Nubeculæ, forces them down along with it.
The Reason why Bodies, when dissolved and reduced to extreme small Parts, are sustain'd in Liquors that are of less specifick Gravity than those Bodies are, hath been pointed at by a late ingenious Member of this Society[7]. He is indeed far from having adjusted all theMomentaof this Affair; however it must be admitted, that, in thedividingorsolutionof Bodies, their Surfaces do not decrease in the same Proportion that their Bulk does. Now the Gravity of a Body, which is the Cause of its sinking or tendency downwards, is commensurate to its Bulk; but the resistance that the Liquor makes, is proportion'd, not to the Bulk, but to the Extent of the Surface of the Body immersed in it. Whence 'tis plain, a Body may be so far divided, that its Parts may be sustain'd in a Fluid, whose specifick Gravity is less than that of the said Body. Nay, 'tis Matter of Fact, that they frequently are so; and we daily seeMenstruasupporting the Parts ofMetals, and other Bodies, that are of six, ten, nay, almost twenty times the specifick Gravity of thoseMenstrua. And as the Parts of Bodies when divided, are thus supported in a Fluid; sowhen they occur and unite again, they must sink of course, and fall to the Bottom.
Upon the whole, 'tis palpable and beyond reasonable Contest, thatWatercontains in it a very considerable Quantity of terrestrial Matter. Now the Question is, to which of these, the Water, or the Earthly Matter sustain'd in it, Vegetables owe their Growth and Augment: For deciding of which, I conceive the following Experiments may afford some Light; and I can safely say, they were made with due Care and Exactness.
I chose severalGlass Vials, that were all, as near as possible, of the same shape and bigness. After I had put what Water I thought fit into every one of them, and taken an Account of the weight of it, I strain'd and ty'd over the Orifice of each Vial, a Piece of Parchment, having an hole in the middle of it, large enough to admit the Stem of the Plant I design'd to set in the Vial, without confining or streightning it, so as to impede itsGrowth. My Intention in this, was to prevent the inclosed Water from evaporating, or ascending any other way than only through the Plant to be set therein. Then I made choice of several Sprigs of Mint, and other Plants, that were, as near as I could possibly judge, alike fresh, sound, and lively. Having taken the weight of each, I placed it in a Vial, order'd as above; and as the Plant imbib'd and drew off the Water, I took care to add more of thesame from time to time, keeping an Account of the weight of all I added. Each of the Glasses were, for better distinction, and the more easie keeping a Register of all Circumstances, noted with a different Mark orLetter,A,B,C,&c.and all set in a Row in the same Window, in such manner that all might partake alike ofAir,Light, andSun. Thus they continued fromJulythe Twentieth, toOctoberthe Fifth, which was just Seventy Seven Days. Then I took them out, weigh'd the Water in each Vial, and the Plant likewise, adding to its weight that of all the Leaves that had fallen off during the time it stood thus. And Lastly, I computed how much each Plant had gain'd; and how much Water was spent upon it. The Particulars are as follow.