Reflections upon Ancient and Modern Learning/Chapter 19
CHAP. XIX.
Further Reflections upon Ancient and Modern Anatomy.
IF after this long Enquiry into the First Discovery of the Circulation of the Blood, it should be found that the Anatomy of the Heart was but slightly known to the Ancients, it will not, I suppose, be a Matter of any great Wonder. (i) De Corde, §. 4.The First Opinion which we have of the Texture of the Heart, was that of Hippocrates (i), that it is a very strong Muscle; this tho' true was rejected afterwards for want of knowing its true Use; its internal Divisions, its Valves, and larger visible Fibres were well known and distinctly described by the Ancients; only they were mistaken in thinking that there is a Communication between the Ventricles through the Septum, which is now generally known to be an Errour. The Order of the Muscular Fibres of the Heart was not known before Dr. Lower, who discovered them to be Spiral like a Snale-Shell, as if several Skains of Threads of differing Lengths had been wound up into a Bottom of such a Shape, hollow, and divided within. By all these Discoveries Alphonsus Borellus (k)(k) De Motu Animalium, Part II. cap. 5. was enabled to give such a Solution of all the Appearances of the Motion of the Heart, and of the Blood in the Arteries, upon Mathematical and Mechanical Principles, as will give a more satisfactory Account of the wonderful Methods of Nature in dispensing Life and Nourishment to every Part of the Body, than all that had ever been written upon these Subjects before those things were found out.
Below the Midriff are several very noble Viscera: The Stomach, the Liver, the Pancreas or Sweet-Bread, the Spleen, the Reins, the Intestines, the Glands of the Mesentery, and the Instruments of Generation of both Sexes; in the Anatomical Knowledge of all which Parts, the Ancients were exceedingly defective.
The Coats of the Stomach have been separated, and the several Fibres of the middle Coat examined by Dr. Willis (l)(l) Pharmaceut. Rational. with more Exactness than formerly; he also has been very nice in tracing the Blood-Vessels and Nerves that run amongst the Coats, has evidently shewn that its Inside is covered with a glandulous Coat, whose Glands separate that Mucilage; which both preserves the Fibres from being injured by the Aliments which the Stomach receives, and concurrs with the Spittle to further the Digestion there performed; and has given a very particular Account of all those several Rows of Fibres, which compose the musculous Coat: To which if we add Steno's Discovery of the Fibres of the musculous Coat of the Gullet, that they are spiral in a double Order, one ascending, the other descending, which run contrary Courses, and mutually cross each other in every Winding; with Dr. Cole's (m)(m) Philos. Trans. numb. 125. Discovery of the Nature of the Fibres of the Intestines, that they also move spirally, though not, perhaps, in a contrary Order, from the beginning of the Duodenum to the end of the streight Gut, the Anatomy of those parts seems to be almost compleat.
The great Use of the Stomach and the Guts, is to prepare the Chyle, and then to transmit it through the Glands of the Mesentery into the Blood; this the Ancients knew very well; the Manner how it was done they knew not. Galen (n)(n) De Usu Partium, lib. 4. cap. 2, 3, 4, 5. held that the Mesaraick Veins, as also those which go from the Stomach to the Liver, carry the Chyle thither, which by the Warmth of the Liver is put into a Heat, whereby the Faeculencies are separated from the more spirituous Parts, and by their Weight sink to the Bottom; the purer Parts go into the Vena Cava. The Dregs which are of two sorts, Choler and Melancholy, go into several Receptacles; the Choler is lodged in the Gall-Bladder and Porus Bilarius: Melancholy is carried off by the Spleen. The Original of all these Notions was Ignorance of the Anatomy of all these Parts, as also of the constant Motion of the Blood through the Lungs and Heart. Herophilus, who is commended as the ablest Anatomist of Antiquity, found out (o)(o) De U. P. lib. 4. c. 19. that there were veins dispersed quite through the Mesentery, as far as the small Guts reach, which carried the Chyle from the Intestines into several Glandulous Bodies, and there lodged them. These are the Milky Veins again discovered by Asellius about Fifty Years ago, and those Glands which Herophilus spoke of, are probably that great Collection of Glands in the Mesentery that is commonly called the Pancreas Asellii. After Herophilus none of the Ancients had the Luck to trace the Motions of the Chyle any further, and so these milky Veins were confounded with the Mesaraicks, and it was commonly believed, That because all Mesaraicks carry the Blood from the Intestines into the Liver, therefore they carried Chyle also when there was any Chyle to carry; and hence probably it was that the Liver was believed to be the common Work-House of the Blood. But when Asellius had traced the Chyle as far as the great Gland of the Mesentery, it was soon found not to lie there. And Pecquet, about Forty Years since, discovered the common Receptacle of the Chyle, whither it is all brought. Thence he also found that it is carried, by particular Vessels through the Thorax, almost as high as the Left-Shoulder, and there thrown into the Left Subclavian Vein, and so directly carried to the Heart. It has also been discovered that in his Canal, usually called Ductus Thoracicus, there are numerous Valves, which hinder the Return of the Chyle to the common Receptacle, so that it can be moved forwards, but not backwards.
Since this Passage of the Chyle has been discovered, it has been by some believed, that the Milk is conveyed into the Breasts, by little Vessels, from the Ductus Thoracicus. The whole Oeconomy of that Affair has been particularly described very lately by Mr. Nuck; before whose Time it was but imperfectly known. He says therefore, that the Breasts are Heaps of Glands, supplied with Blood by innumerable Ramifications of the Axillary and Thoracick Arteries; some of which passing through the Breast-bone, unite with the Vessels of the opposite Side. These Arteries, which are unconceivably small, part with the Milk in those small Glands, into small Pipes, four or five of which meeting together, make one small Trunk; of these small Trunks, the large Pipes, which terminate in the Nipple, are made up; though before they arrive thither, they straiten into so small a Compass, that a stiff Hair will just pass through. The Nipple, which is a Fibrous Body, has seven or eight, or more Holes, through which every Pipe emits its Milk upon Suction; and, lest any one of them being stopped, the Milk should stagnate, they all have cross Passages into each other, at the Bottom of the Nipple, where it joyns to the Breast.
The fore-mentioned Discovery of the Passage of the Chyle obliged Men to reexamine the Notions which, till then, had generally obtained, concerning the Nature and Uses of the Liver. Hitherto it had been generally believed, that the Blood was made there, and so dispersed into several Parts, for the Uses of the Body, by the Vena Cava. Erasistratus, indeed, supposed (p)(p) Galen de U. P. lib. 4. cap. 13. that its principal Use was, to separate the Bile, and to lodge it in its proper Vessels: But, for want of further Light, his Notion could not then be sufficiently proved; and so it presently fell, and was never revived, till Asellius's and Pecquet's Discoveries put it out of doubt. Till Malpighius discovered its Texture by his Glasses, its Nature was very obscure. But he has found out, (1.) That the Substance of the Liver is framed of innumerable Lobules, which are very often of a Cubical Figure, and consist of several little Glands, like the Stones of Raisins; so that they look like Bunches of Grapes, and are each of them cloathed with a distinct Membrane. (2.) That the whole Bulk of the Liver consists of these Grape-stone-like Glands, and of divers sorts of Vessels. (3.) That the small Branches of the Cava, Porta, and Porus Bilarius, run through all, even the least of these Lobules, in an equal Number; and that the Branches of the Porta are as Arteries that convey the Blood to, and the Branches of the Cava are the Veins which carry the Blood from all these little Grape-stone-like Glands. From whence it is plain, that the Liver is a Glandulous Body, with its proper Excretory Vessels, which carry away the Gall that lay before in the Mass of the Blood.
Near the Liver lies the Pancreas, which Galen believed (q)(q) De U. P. lib. 5. cap. 2. to be a Pillow to support the Divisions of the Veins, as they go out of the Liver; and, for what appears at present, the Ancients do not seem to have concerned themselves any further about it. Since, it has been found to be a Glandulous Body, wherein a distinct Juice is separated from the Blood; which, by a peculiar Canal, first discovered by Georgius Wirtsungus, a Paduan Physician, is carried into the Duodenum; where meeting with the Bile, and the Aliment just thrown out of the Stomach, assists and promotes the Business of Digestion.
The Spleen was as little understood as the Pancreas; and for the same Reasons: Its Anatomy was unknown, and its Bulk made it very remarkable; something therefore was to be said about it: And what no Body could positively dis-prove, might the easier be either received or contradicted. The most general Opinion was, that the grosser Excrements of the Chyle and Blood were carried off from the Liver, by the Ramus Splenicus, and lodged in the Spleen, as in a common Cistern: But since the Circulation of the Blood has been known, it has been found, that the Blood can go from the Spleen to the Liver, but that nothing can return back again into the Spleen. And as for its Texture, (r) De Liene.(r) Malpighius has discovered, that the Substance of the Spleen, deducting the numerous Blood-Vessels and Nerves, as also the Fibres which arise from its Second Membrane, and which support the other Parts, is made up of innumerable little Cells, like Honey-Combs, in which there are vast Numbers of small Glandules, which resemble Bunches of Grapes; and that these hang upon the Fibres, and are fed by Twigs of Arteries and Nerves, and send forth the Blood there purged, into the Ramus Splenicus, which carries it into the Liver; to what purpose, not yet certainly discovered.
The Use of the Reins is so very conspicuous, that, from Hippocrates's Time, downwards, no Man ever mistook it: But the Mechanism of those wonderful Strainers was wholly unknown, till the so often mentioned Malpighius (s) (s) De Renibus.found it out. He therefore, by his Glasses, discovered, that the Kidneys are not one uniform Substance, but consist of several small Globules, which are all like so many several Kidneys, bound about with one common Membrane; and that every Globule has small Twigs from the emulgent Arteries, that carry Blood to it; Glands, in which the Urine is strained from it; Veins, by which the purified Blood is carried off to the Emulgent Veins, thence to go into the Cava; a Pipe, to convey the Urine into the great Basin in the middle of the Kidney; and a Nipple, towards which several of those small Pipes tend, and through which the Urine ouzes out of them, into the Basin. This clear Use of the Structure of the Reins, has effectually confuted several Notions that Men had entertained, of some Secundary Uses of those Parts; since hereby it appears, that every Part of the Kidneys is immediately, and wholly subservient to that single Use, of Freeing the Blood from its superfluous Serum.
What has been done by Modern Anatomists, towards the Compleating of the Knowledge of the remaining Parts, I shall omit. That the Ancients likewise took Pains about them, is evident from the Writings of Hippocrates, Aristotle and Galen. The Discoveries which have since been made are so great, that they are, in a manner, undisputed: And the Books which treat of them are so well known, that it will not be suspected that I decline to enlarge upon them, out of a Dread of giving up more to the Ancients in this Particular, than I have done all along.
The Discoveries hitherto mentioned, have been of those Parts of Humours of the Body, whose Existence was well enough known to the Ancients. But, besides them, other Humours, with Vessels to separate, contain, and carry them to several Parts of the Body, have been taken notice of; of which, in strictness, the Ancients cannot be said to have any sort of Knowledge. These are, the Lympha, or Colourless Juice, which is carried to the Chyle and Blood, from separate Parts of the Body: And the Mucilage of the Joints, which lubricates them, and the Muscles, in their Motions. The Discovery of the Lympha, which was made about Forty Years ago, is contended for by several Persons. Thomas Bartholine, a Dane, and Olaus Rudbeck, a Suede, published their Observations about the same Time: And Dr. Jolliffe, an English-Man, shewed the same to several of his Friends, but without publishing any Thing concerning them. The Discoveries being undoubted, and all Three working upon the same Materials, there seems no Reason to deny any of them the Glory of their Inventions. The Thing which they found was, that there are innumerable small, clear Vessels in many Parts of the Body, chiefly in the Lower Belly, which convey a Colourless Juice, either into the common Receptacle of the Chyle, or else into the Veins, there to mix with the Blood. The Valves which Frederic Ruysch found and demonstrated in them, about the same Time, manifestly shewed, that this is its Road; because they prove, that the Lympha can go forwards from the Liver, Spleen, Lungs, Glands of the Loins and Neck, or any other Place, whence they arise, towards some Chyliferous Duct, or Vein; but cannot go back from those Chyliferous Ducts, or Veins, to the Place of their Origination. What this Origination is, was long uncertain, it not being easie to trace the several Canals up to their several Sources. (t) Observat. Anatom.Steno (t) and Malpighius (u) did, with infinite Labour, find, that Abundance of Lympheducts passed through those numerous Conglobate Glands that are dispersed in the Abdomen and Thorax; which made them think that the (u) Epist. de Glandul. Conglobat.Arterious Blood was there purged of its Lympha, that was from thence carried off into its proper Place, by a Vessel of its own. But Mr. Nuck has since (w) Adenograph.(w) found, that the Lympheducts arise immediately from Arteries themselves; and that many of them are percolated through those Conglobate Glands, in their Way to the Receptacle of the Chyle, or those Veins which receive them. By these, and innumerable other Observations, the Uses of the Glands of the Body have been found out; all agreeing in this one Thing, namely, that they separate the several Juices that are discernable in the Body, from the Mass of the Blood wherein they lay before. From their Texture they have of late been divided into Conglomerate, and Conglobate. The Conglomerate Glands consist of many smaller Glands, which lie near one another, covered with one common Membrane, with one or more common Canals, into which the separated Juice is poured by little Pipes, coming from every smaller Glandule; as in the Liver, the Kidneys, the Pancreas, and Salival Glands of the Mouth. The Conglobate Glands are single, often without an Excretory Duct of their own, only perforated by the Lympheducts. Of all which Things, as essential to the Nature of Glands, the Ancient Anatomists had no sort of Notion.
The Mucilage of the Joints and Muscles was found out by Dr. Havers (x). (x) Osteolog.He discovered in every Joint, particular Glands, out of which issues a Mucilaginous Substance, whose Nature he examined by numerous Experiments; which, with the Marrow supplied by the Bones, always serves to oil the Wheels, that so our Joints and Muscles might answer those Ends of Motion, for which Nature designed them. This was a very useful Discovery, since it makes Abundance of Things that were very obscure in that Part of Anatomy, very plain, and facile to be understood: And, among other Things, it shews the Use of that excellent Oil which is contained in our Bones, and there separated by proper Strainers, from the Mass of the Blood; especially, since, by a nice Examination of the true inward Texture of all the Bones and Cartilages of the Body, he shew'd how this Oil is communicated to the Mucilage, and so united as to perform their Office. And if one compares what Dr. Havers says of Bones and Cartilages, with what had been said concerning them before him, his Observations about their Frame may well be added to some of the noblest of all the former Discoveries.
These are some of the most remarkable Instances, how far the Knowledge of the Frame of our Bodies has been carried in our Age. Several Observations may be made concerning them, which will be of Use to the present Question. (1.) It is evident, that only the most visible Things were anciently known; such only as might be discovered without great Nicety. Muscles and Bones are easily separable; their Length is soon traced, and their Origination easily known. The same may be truly said of large Blood-Vessels, and Nerves: But when they come to be exquisitely sub-divided, when their Smalness will not suffer the Eye, much less the Hand, to follow them, then the Ancients were constantly at a Loss: For which Reason, they understood none of the Viscera, to any tolerable Degree. (2.) One may perceive that every new Discovery strengthens what went before; otherwise the World would soon have heard of it, and the erroneous Theories of such Pretenders to new Things would have been exploded and forgotten, unless by here and there a curious Man, that pleases himself with reading Obsolete Books. Nullius in verba is not only the Motto of the ROYAL SOCIETY, but a received Principle among all the Philosophers of the present Age: And therefore, when once any new Discoveries have been examined, and received, we have more Reason to acquiesce in them, than there was formerly. This is evident in the Circulation of the Blood: Several Veins and Arteries have been found, at least, more exactly traced, since, than they were in Dr. Harvey's Time. Not one of these Discoveries has ever shown a single Instance of any Artery going to, or of any Vein coming from the Heart. Ligatures have been made of infinite Numbers of Vessels; and the Course of all the Animal Juices, in all manner of living Creatures, has thereby been made visible to the naked Eye; and yet not one of these has ever weakned Dr. Harvey's Doctrine. The Pleasure of Destroying in Matters of this Kind, is not much less than the Pleasure of Building. And therefore, when we see that those Books which have been written against some of the eminentest of these Discoveries, though but a few Years ago, comparatively speaking, are so far dead, that it is already become a Piece of Learning even to know their Titles, we have sufficient Assurance that these Discoverers, whose Writings outlive Opposition, neither deceive themselves, nor others. So that, whatsoever it might be formerly, yet in this Age general Consent in Physiological Matters, especially after a long Canvass of the Things consented to, is an almost infallible Sign of Truth. (3.) The more Ways are made use of to arrive at any one particular Part of Knowledge, the surer that Knowledge is, when it appears that these different Methods lend Help each to other. If Malpighius's, or Leeuwenhoek's Glasses had made such Discoveries as Men's Reason could not have agreed to, if Objects had appeared confused and disorderly in their Microscopes, if their Observations had contradicted what the naked Eye reveals, then their Verdict had been little worth. But when the Discoveries made by the Knife and the Microscope disagree only as Twi-light and Noon-day, then a Man is satisfied that the Knowledge which each affords to us, differs only in Degree, not in Sort. (4.) It can signifie nothing in the present Controversie, to pretend that Books are lost; or to say, that, for ought we know, Herophilus might anciently have made this Discovery, or Erasistratus that; their Reasonings demonstrate the Extent of their Knowledge as convincingly as if we had a Thousand old Systems of Ancient Anatomy extant. (5.) In judging of Modern Discoveries, one is nicely to distinguish between Hypothesis and Theory. The Anatomy of the Nerves holds good, whether the Nerves carry a Nutritious Juice to the several Parts of the Body, or no. The Pancreas sends a Juice into the Duodenum, which mixes there with the Bile, let the Nature of that Juice be what it will. Yet here a nice Judge may observe, that every Discovery has mended the Hypotheses of the Modern Anatomists; and so it will always do, till the Theories of every Part, and every Juice, be as entire as Experiments and Observations can make them.
As these Discoveries have made the Frame of our own Bodies a much more intelligible Thing than it was before, though there is yet a great deal unknown; so the same Discoveries having been applied to, and found in almost all sorts of known Animals, have made the Anatomy of Brutes, Birds, Fishes and Insects much more perfect than it could possibly be in former Ages. Most of the Rules which Galen lays down in his Anatomical Administrations, are, concerning the Dissection of Apes. If he had been now to write, besides those tedious Advices how to part the Muscles from the Membranes, and to observe their several Insertions and Originations, the Jointings of the Bones, and the like, he would have taught the World how to make Ligatures of all sorts of Vessels, in their proper Places; what Liquors had been most convenient to make Injections with, thereby to discern the Courses of Veins, Arteries, Chyle-Vessels, or Lympheducts; how to unravel the Testicles; how to use Microscopes to the best Advantage: He would have taught his Disciples when and where to look for such and such Vessels or Glands; where Chymical Trials were useful; and what the Processes were, by which he made his Experiments, or found out his Theories: Which Things fill up every Page in the Writings of later Dissectors. This he would have done, as well as what he did, had these Ways of making Anatomical Discoveries been then known and practised. The World might then have expected such Anatomies of Brutes, as Dr. Tyson has given of the Rattle-Snake; or Dr. Moulin, of the Elephant: Such Dissections of Fishes as Dr. Tyson's of the Porpesse; and Steno's, of the Shark: Such of Insects as Malpighius's of a Silk-Worm; Swammerdam's, of the Ephemeron; Dr. Lister's, of a Snail; and the same Dr. Tyson's, of Long and Round Body-Worms. All which shew Skill and Industry, not conceivable by a Man that is not a little versed in these Matters.
To this Anatomy of Bodies that have Sensitive Life, we ought to add the Anatomy of Vegetables, begun and brought to great Perfection in Italy and England at the same Time, by Malpighius and Dr. Grew. By their Glasses they have been able to give an Account of the different Textures of all the Parts of Trees, Shrubs and Herbs; to trace the several Vessels which carry Air, Lympha, Milk, Rosin and Turpentine, in those Plants which afford them; to describe the whole Process of Vegetation, from Seed to Seed; and, in a Word, though they have left a great deal to be admired, because it was to them incomprehensible; yet they have discovered a great deal to be admired, because of its being known by their Means.