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
ought to be in Motion p. 164 The Use of the Lungs in respect of the Body p. 169 To dilate the Ventricles of the Heart p. 174 How obstructing Respiration kills an Animal p. 178 Whether Air be mixed with the Mass of Blood p. 191 Whether Nitre be p. 192 And how p. 193 What Effects it hath upon the Mass of Humors in the Lungs p. 196 How Nitre depresses the Heat of the Blood p. 198 Pag. L. Read 41. 5. Occasion for Accension 53. 18. Motion for Notion 60. 2. Exploded 84. 8. Blood for Body OF THE HEAT OF THE BLOOD EVEN Philosophy in General is so Mysterious and so infinitely out of the reach of our short and weak Capacities that the best of Philosophers may truly be said to have but a slight and superficial Knowledg of it For if that small Part we know be compared with what we know not all our Knowledg is but as an invisible Speck those things to which it extends being inconsiderable if compared with that vast and endless Mass of the Universe But although that Part of the Universe which in some Measure lyes within the Cope of our Senses be small and inconsiderable when compared with the vast Extent of the whole Creation yet when we reflect on the vast Variety of Objects contained within those narrow Dimensions we find and must needs acknowledg it very considerable and superabundantly furnish'd with Matter for our Senses to work upon For the Extension of our Knowledg as to those Objects is bounded by Limits not very spatious notwithstanding the Diligence and Industry of Learned Men and the great Improvements made in most Parts of Knowledg The wisest Men and the most profound Philosophers must of necessity own that of those Things they know most their Knowledg is very imperfect We know but in Part and indeed so small a Part that it chiefly seems to inform us more sensibly of our Ignorance But so pleasant and desirable is Knowledg and we find so much uneasiness in Ignorance when once we have tasted of it that it 's impossible to abstain from a further Pursuit after it at least notwithstanding the vast disproportion betwixt our Knowledg and Ignorance which continually lyes in our way to discourage us And as we thirst after Knowledg with a desire to attain to a more adequate and compleat Apprehension of it so we most eagerly pursue those Parts of it which we hope to understand most clearly and which we expect to make a Progress in with the most considerable Advantage Since then the Microcosm which is as if it were a Type and Epitomy of the Macrocosm lyes much more within the narrow Cope of our Senses since we can dive and search into all and the inmost Recesses of it and come nearer to those Springs and Fountains upon which all the Effects we perceive in it depend we have much more solid and firm Foundations to proceed upon than in any other Parts of Philosophy whatsoever and may much more reasonably hope for Certainty and Truth besides the Pursuit of it must needs be not only more Pleasant but Advantagious And although in a Man's Body some Things are much more apparent clear than others yet the most obscure may easily be so far explained and understood as is necessary and subservient to shew the Use of them and to what Ends they were designed Amongst those that are accounted most obscure the Heat of the Blood is unfortunately one but the Reason why it is so is not that it is less apparent in it self but rather the Inadvertency of those that searched into it If possible such great Men as have writ concerning it may be guilty of so great a Fault which although otherwise no small one is much more excusable in those whose more weighty Concerns take 'em of a deeper Enquiry Since then so many learned Men and those to whom Physick is not least obliged for considerable Improvements have writ on this Subject I think it not only Justice but also Reasonable I should shew upon what Grounds and for what Reasons I have rejected their Opinions before I take leave to propose my own It would be needless to spend time in Informing my Reader that both Antient and Modern Writers have endeavoured to account for it and it would be Information to but a few since none that have made any considerable Progress in Physick can be ignorant of it I shall only as briefly as I can mention the Opinions of the Antients that it may better appear to the more unlearned wherein they are deficient and then I shall consider the most remarkable Opinions of the Moderns that less competent Judges and young Students in Physick may spend less time in convincing themselves how far they come short of explaining the Reason of the Heat of the Blood Amongst the Ancients who wanted those Improvements in Anatomy that have been made of late to direct them in their Judgments some fancied that it proceeded from a Calidum innatum or innate Heat which was fixed and rooted in all the Parts of a Man's Body before his Birth and that This continued Heat by communicating it self successively to the Nourishment of the Parts as soon as it was received by them Which indeed was so weak and superficial an Account of it that it rather served to please the Unlearned then to satisfie the Curious and more Inquisitive Others thought that there was a sort of Flame lodged in the Heart which kindled the Blood as it passed through it But Moderns having learnt by a further and a deeper Insight into Mens Bodies that the former of those was rather the Effect than the Cause and by frequent Dissections that the Heart was altogether incapable of containing such a Flame and also that that which they supposed to be the Pabulum of it to be clotted Blood they have with sufficient Reason rejected them both Wherefore passing by these I shall proceed to consider those Modern Opinions which are thought most worthy our Consideration The first that I shall take Notice of is the Opinion of the most Ingenious Dr. Willis who although in some things he hath had the Fortune to be mistaken with other Learned Men the best being not exempt yet for the most part hath made the greatest Improvements of any of his Predecessors in Theory This Learned Author in the eight Paragraph or thereabouts of his Exercitation concerning the Heat of the Blood takes Notice that there are three Modes or Sorts of Causes by which Liquids grow Hot. First à culido ad moto or by applying them to something that is Hot as when Water boyls over the Fire Secondly when Saline Corrosives mutually act upon one another or on sulphureous Bodies mixed with them by an intense and powerful Agitation Thirdly when a Liquor abounding with much Spirit or Sulphur takes Flame from some other Body And in the next Paragraph
Title does not at all diversify the Action But if any one would rather signify the Heat of the Blood by any of these different Words I shall be equally pleas'd with them or any of them provided they all meet in the Matter signified by them and do not deny that which seems to be true That the Heat proceeds from a swift intestin Motion of it's Particles Which Motion is the Reason why it affects our Sensory so as to cause a Sensation of Heat But as the Reason why it affects our Sensory so is not sufficiently satisfactory to explain what is the Cause and how it comes by that Power of causing such a Sensation In making an Enquiry into the Cause of that I shall beg leave to make Use of that Word which I think to be most expressive viz. Fermentation For since in every mechanical Action there is an Agent and a Patient and the Agent operates upon the Patient by moving powerfully against the Parts of it And in that Motion the Parts of the one strike against and rub upon the other so far it may be called Attrition And if by the force of the Agent the Motion and consequently Attrition be more violent and the consequence of that Attrition be a Production of a Power to cause a Sensation of Heat so far it may be called Fermentation If then in causing the Heat of the Blood there be such a Motion and Attrition and the consequence of it be Heat we may properly say the Blood grows hot by Attrition and Fermentation But because to signify the Heat of the Blood by Attrition and Fermentation would be needless I would signify all that Action by Fermentation And when I say the Blood grows hot by Fermentation I would be understood to mean and signify both that Attrition of Parts which is the Cause of Fermentation and also Fermentation which is the consequence of Attrition yet if any one would rather say it grows hot by Accension they have my assent provided they mean thereby not so high a degree of Heat as is usually signified by that Word but since it sounds rather too harsh and implies too high a degree of Attrition and Fermentation than that which is commonly in the Blood I more willingly make choice of the former viz. Fermentation And since I have said thus much of the Use of Words applyed to signify the Heat of the Blood I shall here take Notice of what was by way of Discourse told me by one to whom I communicated in some Measure my Notion concerning the Heat of the Blood which was this He said he thought he could prove that it was done by Mixture and Pressure and that he could explain the Heat of the Blood by that Notion I shall here conceal the Authors Name because he hath not made it public upon this account though upon some others to very little purpose and because he told me he intended to publish it I shall for his satisfaction and also the satisfaction of those to whom he hath communicated it say that as I have shewn that in mechanical Actions there is a Motion and by that Motion there must be implyed a Mixture to any one that doth but understand the Circulation of the Humors in a Man's Body and it will consequently follow that where there is a Mixture and a Motion of Humors there must needs be also an Attrition of Parts so moved which Attrition implies a Pressure For there can be no Attrition without a Pressure tho' Pressure does not imply Attrition This is all he told me and consequently all that I can Answer but for as much as I cou'd gather from the remaining Part of his Discourse the most Essential Part of his Notion but from what he said it appearing not what Pressure he meant that is a Pressure of what whether of the Particles of Blood with one another or not and it being plain that he did not believe that Animal Spirits circulated through the Nerves I not only concluded that his Pressure was only of the Particles of Blood because there are none other except Serum to mix with it but also that what he had to say for it was rather about the Use of Words then any thing else and therefore I have shew'd him how far his Words are significant in my Hypothesis But Words whereby we signifie the Heat of the Blood being nothing at all to the Cause of it and to dispute whether it may be called Accension or Fermentation not at all informing what are the Principal or Accessory Causes of it I shall proceed to shew how it is begun and carryed on and by what That is what Humors are Active and what Passive in producing Heat or a Power to Heat and how they are so and after what manner as also where they chiefly operate And that it may appear we are to consider that the material and corruptible Part of a Man in which the immaterial and immortal is lodged is made up of Solid and Liquid Parts the Solid Parts are all those Vessels that make the Body a curious contrived Vascular Engin which are filled with and actuated by Liquids and in which they all circulate And as those Vessels carry different sorts of Liquids so they are called by different Names Veins Arteries Nerves c. Through the Arteries and Veins the Mass of Blood continually circulates and Animal Spirits through the Nerves The Veins and Arteries being as if it were both rooted and springing from the Heart are branched up and down the Body both through the External as well as Internal Parts except those that the Vena Porta supplyes and the Nerves taking their Original from the Brain and spinal Marrow are dispersed through the whole and meeting with the capillary Terminations of the Veins and Arteries they being interwoven one with another terminate all together and as I Metaphorically expressed it in my Treatise of Muscular Motion all terminate in small Glands in the Cavities of which both through the substance of the Muscles as well as the Internal Parts the Arteries lay down Blood and the Nerves either mediately or immediately Animal Spirits and having there also proved that a subtile Liquor made and prepared in these Glands by Formentation was according to the different degrees of Spirits sent there by our Appetite not only subtilized but thrust out by a succession of Matter into the Fibers and circulating through them distends 'em and by that means contracts the Muscles and there also having shewn that the Fermentation was caused by a mutual Conflict of the Blood and Spirits I shall now in this Treatise endeavour to explain from that mutual Conflict the Heat of the Blood And because some as yet doubt whether Animal Spirits circulate through the Nerves or not and others though they are willing and find it necessary to grant that Spirits do really run through them yet profess that they cannot be demonstrated
into Motion The volatile Salts and Sulphurs in the Mass of Blood make it more apt to be fermented Which is more or less promoted according to the different Degrees of the Activity of the Spirits Neither the Animal Spirits nor Arterial Blood are wholy Active or Passive That the Heat of the Blood proceeds from Fermentation proved That Heat proceeds from Attrition further proved Not only solid Bodies but also Liquids grow hot by an Attrition of their Particles The Particles of 〈◊〉 of these Humours are first put into Motion by Circulation That the Particles of refined and rarified Matter are by an Inversion of their Motion put into a higher degree of it proved How the Animal Spirits rarifie the Blood That the Animal Spirits according to their different quantities differently exagitate the Mass of Blood prov'd By the observation of People of different Ages As also by different Constitutions And the Practical Part of Physick How Spirit of Harts-horn raises the Pulse That the Spirits according to their different Degrees of Activity variously exagitate the Mass of Blood The sharper the Particles of Blood are the more they corrode the Spirits and put them into Motion The Keason of flushing heats in the Scurvy Proved by comparing the Nature of the Medicines that oppose it and correct it That as the Blood as more or less Volatile it's Parts are put more or less easily into Motion proved And that it is differently promoted according to teir different Degrees of Activity of the Spirits How far the Blood and Spirits are Active or Passive How the Heat of the Blood is continued Some Objections considered and answered The first Objection answered viz. whether the Heat of the Blood be chiefly caused in the Extremities of the Vessels The Reason why the Heat of the Blood in time decays And that Reason proved How Fermentation is carried on in a dying Body and the Reason why it ceaseth when it is quite dead Another Argument to prove that the Heat of the Blood depends on and is caused by Attrition Fermentation Circulation mutually depend on one another The second Objection answered viz. That Fermentation may be performed in so short a time as the Circulation of the Blood admits The Blood is more powerfully fermented in the substance of the Heart than in any proportionable Part of the Body besides Fermentation is not only promoted in the Muscular Parts but also in the internal Bowels Three things requisite to continue the Heat of the Blood The Vse of the Lungs in Respect of the Soul Is to express all it's Conceptions and Reasoning Why the Lungs ought to be in a continual Motion is because It carries off that Superfluous Moisture that supplies them And that their voluntary Motion might less Preternaturally affect our Bodies What Effects it causes when too thick and also why thick foggy Air is troublesom to some People The Vse of the Lungs in respect of the Body Seems to be to perform the Office of another Heart By helping the Blood to force violently enough into the Cavities to distend them against the next Contraction How stopping the Breath of an Animal kills it Why by permitting it to breath again the Circulation of the Blood is renued How the Motion of the Heart is promoted in an Infant unborn The Office of the Lungs is partly voluntary partly involuntary What Effects the Air hath upon the Mass of Blood In respect of it's Colour Nitre depresses the Heat of the Blood What effects Nitre hath upon the Serum of the Blood
about them But though there were no such Contraction upon Inspiration yet the Dilation of the Thorax is not so long continued but that the Lungs renue the vigorous Contractions of the Heart before they are sensibly decreased as I have before explained it From what I have said of the Use of the Lungs with respect to the Rational Soul as well as the Motion of the Heart it appears that the Lungs perform a Sort of a mixed Action partly voluntary and partly involuntary with respect to the Body it is involuntary being carry'd on whether we will or not and when we are able to take no notice of it and with respect to the Soul voluntary it being in our Power to quicken or remit the Motion of them differently to modulate our Voices as occasion and necessity require or our own Will inclines us But besides these extraordinary Offices it performs in promoting both a Circulation of Humors and of Discourse since there is such a great Quantity of Air drawn in by every Inspiration it must needs produce some Effects in the Mass of Blood and those Humors that circulate along with it and since it is so minutely mixed with it by the small and circular Windings of the Blood Vessels about the Bladders of the Trachea the Blood must needs be sufficiently impregnated with Nitrous Particles But it being a Question how the Nitre of the Air comes to be mixed with the Blood and whether the Air it self be mixed with it also before I proceed to shew how the Mass of Blood is affected by it I shall endeavour to solve these two Questions And First That the Air it self is no otherwise mixed with the Mass of Blood but as I have shew'd viz. by the Mediation of the distinct Vessels in which each run is plain because we don't perceive the Effects of it in that Mass and also we may probably guess so because Air would hinder Circulation and much disturb it Air being always unapt to mix with Liquids and to fly from their Embraces there being therefore these Reasons why it ought not to be mixed with the Blood and none that it shou'd nor any Sign of it being so we have Reason to conclude that it is not But Secondly That those Nitrous Particles which swim in the Air are mixed with it we see manifestly by the Effects which are caused by them there being the same Alterations in some Measure made in the Blood as it passes through th Lungs as when exposed to the open Air. But the Question then will be how the Nitre of the Air is mixed with the Mass of Blood and by what means To which it may be answered that if we consider what fine and subtile Bodies those Particles of Nitre are which we draw in by Inspiration and through what minute and small Pores they are capable of passing so that they penetrate the most solid Bodies in Nature well may we suppose that they can find Pores fine enough to pass through the Coats of the Vessels That they pass through the most compact and solid Bodies Bodies that are much more close and less Porous than the Vessels of the Lungs are is certain for otherwise hot Water contained in a brazen Vessel would never grow cold and that the substance of Brass is less porous than the Substance of the Lungs no thing is less dubious Moreover since that the Nitrous Particles of the Air are conveighed into the Blood is so plain from the Effects that are there caused by them they must needs be conveighed through those Pores there being no other ways at all for them to pass by But Another Question which may perhaps be asked will be how the Nitrous Particles of the Air are forced through those Pores which will be easily understood by taking notice that when the Thorax is violently contracted the Air contained in the Bronchia being violently pressed together in order to an Expulsion of it a considerable Number of those Particles of Nitre must needs be pressed through those Pores that are wide enough to receive them and that there are Pores wide enough is visible from what I have said It appearing hence how the Nitre of the Air is mixed with the Blood I shall next consider how it affects it and what Effects it produces in respect of Heat To understand then the Effects that it hath upon all that Mass of Humors that circulates through the Veins and Arteries to wit Blood and serous Lympha we are to consider them both together and apart together that it may appear how they influence each other and a part that we may know for what end each is impregnated with those Nitrous Particles and because when we are acquainted how it alters each singly it will better appear how they influence each other I shall first consider them apart The Effects then which we perceive the Nitre of the Air hath upon our Blood and the Alterations we are sensible it produces are either in respect of it's Colour or Heat That the Air alters the Colour of the Blood and makes it more florid is very plain in extravasated Blood and is so commonly known that I need not take any further Notice of it but shall shew what other Effects it causes in the Blood and how Having therefore explained the Heat of the Blood in the foregoing Treatise and it appearing that it is caused by a swift and violent Agitation of the Particles of the Spirits and Mass of Blood the way to understand how Nitre affects the Heat of the Blood is to consider how it promotes or hinders the Motion of those Parts of Matter which cause Heat which as I conceive and as Reason seems to evince is performed after this Manner The Nitre of the Air consisting of Particles not at all inclined to Motion but on the contrary disposing those Bodies they are mixed with to rest except by accident when they are too powerfully resisted and opposed These I say being mixed with the Mass of Blood inviscate and fetter up the most subtile Spirituous Parts and hinder them from Motion by which means the more gross ones are moved more slow and the Heat of the Blood consequently abated but when the Mass of Blood is so Elastick and the Parts of it move so strong that the Nitre cannot depress them sufficiently and check them the Heat of the Blood is increased the Motion of those Parts being inverted That the Nitre of the Air inclines those Bodies to rest with which it is mixed and consequently the Blood is not evident only by exposing hot Water to a cold freezing Air but even Blood and nothing is less dubious than that excessive Cold extinguishes a moderate Heat But that Nitre when it is not powerful enough to check and extinguish the Heat of the Blood does increase it I have before explained and the manner how it does it and also that it hath never those Accidental Effects upon Liquids