EVEN Philosophy in General is so Our Know­ledg 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 [Page 2] to have, but a slight and super­ficial Knowledg of it: For if that small Part we know, be compared with what we know not; all our Knowledg is but as an invisible Speck; those things to which it extends, being in­considerable, if compared with that vast and endless Mass of the Universe.

But although that Part of the Universe, which in some Measure Which is furnish­ed with Objects too copious for our Senses lyes within the Cope of our Senses, be small and inconsiderable, when com­pared with the vast Extent of the whole Creation; yet when we reflect on the vast Variety of Objects, contained within those narrow Dimensions; we [Page 3] find, and must needs acknow­ledg it very considerable; and superabundantly furnish'd with Matter for our Senses to work upon.

For, the Extension of our Know­ledg, as to those Of which at the best we have but an imperfect Know­ledg. Objects, is bound­ed by Limits not very spatious; & notwithstand­ing the Diligence and Industry of Learned Men, and the great Improvements, made in most Parts of Knowledg: The wi­sest Men, and the most profound Philosophers must of necessity own, that of those Things they know most, their Know­ledg is very imperfect. We know but in Part, and indeed so small a Part, that it chiefly seems to [Page 4] inform us, more sensibly of our Ignorance.

But so pleasant and desirable is Knowledg; and we find so much The Pursuit of Knowledg 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 Knowledg and Ignorance, which continually lyes in our way to discourage us.

And as we thirst after Know­ledg, with a de­sire to attain to Especially of that which is most Ad­vantagious. a more adequate and compleat Ap­prehension of it; so we most eagerly pursue those Parts of it, which we hope to understand [Page 5] 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 Epitomy of the Macrocosm, lyes much more with­in the narrow Cope of our Senses; since we can dive and search into all, and the inmost Recesses of it; and come nearer to those Springs and Fountains, upon which all the Effects, we per­ceive in it, depend; we have much more solid and firm Foun­dations to proceed upon, than in any other Parts of Philo­sophy whatsoever; and may [Page 6] much more reasonably hope for Certainty and Truth; besides the Pursuit of it, must needs be not only more Pleasant, but Advantagious.

And although in a Man's Bo­dy, some Things 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 shew 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 it's Cause. of the Blood is unfortunately one; but the Reason why it is so, is not [Page 7] that it is less apparent in it self, but rather the Inadvertency of those that searched into it: If possible such great Men, as have writ concerning it, may be guilty of so great a Fault, which (although otherwise no small one) is much more excu­sable in those, whose more weighty Concerns take 'em of a deeper Enquiry.

Since then, so many learned Men, and those to whom Phy­sick is not least obliged, for considerable Improvements, have writ on this Subject; I think it not only Justice, but also Reasonable, I should shew upon what Grounds, and for what Reasons I have rejected their Opinions, before I take leave to propose my own.

[Page 8]It would be Both Antients and Moderns have differed as to the Cause of it. needless to spend time in Informing my Reader, that both Antient and Modern Writers have endea­voured to account for it; and it would be Information to but a few; since none that have made any considerable Progress in Physick, can be ignorant of it. I shall only as briefly as I can, mention the Opinions of the Antients, that it may better ap­pear to the more unlearned, wherein they are deficient; and then, I shall consider the most remarkable Opinions of the Moderns, that less competent Judges, and young Students in Physick, may spend less time in convincing themselves, how [Page 9] far they come short of explain­ing, the Reason of the Heat of the Blood.

Amongst the The Opinions of the Antients very Superficial and In­satisfactory. Ancients, who wanted those Im­provements in A­natomy, that have been made of late, to direct them in their Judgments; some fancied that it proceeded from a Calidum innatum, or innate Heat; which was fixed and rooted in all the Parts of a Man's Body, before his Birth; and that This con­tinued Heat, by communicating it self successively to the Nou­rishment of the Parts, as soon as it was received by them: Which indeed was so weak and superficial an Account of [Page 10] it, that it rather served to please the Unlearned, then to satisfie the Curious, and more Inquisi­tive. Others thought, that there was a sort of Flame lodg­ed in the Heart, which kindled the Blood as it passed through it. But Moderns having learnt by a further and a deeper Insight in­to Mens Bodies; that the for­mer of those was rather the Effect; than the Cause; and by frequent Dissections, that the Heart was altogether incapable of containing such a Flame, and also that that which they supposed to be the Pabulum of it, to be clotted Blood; they have, with sufficient Reason, rejected them both. Wherefore passing by these, I shall proceed to con­sider those Modern Opinions, [Page 11] 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 [Page 12] the Heat of the Blood, takes Notice; that there are three Modes or Sorts of Causes, by which Liquids grow Hot.

First, à culido ad moto, or by applying them to something that is Hot; as when Water boyls over the Fire. Secondly, when Saline Corrosives mu­tually act upon one another, or on sulphureous Bodies mixed with them, by an intense and powerful Agitation. Thirdly, when a Liquor abounding with much Spirit or Sulphur, takes Flame from some other Body. And in the next Paragraph, he says, that there are other ways of Calefaction; as Fermentation, Putrefaction, and Attrition; but the seare only observable in so­lid Bodies.

[Page 13]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 it's 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 [Page 14] appear, that in Philosophy, there is but one way, by which all, whether Liquid or Solid grow Hot; and if so, then 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 [Page 15] 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.

[Page 16]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 it self, 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 Sence, we perceive Heat; we must needs conclude, [Page 17] that whatever rarifies Matter, and puts it's 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 seperate­ly, is always joyned 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 puting the Parts of Matter [Page 18] 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 [Page 19] 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 [Page 20] it self; yet there is as much Reason to believe, that it is not; as that a Sword which will cause Pain, is not Pain it self: For those who think that Fire which causes Heat, is Heat it self; 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; [Page 21] 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 [Page 22] 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.

[Page 23]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 carryed 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 [Page 24] them also into a quick Motion▪ from whence proceeds a sensi­ble Heat. In the same Manner, when Saline Corrosives are mixed together, the subtile 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 apply'd 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 [Page 25] that means rarified and expan­ded, are turned into Flame. Lastly, it cannot be deny'd, but that when any thing grows hot by Putrefaction, that heat either proceeds from elastick 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 mix'd Viz. by putting the Parts of Mat­ter into Motion with it, and put it's Parts into a [Page 26] 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 [Page 27] 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 intestin 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 ap­ply'd together; yet it is evi­dent, [Page 28] 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 apply'd 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 Bloods 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 [Page 29] 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 [Page 30] 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 it self, 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 [Page 31] 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 [Page 32] upon the Fire, by driving it back and dissipating the Nitre, it extinguishes it: Whereas, on the contrary if it be supply'd 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 Oyl will flame as violently in the Summer as in the Winter, though Wood and Coal, and [Page 33] 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 yards 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 i'ts 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, [Page 34] 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 Center; 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 en­crease 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 [Page 35] 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 over­powers the Pressure of the Ni­tre.

But Nitre does not only by reverberating the Rays, collect a great Number together, and by that means encrease 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 consum'd in less time.

[Page 36]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 yok'd and lock'd 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 [Page 37] large Glass-Globe, and the Globe being stoped, 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 it's 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 [Page 38] 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 stop'd, it dyes not so much because it is choaked by a Retention of fuliginous Recrements, as by [Page 39] 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 Cloath, which imbibes, as if it were, the Nitre; for we shall be so far from being cooler for it, that in warm Weather, [Page 40] 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 [Page 41] 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 intangling and fettering them up.

[Page 42]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 supplyed with a Sulphureous Pabulum, that nothing is less combustible then 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, [Page 43] 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 it's Recrements; so does the Blood, by the Branches of the Trachea and the Pores of the Body.

That Smoak Which appears widely inconsistent. and Flame are, as if it were, inseperably joyned together; and that a subacid Balsamic Juice continually sweats through the inward Coats of the Trachea, and a [Page 44] 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 Sub­acid Balsamick 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 watred with that Se­rum, to preserve it from withe­ring and becoming too dry; and [Page 45] 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 [Page 46] Mass of Blood, Secondly, be­cause the former if not carried of en­crease it. if stopped, are so far from de­pressing and diminishing the Heat of the Blood; that they encrease it so much; that they present­ly put those that have predis­posed Blood into violent Fevers: But if the Smoak 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 seperated from the Serum of the Blood: For [Page 47] 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 [Page 48] Ashes of the Fuel, hurried along with them by their Motion and the Particles of Nitre: By which means, they loose most of their Vigour, and are more easily overpowered by the Ni­tre; and being fixed and joyned with those Ashes, makes up that which we call Soot; which the longer it lyes 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 [Page 49] 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 seperated, 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 [Page 50] of Flame, and the manner of it's Production, more then I otherwise should have done; I shall beg leave A Digression in which is given the Reason why Flame Ascends rather then 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 it's 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 subtile Particles, are in a swift Motion, and in [Page 51] some measure pinned in, by the ambient Air.

Now though the ambient Air thus press Which is because it hath less Opposition in it's Motion that way. upon it on every side; yet the Particles of Flame, being in too strong a Motion, and also too subtile 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 [Page 52] it self 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 peices of Mettle together, viz. Lead and Iron, for at the same time, that Lead easily yields to the Impression of the Iron, it as powerfully resists the former.

If then, the Air, the nearer [Page 53] it is to the Cen­ter, Because the Air the nearer to the Center 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 Center, 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 [Page 54] 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 Center, 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 Center, 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 [Page 55] 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 [Page 56] 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 [Page 57] 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 [Page 58] with less Resistance; it must needs be granted, that the Of­fice it performs here below, in respect of Flame, is, to keep it's 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 it's Mo­tion upwards, being less com­pact above then below; I shall produce two or three Instances, which prove, that if it had but less Liberty to ascend, by the Opposition of some other Body then to descend it would as naturally fly downwards as it does now upwards, when it is otherwise; and I shall also [Page 59] 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 [Page 60] 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 [Page 61] consider, why Flame may be said naturally to ascend.

Flame then is said naturally to ascend, because it is the Na­ture of it, for the most Part to do so, which is as much as to say, the Nature of Flame in­clines it to ascend; how the Nature of it inclines it to as­cend, I have already shown, and that there are the same Reasons, why the descending Motion, should be termed Natural, will easily be proved; for as it is na­tural for it to ascend, as long as it hath only the Air to op­pose it's Motion, so it is it's Na­ture to descend, when the Or­der of Opposition is changed; and the latter is as much a na­tural Motion, as the former; all that diversifies the tenden­cy [Page 62] of Flame, being those acci­dental Circumstances which are about it; and as a Ball, cast against the bottom of a Room, rebounds upwards; and when it is thrown against the top of it, as naturally flyes down; so Flame, being in a brisk Motion, naturally flyes up or down, as the Parts of Matter it striks against resist it, and cause it to fly back from them.

HAving made this short Di­gression, I shall proceed next to Diemerbroek's Opinion examined. examin Diemer­broek's Opinion; who thinks that the vital Spi­rit, by reason of it's Volatility, [Page 63] always endeavouring to fly a­way, does continually agitate those grosser Particles of the Blood; with which it is en­tangled and detained from flight; and is diversly vibrated and beat back, and so the whole Mass being kept in a continual fermentative Motion; there is a Heat produced in it, which in a greater Agitation, is greater, &c. And so differs, according to the different Degrees of A­gitation.

All that I shall, or need to take Notice of here, is, that that Agitation of Particles, which he says, causes the Heat of the Blood, rather produces a Sensa­tion of Heat, by affecting our Senses, in their Motion, than produce that, which we call [Page 64] 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 [Page 65] 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 Chymical Liquors together; for the Heat [Page 66] often becomes so great, that they often endanger the Vessels that contain them.

But he might as well have said, that there is so great a Dissimilitude betwixt hot Blood and cold Milk, that as soon as the Milk is mixed with it, it will cause an extraordiary Ebul­lition; and that by exposing them to the Air, & running them through Pipes, the Heat would increase; but this is so plain­ly false, that it needs no other Arguments, but Reflection to convince the weakest Reason.

And he might equally as well conclude, that Water would kindle a Fire, and encrease the Flame of it, because Oyl will, as that Chyle will put the Blood into a Heat, because Oyl of [Page 67] Turpentine and Spirit of Wine will grow hot when mix'd to­gether, but the Conclusion be­ing manifestly absurd, I shall in the next Place, endeavour to show the Reason of the Heat of the Blood as evidently as possibly I can.

FROM what I have alrea­dy said, in Answer to Dr. Willis's Opinion, it suffi­ciently appears; that, whether we say, the Blood grows hot per admotum Calidi, Accension, or any other way, it is no more then to express the same Thing several ways; or to make Words [Page 68] different in Sound, to express one and the same thing.

But as all that have writ on this Subject, have made choice of a Antient and Mo­dern Writers have rather disputed a­bout the Ʋse 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, &c. so they have by that means, ra­ther disputed about Names and Words, than any real and fun­damental Difference in their O­pinions. I shall not here enter into a dispute, whether the Blood when it becomes hot, may most properly be said to grow hot, or it's Heat expressed by any one of those Titles, they have [Page 69] been pleased to signify it by; for as in discoursing about the constituent Parts of a Man, it is not necessary to fix any Name upon that Man; but whether it be Thomas, Robert or William, the constituent Parts of him, if he be a perfect Man, will still be the same; so in discoursing concerning the Heat of the Blood, and considering the principal Cause or Agent, and the more remote and accessory Causes; it is no matter at all, whether the Consequence of these Cau­ses be signified by the word Ac­cension, Attrition or Fermen­tation; because the Difference of the Title, does not at all di­versify the Action.

But if any one would rather signify the Heat of the Blood, [Page 70] by any of these different Words, I shall be equally pleas'd with them, or any of them; provi­ded they all meet, in the Mat­ter signified by them, and do not deny that which seems to be true: That the Heat pro­ceeds from a swift intestin Mo­tion of it's Particles. Which Motion is the Reason why it affects our Sensory, so as to cause a Sensation of Heat.

But as the Reason, why it affects our Sen­sory so, is not The Reason why Heat affects our Sensory does not shew 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 [Page 71] 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 [Page 72] 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, [Page 73] which is the consequence of At­trition, yet if any one would rather say, it grows hot by Ac­cension; they have my assent, provided they mean thereby, not so high a degree of Heat, as is usually signified by that Word; but since it sounds ra­ther too harsh, and implies too high a degree of Attrition and Fermentation than that, which is commonly in the Blood▪ I more willingly make choice of the former, viz. Fermenta­tion.

And since I have said thus much of the Use of Words, apply­ed 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 [Page 74] of Discourse told me, by one, to whom I communicated, in some Measure, my Notion con­cerning the Heat of the Blood; which was this. He said he thought he could prove that it was done by Mixture and Pres­sure; and that he could explain the Heat of the Blood, by that Notion.

I shall here conceal the Au­thors Name, because he hath not made it public upon this account, though upon some o­thers to very little purpose; and because he told me, he intended to publish it, I shall for his satis­faction, and also the satisfacti­on of those, to whom he hath communicated it, say; that as I have shewn, that in mechani­cal Actions there is a Motion, [Page 75] and by that Motion there must be implyed a Mixture, to any one that doth but understand the Circulation of the Humors in a Man's Body; and it will consequently follow, that where there is a Mixture, and a Mo­tion of Humors, there must needs be also an Attrition of Parts, so moved; which Attriti­on implies a Pressure: For there can be no Attrition, without a Pressure; tho' Pres­sure does not imply Attrition. This is all he told me, and con­sequently all that I can Answer; but, for as much as I cou'd ga­ther, from the remaining Part of his Discourse, the most Es­sential Part of his Notion; but from what he said, it appea­ring not what Pressure he meant, [Page 76] that is, a Pressure of what, whether of the Particles of Blood with one another or not; and it being plain, that he did not believe, that Animal Spirits circulated through the Nerves; I not only concluded that his Pressure was only of the Par­ticles of Blood; because there are none other except Serum to mix with it; but also, that what he had to say for it was rather about the Use of Words then any thing else; and there­fore, I have shew'd him how far his Words are significant in my Hypothesis.

But Words, whereby we sig­nifie [Page 77] 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 Ac­cessory Causes of it; I shall proceed to shew, how it is be­gun and carryed on; and by what: That is, what Humors are Active, and what Passive, in producing Heat, or a Power to Heat; and how they are so, and after what manner; as also where they chiefly operate.

And that it may appear, we are to consider; The whole Body is made up of Ves­sels and Humors contained in them. that the materi­al and corrupti­ble Part of a [Page 78] Man, in which, the immateri­al and immortal is lodged, is made up of Solid and Liquid Parts; the Solid Parts are all those Vessels, that make the Body a curious contrived Vas­cular Engin; which are filled with, and actuated by, Liquids, and in which, they all circu­late: And as those Vessels car­ry different sorts of Liquids; so they are called by different Names; Veins, Arteries, Nerves, &c. Through the Arteries and Veins, the Mass of Blood con­tinually circulates, and Animal Spirits through the Nerves.

The Veins and Arteries, be­ing, as if it were, By what means the Spirits and Blood are mixed in order [...]o a Fermentation. both rooted and springing from the Heart, are [Page 79] branched up and down the Bo­dy; both through the Exter­nal as well as Internal Parts, ex­cept those, that the Vena Porta supplyes; and the Nerves, taking their Original from the Brain and spinal Marrow, are dispersed through the whole; and meeting with the capillary Terminations of the Veins and Arteries, they being inter­woven one with another, ter­minate all together; and, as I Metaphorically expressed it, in my Treatise of Muscular Motion, all terminate in small Glands; in the Cavities of which both through the substance of the Mus­cles, as well as the Internal Parts, the Arteries lay down Blood, and the Nerves either mediately, or immediately Animal Spirits; [Page 80] and having there also proved, that a subtile Liquor, made and prepared in these Glands by Formentation, was according to the different degrees of Spirits, sent there by our Appetite, not only subtilized but thrust out by a succession of Matter into the Fibers, and circulating through them, distends 'em, and by that means contracts the Muscles; and there also having shewn, that the Fermen­tation was caused, by a mutual Conflict of the Blood and Spi­rits; I shall now in this Trea­tise endeavour to explain from that mutual Conflict, the Heat of the Blood.

And because some, as yet doubt, whether Animal Animal Spirits demonstrated. Spirits circulate [Page 81] 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 shew 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 [Page 82] ignorant what the Animal Spirits are, nor of their Na­ture, which appear as manifest­ly as the Humors of a Mans Body.

But, perhaps it will be a hard Task to Viz. that Muci­laginous oily Moi­sture which we call Brains. perswade 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 [Page 83] were a more gross and sluggish Body, it would be a great deal more Viscid and Phlegma­tick.

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 Tast 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 diverse sorts of Salts, and Phlegmatick crude Serum; so the substance of the Brain is moistened with an oyly sweet Salino-Sulphureous Mass▪ free from those indigested Dregs, that swim along with the Blood▪ being separated from those Im­purities [Page 82] [...] [Page 83] [...] [Page 84] 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 oyly 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 [Page 85] the Animal Spirits, as I think none can deny; since any consi­derable Evacuation of it, present­ly sinks and diminisheth them, then 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 oyly 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 encreasing the stock of Animal Spirits, the Actions of the Body as well as of the Mind be stronger, we must conse­quently [Page 86] believe, that they are moderately performed by them; when that oyly 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 [Page 87] sanguiferous Vessels are so small, that they cannot be seen by good Microscopes, but also the Nervous Fibers are so extreamly 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 joyned▪ 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 chill'd 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 [Page 88] 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 then may the Animal Spirits, whose Portions are so incomparably diminutive, be forthwith chill'd and thicken'd, when they immediately, as soon as they are expos'd to the Air, are almost equalled with Par­ticles of Nitre.

[Page 89]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 [Page 90] 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 imagin 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.

[Page 91]From hence it appearing that that oyly 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 it's Operation.

Which presently appears, if we do but con­sult The Nature of the Animal Spirits considered. our Taste, the Taste of it be­ing oyly, sweet and mucilaginous, that Sub­stance being made up of the most volatile sulphureous and salt Particles of the Mass of Blood, which are incorporated, [Page 92] in some of the most digested and ripen'd 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 our selves most full of Spirit after Meat that abounds with Sulphur, volatile Salts and Oyls; whereas all Acids, Austeres, &c. which thicken Oyl, 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 oyly Matter, is farther manifest, by exposing the Brains of any Animal to [Page 93] the Air; because they present­ly grow rancid and fetid.

It appearing then, that the Animal Spirits are an oyly 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 shew, how the Heat of the Blood is carried on and continued; which, I conceive, to be after this Man­ner.

[Page 94]These oyly 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 dissolv'd, and be­ing put into a swift intestin Motion, they endavour pow­erfully to expand themselves, and to fly away; but being held in, and reverberated, by those grosser Particles; their [Page 95] 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 anothers 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 observ'd, that the Animal How it's 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 [Page 96] 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, [Page 97] 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 Hu­mors 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 joyning with [Page 98] them, encrease 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 it self.

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.

[Page 99] Lastly, we may take No­tice, that neither the Animal Spi­rits, Neither the Ani­mal Spirits nor Ar­terial Blood are who­ly 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, [Page 100] 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 shew, that the Heat of the Blood is caused by such a [Page 101] mechanical Motion of Parts, as I have before mentioned.

That the Animal Spirits then 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 oyly 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 [Page 102] the Effects, that solid or li­quid Substances have on one a­nother, when in Motion; for Amber, by a violent Attrition of it's Parts against a woollen Cloath, feels hot; the Sulphu­reous fat Effluviums being by that Attrition encreased, 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 disyok'd 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 [Page 103] 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 Axle-tree, 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 loos­ned and dissolved, and being put into Motion is rarified and [Page 104] expanded; which being still ground betwixt the solider Parts of the Wood, it's 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 applyed to Gun­powder, by dissolving and grind­ing of it's Parts in Pieces, and putting them into a violent Mo­tion, cause them to expand and explode.

But not only solid Bodies 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 [Page 105] 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 Oyl 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 [Page 106] 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.

[Page 107]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 joyn'd 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 subtile 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 [Page 108] 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 subtile 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 shew'd, 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 intestin Motion of Parts, and since those can be put into Motion no other way but by Attrition; I should in the next Place prove, [Page 109] 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 it self, as also in the Expansion of Gun­powder; [Page 110] for if a Gun be shot against a Wall, the Flame of the expanded Gun-powder striking against it, presently flyes back again, and, by mix­ing with that, which immedi­ately follows it, encreaseth 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.

[Page 111]The gross Parts of the Blood, having thus put How the Animal Spirits rarifie the Blood. the Animal Spi­rits into a swift Motion, and by inverting them in their Mo­tion, having caused them to encrease one anothers Motion; the Spirits at last, set upon the Mass of Blood, and by break­ing and dissolving the Particles of it, rarifie 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 it's Fuel, [Page 112] neither does it only rarifie and expand the Sulphureous Matter of it's 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 easie force, then 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 prov'd. Natural state, by the Methods and Ways, which I have endeavou­red to explain; I shall in the next [Page 113] 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 it's Parts in a more violent or weak­er Motion, and consequently encrease 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, [Page 114] 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 Phlegmatick Constitutions, where the Mass of Blood a­bounds, with dull Phlegmatick Humours, or Acid and Austere Juices, of too close and com­pact Texture, and a large Sup­ply of Spirits is denyed; the Blood is not of so hot a Tem­per, as in Cholerick Constitu­tions; whence it evidently [Page 115] 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 encreased, 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 Physick. and constant Pra­ctice of all Phy­sitians; for when the Natural Heat, as some call it, is lan­guid and weak, and almost ex­tinguished; they give such Me­dicines, [Page 116] as increase the Heat of the Blood, by renuing 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 Harts-horn raises the Pulse. or of Ar­monick-salt, or some other Sa­line or Sulphureous Spirits, which presently joyning with those in the Nerves, encrease 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 renue Circulation, but the Heat of the Blood.

[Page 117]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 Preter-natural Heat; from whence proceeds that Preter-natural Heat in Fevers: And the way, that Physitians 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 [Page 118] by cooling and fixing those predominant Spirits, and eva­cuating other accessory 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.

[Page 119]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 Physitians; I proceed to shew, 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 [Page 120] by the Preter-na­tural Effects, that The Keason of flushing heats, in the Scurvy. Scorbutick Salts cause in some People; for when the Mass of Blood is impreg­nated with Acid Acrid Humors, 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 Preter-natural Heat proceeds from Corrosive Salt Humours, fermenting with the Spirits, is very manifest; since these Symptoms are only cur­red, [Page 121] by such Medicines as cor­rect the Acidity and Acrimony of the Blood, viz. When it most partakes of Acrimony by sweet diaphoretick 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 Pancreatick 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 Humors, which by the aforesaid means being made thin enough, to go off by Urin and insensible Transpiration, are [Page 122] dispersed and carry'd off those ways; and the Mass of Blood, being cleansed of those sharp Humors, 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 vitious Humors, we may learn to know what is the Na­ture of those Humors; we must conclude, that whatever is corrected by Medicines di­rectly contrary to Acrimony, the nature of that Humor is Acrid; and when, by the Use of volatile Salts, the distem­pered Humors of our Bodies, are attenuated, and disposed to Evacuation, and at the same [Page 123] time we know, that volatile Salts by volatizing and prepa­ring the superfluous fixed Acid Acrid Humors 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 Hu­mors,

And that these flushing Heats in the Scurvey, proceed from Acrid Acid Humors 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.

[Page 124]If then, both from the Me­thod of Cure, and the Cause it self augmented by such Sorts of Juices, we gather they pro­ceed from sharp Acrid Acid Hu­mors, we may be certain, that those Symptoms are caused by such Humors grinding and cor­roding the Animal Spirits, and that by putting them into a Preter-natural 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 Humors 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 [Page 125] 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 it self; for it being proved be­fore, that the Heat of the Blood proceeds from a swift in­testin 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 [Page 126] 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 peice of Steel, the more firm and hard the Steel is, the more powerfully it loosneth the Texture of the Flint, and strongly expanding it's 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.

[Page 127]And that the Texture and Constitution of Saline Humors, is more Solid, and their Parts more Corroding, than of a sweet Balsamick 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 Scorbutick Salts, Acidity joyning 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 [Page 128] 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, it's 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 it's Particles being more easily put into Motion, readily joyn with the Animal Spirits, and encrease theirs; and that on the contrary, the more dull and phlegmatic any Body is, the less apt are it's 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 [Page 129] 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 then phleg­matic and melancholly 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 encrease the natural Heat of their Blood, when it is too much depressed, it is not only necessary to take away some of those crude Hu­mors, which stuff up the Ves­sels, and too much depress the Spirits; but also, by volatile and spirituous Medicins, to en­crease the Spirits; and at the [Page 130] same time, to exalt and spiri­tualize the Blood, by absor­bing Acids, and exalting the vo­litile and subtile 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 encrease 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 Aqua­mirabilis, hath upon us from Sack which any one that does [Page 131] but taste must soon acknow­ledg.

It remains in the next Place, that I should How far the Blood and Spirits are Active or Pas­sive. shew, 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, then 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; [Page 132] 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 shew, how it is continued; which will be sufficiently evident, if we do but consider, that the Animal Humors are in a constant and [Page 133] 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 [Page 134] 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 [Page 135] down in the Glands, as well as in the Veins after Fermentati­on; they may think it reaso­nable to conclude, that where­ever 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 [Page 136] the Attrition of these Humors, 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 [Page 137] 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 it's 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 elastick and expansive Motion, [Page 138] 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 subtile 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.

[Page 139]And the Animal Spirits being yet more expanded, do not only continue, but in a great Measure encrease 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 Vigor, 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 [Page 140] 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 [Page 141] 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 ripen'd 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 [Page 142] Cause of Heat is principal­ly in the Glands.

That the Animal Spirits are put into an ela­stick 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 [Page 143] begun and carried on in other Liquors; for when oyl of Vi­triol and Spirit of Armoniac Salt are mix'd 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, [Page 144] 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 grund, betwixt the Parts of the Arterial Blood, expand so weakly, that they scarce a­gitate the Mass of Blood, suf­ficiently to preserve it's 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.

[Page 145]Now, if when the Fermenta­tion is weak, the Heat of the Blood is more remiss and de­pressed; and when Circulation is stoped, 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 stoped, it pre­sently declines, whereas if it were caused in the Vessels, it would continue after Death as [Page 146] well as before; since, it then hath the same Matter, though it wants Circulation and a forcible Mixture; and what I have shewed 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 in­ferr'd from this common Ob­servation, that the Heat of the Blood is encreased by all vio­lent Motion: For upon all vio­lent Motion, a larger Quan­tity of Animal Spirits, being sent to the Parts to be moved, [Page 147] in order to prepare a greater Quantity of subtile 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 it's Parts, which was raised in the precedent Fermentation is spent; it is again renued.

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 [Page 148] and more forcibly back upon the Heart; from whence it ap­pears, that both the Heat of the Blood is encreased, 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 [Page 149] is a continual Chain and Cir­culation of Causes as well as Humors 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 Gun-powder, it immediately puts it's Parts into an Explosion; and that the Blood [Page 150] not only ferments in so short a time, but that it may prepare that subtile 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.

[Page 151]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 shewn; then it must needs follow, that the Heat of the Blood is most pro­moted in those Parts, where Animal Spirits are most predo­minant. [Page 152] And having proved that in order to prepare that subtile Liquor, which causes Contractions of the Muscles, a greater Quantity of Animal Spirits is sent there, it will fol­low▪ that the Blood grows hot­est, being most vigorously fer­mented in those Parts that are in Motion; and then 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 [Page 153] 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.

[Page 154]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 [Page 155] 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 shew hereafter, and also how the Glands in that Part, are sup­ply'd 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.

[Page 156]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 grund 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 oyly Sulphureous volatile Temper; that being more ea­sily rarified and expanded, they [Page 157] 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, perswaded to believe, that the Heat of the Blood thus proceeds from Fer­mentation.

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 [Page 160] 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 [Page 161] 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.

[Page 162]The Use of the Lungs, with a more immedi­ate Respect to The Ʋse 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, produces 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 it's Parts are dif­ferently modulated; so the [Page 163] Air forcibly driven through them, causes different Voices.

In which Action, the Lungs seem chiefly to be an Organ Is to express all it's Conceptions and Reasoning. made, on purpose, to be serviceable to the rational Soul, to express all it's Conceptions and Rea­sons; and to form Voices or Articulate Sounds, to signifie 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 [Page 164] 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.

[Page 165]Another Reason is, that since the Cavities of the Lungs, are It carries off that Superfluous Moi­sture that supplies them. constantly sup­plyed, 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.

[Page 166]Another Reason why the Lungs ought to be always in And that their voluntary Motion might less Preter­naturally affect our Bodies. Motion, is, least they should Pre­ter-naturally af­fect and disturb the Constitution of our Bodies, when put in Motion, as we have a mind to express our selves; 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 Epilepsie; but our Bodies be­ing accustomed to it, and it be­ing made agreeable and consi­stent with Circulation of the Blood; becomes less trouble­some, [Page 167] 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 troublesom 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 [Page 168] of an Asthma, Orthop­naea and Duspnaea, some sorts of Phthisicks, and a great ma­ny more dangerous Sym­ptoms.

For when it is too thick, it sticks fast to the Coats of the Lungs, and not being easily e­nough mixed and incorporated with the Air, the Quantity of it encreases; till it stuffs up the Cavity of the Lungs; and when it is too much in Quantity, though it be thin enough; yet the Air being not able to carry it off fast enough, it runs down the sides of those tender Vessels, and by a gentle Irritation, raises a tickling Cough: Lastly, when the Humor, that moistens the [Page 169] Lungs, is almost Natural as to Quality and Quantity; yet if the Air be thick and moist, it, being so much impregnated with it's own Moisture, is in­capable of carrying off the Moisture, supplyed by the Se­rum of the Blood; whence Peo­ple that are inclined to Ob­structions of their Lungs, in foggy and moist Air, find them more oppressed; that Moisture which ought to be carried off, being left behind.

But if we consider further the Use of the Lungs, with respect to The Ʋse 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 [Page 170] 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 [Page 171] 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, [Page 172] since the Motion of the Heart is only Contraction, and the Di­lation of it's Ventricles only a Cessation from that Motion, how the Blood is forced into them with Vigour enough to distend their Cavities.

For there is so little Reason to expect, that they should di­late of their own Accord; that we should rather believe, they would be continually contract­ed, since all the Weight of Blood contained in the whole Sangui­ferous Vessels of the Lungs, could not possibly dilate them without some other force to help it, for the Substance of the Heart being contracted, and the Cavity of the left Ventricle so [Page 173] considerably diminished, so small a Portion of blood as hath Liberty to press against it's Orifice would make but a weak Pressure and much too small to dilate the Ventricle in so little time as intervenes the successive Contraction, besides the Heart having no Tendency at all to dilate it self, since that would make it unapt to yield to Contractions, we must sup­pose, that a Part of such Sub­stance cannot easily be dilated but would require some Force greater then can be supplyed by an inconsiderable Pressure of Blood faintly intruded by al­most nothing at all.

But the Lungs being almost in a continual Contraction, in respect of the Sanguiferous [Page 174] 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, [Page 175] by the former Contraction, but is assisted by the Lungs, we may easily perceive: For not only the Blood in it's Vessels, but even any Liquor, being forced through Pipes, whose Cavities encrease the fur­ther they run from their nar­row and small Original, al­ways moves with less force the farther it goes: So that although in every Systole, the Blood should be forced forwards from the left Ventricle, by a succes­sive Pressure of subsequent Matter; and the Motion should be strong enough to make it circulate briskly through the narrow and capillary Twigs of the Arteries; yet when it [Page 176] came into the Veins, it would move much more slow, and by that time it came to the Heart again, would want Force suf­ficient to dilate the right Ven­tricle, and the right Ventricle being not duly dilated, so lit­tle Blood would be squeezed into the Lungs, that the Left would want a Supply of Blood to dilate it, and consequently the Pressure of Blood through the Aorta and Vena Cava would be so weak, that the next Di­lation of the Right Ventricle would be weaker than the for­mer, and so Circulation would gradually decrease.

But that weak Motion of the Blood into the Right Ventricle, being encreased by [Page 177] the Force of subsequent Mat­ter from the Left, the Motion of the Blood into the Lungs is consequently more plentiful, and as it passes through them is violently forced into the Left and so on; and by that means, as I said before, the Lungs di­stend the Left immediately and consequently the Right me­diately.

That the Motion of the Blood is thus weakned by so long a Course in the Veins is further evinced; if a Vein and Artery be open'd at once; for the Blood runs out of the Artery much more forcibly; and indeed, it would be reasonable to think it so, though it were not manifest by so plain an Ex­periment; for if Water in a [Page 178] 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 shewed by stopping the Breath of any Animal, which for want of free Circu­lation presently dies, and not because the Flame of the Blood is by that means extinguished; for as long as the Lungs duly perform Respiration, and the Heart violently contracts, and drives the Blood contained in it's Ventricles forcibly out, that Motion of the Blood be­ing by a continued waving Pres­sure [Page 179] 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 [Page 180] Spirits separated in the corti­cal Part of the Brain, being not so powerfully thurst after by an equal Succession of Mat­ter) the Fermentation in the Glands is weaker, and conse­quently the following Contra­ctions gradually decline both in Number and Vigour, till at the last they Why by permit­ting it to breath a­gain the Circulati­on of the Blood is renued. 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 [Page 181] considerable Protrusion of Blood into the Muscular Glands, and also of Spirits through the Nerves; by which means, the Thorax contracting more vio­lently, forces the Blood in grea­ter Quantities into the left Ven­tricle of the Heart; and the Mo­tion of the Heart at the same time increasing, raises Circu­lation to it's natural Force, by squeezing Blood forwards into the Right and so successively.

From hence it appears, that the Blood is forced into the Ventricles of the Heart by the help of the Lungs; for if, when the Motion of the Lungs is obstructed, the Sy­stole and Diastole of the Heart ceaseth in a short time; it must needs follow, that it is in some [Page 182] measure preserved in that Mo­tion by them, and it is further proved, because the Motion of the Heart, does not only sooner stop, when Respiration ceases; but also, because it is increased by a renued Respiration; and any one that would be further satisfied of the Truth of it, let him hold his Breath a conside­rable time, and he will find his Pulse gradually decay, which is again renued by reiterated Breathing.

But though from hence it may appear, that 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 supply'd in [Page 183] unborn Infants; and how their Blood circulates▪ since then their Lungs do not perform the Office of Respiration.

To which I answer, that in an Infant before Birth, the Pla­centa supplys that Defect; for that additional Force which the Infants Blood receives, from the Motion of Nourishment, violently forced into the Umbi­lical Vessels, by the Pulsation of those Arteries, that separate it from the Mother's Blood in the Womb, do prove equiva­lent, and supply the Office of the other; but as soon as the Circulation of the Blood cea­ses to be promoted by a Sepa­paration and Protrusion of that Juice, it immediately, if un­born, dies; and after it is born [Page 184] hath a continual Necessity of Breathing, as long as it lives.

Where it is to be noted, that as in one that breaths, the Lungs more immediately assist the left Ventricle, so in one un­born, the Placenta more imme­diately promotes the Dilation of the right.

Now although it from hence appears, that the Motion of the Heart is promoted, by the re­ciprocal Motion of the Lungs, yet it does not wholly depend upon it, for if it did, the Mo­tion of the Heart would as sud­denly stop, as that of the Lungs; but since it does but partly de­pend upon it, Circulation de­clines by degrees upon the stopping of it.

[Page 185]But that it may be better understood, how the Lungs, promote Circulation, I shall next shew, that the sanguife­rous Vessels in the Lungs, are not only contracted by the Con­traction of the Thorax; but also in every Inspiration.

And since it is known, that the Bladders of the Lungs are encompassed about with the small Twigs and minute Rami­fications of sanguiferous Ves­sels; every Systole of the right Ventricle of the Heart, these must needs be filled and di­stended with Blood; and if so, consequently that Blood must needs be forced by the Contra­ction of the Thorax, through the Vena Arteriosa with a con­siderable Force; and so be dri­ven [Page 186] 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 [Page 187] 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 [Page 188] Blood into the Habit of the Bo­dy, but through the left Ven­tricle is very plain, and Lastly, that not only the left Ventricle is by that means further dila­ted, but consequently the right, by the Assistance of the Lungs is manifest, because Circulati­on is presently quickned by coughing; so that this one Phaenomenon proves all that I have asserted concerning the Use of the Lungs with respect to the Heart.

But it may here also be que­stioned; how the Lungs sup­ply the Heart in Inspiration, when the Cavities of the Lungs are dilated?

To which I answer, that though the Cavities of the Lungs are dilated in Inspirati­on; [Page 189] 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 renue the vigorous Contractions of the Heart, before they are sen­sibly decreased; as I have be­fore explained it.

From what I have said, of the Use of the The Office of the Lungs is partly vo­luntary, partly in­voluntary. Lungs with re­spect to the Rati­onal Soul, as well as the Mo­tion [Page 190] of the Heart, it appears, that the Lungs perform a Sort of a mixed Action; partly vo­luntary and partly involuntary; with respect to the Body, it is involuntary, being carry'd on whether we will or not, and when we are able to take no notice of it; and with respect to the Soul, voluntary, it be­ing in our Power to quicken or remit the Motion of them, differently to modulate our Voices, as occasion and ne­cessity require, or our own Will inclines us.

But besides these extraordinary Offices it performs in promo­ting both a Circulation of Hu­mors and of Discourse; since there is such a great Quantity of Air drawn in by every In­spiration, [Page 191] it must needs produce some Effects in the Mass of Blood; and those Humors that circulate along with it; and since it is so minutely mixed with it, by the small and cir­cular Windings of the Blood Vessels about the Bladders of the Trachea; the Blood must needs be sufficiently impregna­ted with Nitrous Particles.

But it being a Question, how the Nitre of the Air comes to be mixed with the Blood, and whether the Air it self be mixed with it also, before I proceed to shew how the Mass of Blood is affected by it, I shall endeavour to solve these two Questions. And,

First, That the Air it self is no otherwise mixed with the [Page 192] Mass of Blood, but as I have shew'd, viz. by the Media­tion of the distinct Vessels in which each run is plain, be­cause we don't perceive the Ef­fects of it in that Mass, and also we may probably guess so, because Air would hinder Cir­culation and much disturb it: Air being always unapt to mix with Liquids and to fly from their Embraces, there being therefore these Reasons, why it ought not to be mixed with the Blood, and none that it shou'd, nor any Sign of it being so, we have Reason to conclude that it is not. But,

Secondly, That those Nitrous Particles which swim in the Air, are mixed with it, we see manifestly by the Effects, which [Page 193] are caused by them, there be­ing the same Alterations in some Measure made in the Blood as it passes through th Lungs, as when exposed to the open Air.

But, the Question then will be, how the Nitre of the Air is mixed with the Mass of Blood, and by what means. To which it may be answered, that if we consider what fine and subtile Bodies, those Particles of Ni­tre are, which we draw in by Inspiration; and through what minute and small Pores, they are capable of passing, so that they penetrate the most solid Bodies in Nature; well may we suppose that they can find Pores fine enough to pass through the Coats of the Vessels.

[Page 194]That they pass through the most compact and solid Bodies; Bodies that are much more close and less Porous, than the Vessels of the Lungs are, is certain; for otherwise, hot Wa­ter contained in a brazen Ves­sel would never grow cold, and that the substance of Brass is less porous than the Sub­stance of the Lungs, no thing is less dubious.

Moreover, since that the Ni­trous Particles of the Air are conveighed into the Blood, is so plain from the Effects that are there caused by them, they must needs be conveighed through those Pores, there being no other ways at all for them to pass by. But,

Another Question which may [Page 195] 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.

[Page 196]To understand then the Effects that it hath upon all that Mass of Humors, that circulates through the Veins and Arteries, to wit, Blood and serous Lympha, we are to consider them both together, and apart; together, that it may appear how they influence each other; and a part, that we may know, for what end each is impregnated with those Nitrous Particles; and because when we are acquainted how it alters each singly, it will better ap­pear how they influence each other; I shall first consider them apart.

The Effects then, which we perceive the Ni­tre What Effects the Air hath upon the Mass of Blood. of the Air hath upon our [Page 197] Blood, and the Alterations we are sensible it produces, are ei­ther in respect of it's Colour or Heat.

That the Air alters the Colour of the Blood, In respect of it's 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 shew what other Effects it causes in the Blood, and how.

Having therefore explained the Heat of the Blood, in the foregoing Treatise, and it ap­pearing that it is caused by a swift and violent Agitation of the Particles of the Spirits and Mass of Blood; the way to understand, how Nitre affects [Page 198] 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 subtile Spirituous Parts, and hinder them from Motion; by [Page 199] which means, the more gross ones are moved more slow, and the Heat of the Blood conse­quently abated; but when the Mass of Blood is so Elastick, and the Parts of it move so strong, that the Nitre cannot de­press them sufficiently, and check them, the Heat of the Blood is increased; the Motion of those Parts being inverted.

That the Nitre of the Air inclines those Bodies to rest, with which it is mixed, and consequently the Blood, is not evident only by exposing hot Water, to a cold freezing Air, but even Blood; and nothing is less dubious than that ex­cessive Cold extinguishes a mo­derate Heat.

But that Nitre, when it is [Page 200] 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 hindring 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 breifly, yet plainly, appears, that the Ni­tre of the Air alters the Colour of the Blood; and also serves to temper the Heat of it.

[Page 201]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 Oyl, it will be manifest, that it preci­pitates the Watry Parts of the Serum; which joyning with the fixed Salts of the Blood, dis­pose them to be separated, and carryed 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 [Page 202] 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 Urin, besides nothing in Me­dicine, is a more known and common Diuretick, 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 Corde, 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 [Page 203] Animal Oeconomy receives thereby, I shall not now en­quire, yet how inconsiderable a Part of it's 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 shew; That,

The Lungs perform many [Page 204] 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.