To lay readers of Descartes’ work, the fact that he’d worked on medicine might not come as a complete surprise, unlike the significance and depth of this work. Though he’d not published any of his works devoted exclusively to the study of human bodies in his lifetime, the posthumous publication of Treatise on Man (1664) and Description of the Human Body (1664), indicate that Descartes felt he had acquired sufficient expertise in the topic to devote the time it took to write these texts. What is particularly curious about Descartes’ engagement with medicine, though, is the reputation he had developed as a doctor, even before he’d published anything.
In a somewhat recent paper titled Descartes and the Bologna Affair, Gideon Manning, reports on an invitation Descartes received to take the chair of medicine at the University of Bologna . Manning traces this invitation to either late 1632 or early 1633, which places it about 5 years before Descartes published his Discourse on the Method (1637). What makes this even more interesting is that the earliest evidence we have of Descartes’ interest in medicine is in a letter to his friend Mersenne dated 18 December 1629, when he asserts he had begun studying anatomy.
By 1632, Descartes must have becomecomfortable with the typical concerns of both practical and theoretical medicine. In a letter to Mersenne from either November or December 1632 he mentions having read William Harvey’s De Motu Cordis. He claimed that it “differs slightly” from his own view, but he had only seen it after he’d finished writing on the topic. Given that Harvey was at the greatest medical innovator of the time, Descartes’ familiarity with the text, and perhaps more importantly, his feeling that he could argue against some of Harvey’s assumptions and claiming that he had arrived at some similar conclusions, it seems clear that his studies were robust enough to equip him with the mental apparatus to argue with the most learned physicians of the time.
Perhaps it is a loss that Descartes refused this invitation. It certainly was consistent with his character. In the Discourse he remarks that he was more grateful to those who offered him leisure to think than those who offered him honourable positions. Manning notes that it’s unclear whether Descartes was referring to the “Bologna Affair” here, but nonetheless, we know Descartes’ frequently avoided his friends, and he sought solitude. Nonetheless, it remains as a curious and relatively unknown part of his biography.
 Manning, Gideon. “Descartes and the Bologna Affair.” British Journal for the History of Science 47, no. 1 (2014): 1-13.