Chapter VII: Appendix (6)

There are some Difficulties proposed against this Conjecture, which I think may be easily resolved. Some object the distance between the _Tubæ_ or _Cornua Uteri_, and the Testicles; but to this is opposed by _Swammerdam_, and others, the like distance between the _Infundibulum_, in Hens and Frogs, and the Ovary; and yet it cannot be denied that the Eggs are transmitted thro' this into the _Uterus_: And besides _R. de Graef_, and others, have by repeated Observations found that the _Cornua Uteri_ do at certain times after Conception, embrace the _Testes_ on both sides the _Uterus_. They object in the second place the great disproportion between the pretended Eggs in the _Ovary_, and the Aperture of the _Tubæ_ or _Cornua Uteri_, the former being a great deal bigger than the latter: But both _R. de Graef_ and _Malpighius_ have clear'd that Matter, by making appear, that these Bladders in the Ovary are not the _Ova_, but serve to form the _Glandules_ within which the _Ova_ are formed, which break through a small _Papilla_ opening in the _Glandule_, which bears a proportion to the Aperture of the Tube. They object 3, The difficulty to conceive how these Eggs should be impregnated _per semen Maris_, both because there is no Connexion between the _Tubæ_ and the _Ovary_ for its transmission, and for that Dr. _Harvey_ could never discover any thing of it _in Utero_. As to the last, Mr. _Leewenhoeck_ has cleared that difficulty, by the discovery of innumerable _Animalcula Seminis Maris in Cornubus Uteri_, and those living a considerable time after Coition. _Numb._ 174. of the _Transact._ And as to the former, we may either suppose that there is such an Inflation of the _Tubæ_ or _Cornua Uteri tempore Coitionis_, as makes them embrace the _Ovaria_, and such an approach of the _Uterus_ and its _Cornua_, as that I may easily transmit the Seed into the _Ovary_; or else, that the _Ova_ are impregnated by the Animalcles after they descend into the _Uterus_, and not in the _Ovary_; the former seems probable for this Reason, that at least a whole Cluster of Eggs in a Hen will be fecundated by one Tread of the Cock: Now this Fecundation seems to be in the Vitellary, and not in the _Uterus_, as the Eggs pass along from day to day; for it can hardly be supposed that the Animalcles should subsist so long, being scattered loosely in the _Uterus_, as to wait there for many days for the Fecundation of the Eggs as they pass along. The latter Conjecture has this to strengthen it, that the Animalcles are found to live a considerable time in the _Uterus_; and that if they should impregnate the _Ova_ in the Ovary it self, the _Fœtus_ would increase so fast, that the _Ova_ could not pass through the _Tubæ Uteri_, but would either burst the Ovary, or fall down into the Abdomen from the Orifices of the _Tubæ_; and that from hence proceed those extraordinary Conceptions in _Abdomine extra Uterum_. But, 4. Mr. _Leewehoeck_, _Numb._ 147. of the _Transact._ to weaken the third Consideration about the Conceptions, being like unto an _Ovum_ in the Womb, proposes a Parallel between these Animalcles and Insects; and insinuates, that as the latter cast their Skins, and appear of another Shape, so the other which at first seem like Tadpoles, may cast their outer Skin, and then be round; and that this may be the occasion of the round Figure of the Conception in the Womb. To this it may be replied, that according to Mr. _Leewenhoeck_'s own Sentiment, the Animalcles cannot come forward, if they do not find the _Punctum_ or proper place for their Nourishment, to which it seems they must have some _Adhæsion_. Now the Conception in _Viviparis_ is not fastned unto the Womb for many days, nor does adhere to any point of it; so that it seems this roundish Body is not the Animalcle thus chang'd after having cast an outer Skin, but is rather the _Cicatricula_ or little Egg, into which the Animalcle has entred as its _Punctum_ or place of nourishment; else I do not see why they should not be adhering to the Womb from the first Conception, or why (as I have said) many hundreds of them are not conceiv'd and formed together, _&c._

_A short Discourse concerning Concoction: Read at a Meeting of the Royal
Society, _May ... 1699_, by _Clopton Havers_, M. D. Fellow of the
Royal Society._

The manner in which the Digestion of the Aliment is performed, is a thing not very easie to be understood and explained. However, it has not escap'd the Conjectures of some Philosophical Men, who having curiously observ'd the _Phænomena_ of Nature, and enquired into their Causes, have, amongst other things, endeavour'd to account for this. But their Sentiments about it have been various, and the Hypothesis, by which they have studied to explain it, very different. Some have thought the Concoction of the Food to be a kind of Elixation; and that the grosser and more solid Parts being, as it were, boil'd in the Liquid by the Heat of the Stomach, and the Parts adjacent to it, as the Liver, Spleen, and Omentum, are by a long and continued Elixation, first render'd more tender, and then colliquated, and dissolved into minuter Particles, so as to mix more equally with the Fluid, and with that to make one Pulpament, or chylous Mass. And _Hippocrates_, tho' he does not plainly call it an Elixation, yet seems to attribute the Concoction of the Food to the Heat of the Stomach, as the Cause of it, _Sect. 4. Libro de salubri victus ratione_. So where he takes notice of the voiding of such Fæces, as appear to be like the Food that has been eaten; he adds, _Constat enim, sane ventriculum, ciborum copiam, ut concoquat, calefacere non posse_. And there are other Passages in the same Book, from which we may conclude, that he suppos'd the Heat of the Stomach to be the great Cause of the Digestion of the Food.

There are others that make the Stomach itself to be the great Instrument of Digestion, but in a different manner: And they suppose it to be perform'd by an Attrition, as if the Stomach, by those repeated Motions, which are the necessary Effects of Respiration, when it is distended by the Aliment, did both rub or grind off some minuter Particles from the grosser Parts; and by continually agitating the Mass of Food, make those Parts, which are not contiguous to the Stomach, strike one against another, and break one another in pieces, until they are all attenuated. It is evident enough, that the sides of the Stomach do in Expiration press upon the _Contenta_, so as to oblige, at least some Parts of them, every time the Muscles of the Abdomen are contracted, to move and shift their places. So in Inspiration, when the Diaphragm and Liver press upon the upper part of the Stomach, the Aliment must be moved again. So that by these reciprocal Motions, that part of the Food which is contiguous to the Stomach, and moves in a Line parallel to it, must rub against it; and all the other Parts being moved by such a Compression, as gives them a different Tendency, it is certain they must be continually striking one against another. And for Bread, and such things as are made of Flower, that will be softned and dissolv'd with any common Liquid, that Agitation of the Stomach which moves them in Respiration, might seem sufficient to break and dissolve them, when they are sufficiently moisten'd with a Fluid. Yet this cannot be thought enough to break and digest Flesh-meat, Fruits, or any other thing that will not be softned and dissolv'd in Water, or some such Liquid. But although this Motion of the Aliment, caused by Respiration, does not actually digest it, yet it has a great and necessary Use in Concoction, and makes all the grosser Parts, as they are attenuated, mix equally with the Fluid.

Some think that the Bilious Juice; others, that the Spirits are chiefly concern'd in this Affair. _Galen_, in his Book _de Neutralibus Facultatibus_, makes it to be the Effect, not of one, but of several Causes; as a pituitous Juice in the Stomach, the Bile, _&c._ which appears from what he has said, and the Translator thus render'd: '_Verum quanto ii (cibi) qui mansi sunt, iis, qui inhæserunt, magis sunt alterati; tanto etiam his magis ii, qui devorati sunt. Siquidem incomparabilis erit horum alterationis excessus, si & quæ in ventre est Pituita & Bilis, & Spiritus, & Calor, & tota Ventris substantia, æstimentur._'

Some there are that will have the Food to be dissolv'd by a Menstruum, which is supply'd from the Glands of the Stomach, or some other way: But those that do so far agree in the General, as to think Concoction is perform'd by a Dissolvent, do differ in their Notions of the Nature of the Menstruum: For there are some that suppose it to be an Acid, which does erode the grosser parts of the Food, and dissolves them in the same manner as Vinegar, Spirit of Vitriol, or any such-like Acid, will dissolve even so solid a Body as Iron. And it cannot be deny'd, but that Oil of Vitriol will dissolve Flesh-meat, and reduce it to a Pulp; but it is not to be suppos'd, that the Fibres of the Stomach can admit any such strong and corroding Acid, without something to correct it, but it must be injur'd in its Tone, and labour under great and extraordinary Pains. Neither does such a Menstruum, tho' it will digest some things, seem capable of dissolving so great a Variety of Things as we eat, especially when a great many of them are of a contrary Nature. Some will have the Menstruum to be a _nitro-aerius_ Spirit, that is, quick, and very penetrating, and included in its proper Vehicle; which, being in its own Nature apt to penetrate the Mass of the Aliment, does diffuse it self through the Whole, and breaking the Vinculum of the more solid Parts, does dissolve their Compages. By others, it is thought to be some saline Juice in the Stomach, by which the Parts of the Aliment are divided and dissolved, and those which are fit for Nourishment, are volatiliz'd.

_Lastly_, There are some others who reject the Opinions I have already mention'd, and suppose the Digestion of the Food to be perform'd by the Benefit of a Ferment; which, when it is mixed with the Aliment, excites in the Mass an intestine motion; and the different and contrary motions and tendency of the Parts, making some kind of Collision, gradually break off Particles from the grosser, and more solid Parts, till they are so attenuated as to be apt to mix more equally with the Fluid, and with them to make one soft or chylous Substance. But yet there is not amongst them an universal Consent, either about the Nature of this Ferment, or the manner how it is supply'd. For first, some think it to be the Remains of the Food that was last digested; which having lain some time in the Stomach, after the rest is carried down into the Intestines, contracts an Acid, or some other Quality, and is so alter'd, as to partake of the Nature of a Leaven. And this Leaven being a part of the Food, which has been already digested, is so soft and liquid as to be capable of mixing with the Aliment, which is next taken into the Stomach; and being agitated with it by the repeated Pressures of the Diaphragm, Liver, and Abdominal Muscles upon the Stomach in Respiration, does diffuse it self through the whole Mass; and being mixed with it, like Leaven, or Yest added to new Wort, _&c._ puts it into a State of Fermentation; and by this Fermentation, or the Expansion of the Ferment, and the more tenuious Parts, which are first put into motion by it, those which are more solid, and with which they are intermixed, are rent, and divided, and so attenuated, as to become a soft and pulpous matter. And altho' the greatest part of the Food, that is thus broken and concocted, is by the Contraction of the Fibres of the Stomach press'd into the Duodenum; yet they do not contract themselves so as to force out all the Aliment, but leave between the _Rugæ_ or Folds, on the inside of the Stomach, a sufficient Quantity to be a Leaven to the next Meal; and so from time to time.

Some have a Notion, That this Ferment, or Principle of Fermentation, is in the Aliment it self; which being a Congeries of Matter, consisting of various Parts of a different Nature, is no sooner enclosed in the Stomach, and digested in the Heat of that, and the adjacent Parts, but the more spirituous and subtil Particles are put into motion both from that Warmth, and the difference of their Natures, and enter upon a Fermentation. And so by their intestine Commotion, and the Violence they offer to those Parts which oppose the tendency of any of them, they break and dissolve what is more solid.

Again: Some suppose, that this Ferment is supply'd from the Glands of the Stomach.

And Lastly, Others, and perhaps with much better Reason, contend for the Saliva, and make that to be the Ferment, which serves principally for the Digestion of the Food; which in Mastication being mix'd with our Aliment, is with that carried down into the Stomach, where the Parts of it being put into motion by a kindly and agreeable Heat, they do ferment with, and exagitate first those Parts of the Food which are most apt to ferment with it, and then both conspire to break and dissolve the grosser and more stubborn Parts. And _Galen_, in the Book I have before-mention'd, plainly allows that the _Saliva_ is concern'd in the business of Concoction, tho' he supposes the Alteration, which is produc'd by this Juice, to be made in the Mouth, as appears from these Words: _Quæ (alteratio) in ore agitur mutat quidem id (nutrimentum) in alteram speciem manifestè, non tamen ad perfectionem transmutat--Qui mansi sunt cibi primum quidem hac Pituita (oris) imbuunter, & cum ea miscentur----Itaque majorem mutationem consecuti sunt, quam ii, qui in vacuis dentium intervallis fuere impacti_.

Now I have given this short Account of the various Opinions of some Ingenious Men, concerning the manner how Concoction is perform'd; I come now to propose my own Hypothesis, by which I shall endeavour to explain it.

In order to the more easie and effectual Digestion of the Food, Nature has appointed some Parts for the breaking our Aliment, and reducing whatever is gross into smaller Parts, before it is put upon Digestion: Others to supply the Ferment, by which it is to be dissolv'd and concocted, and which, before it comes to be included in the Stomach, does moisten, and make it more soft, that it may more easily be penetrated, and broken by those Parts which serve to divide every Morsel into smaller Pieces, and prevents the Inconvenience and Trouble which would arise from the Nourishment sticking about or between them, when it is dry or viscous.

For the breaking of that part of our Food, which is not liquid, Nature has furnish'd us with Teeth, and those of two sorts: For some are ordain'd to divide and break off smaller Morsels from a larger Mass; others are made for the grinding those Morsels into much smaller parts. The Teeth, which serve to break off Pieces of a convenient Magnitude from a larger Mass, are of two sorts, accommodated to the Nature of the Substance which we eat. These are the _Incisores_, and the _Dentes Canini_. If the Substance, which we have to eat, be not hard, but more easily penetrated and divided, then the _Incisores_ are capable of making an Impression upon it, and fix'd firmly enough in the Jaws to break off that part which they take hold of. But if it be more solid, and not easily penetrated, nor any Piece without difficulty to be separated from that Body, whereof it is a part; then we apply the _Dentes Canini_, or Eye-Teeth, to it, which are not spread, nor have such an edge as the _Incisores_, but are sharp and pointed like an Awl, and so do more readily penetrate a Substance that is hard, and which the _Incisores_ can scarcely make any Impression upon. And as the Parts of a more solid Body are commonly with more difficulty separated, and there must be a greater stress put upon those Teeth which pull it into pieces; so these Teeth are much more firmly fixed in the Jaws than the _Incisores_, tho' they have but one single Root. Besides, the Position of all these Teeth is accommodated to their use, as being planted opposite to the Aperture of the Mouth; so that they may be conveniently apply'd to the Substance which we have to eat, before it is broken, and when it is too large to be admitted within the Mouth.

The Teeth which do by a Compression and Attrition reduce the little Morsels to smaller Parts, are from the manner in which they break the Aliment, called _Dentes Molares_, because they do, like so many Mill-stones, grind the Food between them. And that they might be render'd fit for this purpose, they are made broad at that Extremity, which stands out of the Gums, by which means they retain some Quantity of the Food between them every time the lower Jaw is pulled up and forc'd against the _Maxilla superior_. And as they are broad, so they are formed with Inequalities and Protuberances; and by the motion of the lower Jaw, from one side towards the other, they grind what they have between them into pieces. The Position of these Teeth too is as convenient as that of the _Incisores_, and the _Dentes Canini_: For being design'd to break those pieces of our solid Food, which are taken into the Mouth, and these pieces, when they are compress'd, and mov'd by the _Dentes Molares_, being apt to fly out of the Mouth, if there were no Contrivance to prevent it, they are placed beyond the Aperture of the Mouth, and opposite to the Cheeks, which keep the Food within that Cavity, and not only so, but press it in between the _Dentes Molares_ on one side, as the Tongue does on the other, until they have sufficiently broken and divided it.

At the same time, whilst the _Dentes Molares_ are breaking the Food, there flows into the Mouth a Salival Juice, which mixes with it, and not only serves to moisten it, and to render it more apt and easie to be divided, but seems to be the Ferment, by the Benefit of which the Food is dissolved and digested. And therefore it is intimately mixed with it, by the Teeth agitating or stirring them together in Mastication.

This Liquor, which we commonly call the _Saliva_, or Spittle, seems to be a Composition made of two several Juices, very different in their Nature: And therefore the several Parts of it are separated by their proper Glands, and Nature has planted no fewer than four Pair about the Mouth, which supply the Juices that make the _Saliva_; to wit, the _Parotides_, and the _Glandulæ Nuckianæ_, the _Glandulæ Maxillares internæ_, and _Sublinguales_. Whereas if the _Saliva_ were but one more simple Liquor, a less number of Glands might have been sufficient. At least there appears no Reason why one of every Pair should disembogue itself into the Mouth so very near to the Orifice, by which a Gland of some other Pair throws in its Juice; and they are not rather all planted at more equal distances from one another, so to flow in upon every part of the Aliment at the same time.

Not that I suppose, as there are four Pair of salivatory Glands, so there are four sorts of Juices supply'd from them, to make the _Saliva_; but, as I hinted before, that there are only two different Juices that constitute it. And these are not only sufficient, but more proper to excite and secure that Fermentation, which is necessary to Concoction. For we find that most of those Fermentations, which arise upon Mixtures made for Experiments, are produced from the mixture of two things; and it is not so easie to find out three or four such Liquors of a different Nature, as will, upon the mixtion of them all, produce a Fermentation, and from the omission of any one of them discover no Discord or Disposition to ferment: Besides, it is certain that two do better secure the End, which Nature designs. For, if there were three or four different Juices, of which the _Saliva_ naturally consists, these must all have their proper Qualities preserved to them, or else the Fermentation, which should arise between them, will not necessarily follow upon their mixture; and it is certain, that there would be more Danger, that one of three or four should be deprived of its Natural Quality, than one of two.

What Nature these two Juices are of, I do not pretend positively to determine; but so far as I have been able to make my Conjectures about it from Experiments, I do think one of them to be an acid Juice; the other an oleaginous Liquor, something like Oil of Turpentine. For amongst the many Experiments I have made, there was no one that gave me so much Satisfaction, as that which I made with Oil of Turpentine, and Oil of Vitriol, though I try'd several other things, that will produce a Fermentation upon their Mixture. And it was for this Reason, that I made the Experiment with Oil of Turpentine and the other Oil.

I took a piece of raw Flesh, and having cut it into pieces, but much larger than what our more solid Food is reduc'd to by due Mastication, I mix'd some Crums of Bread with it, then I pour'd in the Oil of Turpentine to them, and upon that the Oil of Vitriol; and having shak'd them together, I digested them about four Hours in _Balneo Mariæ_, and then shaking them again in the Glass, I found the Meat dissolv'd, and they all became a thickish Pulp. I could not but take notice, that Oil of Camphire (though it does not otherwise seem much different in its Nature from Oil of Turpentine) and Oil of Vitriol, which upon mixture will produce an Effervescence as well as the Oil of Turpentine and Oil of Vitriol, yet did not touch the Meat, upon which I poured them, so as in the least to dissolve them. I cannot deny but that an Acid, and a Solution of Salt of Tartar, did dissolve some part of the Flesh-meat, which I mix'd them with, but yet neither so soon, nor so perfectly as the two forementioned Oils. And I do the rather think one of those Juices, which constitute the _Saliva_, to be of the Nature of Oil of Turpentine, than of a fix'd Salt, because it will correct and temper even Oil of Vitriol, so as to render it more tolerable to the Fibres of the Stomach. Not that I suppose the acid part of the _Saliva_ to come near to the Acidity of Oil of Vitriol. For though, when they are mix'd, they will make a Liquor that may not be injurious to the Stomach; yet the acid Juice, if it were so corrosive as Oil of Vitriol, would certainly be injurious and painful to the Salivatory Ducts, which convey it to the Mouth before it is mix'd with the oleaginous Liquor. But I only say it is an Acid, and in some degree approaches to the Nature of that Oil. And Nature, which can much better adapt several Causes for the Production of such an Effect than Art, may attain her End by a more temperate Acid; though, at the same time, we may be able to make some probable and true Conjectures about the Nature of those Causes from Experiments.

It being most reasonable to suppose, that there are but two sorts of Juices, of a different Quality, that make the _Saliva_, I do conceive, that four of the eight Salivatory Glands, or two Pair of the four, do supply one of these Juices, and the other four Glands the other. And this seems to be a very good Reason, why they are so planted, and the Orifice of their Ducts so order'd, that the Juice, which is supply'd by one Gland, is discharg'd into the Mouth, very near to the Orifice, by which the Juice of a different Nature is transmitted from another, so that they must necessarily meet and mix together. Thus the _Glandulæ Nuckianæ_, and _Parotides_, throw in two different Juices by Orifices, which open into the Mouth very near to one another; and the _Glandulæ Maxillares internæ_, and _Sublinguales_, do below supply the same kind of Juices by Orifices, that open so near to one another as to secure the mixture of the two different Juices.

These Glands, I say, do between them afford two divers sorts of Liquors, of such a Nature as are apt to ferment upon their first Mixture, but perhaps more considerably when they come to be digested by the Heat of the Stomach. So that the Colluctation, or Fermentation, which attenuates and concocts the Food in the Stomach, does not ordinarily arise between the Aliment and the _Saliva_, but between the several Parts of the _Saliva_ it self. And indeed, if the _Saliva_ did not consist of two Juices, whose Nature is in such a manner different, as to render them apt to ferment upon their mixture, it would be very hard to conceive how it should so readily and indifferently serve for the Digestion of all Eatables; how it should ferment with, and dissolve so great a variety of Things, not only of a different, but of a contrary Nature; how it should ferment with Acids as well as Alkalies, digest things that are cold, as well as hot or temperate; some things that are salt, others that are insipid, bitter and sweet, mucilaginous, oily, _&c._ But if we suppose, that the Fermentation, which serves for the Digestion of the Food, arises from a peculiar difference in the Nature of two Juices, which constitute the _Saliva_, it will be easie to give a rational Account of our Concoction of innumerable things of a different Nature. And this seems to be as effectual, and a more certain way to attenuate and dissolve the grosser Parts of our Food, than if the Fermentation were made only between the _Saliva_ and the Aliment: Besides, the _Saliva_ seems to discover a Fermentation upon the mixture of its constituent Juices, even at those times when we do not actually eat; for it is always attended with Bubbles, and a Froth, when it has not been at all agitated in the Mouth, and many of those Bubbles will remain for some considerable time after we have spit it out.

Nature therefore having appointed the _Saliva_ for the digestion of the Food, has taken care that it shall be thrown in upon the Aliment on every side. Thus the _Glandulæ Nuckianæ_, and the _Parotides_, supply their Juices to that part of the Food, which lies on the outside of the Gums, between the Cheeks and the Teeth, and the _Glandulæ Maxillares internæ_, and _Sublinguales_, do bestow their Liquor upon the Meat, which is within the Teeth and Gums. Neither has she had a Regard only to that Supply, which is due to all the parts of our Food, but likewise to the mixture of the two different Juices of the _Saliva_, which is necessary to its Fermentation. And therefore, as I have already observ'd, the Orifices of the Ducts, which belong to one sort of Glands, are placed near the Aperture of a Duct, which conveys a Juice from one of the other Glands. So the Ducts of the _Glandulæ Nuckianæ_, and the _Ductus Stenoniani_, do on each side open into the Mouth, near one another; and the salivatory Ducts of the _Glandulæ Sublinguales_, and the _Maxillares internæ_, though they have distinct Orifices, empty themselves under the same _Papillæ_, and the Juices, which are supply'd by them, meet there, and flow into the Mouth together.

The several Parts of the _Saliva_ being discharg'd into the Mouth in such a manner as to meet and begin a Fermentation, the _Saliva_ does, partly as it is agitated, with the Food by the Teeth, and some other parts of the Mouth; partly by its own Fluidity, insinuate it self into, and mixes with the Food, and not only moistens and softens it, but excites the Fermentation, which is to dissolve it. And when the Aliment is thus mix'd with the _Saliva_, which serves to ferment the whole Mass, it is then to be convey'd into the Stomach, that great digestive Vessel of the Body, where the Fermentation is not only continued, but improved.

The Nourishment being convey'd into the Cavity of the Stomach, is there kept for some time in a digestive Heat, all which time it is under a Fermentation, produc'd by the different Parts or Juices of the _Saliva_, which are mix'd with it; which Fermentation does first agitate the more tenuious or subtil parts of the Food, and puts them into motion, and so with the Fermentation of its own, and those Alimentary Parts, which it first communicates a Motion to, improved by the Heat of the Stomach, the _Saliva_ must necessarily act upon the grosser Parts. For the intestine Motion, which is excited in the Mass, does not give the Particles, which are fermented, the same Tendency, but what is so various and confus'd, that they must inevitably strike not only one against another, but against those which are more gross, so as to attenuate them, sometimes by a Collision, which strikes off smaller Particles from the larger Parts; sometimes by a Compression, when the Particles which are in Motion, happen to strike directly against any grosser Part, on every side of it, sometimes by a kind of Explosion. For without doubt the _Saliva_, which is fluid, insinuates it self into the Interstices of the more crass Parts of the Aliment, and whatever is agitated and expanded in those Interstices, requiring a larger space for the Freedom of its Motion, and offering a Violence to every thing that opposes its Tendency, will, like Gun-powder included in a Shell, force its way out, and tear to pieces that Matter, which does endeavour to confine it.

Thus the grosser Parts are broken and divided, until they are at last so far attenuated as to mix more equally with the Fluid, and with them to make one Pulp or Chylous Mass. And although I do not apprehend how the Stomach should by its reciprocal Motions in Inspiration and Expiration, be able to break and attenuate any Matter, that will not be softned and dissolved by Agitation in a Liquid; yet it is certain that these Motions, caused by the Diaphragm and Abdominal Muscles in Respiration, do make those Parts, which are broken off, as they are dissolv'd, mix intimately with the more Liquid; as the Meat which I digested with Oil of Turpentine, and Oil of Vitriol, did by Agitation mix more equally with the Oils, and became a Pulpament.

As the Juices, which constitute the _Saliva_, do ferment upon their mixture, so it is probable, that from their Mixture and Fermentation there results such a _Tertium quid_, as is apt to ferment with the Bile. And therefore, when the Aliment has been under the Fermentation, excited by the _Saliva_, a sufficient time, it is then thrown into the _Duodenum_, where it meets with the bilious Juice, which flows into that Intestine from the Liver, from which a new Fermentation seems to begin; and the Commotion of the Parts of the Aliment being still continued, does carry on the Business of Digestion until the Food is perfectly concocted: Though it is probable, that this new Fermentation serves not only for the more perfect Digestion of the Food, but likewise for the Separation of the Chyle from the feculent Parts.

Neither do I by a random Guess, and an ungrounded Conjecture, suppose that from the Mixture and Fermentation of the two Juices, which constitute the _Saliva_, there results a Matter, which is apt to ferment with the Bile. But to me the Notion seem'd to be confirmed by an Experiment that I made. For considering with my self, that the Bile is generally allow'd to have much of a saponary Nature, I made a Solution of Soap in fair Water, and mix'd it with the Oils of Turpentine and Vitriol first put together, and from their Mixture I observ'd a very easie and gentle Fermentation, which continued for a considerable time.

_A Discourse concerning some Influence of _Respiration_ on the _Motion_
of the _Heart_, hitherto unobserved. By _J. Drake_, M. D. F. R. S._

Tho' divers accurate Treatises of the _Heart_, and its Action, have been written by Learned Men of several Nations, especially by two of our own Country; the Great Dr. _Harvey_, to whose happy Sagacity this Nation owes the Glory of the Invention of the _Circulation_ of the _Blood_; and the incomparable Dr. _Lower_, to whom we are beholden for a compleat Display of the _Mechanical Structure_ of the _Heart_, and a most ingenious Rationale of its Action. Yet there remain several Doubts and Difficulties about it (in my Opinion) not sufficiently accounted for; towards the resolving some of which, I shall offer what my own Thoughts have suggested to me, and leave it to the Consideration of the Reader.

The Learned Dr. _Lower_ (whose accurate Piece on this Argument will insure his Reputation so long as Physical Knowledge shall last in esteem) has so well accounted for the _Systole_, or Contraction of the Heart, from the _Mechanical_ Structure of it, that he seems almost to have exhausted the Subject; and had he been as happy in discovering the true cause of the _Diastole_, he had left little room for the Industry and Sagacity of others about this _Viscus_.

But having judiciously and solidly explain'd the _Systole_, he contents himself to ascribe the _Diastole_ to a motion of _Restitution_, which account gives me no Satisfaction: Because the _Systole_ being the proper, and (as himself confesses) the only motion of the Heart, a State of _Contraction_ seems to be the natural State, and consequently without External Violence, it shou'd have no _Diastole_ at all.

This will appear more plain, if we consider the Circumstances of it, and its Motion, as a Muscle, with respect to other Muscles. That Contraction is the proper Action, and State of all Muscles, is evident from Experience of Fact, as well as Reason. For, if any Muscle be freed from the power of its _Antagonist_, it is immediately _contracted_, and is not by any Action of the Will, or Spirits, to be reduced to a State of _Dilatation_. Thus, if the _Musculi Flexores_ of any Joint be divided, the _Extensores_ of that Joint being by that means free'd from the contrary Action of their _Antagonists_, that Joint is immediately extended without any consent of the Will, and in that State it remains; and so _Vice versa_, if the _Extensores_ be divided. From whence it is plain, that the Muscles have no restitutive Motion, but what they derive from the Action of their _Antagonists_, by which they are balanc'd. Thus likewise the _Sphincters_ of the _Gula_, _Anus_ and _Vesica_, having no proper _Antagonists_, are always in a State of Contraction, and suffer nothing to pass them, but what is forced through them by the contrary Action of some stronger Muscles, which, though not properly to be call'd _Antagonists_, yet on all necessary Occasions perform the Office of such.

That the Heart is a Muscle, furnish'd and instructed for Motion like other Muscles, is (in my Opinion at least) demonstrated beyond Contradiction by Dr. _Lower_ and others. And, as it is a _Solitary_ Muscle without any proper _Antagonist_, and not directly under the power of the Will, nor exercising _Voluntary_ Motion, it approaches nearest to the _Sphincter_ kind, which only has these Conditions in common with it. But in constant and regular Alternations of Contraction and Dilatation, it differs exceedingly from all the Muscles of the Body.

This _reciprocal Æstus_ of the Heart has given the Learned abundance of trouble; who, finding nothing peculiar in the Structure, which shou'd necessarily occasion it, nor any _Antagonist_, whose re-action should produce it, have been extreamly perplex'd to find out the cause of it.

But passing over the various Opinions of Authors, to avoid being tedious, I shall take notice here only of the very Learned Dr. _Lower_'s, in whose Account of the _Systole_, however solid and ingenious, I observe something deficient, and whose _Hypothesis_ of the _Diastole_ I think to be precarious and false.

This Excellent Author, having by sound Arguments drawn from the Structure and Mechanism of the Heart, establish'd the Certainty of its _Muscular Motion_, rests satisfied, without taking notice of any Assistance, that the Heart receives from any other Part, except from the Brain, by the means of the eight pair of Nerves.

[Sidenote: _Part_ 2_d_. _Prop._ 67. _Prop._ 73.]

[Sidenote: _Prop._ 76.]

The Accurate _Borellus_, in his _Oeconomia Animalis_, computes the _Motive_ Power of the _Machine_ of the Heart to be equal to, or to surmount that of a Weight of 3000_l._ The _Obstacles_ to the Motion of the Blood thro' the _Arteries_ he esteems equivalent to 180,000_l._ which is 60 times as much as he rates the Force of the Heart at. Then deducting 45,000_l._ for the adventitious Help of the _Muscular Elastic Coat_ of the _Arteries_, he leaves the Heart with a Force of 3,000_l._ to overcome a resistance of 135,000_l._ that is, with 1, to remove 45.

This stupendous Effect he contents himself to ascribe to the _Energy_ of _Percussion_. But, had he proceeded in his Calculation to the Veins, which he allows to contain constantly a quantity of Blood, quadruple to the Contents of the Arteries, and to which this _Energy_ of _Percussion_ does either not reach at all, or but very languidly, he might probably have seen a necessity for some other Expedient to remove so insuperable a Difficulty.

But not to insist rigorously on the Exactness of this Calculation, (though the great Abilities of the Author in this way, and his Ingenuity and Modesty, are a sufficient Warrant for the Accuracy of his Computations, and the Fidelity of his Accounts) we may allow a much greater Deduction, than would be justifiable, without lessening the Difficulty. But this Account I have taken notice of purely for the sake of the Calculation, which may be of use in the Sequel; the account it self being in other respects more defective than Dr. _Lower_'s, to which we will return.

The Doctor, notwithstanding his great Sagacity, appears (to me) to have overlook'd something of very great moment, and importance in the explication of the Action of the Heart. For, tho' it should be granted, that the _Muscular Fibres_ of the Heart acted by the Nerves, are the immediate Instruments of its _Constriction_ or _Systole_, yet it must not be denied, that the _Intercostal_ Muscles and _Diaphragm_ are of great service to aid and facilitate this Contraction, by opening a Passage for the Blood through the Lungs, which denied would be an invincible Obstacle.

Neither do they promote it that way only. The manner how they farther assist the Heart in its Contraction, will appear manifestly, if we consider the different Posture, Situation, and Capacity of the Blood-Vessels of the Lungs in the several times of _Elevation_ and _Depression_ of the _Costæ_.

The _Pulmonary_ Artery rises from the _right_ Ventricle of the Heart, and runs in one Trunk, till it comes to the _Aspera Arteria_, where it is divided, and sends a Branch along with each Division of the _Aspera Arteria_, according to all the minutest Subdivisions, of which it is likewise subdivided, accompanying all the _Bronchi_, in their whole progress through the Lungs.

The _Pulmonary_ Vein, which empties itself into the _Left_ Ventricle of the Heart, spreads it self on the _Aspera Arteria_ and _Bronchi_, in the same manner that the Artery does.

The necessary confluence of this Disposition if, that this Artery and Vein being co-extended with, and fasten'd to the _Bronchi_, must needs suffer such alteration of _Superficial_ Dimensions, as the _Bronchi_ do in the _Elevation_ or _Depression_ of the _Costæ_.

While the Ribs are in a State of _Depression_ (whether before Commerce with the External Air or after) the _Annular Cartilages_ of the _Bronchi_ shrink one into another, and by that means their _Dimensions_ are exceedingly contracted. In conformity to this condition of the _Bronchi_, the _Pulmonary_ Artery and Vein must likewise, either by means of their _Muscular_ Coats, contract themselves to the same _Dimensions_, or lye in _Folds_ or _Corrugations_, which is less probable.

On the other hand, when the Ribs are elevated, and the _Diaphragm_ bears downward, the Air rushing into the Lungs, shoots out the _Cartilaginous_ Rings, and _divaricates_ the Branches of the _Trachea_, and by them extends and divaricates the several Divisions of the _Pulmonary_ Artery and Veins, and thereby lengthens and enlarges their Cavities.

This enlargement of their Cavities is very considerable, not only upon the score of the addition, which they receive in length thereby, but also upon the account of their _Divarication_. For whereas, when the Ribs are depress'd, and the Lungs subside, the Blood-vessels are not only contracted, (as I have already observ'd) but their Branches, which are exceeding numerous, approach one another, and lie in _juxta-position_, by which their Cavities are very much compress'd and streighten'd: When the Ribs are elevated, and the Lungs turgid with Air, not only the Fibres, by which their Coats in the opposite state were contracted, are extended; but those innumerable Vessels, which lying before in lines almost parallel upon one another, compress'd one another, making an _acute_ Angle at their Junctures, are divaricated and separated from each other, and make an _obtuse_, whereby their Channels are widened.

Thus a passage is open'd to the Blood, from the _Right_ Ventricle of the Heart to the _Left_, through the Lungs, to which it could not otherwise pass; and the opposition, which the Blood contain'd in that Ventricle, must otherwise necessarily have made to its Constriction, is taken off, and the _Systole_ thereby facilitated.

Nor is that all. For the _Diastole_ being caus'd (as I shall in the Sequel shew) by the force of the Blood rushing into the Ventricles, this Ampliation and Extension of the _Pulmonary_ Artery is a sort of _Check_ or _Counterpoise_ to it, and prevents an endeavour towards two contrary Actions at once, which must necessarily frustrate both. For the Heart being a _Springy_, _Compressible_ Body, whose proper Action, which is Contraction, depends on the influx of certain Fluids into its Fibers, or Substance; and containing besides a Fluid in its _Ventricles_, or great Cavities, in one of which is the Mouth of this Artery, the action of this Vessel must in great measure resemble that of a _Syringe_, whose extremity is immers'd in Water, the Enlargement or Expansion of the Chanels of the Artery answering the drawing of the _Embolum_, as the constrictive motion of the Muscle of the Heart does the pressure of the _Atmosphere_ upon the _Surface_ of the Water, the one making way for the fluid, and the other forcing it to follow, where the resistance is least. In this Sense we may allow a sort of Attraction to the _Pulmonary_-Artery, depending wholly upon the Action of the _Intercostal_ Muscles and _Diaphragm_, which we must therefore confess to be very serviceable and instrumental in promoting the _Systole_ of the Heart.

But if the Learned Author be deficient in his Account of the _Systole_; that is, if he has not observ'd all the Mechanism and Contrivance of Nature for the Contraction of the Heart; much less sufficiently has he accounted for the _Diastole_, or Dilatation of it, which he ascribes to a motion of _Restitution_ of the over-strain'd Fibres, which yet he confesses are made for _Constriction_ only. 'Tis true, he immediately after joins the _Influx_ of the _Blood_ as a concurrent Cause; but from the slight notice that he takes of it, 'tis plain, that he did not so much as dream of any great share it had in that Action. His Words are these:

[Sidenote: _De Corde, Pag. 75._]

_Quin & (ut obiter hoc moneam) omnis motus contractione perficiatur, & Cordis Fibræ ad constrictionem solum factæ sint, apparet quoque Cordis motum _totum_ in _Systole_ positum esse; cumque Fibræ ultra tonum suum in omni constrictione eius tendantur, idcirco ubi nixus iste absolvitur, motu quasi _restitutionis_ Cor iterum relaxatur, & sanguine à Venis _influente_ rursus distenditur; à _nullo_ enim cordis motu, nisi _tensionem suam remittente_, & ab _irruente_ sanguine _Diastole_ ejus libratis adeo viribus succedit._

I have transcrib'd the intire Paragraph, because it contains his whole _Hypothesis_ of the _Diastole_, and all the notice that he takes of it through his whole Work. But how slender soever this may prove, it is the most substantial that I have any where met with, except a late one of Mr. _Cowper_, which is properly an Improvement of this, and shall be consider'd in the Sequel.

But if Contraction be the sole Action of these Fibres (as this Great Man confesses it to be) and as indeed it is of all _Muscular_ Fibres, I wonder how so judicious a Writer came to slip into such an Absurdity, as to call their Distention (vulgarly but improperly call'd Relaxation) a Motion of _Restitution_. For from the Nature of those Fibres, and their disposition in the Structure of the Heart, the natural State of the Heart appears manifestly to be _Tonical_, and its Dilatation a State of Violence; and consequently, the Constriction is the _true_ motion of _Restitution_, and the State to which it will _spontaneously_ return, when the Force is taken off, which is the work of the _Intercostal_ Muscles and _Diaphragm_.

Thus we are left still to seek for the true Cause of the _Diastole_, which seems to me to be the main and most difficult _Phænomenon_, relating to the Heart and the Circulation of the Blood. But in Mr. _Cowper_'s ingenious _Introduction_ to his _Anatomy of Humane Bodies_, I find the Share which Dr. _Lower_ hints the Blood to have in that Action, further prosecuted, and improved into the main Instrument of the Dilatation of the Heart, wherein I agree intirely with him. But as to the manner, and reasons of its being so very instrumental, I can't be so perfectly of his mind.

_The Heart (_says this accurate Anatomist_) of an Animal bears a great Analogy to the Pendulums of those Artificial Automata, Clocks and Watches, whilst its motion is performed like that of other Muscles, the Blood doing the Office of a _Pondus_._

This Explication, being but a Simile without a distinct application to Particulars, is beside so very short, that I can at best but give a conjecture at the meaning; which if I mistake, I shall deserve to be excused, and expect to be better inform'd.

By the _Bloods_ doing the Office of a _Pondus_, I suppose he means, that the Blood contributes in the same manner to the motion of the Heart, as the _Weights_ do to that of the _Pendulum_ of a _Clock_. If so, the Blood, according to him, must be the Instrument of _Constriction_; and _Dilatation_ must be the _Natural_ State, or _Spontaneous_ Motion, to which it wou'd, when under no violence, return; the contrary of which, I presume, will appear e're I have done.

But if he means, that the _Blood_ in its reflux, by _gravitating_ on the _Auricles_ and _Ventricles_, dilates and expands 'em, acting therein as a _Counterpoise_ to its contractions as a Muscle, I cou'd wish his Design had not bound him up to so narrow a compass, and that he had given us an explication at large of so abstruse and so important a _Phænomenon_: Because the _Specifick Gravity_ of the Blood seems to me a cause by no means alone adequate to the effect, which it is here suppos'd to produce.

For, if the Blood acts only as a _weight_ by meer _gravitation_, then that part of it only which descends from the Parts above the Heart can be employ'd in that Action. This at the largest computation can't amount to Five pound weight, and must, according to the computation of _Borellus_, force a Machine, that is able to overcome a resistance of 135,000_l._ I leave every Man to deduct what he shall upon examination find reasonably to be deducted, and yet shall rest secure, that it is not to be effected in the least with so small a Weight.

But neither does the _Refluent_ Blood gravitate in any such proportion, as I have here assign'd. For to make a true estimate of its _Gravitation_, we must consider the Circumstances of the Liquor suppos'd to gravitate; in which it very much resembles Water inclos'd in a recurve Tube, of which, if the length of the two Legs be equal, it may be suspended in the Air full of Water, with the Extremities downwards, without losing a drop, although the _Diameter_ of those Legs should be very unequal. The Case of the Arteries and Veins is pretty near a parallel to a Tube, so fill'd and inverted. For, if the Arteries and Veins be continued Tubes, (as by the Microscope they are made to appear) then supposing their contents to have no other determination of motion, than their own weight wou'd give them, the contain'd Fluids must be Counterpoises to each other. For the Veins and Arteries being join'd at the smaller Extremities, and the larger of both terminating in the same parallel Line, it is impossible, according to the Laws of _Hydrostaticks_, that the contents of either shou'd overbalance t'other. How far then must it fall short of forcing the natural Power and Resistance of so strong a Muscle as the Heart, by meer Gravitation?

The Blood indeed has a _Progressive_ Motion through its Vessels, wherein it differs from Water, in a recurve Tube, in the Experiment above-stated. But, if the natural Gravitation of the Blood contributes nothing to the Dilatation of the Heart, this progressive Motion will not be found much more sufficient. For, as this Motion is deriv'd intirely from the Heart's Constriction (as all Accounts hitherto derive it) cou'd the Blood be suppos'd to re-act upon it by the Heart, with all the force first impress'd upon it by the Heart, it would be insufficient, unless we will suppose the _Force communicated_ to be superiour to the _Power Communicant_, which is absurd.

But when the just and necessary Deductions for the Impediments, which the Blood meets with in its Progress through the Vessels, shall be made, the remaining Force will be found so exceeding weak, that to prop the Blood through the Veins may be a task alone too great for so small a Power, without charging it with the additional difficulty of forcing the Muscle of the Heart.

_Alphonsus Borellus_, after a great deal of solemn pains taken to shew his Care and Exactness, and to possess his Reader of the Truth of his Calculations, casts up the force of the Heart, and the _Muscular_ Coat of the Arteries, to be together equal to a weight of 3,750_l._ and allots them a Resistance equal to 180,000_l._ to overcome which is 45 to 1. To make up for a disproportion, by his own confession, incredible to those who have not consider'd the Matter as he had done, he flings into the Scale the additional _Force of Percussion_, which he leaves _indefinite_, and thinks sufficient to _force any quiescent finite Resistance whatsoever_.