The discovery of the pulmonary circulation: A debate spanning centuries

Did You Know...

 ... that the credit for the discovery of the pulmonary circulation is still a topic of debate amongst scientists and historians alike? This argument revolves around whether individual contributions were made independently of one another. Here, we offer the reader a fictitious scene to portray such controversy; the main characters being five legendary names accredited for the discovery of the “lesser circulation” (Figure 1). Excerpts from their original textbooks are italicized for easier referencing. The plot of the scene is adapted from the famous dialectics written by the Greek philosopher Plato; his masterpiece “Apology” in particular, with Plato himself portrayed as the judge between the conflicting scientists.


 It is sometime past midnight... So faint is the rhythmic ticking of the clock, as it has been largely masked by the incomprehensible noises of a group of men congregated by a round table. Mumbling is the only audible sound, and as such, the discussion seems to be going nowhere. Plato’s task is to bring discipline back to the table.

PLATO (angrily): “Order, order, O scientists! At my time of life I ought not to be appearing before you, in the character of a juvenile judge, let no one expect it of me! However, at your request, from me you shall hear the whole truth, and nothing but the truth, however, delivered after your manner, in a set oration duly ornamented with your own words and phrases!1 Now, out of your heated arguments earlier, I could understand that the first recorded mention of the circulation is ascribed to Dr. Galen.2 Well, then, the stage is his to start.”

GALEN (full of pride and majesty): “Your Honor, gentlemen; I suggested that the liver manufactures the natural spirits (blood), and is accordingly the origin of all veins. On the other hand, the heart is the generator of vital spirits and of heat, in addition to being a chief cistern of the blood. In the heart, the thinnest portion of the blood is drawn from the right ventricle into the left, owing to there being perforation in the septum between them: these can be seen for a great part (of their length); they are like a kind of fossae with wide mouths, and they get constantly narrower; it is not possible, however, actually to observe their extreme terminations.”3-5 A constant humming suddenly breaks into the room!

SERVETUS (whispering): “And here begins the fun!”

HARVEY (screaming emphatically): “But, by Hercules, no such pores can be demonstrated, nor in fact do any such exist!”6

GALEN (emphatic in his response): “I can assure you nothing is done by nature in vain, nature has overlooked nothing! And as I observed, the insertion of the vena cava into the heart is larger than the vein which is inserted into the lungs. This suggests that not all the blood given to the heart is driven away again into the lungs, but rather shunted directly to the left ventricle!”3

AL-NAFIS (in his rather deep and tranquil voice): “Based on my observations, I affirm that there are neither visible, nor invisible, passages between the two cavities, the substance of the heart there being impermeable. The pores of the heart there are compact and the substance of the heart is absolutely thick.”7,8

VESALIUS (jumping to the defense of Galen): “Calm down, people! Truthfully, Dr. Galen, I also couldn’t find these holes, and I dared to admit it publicly, for which I was (((he grimaces in disgust))) undeservedly ostracized from Padua’s scientific community! This being said, I would...”

SERVETUS (interjecting loudly, and quite awkwardly): “Oh good God! Ostracized? You think this is bad? Son: me, and all copies of my book, Christianismi Restitutio, were burnt at the stake, punished by the Holy Inquisition, for rejecting Trinity in the Bible! And, believe you me, it still hurts!” Uncomfortable amusement encompasses the room. Plato, however, orders Vesalius to finish his part.

VESALIUS “I was saying: I would attribute Galen’s shortcomings to the fact that he carried out his dissections on primates, mainly Barbary Apes, and not on human cadavers, since the latter had been banned in ancient Rome.”9

PLATO: “Fair enough! May you continue Dr. Galen.”

GALEN (unmoved by the huge opposition so far): “The blood flow through the lungs is unidirectional, I noticed. Part of the blood in the right ventricle passes through the arterial vein (pulmonary artery) to nourish the lungs. The venous artery (pulmonary vein), on the other hand, carries air from the lungs into the left ventricle to mix with blood, and a portion of the spirituous blood moves on the opposite direction for lungs’ refreshment, while fuliginous vapors from the heart escape by it into the lungs.”3

((Poor Galen!)), one has to think, with the group’s impetuous burst of noises! Recognizing his part here is over; he takes a step back and gives his aging body a rest.

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Figure 1: A debate spanning centuries 

Image credit: Ghazwan Butrous ©

SERVETUS (contemplating a golden opportunity to stamp his legacy on the subject, expresses boastfully): “Well, Your Lordship, I think I’m the first to criticize this Galenic doctrine on the lesser circulation! An extract from my book reads: the subtle blood is transferred from the right ventricle, in a brilliant way, by following a long circuit through the lungs, which submits it into a transformation, in order for the blood to come out colored yellow: the arterial vein transports it into the venous artery. From that moment on, the blood is mixed in that very same venous artery with the inhaled air in order to become re-purified from all fuliginous materials. In this way, the entirety of this mixture is finally attracted by the left ventricle of the heart, during the diastole, to serve as a base for the vital spirit.”10

AL-NAFIS (clearly stunned!): “My friend, when did you publish your book?”

SERVETUS: “Back in 1553.”

AL-NAFIS (indignantly): “Then, by the Grace of Almighty Allah, how were you the first to condemn Galen’s hypothesis on the pulmonary circulation, when I already did the same almost 300 years before, in 1242! I explained in my Commentary on the Anatomy of Avicenna’s Canon that when the blood has become thin in the right ventricle, it is passed into the arterial vein to the lung, in order to be dispersed inside the substance of the lung, and to mix with the air. The finest parts of the blood are then strained, passing into the venous artery reaching the left of the two cavities of the heart, after mixing with the air and becoming fit for the generation of pneuma.”7

More murmurs from the crowd….

HARVEY (astonished): “Oh dear Lord; what you mentioned earlier, Servetus, sounds like a faithful translation of what Al-Nafis has just explained!”

SERVETUS (arrogantly): “I cannot be more oblivious of such information, I have to say!” Though tempted by this new piece of evidence from Al-Nafis, PLATO opts to dig deeper for further clarification.

“I think, gentlemen, there is still a missing link here, as Servetus’ active career was mainly in Spain, France, and Italy, while Al-Nafis resided for the most part of his life in Damascus. We should never overlook the broad cultural, geographical, and language borders between the two! This is most critical to settle the issue of whether the Latin West had access to Al-Nafis’ writings, I believe.”

ALPAGO, who had been silent thus far, decides to intervene: “Your Honor, my fellows; I lived in the Middle East, mainly Damascus, for almost 30 years; collecting, translating and editing the works of Arab physicians. On my return to Venice in 1547, I published my Latin translations of several parts of Al-Nafis’ Commentary. I also passed much of my acquired expertise orally or in writings hitherto unpublished to my colleagues in Italy. A sudden burst of activity in the fields of anatomy and physiology happened then after at Padua, which ultimately culminated in Harvey’s great book (De Motu Cordis) published in 1628! Having said that, I don’t strive to take from these great investigators any honor that is their due!”11,12

HARVEY: “No objection, Dr. Alpago! I have always genuinely ascertained that true philosophers, who are only eager for truth and knowledge, never regard themselves as already so thoroughly informed, but that they welcome further information from whomsoever and from wheresoever it may come. I explicitly ratify that my biggest endeavor was to develop a dynamic total concept of the cardiovascular system as opposed to the anatomical descriptions of separate individual structures that had been available up to my time. It was always my conscience that what is true may be confirmed, and what is false set right by dissections, multiplied experience, and accurate observations!”6

 This is the light at the end of the tunnel! A few simple words of wisdom may dissipate all the residual heat of an argument, and signs of contentment are forced back onto the faces of the group.

PLATO (concluding the case): “My friends: so persuasively did each of you speak, that a juvenile judge like me may stumble in his noble pursuit of justice! But, then, why bother making judgments when the collective virtue of a case is conceivably worthier than the minute gains of personal glory! Though scientific discoveries are true portraits of the acts of genius, inspiration, and persistence; they are seldom born on air. Pieces of knowledge are thrown all over the streets waiting for an enlightened person to collect and utilize! Dear all: Thank you! We are most grateful for releasing our minds from the flames of sand and the potency of sky in the barren deserts of ignorance and illiteracy!”




1. Jowett B. The complete dialogues of Plato: Translated into English with analyses and introductions. Apology, p. 2-30: B&R Samizdat Express; 2008.

 2.Wiltz W. Wagner Jr. HBW. History of the Study of Pulmonary Circulation. Seminars in respiratory medicine. 1985;7:117-123.

3. Brock AJ. Galen, On the Natural Faculties. Google Books; 1916.

4. Fisher TN. History of medicine: Galen, Renaissance physiology and the circulation of blood. Marquette Med Rev. 1962;27:100-104.

5. Bylebyl JJ, Pagel W. The chequered career of Galen’s doctrine on the pulmonary veins. Med Hist. 1971;15(3):211- 229.

 6. Bowie A. On the Motion of the Heart and Blood in Animals, by William Harvey. Google Books; 1889.

7. Al-Nafis I. Commentary on the anatomy of Avicenna’s Canon. Arabic eBooks; 2008.

8. Loukas M, Lam R, Tubbs RS, Shoja MM, Apaydin N. Ibn al-Nafis (1210-1288): the first description of the pulmonary circulation. Am Surg. 2008;74(5):440-442.

9. Dunn PM. Andreas Vesalius (1514-1564), Padua, and the fetal “shunts”. Arch Dis Child Fetal Neonatal Ed. 2003;88(2):F157-159.

10. Stefanadis C, Karamanou M, Androutsos G. Michael Servetus (1511-1553) and the discovery of pulmonary circulation. Hellenic J Cardiol. 2009;50(5):373-378.

11. N.K. Singh MZK, M. Zaki Kirmani. Encyclopaedia of Islamic science and scientists. Google Books; 2005.

12. Cournand A. Air and Blood. In: Fishman DWRAP, ed. Circulation of the Blood, Men and Ideas: Oxford University Press; 1964:11-28


Pulmonary Circulation

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PVRI Chronicle Vol 2: Issue 1 cover image

January 2015

PVRI Chronicle Vol 2: Issue 1

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