Puzzle No. 52: When?

Around 1242, the Arab physician Ala al-Din Ibn al-Nafis (c. 1213-1288) set out the first known description of the pulmonary (lesser) circulation of the blood in his Commentary on Anatomy in Avicenna's Canon (Sharh Tashrih al-Qanun). Rejecting the long-dominant teaching of Galen, he argued that the wall (septum) dividing the heart's two ventricles is solid and without pores, so blood could not pass directly from the right to the left chamber. Instead, he reasoned, blood must travel from the right ventricle through the pulmonary artery to the lungs, mingle there with air, and return via the pulmonary vein to the left ventricle. Working in Damascus and later as chief physician at the Nasiri Hospital in Cairo, Ibn al-Nafis reached this conclusion through anatomical reasoning roughly three and a half centuries before William Harvey and Renaissance anatomists such as Servetus and Colombo described the same pathway. His insight was largely lost to later European medicine until the manuscript was rediscovered in 1924 by the Egyptian physician Muhyi al-Din al-Tatawi in the Prussian State Library in Berlin, restoring his standing as a pioneer of circulatory physiology.

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