# Reflections upon Ancient and Modern Learning/Chapter 18

CHAP. XVIII.
Of the Circulation of the Blood.
FRom the Head, we are to look into the Thorax, and there to consider the Heart, and the Lungs. The Lungs, as most of the other Viscera, were believed to be of a Parenchymous Substance, till Malpighius found by his Glasses (s)(s) Epist. de Pulmonibus. that they consist of innumerable small Bladders, that open into each other, as far as the outermost; which are covered by the outer Membrane, that incloses the whole Body of the Lungs: And that the small Branches of the Wind-Pipe are all inserted into these Bladders; about every one of which the Veins and Arteries are entwined, in an unconceivable Number of Nets and Mazes; that so the inspired Air may press upon, or mix with, the Mass of Blood, in such small Parcels as the Ancients had no Notion of. The Wind-Pipe also it self is nourished by an Artery that creeps up the Back-side, and accompanies it in all its Branchings: Which was first found out by Frederic Ruysch, a Dutch Professor of Anatomy at Leyden, about Thirty Years ago.
​But the great Discovery that has been made of the Lungs, is, That the whole Mass of Blood is carried out of the Right Ventricle of the Heart, by the Arteria Pulmonaris, called anciently Vena Arteriosa, through all the small Bladders of the Lungs, into the Vena Pulmonaris, (or Arteria Venosa;) and from thence, into the Left Ventricle of the Heart again. So that the Heart is a strong Pump, which throws the Blood, let in from the Veins, into the Lungs; and from the Lungs, afterwards, into the Arteries; and this by a constant rapid Motion, whereby the Blood is driven round in a very few Minutes. This Discovery, first made perfectly intelligible by Dr. Harvey, is of so very great Importance to shew the Communication of all the Humours of the Body, each with other, that as soon as Men were perfectly satisfied that it was not to be contested, which they were in a few Years, a great many put in for the Prize, unwilling that Dr. Harvey should go away with all the Glory. Vander Linden, who published a most exact Edition of Hippocrates, in Holland, about Thirty Years ago, has taken a great deal of Pains to prove that Hippocrates knew the Circulation of the Blood, and that Dr. Harvey only revived it. The ​(t) Παραρονέουοιν ἐν τῆ νὀσῳ δὶὰ παντος, ἄτε τοῠ αἴυατος ἐφθαρμένου, τε και ἐκκεκινημένου τ εἰωθυῖαν κίνηοιν. De Morbis, lib. i.. §. 30. Edit. Vand.Substance of what has been said in this Matter, is this; that Hippocrates speaks (t) in one Place, of the Usual and Constant Motion of the Blood: That in another Place, he calls (u) the Veins and Arteries the Fountains of Humane Nature, the Rivers that water the whole Body, that convey Life; and which, if they be dried up, the Man dies: That in a Third Place, he says, (w) That the Blood-Vessels, which are dispersed over the whole Body, give Spirit, Moisture and Motion, and all spring from one; which one (u) Άυταὶ πηγαὶ φὑοιος ἀνθρώπου, καὶ οἱ ποταμοὶ ἐνταῠθα ἀνὰ τὸ σῶμα τοῖοιν ἄρδε? τὸ σκῆνος οῧτοι δὲ καὶ ζώην φέρουοι τφ ἀνθρώπῳ κην αὐανθέωοιν ἀπέθανεν ὁ ἄνθρωπος, De Corde, §. 5.(Blood-Vessel) has no Beginning, nor no End, that I can find; for, where there is a Circle, there is no Beginning. These are the clearest Passages that are produced, to prove, that Hippocrates knew the Circulation of the Blood; and it is plain from them, that he did believe it as an Hypothesis; that is, in plain English, that he did suppose the Blood to be carried round the Body by a constant accustomed Motion: (w) Αἁ φλέβες διὰ τοῦ οώματος κεχυμὲναι, τνεῦμα, καὶ ρεῦμα καὶ κίνηοιν παρέχονσ, ἂπὸ μιῆς πολλαὶ διαβλαςάνουσαι καὶ αὕτη μὲν ἡ μία, ὅθεν ἦρκσ, καὶ ᾗ τετελεύτηκεν, οὐκ οἶδα, κύκλου γει γεγρημένου, ἀρχὴ οὒκ εὐρέθη.. De Venis, §. 17.But that he did not know what this constant accustomed Motion was; and that he had not ​found that Course which, in our Age, Dr. Harvey first clearly demonstrated, will appear evident from the following Considerations: (1.) He says nothing of the Circulation of the Blood(x) De Corde, §. 4. in his Discourse of the Heart, where he Anatomizes it as well as he could; and speaks of (x) the Ventricles, and the Valves (y)(y) Ibid. §. 7, 8., which are the immediate Instruments by which the Work is done. (2.) He believes that the Auricles of the Heart (z) are like Bellows, which receive the Air to cool the Heart. Now there are other Uses of them certainly known,(z) Ib. §. 6. since they assist the Heart in the Receiving of the Blood from the Vena Cava, and the Vena Pulmonaris.(a) Ateriæ quidem purum sanguinem & spiritum à corde recipiunt; Venæ autem & ipsæ à corde sanguinem sumunt, per quas corpori distribuitur; De Structura Hominis, §. 2. This cannot be unknown to any Man that knows how the Blood circulates; and accordingly, would have been mentioned by Hippocrates, had he known of it. (3.) Hippocrates speaks of Veins (a), as receiving Blood from the Heart, and going from it: Which also was the constant Way of Speaking of Galen, and all the Ancients. Now, no Man that can express himself properly, will ever say, That any Liquors are carried away from any Cistern, as from a Fountain or Source, through those Canals which, ​to his Knowledge, convey Liquors to that Cistern. (4.) Hippocrates says, the Blood is carried into the Lungs, from the Heart, for the Nourishment of the Lungs; without assigning any other Reason (b).(b) De Corde, §. 10. These seem to be positive Arguments, that Hippocrates knew nothing of this Matter; and accordingly, all his Commentators, Ancient and Modern, before Dr. Harvey, never interpreted the former Passages of the Circulation of the Blood: Neither would Vander Linden, in all probability, if Dr. Harvey had not helped him to the Notion; which he was then resolved to find in Hippocrates, whom he supposed not the Father only, but the Finisher also of the whole Medical Art. It is pretended to by none of the Ancients, or rather their Admirers for them, after Hippocrates. As for Galen, any Man that reads what he says of the Heart and Lungs, in the 6th. Book of his De Usu Partium, must own, that he does not discourse as if he were acquainted with Modern Discoveries; and therefore it is not so much as pretended that he knew this Recurrent Motion of the Blood. Which also further shews, that if Hippocrates did know it, he explained himself so obscurely, that Galen could not understand him; who, in all probability, understood Hippocrates's ​(c) Vitalis Spiritus in sinistro cordis ventriculo suam Originem habet, juvantibus maximè pulmonibus adipsius generationem. Est spiritus tenuis, caloris vi elaboratus, flavo colore, igneâ potentiâ, ut sit quasi ex puriore sanguine lucidus, vapor: generatur ex facta in pulmone mixtione inspirati aeris cum elaborato subtili sanguine, quem dexter ventriculus sinistro communicat. Fit autem communicatio hæc non per parietem cordis medium ut vulgo creditur, sed magno artificio à dextro cordis ventriculo, longo per pulmones ductu, agitatur sanguis subtilis; à pulmonibus præparatur; flavus ejicitur, & à venâ arteriosâ in arteriam venosam transfunditur; deinde in ipsâ arteriâ venosâ inspirato aëri misccetur & exspiratione à fuligine repurgatur; atque ita tandem à sinistro cordis ventriculo totum mixtum per diastolen attrahitur, apta supellex ut fiat spiritus vitalis. Servet. Christian. Restit.Text as well as any of his Commentators, who have written since the Greek Tongue; and much more, since the Ionic Dialect has ceased to be a living Language.
Since the Ancients have no Right to so noble a Discovery, it may be worth while to enquire, to whom of the Moderns the Glory of it is due; for this is also exceedingly contested. The first Step that was made towards it, was, the finding that the whole Mass of the Blood passes through the Lungs, by the Pulmonary Artery and Vein.
The first that I could ever find, who had a distinct Idea of this Matter, was Michael Servetus, a Spanish Physician, who was burnt for Arianism, at Geneva, near 140 Years ago. Well had it been for the Church of Christ, if he had wholly confined himself to his own Profession! His Sagacity in this Particular, before so much in the dark, gives us great Reason to believe, that the World might then have had just Cause to have blessed his Memory. (c) In a Book of his, intituled, Christianismi Restitutio, ​printed in the Year MDLIII. he clearly asserts, that the Blood passes through the Lungs, from the Left to the Right Ventricle of the Heart; and not through the Partition which divides the two Ventricles, as was at that Time commonly believed. How he introduces it, or in which of the Six Discourses, into which Servetus divides his Book, it is to be found, I know not, having never seen the Book my self. Mr. Charles Bernard, a very learned and eminent Chirurgeon of London, who did me the Favour to communicate this Passage to me, (set down at length in the Margin) which was transcribed out of Servetus, could inform me no further, only that he had it from a learned Friend of his, who had himself copied it from Servetus.
(d) Duæ insunt cordi cavitates, h. e. ventriculi duo; ex his alter à dextris est: à sinistris alter; dexter sinistro multò est major; in dextro sanguis adest naturalis, ac vitalis in sinistro: illud autem observatu perpulchrum est, substantiam cordis dextrum ventriculum ambientem tenuem satis esse, sinistram vero crassam; & hoc tum æquilibrii causâ factum est, tum ne sanguis vitalis, qui tenuissimus est, extra resudaret. Inter hos ventriculos septum adest, per quod fere omnes existimant sanguini à dextro ad sinistrum aditum patesieri; id ut fiat facilius, in transiem ob vitalium spirituum generationem tenuem reddi: sed longâ errant viâ: nam sanguis per arteriosam vemam ad pulmonem fertur, ibique attenuatur; deinde cum aëre unà per arteriam venalem ad sinistrum cordis ventriculum defertur; quod nemo hactenus aut animadvertit, aut scriptum reliquit. Reald. Columb. Anat. lib. vii. p.325. Edit. Lut.Realdus Columbus, of Cremona, was the next that said any thing of it, in his Anatomy, printed at Venice, 1559. in Folio; and at Paris, in 1572. in Octavo; and afterwards elsewhere. There he asserts the same (d) Circulation through the ​Lungs, that Servetus had done before; but says, that no Man had ever taken notice of it before him, or had written any Thing about it: Which shews that he did not copy from Servetus; unless one should say, that he stole the Notion, without mentioning Servetus's Name; which is injurious, since in these Matters the same Thing may be, and very often is observed by several Persons, who never acquainted each other with their Discoveries. But Columbus is much more particular; (e) for he says, That the Veins lodge the whole Mass of the Blood in the Vena Cava, which carries it into the Heart, whence it cannot return the same Way that it went; from the Right Ventricle it is thrown into the Lungs by the Pulmonary Artery, where the Valves are so placed as to hinder its Return that Way into the Heart, and so it is thrown into the Left Ventricle, and by the Aorta again, when enliven'd by the Air, diffused through the whole Body.(e) Idcirco quando dilatatur, sanguinem à cavâ venâ in dextrum ventriculum suscipit, nec non ab arteriâ venosâ sanguinem paratum ut diximus unà cum aëre in sinistrum: propterea membranæ illæ demittuntur & ingressui cedunt: nam cum cor coarctatur, hæ clauduntur; ne quod susciperetur per easdem vias retrocedat; eodémque tempore membranæ tum magnæ arteriæ, tum venæ arteriosæ re arteriofæ recluduntur, aditúmque præbent spirituoso sanguini exeunti, qui per universum corpus funditur, sanguiníque naturali ad pulmones delato. Res itaq; semper habet, cum dilatatur, quas prius memoravimus, recluduntur, clauduntur reliquæ; itáque comperies sanguinem qui in dextrum ventriculum ingressus est, non posse in cavam venam retrocedere. Ibid. pag. 330. Vide quoque lib. xi. pag. 411.
​Some Years after appeared Andreas Cæsalpinus, who printed his Peripatetical Questions at Venice, in Quarto, in 1571. And afterwards with his Medical Questions, at the same Place, in 1593. He is rather more particular than Columbus, especially in examining how Arteries and Veins joyn at their Extremities; which he supposes to be by opening their Mouths into each other: And he uses the Word Circulation in his Peripatetical Questions, which had never been used in that Sence before. He also takes notice, that the Blood swells below the Ligature in veins, and urges that in Confirmation of his Opinion.
At last, Dr. William Harvey printed a Discourse on purpose, upon this Subject, at Francfort, in 1628. This Notion had only been occasionally and slightly treated of by Columbus and Cæsalpinus, who themselves, in all probability, did not know the Consequence of what they asserted; and therefore it was never applied to other Purposes, either to shew the Uses of the other Viscera, or to explain the Natures of Diseases: Neither, for any Thing that appears at this Day, had they made any Numbers of Experiments, which were necessary to explain their Doctrine, and to clear it from Op​position. All this Dr. Harvey undertook to do; and with indefatigable Pains, traced the visible Veins and Arteries throughout the Body, in their whole Journey from and to the Heart; so as to demonstrate, even to the most incredulous, not only that the Blood circulates through the Lungs and Heart, but the very Manner how, and the Time in which that great Work is performed. When he had once proved that the Motion of the Blood was so rapid as we now find it is, then he drew such Consequences from it, as shewed that he throughly understood his Argument, and would leave little, at least, as little as he could, to future Industry to discover in that particular Part of Anatomy. This gave him a just Title to the Honour of so noble a Discovery, since what his Predecessors had said before him was not enough understood, to form just Notions from their Words. One may also observe how gradually this Discovery, as all abstruse Truths of Humane Disquisition, was explained to the World. Hippocrates first talked of the Usual Motion of the Blood. Plato said, That the Heart was the Original of the Veins, and of the Blood, that was carried about every Member of the Body. Aristotle also somewhere speaks of a Recur​rent Motion of the Blood: Still all this was only Opinion and Belief: It was rational, and became Men of their Genius's; but, not having as yet been made evident by Experiments, it might as easily be denied as affirmed. Servetus first saw that the Blood passes through the Lungs; Columbus went further and shew'd the Uses of the Valves or Trap-doors of the Heart, which let the Blood in and out of their Respective Vessels, but not the self same Road: Thus the Way was just open when Dr. Harvey came, who built upon the First Foundations; to make his Work yet the easier, the Valves of the Veins which were discovered by F. Paul the Venetian, had not long before been explained by Fabricius ab Aqua pendente, whence the Circulation was yet more clearly demonstrated.
There was one thing still wanting to compleat this Theory, and that was the Knowledge how the Veins received that Blood which the Arteries discharged; first it was believed that the Mouths of each sort of Vessels joined into one another; that Opinion was soon laid aside, because it was found that the capillary Vessels were so extremely small, that it was impossible with the naked Eye to trace them. This put them upon ima​gining that the Blood ouzes out of the Arteries, and is absorbed by the Veins, whose small Orifices receive it, as it lies in the Fibres of the Muscles, or in the Parenchyma's of the Bowels: Which Opinion has been generally received by most Anatomists since Dr. Harvey's Time. But Monsieur Leeuwenhoek has lately found in several sorts of Fishes (f),(f) Letter 65, 66. which were more manageable by his Glasses than other Animals, That Arteries and Veins are really continued Syphons variously wound about each other towards their Extremities in numberless Mazes, over all the Body; and others have found (g)(g) Philos. Transact. numb. 177. what he says to be very true in a Water Newt. So that this Discovery has passed uncontested. And since it has been constantly found, that Nature follows like Methods in all sorts of Animals, where she uses the same sorts of Instruments, it will always be believed, That the Blood circulates in Men after the same Manner as it does in Eels, Perches, Pikes, Carps, Bats, and some other Creatures, in which Monsieur Leeuwenhoek tried it. Though the Ways how it may be visible to the Eye in Men, have not, that I know of, been yet discovered. However this visible Circulation of the Blood in these Creatures effectually removes Sir William Temple's ​Scruple, who seems unwilling to believe the Circulation of the Blood, because he could not see it. His Words are these (h) 44, 45.(h): Nay it is disputed whether Harvey's Circulation of the Blood be true or no, for though Reason may seem to favour it more than the contrary Opinion; yet Sense can'very hardly allow it, and to satisfie Mankind both these must concurr. Sense therefore here allows it, and that this Sense might the sooner concurr, Monsieur Leeuwenhoek describes the Method how this Experiment may be tried in his 66th. Letter: The Inferences that may be made from this Noble Discovery are obvious, and so I shall not stay to mention them.
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