A TREATISE Concerning the HEAT OF THE BLOOD: And also of the USE OF THE LUNGS.  
By RICHARD BOULTON of Brazen-Nose College in OXFORD.  
LONDON, Printed for A. and J. Churchill, at the Black Swan in Pater-Noster-Row, 1698.   

IMPRIMATUR.  
JO. MERE Vice-Can. Oxon. Jan. 24. 1697.   

HUNC Librum (cui Titulus, A Treatise of the Heat of the Blood, etc.) dignum Censemus; quî Imprimatur.  
Thomas Millington, PRAESES. 

Samuel Collins,  
Edward Hulse,  
Richard Morton,  
Charles Goodall,   CENSORS. Martij 5. 1697/ 8.   

TO THE Reverend Dr. JO. MERE PRINCIPAL OF Brazen-Nose College, AND VICECHANCELLOR OF THE University of Oxford.  
SIR,  
IT is not any great Opinion I have of my present Performance, (though there are some who would persuade me, that it is not altogether despicable) that makes me presume to prefix your Name before it.  
Indeed, amongst Men of Sense and Learning, Truth for the most Part brings its own Recommendation along with it, and finds that Candid and ready Reception which it deserves. But the Generality of Mankind will not relish any thing, that bears not in the Front some great and eminent Name.  
And for this Reason it is, that I have made bold to make this Dedication.  
Your real Worth which hath deservedly placed you in two Eminent Stations, to both which you do more Honour than you receive from them: And the Encouragement and Favour you show to all Persons of Industry, Virtue and good Learning under your Government, soon determined me in the Choice of such a Patron; though my small Share of each of the latter, could merit neither of the former.  
And here, according to the usual Mode of Dedications, I might easily enlarge upon so fair a Character; But as it is your peculiar Delight to oblige & do good with all the ease and sweetness imaginable, so with as little Noise and Ostentation possible: And I should sooner hope for your Pardon for this Presumption and the Faults of my Book, than for such an Attempt upon your Modesty.  
I shall therefore only add, that you would be pleased to accept this as a Testimony of my Duty and Gratitude, and that I shall always remain,  
Reverend SIR, Your Ever Obedient and Obliged Servant R. BOULTON.   

To the very LEARNED AND JUDICIOUS Dr. R. ANGEL, Resident in the CITY of CHESTER.  
Learned Sir,  
SIXTEEN Years Education in a University, and a great many more improved in successful and judicious Practice, hath sufficiently qualified You for a Judge and Patron, when I consider the former and withal my own Weakness, I confess I have less Reason to desire the latter: But sinoe it usually happens that those that are least subject to Faults are commonly candid Critics, and most ready to forgive others: I am bolder to beg your Patronage; yet not for its Faults, since that is below your Judgement, but whatever Truth is contained in it, which will scarce be denied by One that is so much an Encourager of Learning.  
But perhaps I ought to make an Apology to You as well as the World, for deviating from the Opinions of some Learned Men; especiatly of that never too much Honoured Dr. Willis, who was One of the Greatest Physicians of his and preceding Ages. And truly all that I can say for myself, is, That as it would be below the Character of so Great a Man, to write any Thing upon any other Consideration, than an Improvement of Knowledge and Truth; so, undoubtedly, he would not desire any Thing he writ should be believed except it seemed so.  
That than which I hope, will be an Apology for such an Attempt, is, That I have considered his Opinion, with no other Design than an Endeavour after Truth, and have offered nothing against his Opinion, but plain and unprejudiced Reasons; and though I have given Reason enough to prove he was mistaken in this Point, yet I must ever have the greatest Veneration and Esteem for all such Men of unparallelled Worth and Learning, and so candidly Ingenuous.  
But whether this little BOOK may pretend to any Reason for what it offers or not, I am more encouraged to ask Your Patronage, it being approved by Men of noted Learning and eminently Judicious, the Precedent and Censors of the College of Physicians, of which Number that yourself is not a Member, no other Reason can be given, but that Your own Choice of a more retired Life hath fixed you in that CITY, where you are now resident, to the Satisfaction and Good of those that commit themselves to your Care.  
But, Learned Sir, That I may not press too much upon your Patience, That Patronage which you were pleased to Give my Last, when I was a Stranger to You, both encourages me to hope for it, now You have been pleased to take me into Your Favour; and also, that You'll Pardon me for taking this Liberty, since it is only designed to testify my Gratitude for those Favours You have already been pleased to Confer on  
Your very Humble and Obliged Servant R. BOULTON.   

THE CONTENTS.  

THE Introduction. Page, 1  
Our Knowledge is very short. ibid.  
— And Imperfect. p. 3  
The Pursuit of Knowledge very desirable. p. 4  
Where most easily attained. p. 5  
The Heat of the Blood not obscure in respect of its Cause. p. 6  
The Opinion of the Ancients very Superficial. p. 9  
Dr. Willis's Opinion answered. p. 11  
But one Way by which Bodies grow hot. p. 13  
Fire is rarified Matter in Motion. p. 16  
Heat not actually in the Body that causes it. p. 19  
Heat only a Sensation. p. 20  
Heat only produced one Way proved further in Answer to Dr. Willis. p. 23  
An Objection answered. p. 27  
His comparison of the Blood's Accension with Flame answered. p. 28  
Several Degrees of Heat without Flame. p. 29  
Nitre makes no Part of the Flame. p. 32  
How Nitre promotes Flame. p. 33  
Why a Candle in a Glass-Globe is extinguished by extracting Air. p. 36  
Whether Nitre promotes the Heat of the Blood. p. 39  
Liquids fetter up Heat without Nitre. p. 41  
Blood may grow hot without a Sulphureous Pabulum. p. 42  
His Comparison of the Recrements of Flame and Blood answered. p. 43  
A Digression why Flame▪ usually ascends. p. 50  
Why it sometimes descends. p. 60  
Diemerbroek's Opinion answered. p. 62  
Dr. Henshaw's Opinion answered. p. 65  
Of the true Reason of the Heat of the Blood. p. 67  
Animal Spirits Demonstrated. p. 80  
That they are in Motion through the Nerves. p. 89  
The Nature of them. p. 91  
The Reason of the Heat of the Blood explained. p. 94  
That Reason of its Heat proved. p. 100  
— By Attrition. p. 103  
How the Animal Spirits rarify the Blood. p. 111  
Why the Heat varies. p. 112  
How Sp. of C. C. raises the Pulse. p. 116  
The Reason of flushing Heats. p. 120  
How far the Blood and Spirits are Active and Passive p. 131  
How the Heat of the Blood is continued. p. 132  
Some Objections answered. p. 134  
Why its Heat declines. p. 139  
Of the Use of the Lungs. p. 159  
— In Respect of the Soul. p. 162  
Why they 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 Humours 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 
Our Knowledge in Philosophy is limited to a small Part of the Creation.  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 Knowledge of it: For if that small Part we know, be compared with what we know not; all our Knowledge 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 
Which is furnished with Objects too copious for our Senses  lies 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 acknowledge it very considerable; and superabundantly furnished with Matter for our Senses to work upon.  
For, the Extension of our Knowledge, as to those 
Of which at the best we have but an imperfect Knowledge.  Objects, is bounded by Limits not very spacious; & notwithstanding the Diligence and Industry of Learned Men, and the great Improvements, made in most Parts of Knowledge: The wisest Men, and the most profound Philosophers must of necessity own, that of those Things they know most, their Knowledge 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 Knowledge; and we find so much 
The Pursuit of Knowledge very desirable.  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 Knowledge and Ignorance, which continually lies in our way to discourage us.  
And as we thirst after Knowledge, with a desire to attain to 
Especially of that which is most Advantageous.  a more adequate and complete 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 
There is more Reason to expect Truth and Certainty in the Microcosm than the Macrocosm.  were a Type and Epitome of the Macrocosm, lies 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 Advantageous.  
And although in a Man's Body, some Things 
Where it is easily attained.  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 show the Use of them, and to what Ends they were designed.  
Amongst those that are accounted most obscure, the Heat 
The Heat of the Blood not obscure in respect of its Cause.  of the Blood is unfortunately one; but the Reason why it is so, is not that it is less apparent in itself, 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 Physic is not least obliged, for considerable Improvements, have writ on this Subject; I think it not only Justice, but also Reasonable, I should show upon what Grounds, and for what Reasons I have rejected their Opinions, before I take leave to propose my own.  
It would be 
Both Ancients and Moderns have differed as to the Cause of it.  needless to spend time in Informing my Reader, that both Ancient 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 Physic, can be ignorant of it. I shall only as briefly as I can, mention the Opinions of the Ancients, 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 Physic, may spend less time in convincing themselves, how far they come short of explaining, the Reason of the Heat of the Blood.  
Amongst the 
The Opinions of the Ancients very Superficial and Insatisfactory.  Ancients, who wanted those Improvements in Anatomy, that have been made of late, to direct them in their Judgements; 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 itself 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 satisfy 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 learned by a further and a deeper Insight into men's 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 
Dr. Willis ' s Opinion considered.  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 
Who asserts that there are three ways by which Liquids grow hot.  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 boils over the Fire. Secondly, when Saline Corrosives mutually act upon one another, or on sulphureous Bodies mixed with them, by a 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, he says, that there are other ways of Calefaction; as Fermentation, Putrefaction, and Attrition; but the sear only observable in solid Bodies.  
The Design 
And that the Blood grows Hot by Accension.  of which, is, to prove, that since the Blood hath not any other Body applied, to communicate Heat to it; and since it is not impregnated with Saline Corrosives; but is sufficiently stocked with Sulphureous Particles; and since Fermentation, Putrefaction, and Attrition are only the Causes of Heat in solid Bodies: It must needs be preserved in a continual Heat, by Accension of its Sulphureous Pabulum.  
But if we do 
To which it is answered that there is but one way in Philosophy by which all things grow hot.  but duly consider how Heat is promoted in all these several sorts of Substances; it will presently appear, that in Philosophy, there is but one way, by which all, whether Liquid or Solid grow Hot; and if so, than it will follow, that whether we say the Blood grows Hot, by applying of a hot Thing to it, or Saline Corrosives; whether by Fermentation, Accension, or Attrition, it will be equivalently the same.  
To make it evident 
Several degrees of Heat differ only in Degrees of a peculiar Power to cause Heat.  then, that there is but one way, by which all Bodies grow Hot; and that to say, that the Heat of it proceeds from the Application of other hot Bodies, Saline Corrosives, Accension, Fermentation, or Attrition, is but to express the same thing several ways; since they are all equivalently performed the same way; we are to consider, what is the Nature of hot Bodies, and wherein their Power consists; either to cause Heat themselves, or to communicate that Power to others: And because several remiss Degrees of Heat, differ only in Proportion from Fire, which is the most intense; and because, That is free from those Masks and Clouds, which intervene it and our Senses, when it is in more remiss Degrees; the best way to understand the Reasons of Heat, will be to consider, wherein the essential Nature of Fire consists.  
Amongst Philosophers, 
And Fire, which is the highest, is rarified Matter in a swift Motion which Masked in different Subjects affects not our Sight.  although it is very dubious, what it is, that causes Fire to differ so much from all other Substances; yet it is by the Consent of most Moderns, and evident from Flame itself, and the manner that it destroys other Bodies by, that it is made up of rarified Matter, whose Particles are in a swift and powerful intestine Agitation, and of a peculiar Figure and Size: And if Fire be nothing else, but Matter rarified and in a swift Motion; and from that swift and intense Motion of Matter, affecting our Organs of Sense, we perceive Heat; we must needs conclude, that whatever rarefies Matter, and puts its Parts into a brisk Motion, is the cause of Heat. And although according to the Diversity of Subjects, that Heat is dispersed through, it hath different Appearances to our Senses, and in most, it's Light; which, when it exists separately, is always joined with it, 'tis obscured by the Interposition and Mixture of other Matter; yet if Heat depends Essentially upon the Effects, that rarified Matter in Motion hath upon our Senses; it is undeniably true, that Heat is caused only one way, Remotely and Proximately, with respect to Matter in Motion, and the Effect it then hath upon us, viz. By putting the Parts of Matter into a brisk Motion, to affect our Senses with Violence enough to cause such a Sensation.  
But, before I proceed to a further Proof of what I have asserted, viz. That there is but one Way in Philosophy, by which all Things grow hot; it being a Controversy, whether Heat be actually in the Body that causes it; or whether Matter in Motion only produceth such an Effect as the Sense of Heat, upon our Sensory; although it is not requisite, I should here Publish my Opinion of it, yet it is necessary I should explain what I mean, when I say, that Heat is only produced one Way; or that Heat is caused, by putting the Parts of Matter into a swift Motion; or that Heat depends on the Effects, which rarified Matter hath upon our Senses, when it is in Motion.  
But if I were here to declare my Opinion of 
Heat is not actually in the Body that causes it, but potentially, because that Body hath a power to cause such a Sensation.  this Point which is so differently held by various Philosophers; I should say, that as far as I can conceive of it, Heat is not actually in the Body that causes it to be perceived, by our Senses, but potentially; in as much as that Body hath a Power to cause such a Sensation.  
And although a great many may wonder; that Fire, which causes Heat, should not be hot itself; yet there is as much Reason to believe, that it is not; as that a Sword which will cause Pain, is not Pain itself: For those who think that Fire which causes Heat, is Heat itself; take the Cause for the Effect, and affirm it to be so.  
Besides, Heat being only a Sensation; and it 
Heat is only a Sensation which is actually where there is Sense to perceive it.  being impossible there should be a Sensation, where there is no Sense; it is impossible there should be Heat, where there is only Fire, and no Sense for it to work upon: For Heat is not a Mode of Matter rarified and in Motion; but an Effect of Matter so modified. But, say they, it is impossible for us to think so; truly, if we are not directed in our Thoughts by Reason we may irrationally think, that Matter in Motion, which only causes Heat, is Heat; but if our Reason proceeds upon those Mediums which our Senses furnish us with, and certainly we can on no other, we shall easily be induced to believe, that the Cause is not the Effect; there being a great deal of Reason for us to believe so; though, none to the contrary.  
When then I say, that Heat is only produced one Way; I mean that there is but one Way to modify Bodies, so, as to make them capable of causing Heat; when they affect our Sensory: And when I say, that Heat is caused by putting the Parts of Matter into Motion, I mean, that a Power of producing Heat is caused so: And when I say, that Heat depends on the Effect, that rarified Matter hath upon our Senses, I mean, it is caused by those affecting our Senses.  
And because, always when I have occasion to mention the Cause of Heat, it would be too much Circumlocution to say, the Power of causing Heat is produced so, or otherwise; I shall use the Word Heat, sometimes to signify that Motion of rarified Matter, which is sufficient to cause Heat; and shall call that Motion, Heat in respect of the Effects which it causes.  
But, to proceed to a further and more evident Proof; That Heat, 
That Heat is only produced one way further proved.  or a Power to produce it, is only caused one Way; we are to consider, how the Motion of Particles is carried on in all those, which Dr. Willis calls, different Ways of causing Heat, viz. per admotum Calidi, Saline Corrosives, Accension, and even Fermentation and Putrefaction.  
And first, when Water is put over the Fire, and heated per admotum Calidi, the fine Particles of Fire penetrating the Vessel, are imbibed into the Water, and being fettered up, and kept from flying away, by the Parts of the Liquor, put them also into a quick Motion▪ from whence proceeds a sensible Heat. In the same Manner, when Saline Corrosives are mixed together, the subtle Effluvia, of each, first begin powerfully to oppose one another; and being by that means reverberated and struck back upon the Particles of those Bodies, of which they are the Effluvia, put them into Motion; and as the Motion so begun, grows stronger and more violent, so the Degrees of Heat become more intense And when a Flame is applied to any Sulphureous Body, the Particles of that Flame, being forcibly agitated against the Sulphur, put the Particles of it into a brisk and swift Motion; and they being by that means rarified and expanded, are turned into Flame. Lastly, it cannot be denied, but that when any thing grows hot by Putrefaction, that heat either proceeds from elastic and fermentative Particles within, working upon one another, or from something from without.  
Now in all these ways, as he is pleased to call them, since Heat is produced by the same Method in Philosophy; so it is reasonable to affirm, that there is but one Way, by which all Things become hot, viz. By Attrition.  
For Water grows hot, because the Particles of Fire are mixed 
Viz. by putting the Parts of Matter into Motion  with it, and put its Parts into a swift Motion: And the Effluviums of Corrosives, being very volatile and in a strong and powerful Motion, by an Attrition, and grinding upon one another cause Heat. So also the Particles of Flame, by Attrition turn Sulphur into Flame: And by Motion, only not so intense, a less violent degree of Heat is produced in Putrefaction; so that in all these ways, Heat only proceeds from rarified Matter, put into a violent Motion by Attrition; and the consequence of that Attrition, is Fermentation.  
After the same manner, Heat is produced in solid Bodies: For when Flint and Steel are violently struck together, the Sulphureous Particles being scattered and dissolved by that Force, are put into a brisk and swift Motion.  
But, although from hence it appears, that all Bodies whatsoever, 
A seeming Objection answered.  grow hot by being put into Motion, by an intestine Collision and Attrition of Particles; and consequently but one way: yet some will be apt to think, that since there is so much difference betwixt Water, Corrosive Salts, and Sulphureous Bodies; that there must needs be some difference in their way of working upon one another.  
To which, all that I need to say more, is, That though different Bodies are differently applied together; yet it is evident, that they only operate by those Particles that are in Motion, and which communicate Motion to each other; and one may as well say, that Sulphur kindled by a Flame, is made hot per admotum Calidi, as that Water is: For as Flame is applied to one, so the dispersed Particles of Fire are communicated to the other.  
This Learned Author, having laid these Premises to establish 
His Comparison of the Blood's Accension, with Flame considered.  a Rational Hypothesis upon; and concluding that the Blood of a Man's Body, could not become hot any other way, but by Accension, goes on to compare the Accension of the Blood, with the burning of the Flame; and because, as he thinks, the same things are requisite, to continue both, viz. First, a free and continual Access of Air. Secondly, a fresh supply of a constant Sulphureous Pabulum. Thirdly, a perpetual Avolition of fuliginous Recrements; he concludes that it must needs be kept hot by a continual Sort of Flame.  
But, he might as well say, that Water over a Fire, could not 
There are several degrees of Heat produced without visible Flame.  become hot, except it was put into a Flame, as that the Mass of Blood, cannot grow hot without Accension; but since every Body knows that hot Water is not Flame; there is no doubt, but that Blood may be hot without Accension too.  
That to produce Heat, there is no need of a Flame to be always accended, is evident; since there are several degrees of hot Bodies, in which no Flame at all is apparent; and even Blood itself, immediately as soon as it is extravasated, seems so unlikely Pabulum, for a Flame; that Water will not sooner extinguish it, but to produce several degrees of Heat in Liquids', it is sufficient the Particles of those Bodies that so affect our Senses, be put into a swift Motion; although not into so high a degree as to make a Flame. So by rubbing of two Flint-stones together moderately, is produced an evident Heat: and when they are moved against one another more violently, the Heat is stronger; and by a Collision yet more violent, those Sulphureous Particles, that before caused a gentle Heat, constitute a Flame  
He says, that a Flame may be continued, it should always have a free Access of Air; for all sublunary Fire, and especially Flame is composed of Sulphureous Particles, breaking out of the combustible Matter; and of Nitrous Particles which always abound in the Air, and these Nitrous Particles, he says, are so necessary to the production of Flame, that in the Summer, if the Sun does but shine upon the Fire, by driving it back and dissipating the Nitre, it extinguishes it: Whereas, on the contrary if it be supplied with a sufficient Quantity, it burns more clear and brisk.  
Indeed, it is so manifestly certain, that Fire burns brisker and 
Nitre makes up no part of the Flame.  fiercer, when it hath a sufficient quantity of Nitre about it, than when it hath not; that to contradict it would be to deny what is sensibly apparent; but yet it does not therefore follow, that Nitre makes up part of the Flame: For Sulphur and Oil will flame as violently in the Summer as in the Winter, though Wood and Coal, and other combustible Matter will not.  
Besides, if Nitre made any Part of the Flame, though it might readily mix with the outward side of it, I would willingly understand, how when a Flame is two or three yard's Diameter, it is possible for it to be mixed with the middle of the Flame; which we perceive is more violent than the Borders of it, where Nitre abounds.  
But, the Reason why Flame will not burn without some degree 
The Nitrous parts of the Air promote Flame by keeping its Matter from dispersing too soon.  of Nitre, is not that it makes up any Part of it, but because the Particles of Fire are in so very swift and violent a Motion, that they would immediately be dispersed and fly away; if the Nitrous Particles of the Air did not prevent them, by closing round about them, and keeping them up to a Centre; by which means Flame is not only made of a longer continuance, but it's Power of heating us is more violent; those moving Particles being reverberated, and working mutually on one another, so as to increase their Motion, and consequently their Effects.  
And as the Rays of the Sun, collected into a Point by a Burning-Glass, makes 'em more violent, so do the Nitrous Particles enerease the Vigour of the Flame: And again, as Banks cast up about a Spring prevent the Water from streaming away till a greater Quantity is gathered together, and it breaks out violently; so are the Particles of the Fire heaped up, and kept in till their Motion over-powers the Pressure of the Nitre.  
But Nitre does not only by reverberating the Rays, collect a great Number together, and by that means increase their Vigour; but also by inverting their Motion, turns them back again upon, and causes them by striking against, the combustible Matter to dissolve, and put the Particles of it into Motion sooner, wherefore it burns more briskly, and is consumed in less time.  
And this is the Reason that Fire burns better in the Winter, 
Wherefore Fire burns better in the Winter than in the Summer.  than the Summer: For in the Summer for want of a close condensed Nitrous Air, to bind up and collect the Particles of Fire, they are dissipated and scattered immediately; but in the Winter, being as if it were yoked and locked up together, they affect our Senses more vigorously.  
To prove, That Nitre is Part of the Pabulum of Flame, 
Why a Candle in a Glass. Globe is extinguished by extracting the Air.  he instances an Experiment, from the Famous Mr. Robert Boyl, viz. That a lighted Candle being put into a large Glass-Globe, and the Globe being stopped, as soon as the Air is sucked out, the Flame expires. But this is so far from proving, that the Air is part of the Pabulum of Fire, that it is the strongest Proof of what I just now said: for as long as the Particles of the Air closing about the Candle, keep all the Rays together; and by inverting their Motion, cause them to turn upon the Fat, that they may, by dissolving of it, and putting its Parts into Motion, turn it into Flame, so long it burns; but as soon as the Nitre is exhausted, the Rays being immediately dispersed, and scattered by their own agility; fly away from, and cease to convert the remaining Part of the Fat into Flame; and that which makes more for what I have said, is, that as the Air is gradually drawn out, so the Flame is gradually diminished: For when there is less Nitre to oppose the Motion of the Rays, they are sooner dispersed; and the Nitre by giving them that liberty, leaves less flame about the Candle.  
He says further, as Flame is extingushed by taking away the 
His Comparison of extinguished Flame, compared with the Death of an Animal considered.  Nitrous Pabulum of it; so when the Breath of an Animal is stopped, it dies not so much because it is choked by a Retention of fuliginous Recrements, as by robbing the Blood of the Nitrous Pabulum.  
How an Animal comes to die by stoping Respiration, I shall hereafter give an Account, when I speak concerning the Use of the Lungs; in the mean time, I shall here make it evident, that the Nitre of the Air, is so far from promoting the Heat of the Blood; that the less Nitrous the Air is the hotter it grows.  
This is sufficiently manifest, 
Nitre does not promote the Heat of the Blood but rather depresses.  if we do but take our Breath through a warm Woollen Cloth, which imbibes, as if it were, the Nitre; for we shall be so far from being cooler for it, that in warm Wether, when our Bodies are a little predisposed, it causes us to sweat, whereas if Nitre promoted the Heat of the Blood, we should rather be cold, the Flame of the Blood according to him being extinguished for want of a Supply of Nitrous Pabulum.  
But, although this would not be a sufficient Argument to convince us; yet a cold Winter and a hot Summer would be Arguments strong enough; for we always find, that in the Winter, when the Air is full of Nitre, we are much more cold, then in the Summer when in the Heat of the Sun, we want that Supply of Nitre: From whence it sufficiently appears, that Nitre does not contribute to the Heat of the Blood, but rather depresses it.  
Neither, in Liquids' is there 
For in Liquids' the volatile Parts are sufficiently opposed by the Parts of the Blood and kept from flying away.  any accension as there is in Flame, for Nitre to lock up and keep the Heat from dispersing; for Water will be Hot, though it be placed in the Middle of a Fire, where no Nitre can come near it; the Particles which make up that Liquid Substance, being sufficient to reserve those Particles of Matter, which cause Heat upon our Sensory, from flying away so soon, by entangling and fettering them up.  
The second 
Blood may grow hot without a Sulphureous Pabulum.  Thing, that he says, is requisite to preserve Heat, is a continual supply of Sulphur. That Flame cannot be continued without a Supply of combustible Matter, I do not deny, yet we are certain, that Blood may grow Hot, without such Pabulum; for the Blood of Horses, and other Beasts, is so far from being supplied with a Sulphureous Pabulum, that nothing is less combustible than Grass and Water, which are their constant Food; and which have different Effects upon our Senses from Sulphur; and the daily Food we eat, is so far from kindling a Flame, that it would presently extinguish it.  
The Third and 
His Comparison of the Recrements of Flame and of Blood considered.  last Thing, he supposes, requisite to continue a Flame is that the Fuliginous Recrements be carried of; and as Flame requires a continual Avolition of its Recrements; so does the Blood, by the Branches of the Trachea and the Pores of the Body.  
That Smoke 
Which appears widely inconsistent.  and Flame are, as if it were, inseparably joined together; and that a subacid Balsamic Juice continually sweats through the inward Coats of the Trachea, and a saltish Serum through the Pores of the Skin is most certain; but in the carrying on of each of these Phaenomena, there is a very wide difference; for in an 
First, because that Juice that sweats through the Coats of the Trachea and the Skin is not Recrementitious.  Animal that Sub-acid Balsamic Juice, which sweats through the inward Coats of the Trachea, is designed to moisten the Cavities of it, to prevent them from drying and becoming useless, and partly to preserve them from the sharpness of the Nitrous Particles of the Air: and in like manner, the Skin is continually watered with that Serum, to preserve it from withering and becoming too dry; and though these Humours are not sucked up again into the Blood, yet that is not because they are Fuliginous Recrements, and Useless Parts of the Serum of the Blood; but because, since those Parts must needs be kept from drying; it would be impossible for Vessels to be so framed as to receive and return them to the Mass of Blood again: For the outward side of those Vessels would still be dry and want Effluviums, to moisten them ad 
And the Fuliginous Effluviums of Fire are Recrements.  infinitum. But the Fuliginous Effluviums of Fire are altogether Recrements and Useless in respect of Fire.  
Besides, the Effluviums of the Mass of Blood, 
Secondly, because the former if not carried of increase it.  if stopped, are so far from depressing and diminishing the Heat of the Blood; that they increase it so much; that they presently put those that have predisposed Blood into violent Fevers: But if the Smoke 
But Smoak extinguishes Fire.  of a Fire, or of a Candle, be reflected upon the Flame, it is presently extinguished.  
But it is a Question, whether Smoak be 
Smoak is not altogether an Effluvium of Flame.  altogether an Effluvium of Fire? whereas, no Body doubts, but that the Moisture, which supplies the Lungs and insensible Transpiration is separated from the Serum of the Blood: For Smoak, as I conceive, is made up of the Nitre of the Air, fixing the Particles of the Flame, together with the Ashes of the Fuel, that are raised and forced up by the quick and violent Motion of the Fire; which I believe is carried on after this Manner,  
The Particles of the Fire, being in a very 
Smoak thus compounded.  brisk and violent Motion, endeavour to expand, and powerfully to fly away, from the Fuel that supplies them; but the Nitre of the Air, strongly opposing them, partly presses them back, till their Motion being increased and more intense, they violently scatter themselves in the ambient Air, both amongst the Dust and Ashes of the Fuel, hurried along with them by their Motion and the Particles of Nitre: By which means, they lose most of their Vigour, and are more easily overpowered by the Nitre; and being fixed and joined with those Ashes, makes up that which we call Soot; which the longer it lies together, grows more Bitter, the Sulphureous Particles of the fixed Flame, being by an Intestine Sort of Motion, exalted, and overpowering the more dull and effete Parts of Matter.  
From whence it appears, that Soot is not altogether a Recrement of Fire; but is made up of effete Ashes, Fire and Nitre.  
But though Soot were wholly a Recrement of Fire, yet it does not follow, that that Moisture, which supplies the Lungs, is a Recrement of the Blood, though it were to be called a Recrement: For it is separated, as a Part of the Serum and Lympha, and not of the Blood.  
FRom what I have said, I think, it plainly appears, that neither the Simile he uses, is in any considerable Circumstances agreeable; nor can he from thence deduce the Reason of the Heat of the Blood; and being led as if it were by a Necessity, in Answer to his Opinion, to consider the Nature of Flame, and the manner of its Production, more than I otherwise should have done; I shall beg leave 
A Digression in which is given the Reason why Flame Ascends rather than Descends.  to make a small Digression here, which though it may seem foreign to a Discourse of the Heat of the Blood; yet it may not be improper, after what I have already said of Fire, to endeavour to give a Reason, why Flame, when it is left to its own Liberty, always ascends.  
To understand then the Reason, why Flame always ascends, we must again remember, that Fire is, for as much as appears to our Senses or Reason, a light rarified Body, whose minute and subtle Particles, are in a swift Motion, and in some measure pinned in, by the ambient Air.  
Now though the ambient Air thus press 
Which is because it hath less Opposition in its Motion that way.  upon it on every side; yet the Particles of Flame, being in too strong a Motion, and also too subtle to be totally resisted, and altogether confined; must needs break out that way, which it forces most easily, and where it is least powerfully resisted.  
That Flame is only a rarified Body in swift Motion, I take for granted; and that it is pressed upon on every side by Air, none sure will deny; and it must needs be most reasonable for us to believe, that it will be subject to spread and expand itself that way it finds the least resistance: Therefore all that I need to prove, is, that Flame exposed to the open Air, finds less resistance in Ascending then Descending.  
That Flame finds less resistance in Ascending then Descending, will easily be proved, if we will but allow, what is beyond Contradiction, viz. That the more solid and compressed any Body is, the more Powerfully it repels those Bodies that move against it; which plainly appears, if we strike two pieces of Mettle together, viz. Led and Iron, for at the same time, that Led easily yields to the Impression of the Iron, it as powerfully resists the former.  
If then, the Air, the nearer it is to the Centre, 
Because the Air the nearer to the Centre makes stronger Opposition than that above.  be more Solid and Firm, consequently it will resist the motion of Bodies that strike against it, with greater Vigour; and when the Particles of Flame are forcibly driven against it, they, being more strongly resisted, by that Air, which is below, than the Air above, with less difficulty make way for themselves upward, and so ascend.  
That the Air, the nearer it is to the Centre, is thicker and more compact, consequently will be abler to resist the Notion of the Flame; we have a great deal of Reason to believe▪ if we consider, what a vast and unaccountable Weight of incumbent Air, presses upon it; for, as in a Pillar of Stone, the nearer to the Foundation, the harder it is to force a Stone out of it, because it is held faster by the weight of those that lie upon it; so we must needs conceive, that those Particles of Air next the Centre, will be made more compact and able to resist the Flame by the weight of those that lie upon them.  
But to prove it more evidently, 
Which is proved by these Experiments.  viz. That the Air next to the Centre, makes a stronger Resistance; I shall produce a common, yet very remarkable, Experiment, which is this. If a Bladder be blown full of Air, at the bottom of the Mountain Teneriff, and be carried up to the Top of that Hill, it will presently burst: The Reason of which is plainly this, a great quantity of Air at the bottom of the Hill, being pressed and squezed close together, by the weight of all that condensed Air, that lies upon it, the Springs of it being by that means, as if it were wound up, and made more compact, as soon as that weight is wanting to keep them close together, at the Top, they fly open and expand themselves, to a more lax and open Constitution of Parts; which Reason is confirmed by another Experiment, viz. By blowing a Bladder full of Air at the Top of the same Mountain; for as it is brought down to the bottom of the Hill, it gradually subsides; and though it was as full as it could be blown at the Top of the Hill; yet at the bottom, it will seem not near fully distended, the Spring of the Air that was above expanded, being now pressed together by the weight of the Air above it.  
Another Observation, which I shall bring, for 
It is also proved by the Expansion of Gunpowder.  a Confirmation of it, is, That a Musket shot off at the Top of that Hill, makes no considerable Noise, compared with the Sound it causes at the bottom. The Reason of which difference can be no other, but this, that the Air being more compact and solid below, causes the Collision of the small Particles of Matter, to be more violent, by a stronger Opposition; and consequently the Sound is by that means louder.  
Besides, the Particles of expanded Gunpower fly away and dissipate themselves, a great deal more easily above then below; which confirms what I have said before, of the Reason, why Nitre is beneficial to the maintanance of Flame; for if the Air, when it is more condensed, binds up and causes the Particles of Fire, to work more powerfully upon one another; and by that means a stronger Collision of Particles; and if when it is less condensed, it more easily yields to them, and gives them Liberty to fly away with less Resistance; it must needs be granted, that the Office it performs here below, in respect of Flame, is, to keep its Parts from flying away too easily.  
But for a further Proof and Confirmation of the Reason I have given, why Flame flies upwards, viz. Because the Air yields more readily to its 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 
The Motion of Flame downwards is a natural Motion in Philosophy.  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 its Motion, so it is its 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 flies down; so Flame, being in a brisk Motion, naturally flies up or down, as the Parts of Matter it strikes against resist it, and cause it to fly back from them.  
HAving made this short Digression, I shall proceed next to 
Diemerbroek's Opinion examined.  examine Diemerbroek's Opinion; who thinks that the vital Spirit, by reason of its 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 diversely 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, etc. 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 
Dr. Henshaw ' s Opinion considered.  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 Chemical 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 increase the Flame of it, because Oil will, as that Chyle will put the Blood into a Heat, because Oil of Turpentine and Spirit of Wine will grow hot when mixed 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 than 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 
Ancient and Modern Writers have rather disputed about the Use of Words, than much difference observable in their Opinions.  different Name to signify the Heat of the Blood by; whilst some would have it done by Accension, others by Attrition, etc. 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 its 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 accessary 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 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 pleased 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 intestine Motion of its 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 
The Reason why Heat affects our Sensory does not show how it comes by that Power.  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 
The Blood grows hot by Attrition the Consequence of which is Fermentation.  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 
Attrition and the consequence of it both to be signified by the Word Fermentation.  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, applied 
How far the Heat of the Blood proceeds from Pressure and Mixture.  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 Author's 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 shown, that in mechanical Actions there is a Motion, and by that Motion there must be employed a Mixture, to any one that doth but understand the Circulation of the Humours in a Man's Body; and it will consequently follow, that where there is a Mixture, and a Motion of Humours, 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 could 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 than any thing else; and therefore, I have showed him how far his Words are significant in my Hypothesis.  
But Words, whereby we signify the Heat of 
To dispute about Words is not material in an Enquity after the causes of Things.  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 Accessary Causes of it; I shall proceed to show, how it is begun and carried on; and by what: That is, what Humours 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; 
The whole Body is made up of Vessels and Humours contained in them.  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 Engine; 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, etc. 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, 
By what means the Spirits and Blood are mixed in order ●o a Fermentation.  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 supplies; 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 subtle Liquor, made and prepared in these Glands by Formentation, was according to the different degrees of Spirits, sent there by our Appetite, not only subtilised 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 shown, 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 
Animal Spirits demonstrated.  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. I shall before I proceed to show how the Heat of the Blood is caused, endeavour to demonstrate those Spirits; and prove, that they circulate through the Nerves, as plainly as we can by the help of our Reason, and the Testimony of our Senses, demonstrate any, and the most apparent Things whatsoever.  
For any one, that does but look into the Substance 
In the substance of the Brain.  of the Brain, I think, needs neither doubt, nor be ignorant what the Animal Spirits are, nor of their Nature, which appear as manifestly as the Humours of a Man's Body.  
But, perhaps it will be a hard Task to 
Viz. that Mucilaginous oily Moisture which we call Brains.  persuade some, that that oily and clammy Moisture in the Brain, is Animal Spirits; since it seems, as some say, to be as gross a Substance, as any Liquid in the Body.  
To this I answer, that if we take Animal Spirits, 
An Objection Answered.  or that Moisture in the Brain, and compare it with coagulated Blood, it is much more fine and pure, and not half so tough and clammy; whereas, if it were a more gross and sluggish Body, it would be a great deal more Viscid and Phlegmatic.  
But if we further compare the Taste of the 
That it is the most spirituous Part of the Blood and consequently Animal Spirits proved.  Brain, with the Taste of the Blood, it will be evident; that that sweet Substance is the Spirit of the Blood; and consequently that it is Animal Spirit; For as the Blood is a sweet Mass, inpregnated with divers sorts of Salts, and Phlegmatic crude Serum; so the substance of the Brain is moistened with an oily sweet Salino-Sulphureous Mass▪ free from those indigested Dregs, that swim along with the Blood▪ being separated from those Impurities' in the cortical Part of the Brain, now if a Spirit partakes of the Nature of that Body, it is separated or drawn from, this is an Argument strong enough to convince any Rational Man, that that Moisture is the Spirit of the Body▪ since we learn by our Taste, that it is the purest and most refined Part of the Blood; as a Spirit ought to be.  
But some think it too gross a Humour, to 
That oily Substance is capable of performing all those Actions which we can suppose the Animal Spirits do.  perform all those Actions, which they think, the Animal Spirits do; yet if they grant that the Mass of Blood is the Pabulum of the Animal Spirits, as I think none can deny; since any considerable Evacuation of it, presently sinks and diminisheth them, than it will be very manifest, that those Spirits are able to perform all those Actions, that we can truly suppose Animal Spirits to do; for if by withdrawing that sweet Viscid Pabulum, that sweet oily Mucilaginous Moisture in the Brain, be diminished, and upon that Diminution the Animal Spirits are presently less vigorous; and on the contrary; if by enriching the Blood, and consequently increasing the stock of Animal Spirits, the Actions of the Body as well as of the Mind be stronger, we must consequently believe, that they are moderately performed by them; when that oily Substance, neither too plentifully abounds, nor is too much spent and consumed.  
But some People will not believe, That to 
Another Objection answered.  be Animal Spirit; because they say, they cannot get so much as one drop of it out of the Vessels.  
To which I answer, that if they deny it to be Animal Spirits, because they cannot gather it in drops; by the same Reason they may deny Blood to be Blood, because in small capillary Veins, when it is coagulated, it cannot be dropped out: For not only the capillary sanguiferous Vessels are so small, that they cannot be seen by good Microscopes, but also the Nervous Fibers are so extremely diminutive and fine, that they have been computed to be fourscore times as Fine as a Hair, and consequently the Liquor contained in each must be so little, that five or six Hundred Vessels must be joined▪ together, to make one Drop; so that, being separated and divided into very small Portions, by the Intermixture of the Vessels, it is no sooner exposed to the Air, but is immediately chilled and coagulated.  
Which we may more easily believe, when we take Notice, how thin and fluid the Mass of Blood is, as long as it is in a swift and constant Circulation, that if a capillary Vessel be but pricked with a small Pin, Blood immediately spurts out; yet how soon when exposed to the Air, does it thicken and coagulate, though it be exposed in great Quantities▪ so that one would scarce think it fit to move through Veins so small, that they cannot be discerned by the best Microscopes; much rather than may the Animal Spirits, whose Portions are so incomparably diminutive, be forthwith chilled and thickened, when they immediately, as soon as they are exposed to the Air, are almost equalled with Particles of Nitre.  
But be it never so evident, that these are 
That these Spirits are in a constant Motion proved.  the Animal Spirit's that are in the Brain; yet most deny them a constant and free Circulation. But since we see, that Blood, which is much more gross and thick, than Animal Spirits, when coagulated, as long as it is in a quick and brisk Motion, can move through the smallest Capillaries, we have great Reason to believe that the Animal Spirits would move much more swift, when separated and preserved from the Nitre of the Air; and although they immediately thicken, when exposed to the Air; yet are they much more thin and liquid, when in Circulation.  
But it is not only evident, that these Spirits are in a continual Motion, but also highly necessary: For either they must be in Motion, or stagnate; and if they should stagnate; they would in a short time corrupt and putrify. Besides, since there is a continual and constant Supply, separated in the Cortical Parts of the Brain, there must be a continual Decrease, or otherwise, there would be no room to receive them, which Evacuation we can rationally imagine to be no other way, but through the Branches of the Nerves; and also, because we perceive the Effects of them in the Musculous Parts.  
From hence it appearing that that oily Substance in the Brain is separated from the Mass of Blood; being the sweetest and most spirituous Part of it; and that it must needs circulate continually▪ through the Nerves; I shall now consider the Nature of it, that we thence may gather more clearly the Manner of its Operation.  
Which presently appears, if we do but consult 
The Nature of the Animal Spirits considered.  our Taste, the Taste of it being oily, sweet and mucilaginous, that Substance being made up of the most volatile sulphureous and salted Particles of the Mass of Blood, which are incorporated, in some of the most digested and ripened Serum of the Blood, and by that means appear in the Form of a Mucilage.  
That these Spirits are made up of the finest Sulphureous Particles and the most volatile Salts of the Blood, is apparently proved by our constant Diet; for we always perceive ourselves most full of Spirit after Meat that abounds with Sulphur, volatile Salts and Oils; whereas all Acids, Austeres, etc. which thicken Oil, and take of the Force of volatile Salt and Sulphur, depress our Spirits and keep them too low.  
That these Spirits are full of sulphureous oily Matter, is farther manifest, by exposing the Brains of any Animal to the Air; because they presently grow rancid and fetid.  
It appearing then, that the Animal Spirits are an oily mucilaginous Substance, abounding with the most volatile Salts and Sulphurs of the Blood; and that they are in a continual Circulation from the Brain and spinal Marrow through the Branches of the Nerves; and that being forcibly laid down in the Glands, there meet with the Arterial Blood▪ I shall next endeavour to show, how the Heat of the Blood is carried on and continued; which, I conceive, to be after this Manner.  
These oily Salino-Sulphureous Spirits, being violently driven 
The Reason of the Heat of the Blood explained.  through the Nerves, meet with the Arterial Blood in the Glandules; and these two Liquors being forcibly driven one against another, the Particles of them are intimately mixed together; by which means the Animal Spirits are, as if it were, ground and rubbed betwixt the fixed and more solid Particles of the Blood; whereby they are minutely dissolved, and being put into a swift intestine Motion, they endavour powerfully to expand themselves, and to fly away; but being held in, and reverberated, by those grosser Particles; their Motion is by that means inverted, and that Force, which, if they had but Liberty, would be lost in a further Expansion, being inverted and driven forcibly upon the other Particles, they mutually increase and promote one another's Motion; by which Motion the Blood, when it affects our Sensory, causes us to perceive Heat.  
In carrying on of which, it is to be observed, that the Animal 
How its Heat is promoted.  Spirits being thus accidentally expanded, and put into Motion, by the grosser Parts of the Blood, and being thus held in, and struck back, by them; does not only by that Means fly back and increase each others Motion▪ but also hurry the grosser Particles of the Blood along with them, and so increase their Motion, and by striking against them, and knoking them together, break them, as if it were into smaller Parts, and consequently ratify and expand Them also.  
It is further to be observed, that as these Spirits 
The Heat of the Blood varies according to the different Quantities of them.  are more or less in quantity, so (the gross Parts of the Blood, grinding them together and putting them in Motion,) they more powerfully, or less vigorously expand, and moving accordingly, digest and rarify the Mass of Blood to a higher or lower Degree; and consequently, put the Parts of it into a stronger or weaker Motion.  
We may further take Notice also, that the sharper the Particles 
It varies also according to the sharpness of those Humours that put the Animal Spirits into Motion.  of the Blood are, so they corrode and grind the Spirits into Parts, with greater Violence, and consequently sharpen their Motion.  
Again, when the Mass of Blood is very full of, and plentifully 
The volatile Salts and Sulphurs in the Mass of Blood make it more apt to be fermented.  abounds with, volatile Salts & Sulphur, the Particles of it, are with less difficulty put into Motion by the Spirits; and joining with them, increase their Motion; and, on the contrary, when the Mass of Blood is more dull and phlegmatic, it neither so powerfully grinds the Animal Spirits, nor is so easily put into Motion itself.  
Furthermore, The Animal Spirits do not only according to 
Which is more or less promoted according to the different Degrees of the Activity of the Spirits.  their different Quantities, differently exagitate the Mass of Blood; but also, according to their different Degrees of Activity; whence the more volatile and stronger the Spirits are, the more conspicuous are their Effects.  
Lastly, we may take Notice, that neither the Animal Spirits, 
Neither the Animal Spirits nor Arterial Blood are wholly Active or Passive.  nor the Mass of Blood, are altogether Active or Passive, in producing these Effects; but mutually both of them, and by Turns.  
Having premised this short Account of the Heat of the Blood, without any manner of Proof, to the end, that we might have a more clear and entire View how it was caused; without the Interruptions it would have made, to prove every Paragraph as I proposed it; I shall now proceed to a Proof of what I have proposed collectively, for the Material, Formal and Efficient Causes of it.  
And First, That the Animal Spirits and Arterial Blood are both forcibly laid down in the Glandules; I have given sufficient Reasons to evince, in my Treatise of Muscular Motion, and have given further Proof of it here.  
To prove then, that the Heat of the Blood does proceed 
That the Heat of the Blood proceeds from Fermentation proved.  from that Fermentation, it being necessary to explain the mechanical Motion of the Parts of those Liquors, that work mutually one upon another; I shall in the next Place show, that the Heat of the Blood is caused by such a mechanical Motion of Parts, as I have before mentioned.  
That the Animal Spirits than are forcibly driven against the Arterial Blood, is so self evident, that it needs no Proof; and if so, it must needs follow that the Particles of the one will be intimately mixed with the other; and it is undeniably True, that the Animal Spirits will by that means, be ground and rubbed betwixt the Particles of the Blood, which are in Motion, and amongst which, they are mixed; and the Animal Spirits, being of an oily Salino-Sulphureous Nature will consequently be expanded and rarified, and put by that means into a swifter degree of Motion, is evident; whether we consider the Effects, that solid or liquid Substances have on one another, when in Motion; for Amber, by a violent Attrition of its Parts against a woollen Cloth, feels hot; the Sulphureous fat Effluviums being by that Attrition increased, and caused to fly out in greater Quantities. It is evident also, by striking of a piece of Flint against Steel, that the sulphureous Particles of the Flint, being, as if it were disyoked from the Embraces of the more firm and solid Particles of the Stone, and being rubbed and ground betwixt them are put into a violent Motion; which causes them so much to rarify and expand, that whenever they affect our Sensory, they cause that Sensation we call Heat; which is accordingly violent, as their degrees of Motion are more or less intense; and so Amber, by a mild Attrition is moderately warm, and by a violenter, more sensible.  
Again, It is observable in the turning of any large and 
That Heat proceeds from Attrition further proved.  weighty Wheel, where the extraordinary Weight makes such a forcible Pressure of those Parts that lie about the Axletree, that by strong and frequent Attritions of the Parts together, the crude Sulphur, which is fettered up in the Substance of the Wood, is by degrees loosened and dissolved, and being put into Motion is rarified and expanded; which being still ground betwixt the solider Parts of the Wood, its Parts are yet put into so strong a Motion, that they break and dissolve that solid Substance, and by creating a Flame consume and burn it.  
In like manner, the Particles of Fire being applied to Gunpowder, by dissolving and grinding of its Parts in Pieces, and putting them into a violent Motion, cause them to expand and explode.  
But not only solid Body's cause Heat, by 
Not only solid Bodies but also Liquids grow hot by an Attrition of their Particles.  grinding of volatile sulphureous Particles betwixt them, and so by putting them into Motion; but also the Patticles of Liquids', by grinding one upon another, put themselves into so violent a Motion, as not only to cause Heat; but sometimes so high a degree of it, as actual Flame; as, when Spirit of Wine and Oil of Turpentine are mixed together: And that Heat proceeds from an Attrition of sulphureous Particles, and their violent Motion; I have not only brought Instances enough to make it appear, but have sufficiently proved it before in my Answer to Dr. Willis's Opinion.  
And now, since not only Solid, but also Liquid, Bodies grow hot, by an Attrition of their more volatile and sulphureous Particles, betwixt the more gross ones, and since there appears from what I have before said, but one way, by which all Bodies grow hot; we must needs conclude, that the volatile salino-sulphureous Particles of the Spirits grow hot, by being ground betwixt the grosser Particles of Arterial Blood; and that those, by putting the whole Mass into a more violent Agitation, cause the Heat of the Blood.  
But some will perhaps say, that in all those Phaenomena, I have mentioned, these grosser Parts of Matter, which grind upon the sulphureous Particles, are put into Motion by something else: But they do not perceive, how the grosser Parts of the Blood are put into Motion first.  
To which I answer, that the Particles of the 
The Particles of 〈◊〉 of these Humours are first put into Motion by Circulation.  Mass of Blood, are put into Motion by that force, which is always inseparably joined with Circulation; so that in a Man's Body, as there is a continual Circulation of Humours; so there is of Causes; for the Fermentation, in the musculous Glands, is raised by the Mass of Blood, grinding the Animal Spirits betwixt the Parts of it; in which Fermentation a subtle Liquor is prepared, which being forced into the Fibres of the Heart, cause it to contract; which Contraction forces the Blood, and consequently the Nervous Juice, through their distinct Vessels; and so causes them again to meet, and ferment a second time, in the Glandules; and as Circulation is preserved and carried on by the subtle Liquor, which is continually prepared in this Fermentation, so the Particles of the Blood are mixed with the Spirits, and preserved in Motion by Circulation.  
Having thus showed, that the Heat of the Blood may as probably proceed from Attrition, as Heat in any other Bodies; since Heat is nothing else, in respect of that which causes the Sensation, than a quick intestine Motion of Parts, and since those can be put into Motion no other way but by Attrition; I should in the next Place prove, that the Particles of refined and rarified Matter always expand and endeavour 
That the Particles of refined and rarified Matter, are by an Inversion of their Motion put into a higher degree of it proved.  to fly away but, being reverberated by the Opposition of those gross ones, with which they swim, their Motion is inverted, and by that means much increased. But it is so evidently True, that it needs not; for we always observe, that where any two Bodies meet together, and strike against one another, that which is less yields to that which is most solid, and makes the strongest Opposition; this is manifest in Flame itself, as also in the Expansion of Gunpowder; for if a Gun be shot against a Wall, the Flame of the expanded Gunpowder striking against it, presently flies back again, and, by mixing with that, which immediately follows it, increaseth the force of it; and for this Reason, a Gun which is charged with a greater weight of Shot, more forcibly recoils; the Powder not finding free Liberty to expand, but flying backward with a greater Force: It is also further evident, from the Reason which I have given, why Nitre is beneficial-in continuing Flame, and making it more vigorous.  
The gross Parts of the Blood, having thus put 
How the Animal Spirits rarify the Blood.  the Animal Spirits into a swift Motion, and by inverting them in their Motion, having caused them to increase one another's Motion; the Spirits at last, set upon the Mass of Blood, and by breaking and dissolving the Particles of it, rarify them and cause them to expand also; so the Rays of the Sun, being in a swift Motion, and gathered into a Point by a burning Glass, grow more vigorous, so as to dissolve and burn even solid Bodies; and after the like manner Flame, by the force of it, subtilizeth and attenuates the Sulphureous Parts of its Fuel, neither does it only rarify and expand the Sulphureous Matter of its Fuel, but also carries violently the Ashes of the calcined Matter along with it, where it may be observed, that as the Particles of Animal Spirits are not in so strong a Motion, as those of Fire, so the Particles of the Blood are moved with a more easy force, than Ashes which are far more Solid.  
But for a further Proof, that the Mass of Blood grows hot, in a 
That the Animal Spirits according to their different quantities differently exagitate the Mass of Blood proved.  Natural state, by the Methods and Ways, which I have endeavoured to explain; I shall in the next place prove, that the Animal Spirits, being put into Motion, according to their different Quantities, differently expand themselves, and exagitate the Mass of Blood, and put its Parts in a more violent or weaker Motion, and consequently increase or diminish the Heat of it.  
And this is easily manifest, if we do but observe, that young 
By the observation of People of different Ages.  & healthful People, whose Nerves as well as the Fountains from whence they spring, are full of, and abound with, Spirits, are always of a more brisk and vigorous Heat then People of a declining Age, whose Nerves are less plentifully stocked with them.  
But it is not only observable in People of different 
As also by different Constitutions.  Ages, but also in different Constitutions, that as the Pabulum of the Animal Spirits is more plentiful and yields a more constant and large Supply; so the Heat of the Blood is more powerful and intense; as in cold and Phlegmatic Constitutions, where the Mass of Blood abounds, with dull Phlegmatic Humours, or Acid and Austere Juices, of too close and compact Texture, and a large Supply of Spirits is denied; the Blood is not of so hot a Temper, as in Choleric Constitutions; whence it evidently appears, that the Heat of the Blood depends on the Vigour of the Animal Spirits; for if when the Vessels are filled with Spirits and plentifully supply the Glands, that Fermentation is raised higher, and by that means the Heat of the Blood is accordingly increased, it is a most certain Conclusion, that the Heat of the Blood depends upon the Effects, that the Animal Spirits have in that Fermentation.  
Which is further confirmed, by the common 
And the Practical Part of Physic.  and constant Practice of all Physicians; for when the Natural Heat, as some call it, is languid and weak, and almost extinguished; they give such Medicines, as increase the Heat of the Blood, by renewing the Vigour of the Spirits; whence to People that are almost a dying, their Spirits being dulled or exhausted, nothing is more usual then to give them Spirits of Hartshorn 
How Spirit of Hartshorn raises the Pulse.  or of Armonick-salt, or some other Saline or Sulphureous Spirits, which presently joining with those in the Nerves, increase the Fermentation in the Glands, and by that means put the Mass of Blood into a more swift Exagitation; and by raising the Fermentation, not only renew Circulation, but the Heat of the Blood.  
On the contrary, when the Animal Spirits are too high and 
That the Spirits according to their different Degrees of Activity variously exagitate the Mass of Blood.  volatile, or too much in Quantity, they raise this Fermentation so high, that the Blood is presently put into a Preternatural Heat; from whence proceeds that Preternatural Heat in Fevers: And the way, that Physicians either do, or can take, in such Cases is, either to take down the Animal Spirits, by withdrawing Part of their Pabulum, and by Acids given internally, to harden the Texture of the Blood, and make it less subject to grow too Hot by Fermentation; or otherwise by cooling and fixing those predominant Spirits, and evacuating other accessary Causes, by proper Excretories and Emuctories of the Body.  
Lastly, That the more any rarified Sulphureous Body is expanded betwixt the more gross and solid Parts of Matter, those gross ones are put into a stronger Motion, is evident from a Musket charged with Shot, which, with a small quantity of expanded Matter, will scarce be moved; but by a greater quantity of exploded Matter, are put into so swift a Motion, that they fly forcibly a considerable way.  
Having thus far proved, what I proposed, to be reasonable 
The sharper the Particles of Blood are the more they corrode the Spirits and put them into Motion.  and likely, and nothing but what is consonant to the Practice of most Rational Physicians; I proceed to show, that the sharper the Particles of the Blood are, they corrode and grind the Spirits into small and minute Particles with a great deal more Violence, and by that means cause them to expand more vigorously, and by putting them into a strong Motion, cause a higher Degree of Heat.  
This is sufficiently proved by the Preternatural Effects, that 
The Keason of flushing heats, in the Scurvy.  Scorbutic Salts cause in some People; for when the Mass of Blood is impregnated with Acid Acrid Humours, these, meeting with the Spirits, cause Preter natural flushing Heats; which appear in several Parts of the Body, and sometimes in the whole; which are so violent, that those, that are affected with them, complain; that they feel themselves as Hot, as if they were in a Stew or a Bagnio.  
That this Preternatural Heat proceeds from Corrosive Salt Humours, fermenting with the Spirits, is very manifest; since these Symptoms are only curred, by such Medicines as correct the Acidity and Acrimony of the Blood, viz. When it most partakes of Acrimony by sweet diaphoretic Decoctions, or some sort of Acids, which dull and take off their corroding Edges, or when they are more Acid, by volatile Salts that carry them off by Sweat or Urine; or by Acid Absorbers, which by correcting the Acidities of the Pancreatic Juice, leave the Ferment of the Liver more predominant; and the bitter Choler, being by that means bred a great deal more plentifully, digests and carries off those crude Humours, which by the aforesaid means being made thin enough, to go off by Urinal and insensible Transpiration, are dispersed and carried off those ways; and the Mass of Blood, being cleansed of those sharp Humours, is reduced to a healthful State.  
If then by considering the Nature of those Medicines, that 
Proved by comparing the Nature of the Medicines that oppose it and correct it.  correct vicious Humours, we may learn to know what is the Nature of those Humours; we must conclude, that whatever is corrected by Medicines directly contrary to Acrimony, the nature of that Humour is Acrid; and when, by the Use of volatile Salts, the distempered Humours of our Bodies, are attenuated, and disposed to Evacuation, and at the same time we know, that volatile Salts by volatizing and preparing the superfluous fixed Acid Acrid Humours of the Mass of Blood, dispose them to be carried off, we have all the Reason imaginable to conclude, that when we find those Medicines carry off such Symptoms, that they are caused by such Humours,  
And that these flushing Heats in the Scurvy, proceed from Acrid Acid Humours is plain, because all Salt Meat, that abounds with Acids; and all sharp Acrid Bear, that hath an Acrid Fluid Salt predominant in it, as also Vinegar and such like, make those Symptoms more violent.  
If then, both from the Method of Cure, and the Cause itself augmented by such Sorts of Juices, we gather they proceed from sharp Acrid Acid Humours, we may be certain, that those Symptoms are caused by such Humours grinding and corroding the Animal Spirits, and that by putting them into a Preternatural Motion, they are the Causes of such Sensations.  
And that those Sensations only proceed from thence, we may easily conceive; for since, as long as those Humours circulate with the Mass of Blood, and forcibly meet with the Animal Spirits, they can only affect them, by moving amongst them; they must needs put them into a more swift Motion, and an unusual Expansion, by corroding and grinding them more powerfully, betwixt their Particles, which is evident from the cause of those flushing Heats I just now mentioned, and from the Reason I have before given of Heat.  
But that the sharper the Mass of Blood is, the more the Animal Spirits are ground and expanded betwixt the Particles of it, is evident from Reason itself; for it being proved before, that the Heat of the Blood proceeds from a swift intestine Motion of the Particles of the Blood and Spirits, caused by Attrition; nothing is more Reasonable than that the more solid the Mass of Blood is, the stronger the Attrition is, and consequently the Motion of Particles, which upon our sensory cause heat, must be more violent; and as in striking of a Flint with a piece of Steel, the more firm and hard the Steel is, the more powerfully it loosneth the Texture of the Flint, and strongly expanding its Sulphureous Particles, puts them into that Motion, which constitutes Flame; so by Parity of Reason, we may expect, that the Particles of Blood will cause the Sulphureous volatile Parts of the Spirits, to expand more powerfully, the more solid and compact they are.  
And that the Texture and Constitution of Saline Humours, is more Solid, and their Parts more Corroding, than of a sweet Balsamic Liquor, I think, none can deny, who compares Vinegar and Spirit of Vitriol with Tincture of Sulphur, and although in Fevers, where the Blood abounds with too much exalted Sulphur, Spirit of Vitriol and other Acids, cool the Blood, by fixing the Spirits, and Coagulating the Sulphur; yet when the Blood is impregnated with Scorbutic Salts, Acidity joining with Acrimony, causes Heat, by corroding the Spirits, when they want a Mixture of crude Sulphur, to dull their Edges, of which it would be no difficulty to convince, those that are considerably troubled with scorbutic Symptoms.  
But furthermore, I shall prove that the Mass of Blood, the more 
That as the Blood as more or less Volatile, its Parts are put more or less easily into Motion proved.  it abounds with volatile Salts and Sulphurs, is more easily put into a violent Heat; and that its Particles being more easily put into Motion, readily join with the Animal Spirits, and increase theirs; and that on the contrary, the more dull and phlegmatic any Body is, the less apt are its Particles to be put in Motion.  
And as it is commonly taken notice of, in all Bodies, so it is not less observable in the Mass of Blood; for we always find, that the least quantity of any volatile Liquor inflames the Blood of those, that are of a tender and open Constitution, much sooner than phlegmatic and melancholy Peoples, and as the former is evident in those that are subject to Fevers; so the latter is not less remarkable in those of cold Constitutions; for to increase the natural Heat of their Blood, when it is too much depressed, it is not only necessary to take away some of those crude Humours, which stuff up the Vessels, and too much depress the Spirits; but also, by volatile and spirituous Medicines, to increase the Spirits; and at the same time, to exalt and spiritualise the Blood, by absorbing Acids, and exalting the volitile and subtle Parts, to render them predominant.  
Moreover, that the Animal Spirits do not only according 
And that it is differently promoted according to teir different Degrees of Activity of the Spirits.  to their different Quantities, and the different State of the Blood, variously exagitate and increase the Heat of it; but also, according to their different Degrees of Activity and Strength is put beyond Dispute by the different Effects that Spirit of Wine, or Aqua-mirabilis, hath upon us from Sack which any one that does but taste must soon acknowledge.  
It remains in the next Place, that I should 
How far the Blood and Spirits are Active or Passive.  show, how far the Animal Spirits are Active, and how far Passive, in causing these Effects, as well as the Blood, which evidently appears from what I have already said: For when the Spirits and Blood are forcibly driven together, than they seem to be mutually Active and Passive, the Spirits being forced betwixt the Particles of the Blood, and vice versâ; but the Animal Spirits being ground and rarified betwixt the Particles of the Blood, are so far Passive; but being by that means expanded, by a powerful expansive and elastic Motion exagitate the Mass of Blood, and by that means are active; so that throughout the whole Process it appears, that neither of them singly are altogether Active or Passive, but both, mutually and by turns.  
From what I have said it appearing, how the 
How the Heat of the Blood is continued.  Heat of the Blood is caused; I shall in the next Place proceed to show, how it is continued; which will be sufficiently evident, if we do but consider, that the Animal Humours are in a constant and continual Circulation; for since all the Blood in a Man's Body, is allowed to circulate through the Heart, several times in an hour; and that the Blood from thence is continually forced and dispersed through the Parts of the Body, and so great a Quantity of Blood is at one Pulsation, laid down in the whole Habit of the Body, and ferments at the same time, with the Animal Spirits; there must needs be raised in the Blood, a considerable Heat, or in other Words, the Parts of the Blood and Spirits must of necessity be put into, so swift and intense a Degree of Motion, as to enable them to produce an extraordinary Heat, when they strike upon our Sensory. The whole Mass then circulating thus, through the Extremities of the Vessels, there is not only a great deal of Blood fermented, every Pulsation; but also by a continual Succession of Pulsations, the Blood, being forced into a Fermentation, by the expansive Motion of the Spirits, is by that Means preserved in a constant and continual Heat.  
But I know, here will some Difficulties offer themselves, and 
Some Objections considered and answered.  perhaps some may doubt, whether the Blood only ferments in the Extremities of the Vessels, and not in the Vessels themselves; and since it is hot in the Arteries, before it be laid down in the Glands, as well as in the Veins after Fermentation; they may think it reasonable to conclude, that wherever it ferments, there it's Fermentation is caused; and because there is a great deal of Blood betwixt their Extremities, and the larger Vessels; they may think, that the Fermentation in the Extremities, cannot be the Cause of the Heat of the Blood in the larger Vessels; it being an old Maxim, that, tolle Causam tollitur Effectus; which is as much as to say, the Cause immediateley goes before the Effect.  
Another Doubt which perhaps may arise will be, that since I affirm, that there is such a mutual Action and Passion in the Attrition of these Humours, in order to a Fermentation; whether Fermentation can be carried on, in such a manner, in so short a Time, as the quick Circulation, and consequently Protrusion of the Blood from the Extremities of the Vessels admits?  
As to the First, To wit, whether the Fermentation of the 
The first Objection answered, viz. whether the Heat of the Blood be chiefly caused in the Extremities of the Vessels.  Blood be caused in the Extremities of the Vessels, or the large ones; I affirm, that it is chiefly and originally caused in the Extremities of the Vessels, just where the Nerves and Arteries meet, and where their contents are first mixed together; and that the Fermentation in the larger Vessels is but a Continuation of the Effects of the same Original Cause; and as when Water is heated over a Fire, that Part of the Water, which is at the top of the Vessel that contains it, is as truly said to receive its Heat from the Fire, as that in the Bottom, so that Blood which is in the Body of the Vena Cava is as really put into a Fermentation, by a Mixture of Spirits, as that in the Extremities; for the Animal Spirits, being mixed with the Arterial Blood in the Glands, and ground betwixt their Particles, and being by that means put into an elastic and expansive Motion, they powerfully ferment and exagitate the whole Mass. This Blood then, so fermented, is thrust out of the Glands, by a Succession of Matter forced in the next Pulsation, and so forwards, by the next, successively, till it be driven into the Vena Cava.  
Now as soon as it is thrust out of the Glands, those Spirits which did so powerfully expand before, and the remaining Part of them, which are not mixed with that subtle Liquor, that circulates through the Fibres; being yet further corroded and exagitated by Pulsation, still continue to expand themselves, and by that means, keep the Blood in a continual Heat.  
And the Animal Spirits being yet more expanded, do not only continue, but in a great Measure increase the Heat of it.  
But these Spirits, being frequently opposed 
The Reason why the Heat of the Blood in time decays.  in their Expansion, by striking against the Blood, loose in a short time a great deal of their Vigour, the Particles that before grund the Animal Spirits betwixt them, obstructing their Motion; and the Animal Spirits, not being able any longer to keep them in a just Motion, sufficient to continue the Heat, which is Natural to human Blood; they are, as if it were, linked and fettered up, betwixt those grosser Parts, & are incorporated into one Substance with them, which is the Reason, that the Blood by frequent Circulations, is ripened and digested; and for this Reason the flesh of a Hare grows tenderer, by being coursed along time.  
The Blood, being thus impregnated with Animal Spirits, and by that means wanting Spirits in a free and strong Motion, would by degrees grow cold; but the Intervals of time, while the Blood moves from the Extremities of the Vessels to the Heart, and from the Heart to the Extremities of the Vessels again, being very short; before there can be any sensible or considerable Decay of it, the Blood is anew fermented in the Glands; and so by a continual Circulation, the Heat of the Blood is preserved; and because by this time the Animal Spirits mixed in the first Fermentation with the Blood, are almost spent, being incorporated with it; and because Part of it is continually separated in the Brain, it meets a second time with new Supplies, and also by repeated Fermentations is more impregnated with Spirits as well as digested and ripened to a higher Degree of Maturity.  
Thus I have given an Account, how the Heat of the Blood is carried on in the Vessels, that it might more clearly appear, how the Original Cause of Heat is principally in the Glands.  
That the Animal Spirits are put into an elastic 
And that Reason proved.  Motion in the Glands, I have before proved, by the grosser Particles of the Blood; and that the Blood, so fermented, is successively cast out into the Veins, is plain enough, to any one that does but understand Circulation; to prove then, that the Blood, being thrust out of the Glands, does by a further Expansion of those Spirits, for a while increase the Fermentation; and that, when the Vigour of the Spirits is spent, it will gradually decay; we need but take Notice, how Fermentation is begun and carried on in other Liquors; for when oil of Vitriol and Spirit of Armoniac Salt are mixed together, the Parts of each being in some measure mixed, and put into Motion, by dropping the one into the other, they presently begin to ferment; which fermentation is gradually exalted, till by a frequent Collision and Attrition, the most Fermentative Parts fly away, or their Vigour is lost; and then Fermentation gradually decreaseth; and in like manner, all other Liquors, that for a time ferment with a sensible Heat.  
But if possible, it will further appear, that the Original & Principal Cause of Fermentation is in the Glands, if we do but consider, how Fermentation is carried on in a dying Body.  
For in a Body that is about to die, the Vigour as well as 
How Fermentation is carried on in a dying Body, and the Reason why it ceaseth when it is quite dead.  Quantity of Animal Spirits, being diminished, and those too, being less vigorously ground, betwixt the Parts of the Arterial Blood, expand so weakly, that they scarce agitate the Mass of Blood, sufficiently to preserve its Heat, but as soon as the Blood and Spirits cease to circulate, the Heat of the Blood presently grows milder, till at last it is quite extinguished.  
Now, if when the Fermentation is weak, the Heat of the Blood is more remiss and depressed; and when Circulation is stopped, it consequently ceaseth; it must needs follow, that the Animal Spirits are the Cause of that Fermentation; and that it is promoted by driving those two Liquors forcibly together; and that the Fermentation is chiefly caused in the Glands, is plain, because when the Spirits and Blood cease to be driven together, and there fermented, the Heat of the Blood decreaseth; and that it is not in the Vessels is evident, because after Circulation is stopped, it presently declines, whereas if it were caused in the Vessels, it would continue after Death as well as before; since, it than hath the same Matter, though it wants Circulation and a forcible Mixture; and what I have showed to be the Consequences of it.  
I shall only bring one Argument more to prove, that the 
Another Argument to prove, that the Heat of the Blood depends on, and is caused by, Attrition.  Heat of the Blood depends upon the Attrition and Fermentation in the Glandules; which may be inferred from this common Observation, that the Heat of the Blood is increased by all violent Motion: For upon all violent Motion, a larger Quantity of Animal Spirits, being sent to the Parts to be moved, in order to prepare a greater Quantity of subtle Liquor, to distend and dilate the Fibres; the Fermentation is not only raised higher in the Glandules, but the Motion of the Heart, being thus accidentally increased, quickens the Circulation of the Blood so much, that before the vigorous Motion of its Parts, which was raised in the precedent Fermentation is spent; it is again renewed.  
But the Circulation of the Blood is not only quickened by the Contractions of the Heart; but also by the frequently repeated Contractions of the Muscles: For the Heart contracting sends it out into the musculous Parts; and again, those Muscles drive it sooner and more forcibly back upon the Heart; from whence it appears, that both the Heat of the Blood is increased, by being often fermented in those Glandules, and consequently, that it depends on the Mixture and Fermentation of the Animal Spirits, and Arterial Blood.  
From hence it is manifest, how far Circulation is beneficial, 
Fermentation & Circulation mutually depend on one another.  in carrying on the Heat of the Blood; and if we consider the Reason, which I have given of Muscular Motion; we shall see, that as Fermentation depends on Muscular Motion, so Muscular Motion depends on Fermentation; so that, as I said before, there is a continual Chain and Circulation of Causes as well as Humours in a Man's Body.  
To proceed therefore to the second Objection, I supposed some 
The second Objection answered, viz. That Fermentation may be performed in so short a time as the Circulation of the Blood admits.  might raise, viz. Whether this Fermentation can be carried on, in so short a time as a continual and quick Circulation will admit: This does not only appear Possible from evident Matter of Fact; but also if we consider, that in much less Time than what is allowed for Fermentation in the Glandules, if a Spark of Fire be put to Gunpowder, it immediately puts its Parts into an Explosion; and that the Blood not only ferments in so short a time, but that it may prepare that subtle Matter, which circulates through the Muscular Fibres, we may, with a great deal of Reason believe, if we do but take notice; that warm Milk, if it be but forcibly milked into Vinegar, it presently is separated into two Parts▪ viz. Curd and Whey. If then by mixing these two Liquors, they cause so great a Change on one another; I cannot conceive any Reason, why Part of the Animal Spirits, fermenting with the Blood, may not as soon be mixed with some Part of the rarified Succus Nutritius, and forced forward into the Fibres.  
But from what I have said, it appearing, that 
The Blood is more powerfully fermented in the substance of the Heart than in any proportionable Part of the Body besides.  the Heat of the Blood Is caused in the Glandules by Fermentation; and how it is continued in the Musculous Parts; I shall in the next Place consider, in what Parts it is most vigorously fermented; which will appear only by considering where the Spirits are most plentifully laid down; for if Fermentation depends on, and is chiefly caused by, the Animal Spirits, as I have shown; then it must needs follow, that the Heat of the Blood is most promoted in those Parts, where Animal Spirits are most predominant. And having proved that in order to prepare that subtle Liquor, which causes Contractions of the Muscles, a greater Quantity of Animal Spirits is sent there, it will follow▪ that the Blood grows hottest, being most vigorously fermented in those Parts that are in Motion; and than it will follow, that the Heart being a Part▪ in constant Motion, and that Motion proceeding from a successive Supply of Spirits, the Blood must needs acquire the most considerable Degree of Heat, in the Substance of it.  
But although I say that the Blood, for these Reasons, acquires a greater Heat in the Heart, then in any other Part; I would not be thought to mean, that it grows hot so in the Ventricles of the Heart: For the Use of the Heart, being only to force the Blood out of it, and by dilating to receive it in again, for another Expulsion, and so to keep it in Circulation, it can get no great Heat there; since it wants Spirits to ferment with it; but I only mean, that considering the Substance and Dimensions of the Muscular Part of the Heart, and that small Portion of Blood contained in the Arteries dispersed through it, that that Blood acquires a greater Heat than that Quantity of Blood does in another Part, that is not in Motion.  
But there being, besides Muscular Parts, many 
Fermentation is not only promoted in the Muscular Parts, but also in the internal Bowels.  considerable Internal Parts, in a Man's Body, in which a great Number of Blood Vessels are distributed, it perhaps will be asked, whether Fermentation be carried on in these too? To which I answer, that Animal Spirits and Arterial Blood, being either mediately or immediately, laid down in them all, there must needs be a Fermentation; which being proved, upon such Premises, by what I have already said, there is no need I should repeat it again.  
But since Anatomists have not as yet discovered Nerves to be distributed through the Liver, although Blood be communicated to it, by the Vena Porta, which supplies the Office of an Artery to the Liver, it perhaps may be doubted, whether Fermentation is carried on after the same Manner there; and consequently, whether the Office of the Liver be performed by Fermentation▪ or not; that it is, I shall show hereafter, and also how the Glands in that Part, are supplied with Spirits.  
From what I have hitherto said, it appears, what are necessary to continue the Heat of the Blood; and also, what is the Cause of it.  
For First, It is necessary▪ that the Animal Spirits and Blood 
Three things requisite to continue the Heat of the Blood.  should be in a continual Circulation, that being forcibly driven together▪ their Particles might be intimarely mixed one with another. And▪  
Secondly, That the Animal Spirits should be ground betwixt the Parts of the Mass of Blood, that they may be thereby rarified and expanded, and their Particles put into a swift Motion. And,  
Thirdly, It is requisite, that the Animal Spirits, should be of an oily Sulphureous volatile Temper; that being more easily rarified and expanded, they may be presently put into Motion, and cause the whole Mass to ferment.  
Having then explained the Heat of the Blood, and proved it agreeable to these Circumstances; I am for the Reasons, before mentioned, persuaded to believe, that the Heat of the Blood thus proceeds from Fermentation.   

OF THE USE OF THE LUNGS.  
FOR as much as appears from the Books of several Learned Men; the Use of the Lungs hath not been hitherto indisputable, no more than the Use of other Parts: For as there are several Opinions concerning others, so there are no less Disputes about this; whilst some would have it to be, only a sort of Fan to cool and air the Blood: And others, that it was designed to kindle and put the Blood into a Flame, by continually supplying it with Nitre.  
Whether of these is most probable, may easily be gathered, by considering the Effects that Air hath upon us: For since the Air is continually drawn in, and thrust out again, in Respiration, any one that does but know, what Effects it hath upon himself, cannot be ignorant of the Use of the Lungs, in respect of the Heat of the Blood, evidently finding himself cooled by it; and if any one, that, by daily Experience, finds that it cools him, can conclude thence, that it kindles and promotes the Heat of the Blood, he may be pleased with his Notion, but no Body else will with such as contradict self-evident Truth.  
But that it may appear, how far the Lungs may be said to be a Fan or Ventilabrum to the Blood; and whether the Air promotes the Heat of it or not; I shall take this Method; First, consider the Use of the Lungs with respect to the Rational Soul; and Secondly, with respect to the Body.  
The Use of the Lungs, with a more immediate Respect to 
The Use of the Lungs in Respect of the Soul.  the Soul, appears to be nothing else, but as a large capacious Vessel, endued with a Cavity, to contain a great Quantity of Air: so that it performs the same Office in the Body, as a Pair of Bellows to Organs: For as in Organs, the Bellows supply Pipes of different sizes with Air, and that being driven through them, produceth different Sounds; so the Lungs dilated and extended by the Motion of the Thorax, and being full of Air, contract; and accordingly as the Pharinx and its Parts are differently modulated; so the Air forcibly driven through them, causes different Voices.  
In which Action, the Lungs seem chiefly to be an Organ 
Is to express all its Conceptions and Reasoning.  made, on purpose, to be serviceable to the rational Soul, to express all its Conceptions and Reasons; and to form Voices or Articulate Sounds, to signify those Notions contained in, and apprehended by, it; that those Things, which must otherwise remain in silence, might be communicated, to promote a mutual Commerce and Conversation amongst Men.  
But here some may ask, if it be chiefly designed to form articulate Sounds, as it really seems to be, why do we take our Breath continually? Or why are our Spirits constantly consumed, by keeping the Part in a perpetual Motion? Since sometimes we use it very little for a long time, to express any Thing by; one half of our Lives, and the larger too, being passed away in Silence.  
To which it may be answered, that it is necessary, the Lungs 
Why the Lungs ought to be in a continual Motion is because.  should be in a constant, and continual Motion, that they might be kept in readiness, to express what and whenever, we have a Mind.  
Another Reason is, that since the Cavities of the Lungs, are 
It carries off that Superfluous Moisture that supplies them.  constantly supplied, with a serous Lympha, to moisten their Coats, and to moderate the Acrimony of the Air, it is necessary there should be a constant and continual Respiration, to carry that serous Lympha off; which would otherwise stuff up the Bladders of the Lungs, that they would be incapable of receiving Air; but every Inspiration, that superfluous Moisture being mixed and incorporated with the Air, is by every Expiration carried off; which prevents those ill Consequences, which would otherwise follow.  
Another Reason why the Lungs ought to be always in 
And that their voluntary Motion might less Preternaturally affect our Bodies.  Motion, is, lest they should Preter-naturally affect and disturb the Constitution of our Bodies, when put in Motion, as we have a mind to express ourselves; for if the Lungs were at other times quiet and still, our Bodies would be put into such Disorder, by violent and sudden Motions, that we should be as unfit to discourse of any thing, as one that's in a Fit of the Epilepsy; 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 
What Effects it causes when too thick, and also why thick foggy Air is troublesome to some People.  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 increases; 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 Humour, 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 its own Moisture, is incapable of carrying off the Moisture, supplied 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 Use of the Lungs in respect of the Body.  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 
Seems to be to perform the Office of another Heart.  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 its 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 its 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 itself, 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 than can be supplied 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 
By helping the Blood to force violently enough into the Cavities to distend them against the next Contraction.  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 its Vessels, but even any Liquor, being forced through Pipes, whose Cavities increase 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 increased 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 weakened by so long a Course in the Veins is further evinced; if a Vein and Artery be opened 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 
How stopping the Breath of an Animal kills it.  assist the Dilation of the Heart; as I have showed 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 its 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 thirst 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 
Why by permitting it to breath again the Circulation of the Blood is renewed.  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 its 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 renewed 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 renewed by reiterated Breathing.  
But though from hence it may appear, that 
How the Motion of the Heart is promoted in an Infant unborn.  the Motion of the Heart is promoted by the Assistance of the Lungs; yet it perhaps may be a Question, how this Defect is supplied in unborn Infants; and how their Blood circulates▪ since than their Lungs do not perform the Office of Respiration.  
To which I answer, that in an Infant before Birth, the Placenta supplies that Defect; for that additional Force which the Infant's 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 breathes, 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 show, 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 quickened 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 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 renew 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 
The Office of the Lungs is partly voluntary, partly involuntary.  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 carried 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 Humours 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 Humours 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 itself be mixed with it also, before I proceed to show how the Mass of Blood is affected by it, I shall endeavour to solve these two Questions. And,  
First, That the Air itself is no otherwise mixed with the Mass of Blood, but as I have showed, 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 guests 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 should, 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 than 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 subtle 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 conveyed into the Blood, is so plain from the Effects that are there caused by them, they must needs be conveyed 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 Humours, 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 altars 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 
What Effects the Air hath upon the Mass of Blood.  of the Air hath upon our Blood, and the Alterations we are sensible it produces, are either in respect of its Colour or Heat.  
That the Air altars the Colour of the Blood, 
In respect of its Colour.  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 show 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, 
Nitre depresses the Heat of the Blood.  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 subtle 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 Elastic, 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, except by hindering the fierce volatile Parts which ought to be dissipated, from flying away through the Pores of the Skin, which being increased thereby to too great a Quantity, exagitate the Mass of Blood too much,  
From hence it briefly, yet plainly, appears, that the Nitre of the Air altars the Colour of the Blood; and also serves to temper the Heat of it.  
I shall now consider, what Effects it hath upon the serous 
What effects Nitre hath upon the Serum of the Blood.  Lympha; and if we may but compare it to Milk which differs only from Chyle, by being less impregnated with Oil, it will be manifest, that it precipitates the Watery Parts of the Serum; which joining with the fixed Salts of the Blood, dispose them to be separated, and carried off by the Urinary Passages.  
This is so strongly proved, both by Non-Naturals and Medicine, that to deny it would be to contradict Reason, and plead Ignorance of those Things it is almost impossible for us not to take notice of; for if we sit by a Fire in a close warm Room, and drink a good Quantity of Beer, which is not very strong; it presently, if we go into the cold Air runs off by Urinal, besides nothing in Medicine, is a more known and common Diuretic, than Sal. Prunel. which is purified Nitre concentered and condensed; and it is no less observable in an Experimental Observation of the Famous Dr. Lower's who in his Book de Cord, takes notice, that as much Serum is precipitated in a short time after we rise from Bed, as in the whole night, when we are less affected with the ambient Air.  
How Beneficial Nitre is in Precipitating the Serum of the Blood, and what Advantages the Animal Oeconomy receives thereby, I shall not now inquire, yet how inconsiderable a Part of its Office soever it may seem, yet if it be duly weighed, it will appear very useful.  
From what I have said concerning the Alterations made on the Blood and it's Serum; I should now proceed to consider, how they influence each other; but since as much as is sufficient for our present Purpose, may be gathered from what hath gone before, it being plain that the cool Serum will help to temper the Heat of the Blood, and vice versa; I shall wave a further Notice of it here, and should rather show; That,  
The Lungs perform many more and considerable Offices in respect of each Part; But to explain them would not only be to treat of the Lungs, but the whole Body, and the Use of all the Parts; which being not my present Design, I shall omit giving an imperfect Account of them, because they are so interwoven mutually with one another, that they cannot truly be understood, without an Account of the whole.  
FINIS.