AN ENQUIRY Into the EXILITY of the VESSELS In a Human Body,
&c.
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AN ENQUIRY Into the EXILITY of the VESSELS In a Human Body: WHEREIN ANIMAL IDENTITY is Explained, and shewn Incommunicable to any Individual throughout the whole Species.
By
CLIFTON WINTRINGHAM,
Jun. Fellow of the
Royal Society.
Profecto verisimile est, & Hippocratem & Erasistratum & quicunque alii, non contenti Febres & Ulcera agitare, verum quoque Naturam aliqua ex parte scrutati sunt, non ideo quidem Medicos fuisse, verum ideo quoque majores Medicos extitisse.
CELSUS in Praefat.
LONDON:
Printed for THOMAS OSBORNE in
Gray's-Inn.
MDCCXLIII.
TO Edward Wilmot, M.D. Physician in Ordinary to His Most Sacred MAJESTY the KING of
Great Britain,
and to his Royal Highness the Prince of
Wales;
Fellow of the College of Physicians in
London,
and of the
Royal Society.
SIR,
T HE following Enquiry containing several Particulars, which, tho' they have not been hitherto either regarded, or perhaps understood by vulgar Anatomists, may not on those Accounts at all the less tend to illustrate the surprizing Structure of Animal Bodies, requires the Protection of One, whose known Abilities in every Branch of Physick, may silence the Cavils of those, whose Penetration ends with the Edge of their Knife, or the Flowing of an Injection. This Consideration alone, had I no other, is a sufficient Warrant for my Application to you. But if the spontaneous conferring of Favours on such, as had no Claim to them, but the mere Benevolence of the Donor, demands a publick Acknowledgment; I should be wholly unpardonable, did I not take this Opportunity of returning you my Thanks for those singular Lights you was pleased to afford me during my Attendance at St.
Thomas
's Hospital, where I had not only my own Doubts resolved, but new Steps pointed out, by that uncommon Sagacity, which has raised you to the highest Pitch of the Profession, and rendered you so justly esteemed by all, who have the Honour of your Acquaintance. As these, Sir, were the Motives of this my Application to you, I thought myself excusable in not acquainting you with it, lest you should prevent me from thus acknowledging the Obligations I lie under, as well as declaring how much I am,
Sir, Your most obliged humble Servant,
C. Wintringham.
Feb. 3. 1742.
Bennet-Street, St. James's.
AN ENQUIRY Into the EXILITY of the VESSELS In a Human Body,
&c.
T HE Structure of the Animal Body, whether we consider the Size, Situation and Uses of its larger and more complex Parts, with relation to each other, and their Subservience to the whole, or by diving deeper into the secret and more mysterious Parts of Nature, we scrutinize the several Parts of which these are composed, exhibits to our View such an amazing Scene of unbounded Power and Wisdom, as infinitely exceeds all the Contrivance of the rest of the visible Creation, how great the Bodies, or astonishing soever their Motions and Revolutions may upon a strict Enquiry appear to us.
Arist. Ethic. lib. 5. cap. 1.
.
But tho' this Position is sufficiently evident from the Structure of every Organ in the Animal Body, yet it is in no Part so singularly astonishing, as in the Growth of Animals, from their first original Stamina in the Animalcule, till they arrive at their appointed Size.
That every Vessel and Fibre in the Body is contained in Miniature in an Animalcule, few, I believe, will dispute, it being absolutely impossible, that mere Matter and Motion, without its being conducted by the Vessels proper to an Animal, should produce an Animal at all; and still more absurd, if there can be Degrees in Absurdity, to suppose such a Cause capable of producing that Variety of Species, in their regular Order, which, we see, is constantly kept up thro' so great a Series of Years and Generations; but that instead of a Calf, a Cow might as naturally produce a Lion, Camel, or any other Creature, as frequently as its own proper Species.
Besides, could the Parts or Limbs, or even the most minute Organ be produced by the Motion of the Fluids, without their being conducted by the Vessels of the Organ itself already latent in the Stamina, what should hinder, why any Part taken away by Amputation should not again be perfectly formed and restored, since all the adductory Vessels continue in their former State, and are capable of supplying the same Fluids as before? Consequently since the most minute Organ cannot be supplied by any other than the forementioned Method, can any thing be so absurd, as to suppose that all the regular Order of Vessels necessary to compose the whole Bodily Machine should be produced by such a Cause, as is utterly incapable of forming the least Part imaginable in a regular Manner? This is no less exemplified in the Seeds or proper Embryos of Plants. Thus the Seed of the Fir-tree, whose Bulk with all its Integuments scarce equals the Head of the smallest Pin, has its Fibres and Vessels so enlarged by the Addition of fresh Particles, as to grow to an enormous Size, without ever deviating (in whatever Soil it grows) from its own Species into any other kind of Tree. Which can be owing to no other Cause than the original Stamina latent in its Seed; which not only separate, but conduct the Particles proper for its Nourishment, each to its proper Place in a manner peculiar to itself, thereby distinguishing it from all other Vegetables of what kind soever. But a Branch once lopped off can no more be restored by the Gardener's Art, than an amputated Limb by the Surgeon's: 'Tis true, indeed, new Buds may be thrust forth by the redundant Nourishment, both in the adjacent and more remote Parts, to compensate in some measure this Defect: but whether this Mutilation of the Plant be of its Summit, or of a lateral Branch, the Extremity must shrivel and dry up, and will bud and blossom no more.
If therefore mere Matter, altho' supposed to be in Motion, must be thus conducted by the Vessels of an Animal, it must be conducted by the Animal itself, no Application of different Forces
ab extra
to the Vessels (was there any such thing, as it is evident from the Structure of the Uterus, there is not) being capable of regulating and directing such an innumerable Variety of Motions, or indeed of contributing to its Operations, any farther than supplying it with a proper Nidus, and furnishing it with Materials ready prepared for the Purpose, as sufficiently appears, not only from the Observations of the accurate Malpighi, Bellini, Redi, Merian and others, but discovers itself to our Senses, in the Generation of innumerable other Species of Animals, some depositing their Eggs on Vegetables, or in the Earth, to be brought to Light by the genial Warmth of the Sun, others in Dunghills, and other putrefying Substances, and others in Streams of Water, where it is impossible for any such Force to be applied.
Hence then Nutrition must consist not only in the mere Distension, but in the Apposition of new Particles into such Parts of the Animal Body, as by the Enlargement of the Pores, and Vacuities in the Solids, are fitted to receive them, as I have elsewhere shewn by Experiment
See Sect. 7. Exp. 11. of an Experimental Enquiry on some Parts of the Animal Structure.
: And, indeed, was it otherwise, the Animal would have a Power of making its own Fibres and Vessels, and consequently of producing itself; nay the Circulation of the Fluids must be performed in Vessels, before the Vessels themselves, thro' which it is to be conveyed, have a Being; which are such Absurdities, as I shall not give myself the Trouble of confuting.
That these new Particles by adhering firmly to the original Stamina increase the Bulk of the Animal, till such time as it arrives at the Perfection its Structure is capable of, needs no Proof; but that the Strength of the original Animal owes its gradual Improvement to the same Cause, is likewise evident from the common Practice of several of our mechanic Workmen, who by steeping and saturating porous Woods, or the like light and brittle Substances in glutinous Decoctions, vastly increase their natural Strength, without any Addition to their external Bulk, which would be still farther increased, was that also enlarged by a regular Distension of Parts, as in the Case of Animal Bodies.
Hence then it will follow, that these adventitious Particles, which by their Cohesion with the original Stamina, increase the Bulk and Strength of the Body, and thereby enable it to perform the proper Offices, for which it was created, are not really any Part of the Body itself, but extraneous to it, actuated and regulated intirely by it, and consequently contribute no farther to its exercising the Powers, it is designed to exert when perfect, than would be performed by a strong Lever acting with such a Power, as would be impossible for a weak one to sustain, tho' in all other Respects the Case might be exactly parallel.
Nor is this less true with regard to the Sensations, than Strength of the Body. A proper Tension in the nervous Fibres being as requisite in this Case, as Strength in those designed for Muscular Motion, as appears from the pernicious Effects of too great Laxity, as well as Rigidity, in several Diseases, the one rendering the Sensations so languid and slow thro' their weak Vibrations, as not to affect the Animal with sufficient Force and Vivacity; whilst the other, thro' too great Stiffness and Inflexibility, scarce allows them to vibrate at all, as is the Case in old Age; or lastly by being too springy and elastic, and thence exciting too strong and frequent Vibrations in such as are younger, either renders their Sensations painful and uneasy, or so quick in their Successions to each other, as to prove useless, nay often prejudicial to the Animal, as is the Case in Phrensies, Maniacal Persons, and the like.
How far the Strength of the Body depends upon the adventitious Particles derived to it by Nutrition has been explained above, and it is hence no less evident, that they cannot possibly contribute farther to its Sensations, than as they add such a Degree of Firmness, as may prevent any external Species from acting upon the nervous Fibrils so forcibly, as to injure them; whilst at the same time by their intimate Adhesion with the original sensitive Organs, they cannot act upon the one, without exciting a proper Degree of Motion in the other; and consequently the real Sensitive Part of an Animal can contain no greater Quantity of Matter, than is included in the Nervous Parts of the Animalcule.
This then being the State of an Animal when arrived at its Perfection, how amazing must it be to consider, how small and weak Organs do really actuate the whole Machine! But that this may more fully appear, and also afford us some determinate Idea of their extream Tenuity, I shall endeavour to reduce such Microscopical Observations as are of best Credit to a certain Standard; that by comparing them with each other, and reducing them to Numbers, our Notions of them may not be altogether so vague and indeterminate as at present they are.
Leeuwenhoek,
that curious and diligent Inquirer into those Works of Nature, which till his Time had by their Minuteness escaped all Discovery, has by his repeated Microscopical Observations on the
Semen Masculinum
of Animals, not only shewn, that it abounds with Animalcula proper to each Species, but that, according to his Judgment, a thousand of them would scarce be equal in Thickness to a Grain of Sand
Leeuwenhoek
Epist. 41. Tom. IV.
; and consequently that a cubical Inch would contain a thousand Millions of Millions of these little Beings. Professor
Keil
indeed, in his elegant Inquiry into the actual Divisibility of the Particles of Matter, has from a Principle of Dioptrics computed their Magnitude to be somewhat greater than that just now mentioned; but he has however demonstrably shewn, that the Length of a single Animalculum cannot possibly exceed the 3
divisor
100000th Part of an Inch
Introductio ad veram Physicam,
p. 48.
. That our present Enquiry may therefore be wholly confined within the Limits of Truth, rather than proceed upon probable Conjecture, we will make Choice of this latter Estimate, and for the further Conveniency of Calculation, take it for granted, that when the Foot is decimally divided, even such a Cubical Inch will exceed the Bulk of a single Animalculum, in no greater a Proportion, than that of a thousand Millions of Millions to 27.
Now the specific Weight of the various Parts of an Animal Body reduced to a Medium amounts to a little more than the Weight of an equal Bulk of Water; if therefore we suppose one of these Animalcula to be to Water, as the other Parts of young Animals are, (and greater it cannot be, as appears from what I have elsewhere demonstrated with relation to the increased specific Gravity in the Arteries of aged Animals
Sect. 5. Exp. 11. of an Experimental Enquiry on some Parts of the Animal Structure.
, it follows, that as a Cubical Inch of Water is equivalent to 0.5271 parts of an Ounce Troy, the Weight of a single Animalcule will be equal to the 1
divisor
140391450739th part of a Grain nearly.
But by the Experiments of the ingenious Dr.
Keil
it appears, that in a Man of 12 Stone-weight, the Fluids are to the Solids when taken at a Medium, at the least in the Proportion of 8 to 3
Essays on several Parts of the Animal O Economy,
p. 38.
to
63.
, exclusive of those, which by the Help of Fire and a Chymical Process may be extracted without the Destruction of a single Fibre, which amounts to no small Quantity. It has also been farther shewn by Experiment, that the Vessels in young Animals bear a much less Proportion to their Cavities, than the like Vessels in old ones of the same Species bear to theirs
Sect. 3. Exp. 11
of the Experimental Enquiry,
&c.
; consequently, since the Density of any Body is as the Weight of the Body directly, and its Magnitude inversely, we shall find, by comparing the foregoing Proportions of the Fluids and Solids together in each different State of the Animal, as well before its Birth, as after it has arrived at full Maturity, that all the Stamina, from which so noble a Being as Man himself was at first derived, could not contain so much solid Matter as would be equal in Bulk, to that of a Quantity of Water, of no greater a Weight than the 1
divisor
92408129934910602442073752000th part of a Grain.
If the preceding Exility of the Solids in general be so surpizingly small, That of the Sensitive Parts alone, could their Relation to the rest be once adjusted, would doubtless, to speak in the Language of the Mathematicians, appear a mere Infinitesimal. For even
Leeuwenhoek
has declared in express Words, that
"
Hae Cerebri Fibrillae, tenuibus puto amiciuntur Membranulis, quae ob insignem Exilitatem nunquam sese nudabunt conspectui nostro: Quod nisi statuamus, quo pacto Fibrillarum Disparationem vel Distinctionem Oculis assequeremur?
Leeuwenhoek
Epist. 34. Tom. IV.
"
To which he might have added our Intellectual Faculties also, it being scarce possible to conceive Fibres always growing and encreasing in Bulk, should be kept separate, and perform their various Operations, but must soon prove immoveable, without being divided from each other by these slender Partitions.
This is not only evident from the Nature of the Fibres, but demonstrable from Fact in the larger Parts even of full-grown Animals; which, when contiguous and deprived of their proper Integuments, never fail to adhere and unite firmly to each other, as is sufficiently known to the Practitioners in Surgery. How much sooner then would this Adhaesion be produced in growing Animals, where the Fibres are not only more supple, and thence more easily united, but if deprived of these Membranes, would daily as they increase in Bulk, press more strongly against each other?
The Writers in Geometry have laid it down as an established Maxim, that
ubicunque deficit Modulus, in aeternum latebit Mensura;
on which account, tho' we may rest satisfied, that the Subtility of the sensitive Parts in an Animal Body must necessarily so far surpass the Extent of human Abilities, as to put their Bulk beyond a Possibility of being ever determined to a Mathematical Exactness; yet even the Nerves themselves, those delicate Instruments of all our Knowledge, may be brought under such an Examination, as to afford us a much clearer Idea of their exquisite Minuteness, than what can be obtained from those conjectural Descriptions, the Anatomists have hitherto given us concerning it.
For it is evident, that all the Membranes of an Animal Body have Muscular Fibres, and that even the greatest Number of them are principally made up of such; consequently we could not err very far from the Truth, were we to estimate the Bulk of the Membranous Fibres in the same Proportion with the Muscular ones. But we shall examine the Bulk and Proportion they bear to each other a little more distinctly.
Now
Leeuwenhoek
in his Observations on the Muscular Fibres has shewn, that some of them were equal to the 1/9th, others to the 1/16th part of a Hair
Leeuwenhoek,
Epist. 6. Tom. IV.
; consequently supposing each Fibre to be the Length of a Decimal Inch, there will be contained in such a Cubic Inch seven Millions two hundred ninety thousand of the former, and twenty-three Millions forty thousand of the latter Kind. But these Muscular Fibres are by later Observations found to be really small Muscles, consisting of Parts similar to the large one, which they constitute, and terminating in Tendons after the same Manner as the former; and consequently the Fibres, of which the more lax and cavernous Parts of the Muscle are composed, must be much smaller than the muscular Fibres rendered visible by his Glasses. Whether these be the same individual Fibres, which constitute the Tendon, by being more closely compacted in their Parts, I shall not undertake to determine; but this we learn from the forecited Author, that a hundred of these exceed not the Bulk of a Hair
Leeuwenhoek
Epist. 14. Tom. IV.
, and consequently nine hundred Millions of them will be contained in the forementioned Cubic Inch.
But these are far from being the smallest Fibres in the Body. For that the pellucid Membranes consist of Fibres of still smaller Dimensions, decreasing probably to the 1
divisor
300th part of a Hair, or upwards, is evident from the Structure of those fine Capillary Arteries, which are destined to convey a Fluid to them. For the whole Diameter of such an extream Artery does not exceed the 1
divisor
1620th part of an Inch
Hale's Haemaest.
Exp. 9.
that is, the 1
divisor
5th of a Hair nearly, and yet the Coat of this Vessel is made up of at least three distinct Species of Membranes, each of them furnished with Vessels peculiar to itself. And farther, if we consider, that the transverse Section of every Vessel is of a circular Form, we must necessarily allow, that the Longitudinal Fibres must be much smaller than any of those abovementioned; otherwise instead of a Circle, a Polygon would be produced, as is evident from Geometry.
Now even these are bulky Substances, when compared with the nervous Fibrils destined to Sensation, as appears from those which form the Retina. For these Fibres were manifestly before their Expansion into this Membrane collected within the Bulk of what is styled by Anatomists the Optic Nerve, and are, as the ingenious Professor
Monro
assures us, so extreamly small, that it is demonstrable, they cannot exceed the Thickness of the 1
divisor
32400th part of a Hair
Monro
's Anatomy of the Human Bones and Nerves, p. 3.
. If therefore we reject the odd four hundred in the foregoing Fraction, and suppose, that no more than 32000 of these Nervous Fibrils are necessary to make up a Thickness equal to that abovementioned, and also set the Muscular, Tendinous, and Membranous Fibres to be at a Medium, of no greater a Thickness than the 1
divisor
200th Part of a Hair, (which, from what has been just now explained above, is apparently a very large Allowance with respect to the Subtility of the Fibres in general) it will then follow, that the Thickness of one of these Fibrils in the Retina will be to that of such Fibres, as constitute the other Membranes and Organs of the Body, in the proportion of 1 to 160. But we have already shewn, that all the Stamina in an Animalcule could not contain so much solid Matter, as is equal in Bulk to a Particle of Water weighing the 1
divisor
92408129934910602442073752000th part of a Grain; consequently, if we suppose, that a Nervous Fibril does accompany every individual Fibre in the Animal System, and compare the Proportions they bear to each other as given above, we shall find, that the whole sensitive Parts in the Animalcule taken together could not amount to a greater Bulk than that of the 1
divisor
3764060396563654679984851840619241th part of a cubical Inch, or that all the solid Matter of the Nerves, by which the Sensations in the human System are actually communicated to the Mind, cannot possibly weigh the 1
divisor
14877708919520606993173874072000th part of a Grain.
That the stupendous Expansion and Action of the Fibres and Vessels of an Animalcule up to that of a full grown Man should be owing to an Entity like this, a mere fluxionary Increment with respect to Quantity and Magnitude, will, I doubt not, to many appear impossible, to all incomprehensible; but are not all other of the Creator's Works equally so? Or is this more than infinite Power acting on Matter infinitely divisible is capable of, whose Particles must be still higher subtilised, and spun into Fibres inconceivably more minute in the Bodies of Insects, than is here specified of the human, as they are all furnished with Arteries, Veins, Nerves, Muscles, Bones, and Tendons suitable to their various Structures, and Manner of subsisting.
The incomparable Mr.
Locke,
speaking of the Identity of the same Person, resolves it wholly into its Consciousness, even though the whole Substance, material or immaterial, should be intirely changed. Many Physicians have also been of opinion, and some even laid it down as a Maxim, that the whole Substance of the BOdy, during the Length of an ordinary Life, is several times so intirely changed, as to consist wholly of new Particles, of the same Nature and Kind as the preceeding. How far these Opinions may agree with what is taught by Divine Revelation, where this very Sameness, in its strictest Acceptation, seems to be expressly declared, is not my province to determine. But this we may plainly deduce from what has been premised, that the whole Substance of the Body, except these original Stamina of the Animalcule, may be many times changed, and yet the real Body continue the same, and be possessed of the same personal Identity, with regard both to Body and Mind, at the End of the longest Life, as it was at the instant of its Birth; nay even in the Animalcule itself.
That these original Stamina should all remain unhurt, and fit to perform their several Functions to the End of Life, is a Position not to be admitted; but that without a competent Number of them so remaining, the Animal will decline both in its vital and intellectual Faculties, notwithstanding the Body be replenished with a sufficient Number of homogeneous Particles to supply the Place of such Parts as are abraded and worn away, or otherwise hindered from performing their natural Functions, seems equally certain; both from the Decay of our intellectual Faculties, and the gradual Loss of Vigour in the Body, even whilst the Force of the vital Organs seems no ways impaired. Consequently something more must be necessary, than the mere Application of homogeneous Matter to supply this Demand. But that can be no other, than that particular Texture, with which they were originally formed, and by which they become capable of transmitting the Effects of external Agents to the Mind.
It may possibly be objected, that all Matter being equally incapable of Sensation, no Reason can possibly be assigned, why such homogeneous Matter, as supplies the constant Loss, the Body sustains by the Attrition of its Parts on each other, and serves for its Accretion, Strength, and Nutrition, may not be equally capable of conveying our Sensations to the Mind, as the original Stamina above mentioned. But if we may reason from what ensues in the larger Parts, which are compounded of these very Stamina, upon their being wounded, or broken with Loss of Substance, 'tis evident, that though by the Addition of homogeneous Matter to the different Species of Vessels, the Body to Appearance, may have received no great Detriment, and be sufficient for the principal Purposes of Life; yet are such Parts of very dull and obscure Sensation, if they may be said to enjoy it in any other manner, than by their Union with the original Stamina. So that could we suppose these Stamina quite destroyed, and the Body so far changed, as to consist only of such homogeneous Matter, though with Vessels in Form and Bulk similar to the former, yet these united by a Texture different from that of the original Fibres; 'tis evident from what ensues upon a like Change in the Fibres constituting the larger Parts, that such a Person, if he had either Sensitive or Intellectual Faculties at all, must have them in a manner vastly different from those of the former. And consequently this Sameness or Identity must remain in a great Measure fixed and unalterable in the Body from its Birth to its Dissolution.
Nor is this Difference in the original Stamina confined in its Effects to the fibrous Parts of the Body only, but communicates them to the circulating Juices themselves, distinguishing thereby the different Kinds of Flesh of each Species of Animals from each other, even where they are sustained by the same Kind of Food. Otherwise it would happen in Cases of this Kind, that the Taste, Complexion, Odour, and Cohesion of the Flesh would of Necessity be nearly the same in all.
The same would be the Consequence with regard to the Glands of the same Body, which would separate nearly the same Kind of Juice, and consequently be useless, or perhaps prejudicial, was it not prevented by the different Structure both of the Strainer itself, and the Preparatory Vessels. For howsoever we may imagine the Juice to be separated from the circulating Mass, we cannot with any Colour of Reason suppose such a various and exquisite Contrivance, as is discovered not only in the Formation of the Gland itself, but also in that of the Vessels leading to and from it, so widely differing among themselves in their Structure, Texture, and Capacity
Sect. 6. Exp. 47. of the Experimental Inquiry on, &c.
, should ever be designed only to perform what any one Species of them was capable of.
Hence then it must follow, that the principal Differences in Animal Bodies are owing to the different Structure of the original Stamina, with regard not only to their exterior Shape and Actions, but that even the Fluids themselves, and that solid Part called the Flesh, derive their chief and principal Difference from this Source; and consequently, that there is a real Identity of Animal Bodies incommunicable to any other, depending on this very Cause.
Nor is this relating to the Fluids a mere Conjecture, but a real Fact, as appears from those morbid Cases, where either the Glands, Preparatory Vessels, or even the fleshy Parts are vitiated and depraved; which never fail to separate unnatural Juices, tho' derived from the most healthful Blood.
Analogous to this we see in the Vegetable World, that it is not the Root, or even Trunk of the Tree, tho' all the Juices are thereby supplied, but the Bud or Scion only, which governs the whole, and produces the Species of Blossoms and Fruit peculiar to itself. In like manner the Vessels of the Animalcule, of what Species soever it be, convert the Juices designed for its Nourishment, each, into such as are suitable to their different Structures; and thence keep up an infinite Variety in Animals, tho' supplied by the same kind of Food, according to the different Vessels by whose means it is elaborated and perfected, being in some highly volatilised and attenuated, which gives the high Taste; in others more viscous and inactive, which produces the opposite, and are therefore less pleasing to a voluptuous Appetite.
I am not here supposing, that the Qualities of the circulating Juices of Animals depend so intirely upon the Structure of the Solids, that the Diversity of Food is herein of no Consequence, daily Experience sufficiently confuting so absurd an Opinion. But only that in those of a different Species, the Taste, Odour, and other Qualities of their Juices, are principally owing to this different Structure; as is manifest from hence,
viz.
that the Qualities of the Juices of differing Animals, though sustained with the same Kind of Food, are more dissonant to each other, than are those of the same Species, though sustained with Food of a very different Nature; and consequently, this Identity in the various Species of Animals, must principally consist in the Structure of the Solids, or, in other Words, in the original Stamina of each individual Species.
Thus has our Reasoning at length led us to the Discovery and Demonstration of a Truth, which at first Sight must appear beyond all Probability, and we can now with Certainty affirm, that from so simple a Cause as the different Modification of the same Matter, the wise Author of Nature has produced not only one kind of Flesh of Men, another of Beasts, another of Fishes, and another of Birds; but these also infinitely different in the different Species of each.
Hence we may see, why some Animals shall necessarily require such a Degree of Warmth, to preserve their Juices sufficiently exalted and attenuated for their comfortable Subsistence, as others cannot sustain without Prejudice, even scarcely without a Dissolution; and
vice versa,
why such a Degree of Cold, as is only agreeable, or perhaps necessary to the Health of these, should prove so far destructive of others, as on the least Condensation of the Fluids from that Cause, to render them torpid, motionless, and seemingly dead, till restored by the kindly Influence of the approaching Summer.
Hence also it is obvious, why the Blood and Juices of some particular Species of Animals shall be affected with Diseases of a Pestilential Nature with regard to them, from such Causes, as shall produce very few Inconveniences to many other Kinds.
Hence also we may see the Reason, why each individual Person has some Particularities in his Constitution peculiar to himself, not to be found in the Generality of the Species, nor depending on his Manner of Life, by which he is as it were distinguished from the rest: Which also probably may sometimes be the Case in Brutes, tho' more rarely than in Men, could we equally arrive at the Knowledge of it, as is manifest from the different Sprightliness, Vigour, and Activity of some compared with others of the same Species.
Lastly, hence we may see, why an intire Change of the Constitution should be attended with almost insuperable Difficulties: Why great Alterations require a long and gradual Process, nor are to be attempted by hasty Methods, lest the Patient, instead of Relief, meet with certain Ruin and Destruction.
FINIS.