Where does the blood go?

Look for the chambers, the vessels that enter and leave them, and the direction in which blood is said to move. Ask which claims about the route you can trace on the diagram and which you must take from the text.

Look at the second passage and the diagram. On folio 65 recto and verso, Ibn al-Nafis repeats that there is no passage at all between the ventricles, and that the septum is thicker than the rest of the heart to stop the blood passing ². Then he says that the blood enters the left ventricle from the lung, after it has been heated in the right ventricle and risen from it ². In a third passage, on folio 46, he says that there are perceptible passages, manafidh, between the pulmonary artery and the pulmonary vein ². The diagram in the record of the pulmonary circulation sets two schemes side by side: Galen's, in which the blood crosses the septum, and Ibn al-Nafis's, in which it passes through the lung ². Trace each route on a drawing of the heart.

No sentence in the record gives Ibn al-Nafis's reason for denying the pores in his own words. What it shows is the problem they solved. The pores puzzled anatomists for more than a thousand years, yet Galen's scheme needed them, because nobody yet knew that a large amount of blood flows from the lungs to the heart ². His book is a commentary on the Canon: he takes Ibn Sina's framework and parts from it at the septum ².

Did Servetus know Ibn al-Nafis's work? The source does not dispute that Ibn al-Nafis described the passage of blood through the lungs about three hundred years before anyone in Europe; the question it raises is whether Servetus and those after him knew his work ². Servetus's words on the septum and the lungs resemble Ibn al-Nafis's, which might suggest he knew the earlier work ². A 1940 study by Owsei Temkin pointed out inconsistencies between the two statements, and the 1547 Latin translation of the Commentary on Compound Drugs apparently said nothing about the pulmonary circulation ². West writes that many historians believe Servetus did not know Ibn al-Nafis's work; if so, both deserve credit, each in his own time ².

The source does not say that the account spread in Islamic medicine after Ibn al-Nafis, and it does not trace the copies of the commentary or its readers ³. The passage is not known to have reached the West before the twentieth century ². Muhyi al-Din al-Tatawi came across the manuscript in the Prussian State Library in Berlin while writing a doctoral thesis, submitted in 1924, and the thesis was never published; Max Meyerhof learned of the discovery, wrote about it and translated the passages, and so saved it from oblivion ². The Wellcome Collection's catalogue describes its manuscript, WMS Or. 51, as containing the first description of the pulmonary circulation ⁴.

The record gives three pieces of evidence on whether Servetus read Ibn al-Nafis: a resemblance between the two statements, inconsistencies that Temkin pointed out, and a Latin translation of another book that apparently said nothing about the lungs ². Which of the three matters most for deciding, what would a critic say in reply, and why?

• The pulmonary circulation: the three parts of the account, the diagram of the two schemes and the manuscripts.
• Ibn al-Nafis: the biographical entry on his work and his endowment.
• The Commentary on the Anatomy of the Canon: the book that holds the passages.
• The Canon of Medicine: Ibn Sina's book, whose framework the commentary takes up.