more readily to it's Motion upwards being less compact above then below I shall produce two or three Instances which prove that if it had but less Liberty to ascend by the Opposition of some other Body then to descend it would as naturally fly downwards as it does now upwards when it is otherwise and I shall also prove that if it had but an equal Resistance on each side it would expand orbicularly And First that if Flame had but an equal Resistance from ambient Bodies on each side it would expand Orbicularly will be proved by this Experiment viz. fill a hollow Globe with Gunpowder one side of which is a little thinner than the other and whatever way that thin side is turned whether down upwards or horizon-ward the Gunpowder will expand and break out that way Secondly to prove that if there were but more liberty for the descent than ascent of it Flame would naturally fly downwards we need but shoot a Gun off with the Mouth downwards for the explauded Gunpowder finding an open and easy Passage downwards and being resisted upwards and on each side it naturally descends But some perhaps that do not throughly understand why a Thing is said naturally to ascend or descend may be unwilling to believe that when a Gun is shot downwards the Motion of the Flame is a natural Motion but may rather think it Preternatural But that it may appear that it is as truly a naral Motion in Philosophy as the ascending Motion of it I shall consider why Flame may be said naturally to ascend Flame then is said naturally to ascend because it is the Nature of it for the most Part to do so which is as much as to say the Nature of Flame inclines it to ascend how the Nature of it inclines it to ascend I have already shown and that there are the same Reasons why the descending Motion should be termed Natural will easily be proved for as it is natural for it to ascend as long as it hath only the Air to oppose it's Motion so it is it's Nature to descend when the Order of Opposition is changed and the latter is as much a natural Motion as the former all that diversifies the tendency of Flame being those accidental Circumstances which are about it and as a Ball cast against the bottom of a Room rebounds upwards and when it is thrown against the top of it as naturally flyes down so Flame being in a brisk Motion naturally flyes up or down as the Parts of Matter it striks against resist it and cause it to fly back from them HAving made this short Digression I shall proceed next to examin Diemerbroek's Opinion who thinks that the vital Spirit by reason of it's Volatility always endeavouring to fly away does continually agitate those grosser Particles of the Blood with which it is entangled and detained from flight and is diversly vibrated and beat back and so the whole Mass being kept in a continual fermentative Motion there is a Heat produced in it which in a greater Agitation is greater c. And so differs according to the different Degrees of Agitation All that I shall or need to take Notice of here is that that Agitation of Particles which he says causes the Heat of the Blood rather produces a Sensation of Heat by affecting our Senses in their Motion than produce that which we call Heat in the Blood But to know the true Reason of the Heat of the Blood we must understand how those Particles are put into Motion which by affecting our Sensory cause such a Sensation So that he seems to me to say no more then that that which hath a Power to cause Heat is the Cause of that Power when he ought in order to explain the Heat of the Blood to have shown from whence that Power proceeds the Reason of which I should have taken in some measure for the Reason of the Heat potentially in the Mass of Blood but from what he hath said it appears that he hath not explained the true Reason of the Heat of the Blood so plainly that I need say no more against it Dr. Henshaw thinks that the Dissimilitude betwixt the Chyle and Blood is so great that it becomes immediately the Cause of an extraordinary Ebullition upon their mixture together which is very much increased by the reciprocal Motion of the Lungs whereby the Blood is wrought into a froth by that time it gets into the left Ventricle of the Heart Which sudden Excess of Heat he thinks not unlike what happens upon the mixing of several Chymical Liquors together for the Heat often becomes so great that they often endanger the Vessels that contain them But he might as well have said that there is so great a Dissimilitude betwixt hot Blood and cold Milk that as soon as the Milk is mixed with it it will cause an extraordiary Ebullition and that by exposing them to the Air running them through Pipes the Heat would increase but this is so plainly false that it needs no other Arguments but Reflection to convince the weakest Reason And he might equally as well conclude that Water would kindle a Fire and encrease the Flame of it because Oyl will as that Chyle will put the Blood into a Heat because Oyl of Turpentine and Spirit of Wine will grow hot when mix'd together but the Conclusion being manifestly absurd I shall in the next Place endeavour to show the Reason of the Heat of the Blood as evidently as possibly I can FROM what I have already said in Answer to Dr. Willis's Opinion it sufficiently appears that whether we say the Blood grows hot per admotum Calidi Accension or any other way it is no more then to express the same Thing several ways or to make Words different in Sound to express one and the same thing But as all that have writ on this Subject have made choice of a different Name to signify the Heat of the Blood by whilst some would have it done by Accension others by Attrition c. so they have by that means rather disputed about Names and Words than any real and fundamental Difference in their Opinions I shall not here enter into a dispute whether the Blood when it becomes hot may most properly be said to grow hot or it's Heat expressed by any one of those Titles they have been pleased to signify it by for as in discoursing about the constituent Parts of a Man it is not necessary to fix any Name upon that Man but whether it be Thomas Robert or William the constituent Parts of him if he be a perfect Man will still be the same so in discoursing concerning the Heat of the Blood and considering the principal Cause or Agent and the more remote and accessory Causes it is no matter at all whether the Consequence of these Causes be signified by the word Accension Attrition or Fermentation because the Difference of the
any thing as one that 's in a Fit of the Epilepsie but our Bodies being accustomed to it and it being made agreeable and consistent with Circulation of the Blood becomes less troublesome when we have occasion for Extraordinary Respirations For these Reasons it is plain why the Lungs ought to be in a continual Reciprocal Motion the first of which is self-evident and needs no further Proof and the second is sufficiently evinced by the Consequences that follow when this Lympha is not evacuated When it is too thick or too much in Quantity or on the other side the Air which we breath is too thick and moist and it is not duly carried off there follow Obstructions of the Ducts of the Trachea from whence proceed Symptoms of an Asthma Orthopnaea and Duspnaea some sorts of Phthisicks and a great many more dangerous Symptoms For when it is too thick it sticks fast to the Coats of the Lungs and not being easily enough mixed and incorporated with the Air the Quantity of it encreases till it stuffs up the Cavity of the Lungs and when it is too much in Quantity though it be thin enough yet the Air being not able to carry it off fast enough it runs down the sides of those tender Vessels and by a gentle Irritation raises a tickling Cough Lastly when the Humor that moistens the Lungs is almost Natural as to Quality and Quantity yet if the Air be thick and moist it being so much impregnated with it's own Moisture is incapable of carrying off the Moisture supplyed by the Serum of the Blood whence People that are inclined to Obstructions of their Lungs in foggy and moist Air find them more oppressed that Moisture which ought to be carried off being left behind But if we consider further the Use of the Lungs with respect to the Body we shall find other Reasons not only why it should be in a constant Motion but also we may understand why we cannot live without a continual and free Circulation For in respect of the Body the Lungs seem in some Measure to perform the Office of another Heart and as the left Ventricle of the Heart contracting sends out the Blood into all the Parts of the Body by the Ramifications of the Sanguiferous Vessels so the Lungs contracting force the Blood contained in the Sanguiferous Vessels which are distributed through their Lobes into the left Ventricle of the Heart and the left Ventricle being by that means more vigorously dilated and more plentifully filled with Blood a larger Quantity of it is forced out into the Aorta and consequently the Blood in the Branches of the Aorta is more copiously pressed by subsequent Matter into the Roots of the Vena Cava and so forwards into the right Ventricle of the Heart so that by the help of the Lungs the Dilation of the left Ventricle of the Heart is immediately and the Dilation of the right mediately promoted That the Lungs thus promote the Dilation of the Ventricles of the Heart it is very reasonable to believe not only because it is self-evident but because otherwise it will be very hard to conceive since the Motion of the Heart is only Contraction and the Dilation of it's Ventricles only a Cessation from that Motion how the Blood is forced into them with Vigour enough to distend their Cavities For there is so little Reason to expect that they should dilate of their own Accord that we should rather believe they would be continually contracted since all the Weight of Blood contained in the whole Sanguiferous Vessels of the Lungs could not possibly dilate them without some other force to help it for the Substance of the Heart being contracted and the Cavity of the left Ventricle so considerably diminished so small a Portion of blood as hath Liberty to press against it's Orifice would make but a weak Pressure and much too small to dilate the Ventricle in so little time as intervenes the successive Contraction besides the Heart having no Tendency at all to dilate it self since that would make it unapt to yield to Contractions we must suppose that a Part of such Substance cannot easily be dilated but would require some Force greater then can be supplyed by an inconsiderable Pressure of Blood faintly intruded by almost nothing at all But the Lungs being almost in a continual Contraction in respect of the Sanguiferous Vessels and consequently squeezing out the Blood contained in them help to dilate and extend the Left Cavity of the Heart and consequently the Right That the Dilation of the Ventricles of the Heart is only a Resolution or Cessation from Contraction is allowed and agreed upon to prove then that the Venal Blood cannot return with Force sufficient to dilate the Right Ventricle of the Heart nor is sufficiently able duly to extend the Left in order to the next Contraction by that force it received from and was put into by the former Contraction but is assisted by the Lungs we may easily perceive For not only the Blood in it's Vessels but even any Liquor being forced through Pipes whose Cavities encrease the further they run from their narrow and small Original always moves with less force the farther it goes So that although in every Systole the Blood should be forced forwards from the left Ventricle by a successive Pressure of subsequent Matter and the Motion should be strong enough to make it circulate briskly through the narrow and capillary Twigs of the Arteries yet when it came into the Veins it would move much more slow and by that time it came to the Heart again would want Force sufficient to dilate the right Ventricle and the right Ventricle being not duly dilated so little Blood would be squeezed into the Lungs that the Left would want a Supply of Blood to dilate it and consequently the Pressure of Blood through the Aorta and Vena Cava would be so weak that the next Dilation of the Right Ventricle would be weaker than the former and so Circulation would gradually decrease But that weak Motion of the Blood into the Right Ventricle being encreased by the Force of subsequent Matter from the Left the Motion of the Blood into the Lungs is consequently more plentiful and as it passes through them is violently forced into the Left and so on and by that means as I said before the Lungs distend the Left immediately and consequently the Right mediately That the Motion of the Blood is thus weakned by so long a Course in the Veins is further evinced if a Vein and Artery be open'd at once for the Blood runs out of the Artery much more forcibly and indeed it would be reasonable to think it so though it were not manifest by so plain an Experiment for if Water in a Cistern be put into a violent Motion at one end the further it runs along the less violent is the Force of it And it is further evident that the Motion of
the Lungs does assist the Dilation of the Heart as I have shewed by stopping the Breath of any Animal which for want of free Circulation presently dies and not because the Flame of the Blood is by that means extinguished for as long as the Lungs duly perform Respiration and the Heart violently contracts and drives the Blood contained in it's Ventricles forcibly out that Motion of the Blood being by a continued waving Pressure decreased is enabled by the Assistance of the Motion of the Lungs to dilate the Ventricles of the Heart with a sufficient Quantity of Blood to be forced out the next Contraction but as soon as the Lungs cease to assist the languid Motion of the Blood in dilating the Ventricles it is not only less plentifully forced successively thus into the Ventricles of the Heart but by a weaker Pressure of the Contents of them thrust out each succeeding Pulsation the Arterial Blood is less plentifully driven forwards so that the whole Mass circulates flower by degrees and also the Animal Spirits being driven less violently into the Muscles that Supply of Spirits separated in the cortical Part of the Brain being not so powerfully thurst after by an equal Succession of Matter the Fermentation in the Glands is weaker and consequently the following Contractions gradually decline both in Number and Vigour till at the last they cease But if before the Circulation of the Blood be quite stopped that Animal be again permitted to breath the contractive Force of the Lungs drive Blood more forcibly into the left Cavity of the Heart so that the next Pulsation a greater Quantity of Blood is forced into the Arteries which makes a more considerable Protrusion of Blood into the Muscular Glands and also of Spirits through the Nerves by which means the Thorax contracting more violently forces the Blood in greater Quantities into the left Ventricle of the Heart and the Motion of the Heart at the same time increasing raises Circulation to it's natural Force by squeezing Blood forwards into the Right and so successively From hence it appears that the Blood is forced into the Ventricles of the Heart by the help of the Lungs for if when the Motion of the Lungs is obstructed the Systole and Diastole of the Heart ceaseth in a short time it must needs follow that it is in some measure preserved in that Motion by them and it is further proved because the Motion of the Heart does not only sooner stop when Respiration ceases but also because it is increased by a renued Respiration and any one that would be further satisfied of the Truth of it let him hold his Breath a considerable time and he will find his Pulse gradually decay which is again renued by reiterated Breathing But though from hence it may appear that the Motion of the Heart is promoted by the Assistance of the Lungs yet it perhaps may be a Question how this Defect is supply'd in unborn Infants and how their Blood circulates since then their Lungs do not perform the Office of Respiration To which I answer that in an Infant before Birth the Placenta supplys that Defect for that additional Force which the Infants Blood receives from the Motion of Nourishment violently forced into the Umbilical Vessels by the Pulsation of those Arteries that separate it from the Mother's Blood in the Womb do prove equivalent and supply the Office of the other but as soon as the Circulation of the Blood ceases to be promoted by a Sepaparation and Protrusion of that Juice it immediately if unborn dies and after it is born hath a continual Necessity of Breathing as long as it lives Where it is to be noted that as in one that breaths the Lungs more immediately assist the left Ventricle so in one unborn the Placenta more immediately promotes the Dilation of the right Now although it from hence appears that the Motion of the Heart is promoted by the reciprocal Motion of the Lungs yet it does not wholly depend upon it for if it did the Motion of the Heart would as suddenly stop as that of the Lungs but since it does but partly depend upon it Circulation declines by degrees upon the stopping of it But that it may be better understood how the Lungs promote Circulation I shall next shew that the sanguiferous Vessels in the Lungs are not only contracted by the Contraction of the Thorax but also in every Inspiration And since it is known that the Bladders of the Lungs are encompassed about with the small Twigs and minute Ramifications of sanguiferous Vessels every Systole of the right Ventricle of the Heart these must needs be filled and distended with Blood and if so consequently that Blood must needs be forced by the Contraction of the Thorax through the Vena Arteriosa with a considerable Force and so be driven into the left Ventricle of the Heart with more case where we may by the way take Notice that the Blood in the Arteria Venosa from the Orifice of the right Ventricle is not only by that means thrust into the minute Vessels of the Lungs more easily but also the Blood that is to be forced forwards by the next Pulsation is more readily received by the Vena Arteriosa and the Ventricle more easily contracting when the Vessels of the Lungs are thus emptied by a Contraction of the Thorax than if they were distended that subsequent Matter in the depending Parts is received and driven after it with less difficulty the resistance that distended Vessels would make to the Egress of it being thus prevented by the help of the Lungs That the Blood is thus forced out of the Lungs into the Ventricle of the Heart is not only evident from Reason but also Experience for in violent Coughing where the Lungs are almost in a continual Contraction the Blood is more violently driven into the Habit of the Body that it is forced into the Face visibly appears and that it also flows into the Habit of the Body is evident in People that are let Blood which by coughing much is plentifully forced out of the Orifice and that the Contraction of the Lungs in coughing can no otherwise force the Blood into the Habit of the Body but through the left Ventricle is very plain and Lastly that not only the left Ventricle is by that means further dilated but consequently the right by the Assistance of the Lungs is manifest because Circulation is presently quickned by coughing so that this one Phaenomenon proves all that I have asserted concerning the Use of the Lungs with respect to the Heart But it may here also be questioned how the Lungs supply the Heart in Inspiration when the Cavities of the Lungs are dilated To which I answer that though the Cavities of the Lungs are dilated in Inspiration yet the Bladders which are swelled and dilated with Air even then make a moderate Pressure upon and consequently a Contraction of the Blood Vessels that are