To these may be added the Singultus or Hiccough, by which the Ventricle, when too full, endeavours to relieve her self, either by throwing off some of the rarifi’d Contents by the Gullet, or perhaps by the Pylorus.
Lastly, Let us consider how Laughter affects us, and it will appear, that this Contrivance of Nature, wherein the Body does sympathize with the Mind, proves so beneficial, by the playing of the Muscles of the Thorax, and the pressing out of the saline Particles, so frequently and sensibly as it does in some chearful People, to whom it is more habitual than others, insomuch that it comes to be Proverbially, a Cause of Fatness. All these Instances shew, that Nature seems to receive more Relief from the Compression or acting of the containing Parts strictly taken, than most Men easily imagine.
As to extraordinary Efforts of Nature, to pass by what happens upon a sudden Surprize, Fear, Passion, or the like; it is certain, that Torture will raise the Spirits for some time very much, and there are as great Effects follow upon Irritation, which does not come up to the perfect Notion of Torture. What wonderful Effects do we see produc’d by strong Emeticks given by Surgeons in some Cases of the Limbs and extreme Parts? Where a Person so griev’d has oftentimes a robust Constitution and perfect Health, there the Medicines, tho’ given inwardly, cannot be suppos’d to act after the common manner of Alteratives, by passing into the Blood, by the Spirituousness of their Parts, or the like; for the Person being in Health needs no Alteration to be made in the Blood, and other Juices, which are as good as they can be desir’d to be; but by the Irritation of the Fibres in the Ventricle, the Spirits are rais’d to the highest pitch they are capable of, and brought to communicate that Elasticity to the whole Body, all the Springs of Life are wound up, all the Pumps of Nature (if I may so speak) set a playing, and by these means the Agony is extended to the extreme Part affected, and the Matter fixt there is attenuated and brought to flow, that it may be absorb’d by the Blood, and discharg’d in the Circulation; Nay, we may take notice of the great Power of a more gentle Irritation of those Fibres in those weaker Hysterical People, whose Spirits are of so fine a Make, or so scatter’d and weakened, that they can’t long bear Fasting, without very troublesome Symptoms following upon it, for they, we may perceive, are in a sense strengthen’d at those times that the Contents of the Stomach happen to be so rarifi’d, as to cause a gentle Ægritudo, a lingring Sickness and Nauseousness, tho’ not sufficient to cause ’em to vomit, for they shall then dispense with the want of that Food, without which at other times they could not possibly subsist with any tolerable Ease, and find themselves as strong and as free from their Tremors, Shiverings, and other ill Symptomes, as if they had eat and drank plentifully; and likewise during that Sickness the Salts shall come off plentifully in the Urine, which will then recover its proper Colour, tho’ it was before as limpid as common Water; from hence it is manifest, that the Animal Spirits may be made to expand, dilate, or in some ways act upon themselves, without the encreasing their quantity by such internal Medicines as may be suppos’d to be converted into their Substance.
Having premis’d these things, I shall proceed to enquire, after what manner Nature endeavours to clear her self of some few Distempers, which I shall consider in their proper place, and likewise how she may the more easily succeed in those Endeavours, if duly assisted by moderate Exercise; which Assistance, if it at first View may seem too slow and gentle to produce so great Effects, will yet with the Allowance justly due to all sorts of Alterative Physick, viz. of a Habit or frequent Repetition, appear to be sufficient to procure those Ends I shall assign to it.
There is this Difference between the most compleat Productions of Humane Artifice, and that Divine Piece of Mechanism, the Body of Man, that the former are always the worse for wearing, and decay by Use and Motion; the latter, notwithstanding the Tenderness of its Contexture, improves by Exercise, and acquires by frequent Motion an Ability to last the longer; and tho’ the Circulation, and continual and infinite Succession of Particles, are the immediate Cause of Life, yet the Health, the Strength, the Well-being of the Individual, is in great part owing to the Effects of a General Motion superinduc’d to these internal Motions; which it is so far from disordering, that it aids and assists ’em to a greater degree than we are wont to imagine; for in our Considerations of the Animal Oeconomy, we seem to regard Nature only as in a quiescent State, without a due Allowance for the Alterations caus’d by the Motion of the whole, which yet are confess’d by all to be sometimes of great Consequence: for that General Motion acting both on the Fluids and Solids of the Body, may sometimes prove the last and best Resort for the Restoring the Æquilibrium between ’em.
As for the Fluids; One would think the Shape and Make of the Blood-Vessels were sufficient alone to lead us into an Opinion of the Necessity of Exercise; by reason they all terminate in a Cone, they must needs resist the Passage of the Blood incomparably more than they would have done if they had been Cylindrical; and tho’ all the Branches of the Capillary Arteries, would, if taken Collectively, make a greater Diameter than that of the great Artery, yet the Consistence of the Blood, and the extreme Fineness of those invisible Meanders, require the frequent Pressure and Assistance of the Muscles to encrease the Circulation, which accordingly we always find very much augmented by those Means; yet ’tis the Result of this swifter Current of the Blood, which should be most valuable to us, I mean the better Digestion and Mixture of the various Particles convey’d into the Blood. I believe it will be allowed on all hands, that the best way to bring an Animal Fluid to a greater degree of Perfection, is Digestion; and the Excellency of that Operation consists in the just Degree of Heat which causes it; or, to speak perhaps more properly, in the just Agitation or intestine Motion of the Particles which may be suppos’d to occasion that Heat. The Standard or Measure of this Heat or Agitation in the Animal Oeconomy, is to be taken from what we observe in a Man in perfect Health, and in the Prime of his Age; when his Blood flows with its due Velocity, when there is an uninterrupted Secretion of all that is disagreeable to it, and it is wrought up to its florid Consistence, and a just proportion between the Serous and Grumous parts. Now this we may successfully imitate by repeated Exercise, when the Blood happens to be impoverish’d and Languid, we may encrease the Velocity of the Circulation, and consequently the Heat following upon it, by which a great many crude Particles will be attenuated and ripen’d, either for Mixture or Secretion, and there will be an equal Distribution of the attenuated Particles to the several Emunctories of the whole Body, by reason of the Solids co-operating with the Fluids; whereas it is often quite otherwise, when an internal Medicine is given design’d for one Secretion only, which may promote that, and perhaps hinder another; as a Medicine which agrees with the Stomach, sometimes offends the Head; for the Nervous Parts being, as it were, Passive in the Case, the Secretions cannot be so equally performed as when the whole Body is exercis’d. I would not be here mis-understood, as if I suppos’d that this first Effect of Motion, this Digestion, would avail in many Cases, as where an ill Ferment is lodg’d in the Glands, or where the Morbifick Particles have been long a forming, and are strongly combin’d in the Blood, but this may take place where a greater degree of Agitation is absolutely necessary; as when the Blood is Effete and Languid, when the Chyle comes into it dispirited, and when even a proper Medicine proves offensive and burthensome, and there is scarce Power enough left in the Blood to master its Particles, and apply ’em to their proper Uses; then, I say, ’tis time to make the Solids assist the Fluids in the dispensing of this Load which lies so hard upon ’em, which by gentle and close Exercise may be more easily done than many imagine; besides there may be a Distemper occasion’d by Particles of a looser Texture in the Blood, than is usual in most Cases, where Nature may contend and struggle with the hostile Particles, and yet not be able to get the Victory; where there may not be a perfect Fever, nor yet a quiet Coalition between the Blood and those foreign Particles. In such a Distemper as this, it must needs be very proper to give a due Agitation to the Blood, to prepare those Particles for the several Emunctories that are ready to receive ’em: and this may be perform’d by a just Digestion, if we do but consider how much the Body is adapted to it, and how much more Noble the Digestions are in the Animal Oeconomy, than those produc’d by humane Contrivance. In all artificial Digestions the Particles which are to be separated by the Agitation of the Liquor, must either evaporate, or subside; but in the Body there are a multitude of excretory Ducts ready to receive the Particles, of such a determinate Figure, as renders ’em excrementitious, and proper to be cast off; so that nothing is left but what is proper to the Animal Fluids, and which the Vehemence of the Motion mixes and unites at the same time that it breaks and moulds the others for their proper excretory Chanels; so that the Agitation is in this Case (as Dr. Grew very well expresses it in his Treatise of Mixture) as “carrying the Key to and fro, till it hit the Lock; or within the Lock, till it hit the Wards.” How do we know the exact Degree of Agitation, that is requisite to unite the Particles of the Fat, which are continually flowing in a very great quantity into the Blood, with the Aqueous, by the Means of sulphureous or saline Particles? Do we not frequently observe in scorbutick Persons, who have lead a sedentary Life, that their Urines are cover’d with an oily Film of several Colours? and is it not very natural to suppose from thence, that the Blood wants a due Motion to keep those oily Parts united with the others? But it is no wonder, if these things are not well consider’d, when there is scarce any who makes Allowance enough for the quantity of the fat Particles, which are continually passing into the Blood, which must needs be very great, seeing the whole Skin is lin’d with its Vessels, besides what is heap’d up about the Omentum and the Kidneys; so that Unctuous Medicines are copiously intruded upon the Habit of the Body when there is a great Wasting of the Flesh, without regarding that the Blood is not able to master the natural Pinguedo, but gives it down daily, in all probability, for want of a just degree of Agitation or Digestion, to keep it suspended in the Blood, and to apply it to its proper Uses, and prepare it for its proper Vessels.
Besides the Power of Exercise on the Secretions of Particles purely Excrementitious, and the better Mixture of those which are Homogeneous; it is to be consider’d, that there are in the Oeconomy Secretions made to return with Advantage into the Blood, out of which they are made; and the Consideration of the Nature of these does afford us fresh Reasons to set a Value upon the Use of Exercise, because the Body is so fram’d and adapted, as to require it, in order to the furthering and increasing these Operations; and if in the Business of Fermentation, which is only a gradual Separation of the Must from the Spirituous Particles of the Liquor, we find that the Motion of the Vessels in which the Liquor fomenting is contain’d, does so much improve that Operation, as we are convinc’d it does, by the Effects of the Carriage by Sea on Wines and other Liquors in Casks; of how much greater Importance must the Motion of the Body be, in order to the perfecting the Animal Fluids, in a System of Mechanism so contriv’d, as to expect and demand such an Assistance? Where the Solids are so fine-spun, as to determine the very Shape of the Particles of a Fluid; and where they are so dispos’d, that a Fluid never passes by ’em but it carries off some Melioration and Improvement, and therefore cannot well arrive too frequently at those Passages where it receives so happy an Alteration. Let us suppose the Blood to pass the most extreme Parts twelve times in an Hour, when the Body is not mov’d; if the Motion of the Body encreases this to fifteen or sixteen times in an Hour, it will necessarily follow, that the Quantity of the Secretions by the Liver, the Spleen, the Brain, and the rest of the Glands, which separate the beneficial Juices, of which I am speaking; the quantity of these, I say, must needs be augmented; which in Process of Time, when this is brought to a Habit, must be of some Consequence. To insist but on one of these Secretions; I take it to be no Paradox, that the more a Man stirs himself, the more Animal Spirits are made in the Brain; tho’ it will be strait retorted, that by the very same Motion and Exercise, there will be a Waste of the Spirits by Perspiration, more than proportionable to the Overplus that is made in the Brain; and tho’ I grant this, it will not suffice to discompensate the Benefit which the Blood reaps from the Augmentation of the Quantity of the Animal Spirits infus’d into it (if I may so speak) from the Brain; because the true Animal Spirits have their Work to do in the Blood, before they come to pass off at the Skin; they are not of that Fugitive Make, which at first Thought most Men are apt to suppose ’em to be; they seem to be destin’d to contemperate the Acrimony of the Blood, to embrue it with a Plastick Quality, and may serve to execute other Functions, besides that of Motion; so that it is not at all to be wonder’d, if a Person, much accustom’d to Exercises, notwithstanding the daily Expence of a greater Perspiration, should have his Blood of a better Condition, and more Rich than that of another Person living a sedentary Life, by reason of the greater Impression, the greater Tincture (if I may be allow’d so to speak) of this most exquisite and inimitable Fluid.
These Things are not to be stated exactly, and yet they are not to be accounted altogether precarious; for tho’ we shall never perhaps be able to know exactly what the Animal Spirits are, yet we may make a shift to distinguish what they are not. According to the common Notions, a well-prepar’d volatile Salt, after it has pass’d the Lacteals, and comes into the Blood, might be taken to be a pure Animal Spirit; and yet, undoubtedly, the Fluid, prepar’d by the Glands of the Brain, has something in it transcendently preferable to any thing that can be the Effect of Art. Whether those Glands are so dispos’d, as to unite some Nitro-Aerial Particles with others proper to serve as a Vehicle to ’em, is not to be determin’d by me or any Body else; but it may not be altogether so absurd, to guess at some such thing, since we know nothing in Nature that can afford Particles of that Elasticity as Nitre does; and we may discern, that the Animal Spirits seem to consist of a Fulgur, an Impetum faciens, something that is Irraditating; and yet withal there seems to be something extremely Mild and Plastick, and as it were Tenacious, combin’d with the Elastick. I hope I don’t run into an Hypothesis; I would carry this no farther than it can be kept in Countenance by Phænomena arising in the Cure of Distempers; for thus we see in the Nervous Atrophy, tho’ the Spirits, taken as Impetum facientes, pass freely, and are not obstructed, as in the Palsie, yet the Benign Plastick Quality seems to be wanting, because the Habit of Body does not thrive, tho’ the Spirits are brought all over it; and that the Spirits, when they are in their true Purity, are concern’d in Nutrition, is plain enough; because the intercepting of ’em, by cutting off a Nerve, always causes the wasting of the Part to which that Nerve lead.