1532-1538. Studies of medicine in Paris

As "Villeneuve" Servetus studied mathematics and medicine at colleges in Paris, then a center of religious ferment. Nicholas Cop, Rector of the University, was forced to flee the city after an inaugural address deemed too Protestant. A young student of Servetus' acquaintance, John Calvin, who may have written the address, had also to leave town and to go into hiding. Sometime during the next year Calvin risked his life to return to Paris that he might meet Servetus and respond to his theological challenges.

Servetus, perhaps afraid of being seen with a fugitive, did not show up. Driven to witness for his religious cause, he yet felt unready to be its effective champion. "On this account I delayed," he recalled, "and also because of imminent persecution, so that with Jonah I longed rather to flee to the sea or to one of the New Isles."

Servetus left temporarily Paris and began to support himself in France by working as corrector of proof in Lyon, which ranked next to Paris as a publishing center. He was employed for over two years by Treschel, a famous publishing house. In this capacity Servetus served as editor of a new edition of Ptolemy’s Geography (1535), which the recent explorations in the New World had made necessary. This work was enriched by many pungent notes, and one of these, which spoke of Palestine as a very poor country for a “promised land,” afterwards brought him into trouble as a defamer of Moses.

Inspired by some of the medical works published by Trechsel, Servetus decided to return to the study of medicine. From 1536-38 he was a medical student at the University of Paris. He followed Andreas Vesalius as assistant to Hans Gunther in dissection. Gunther wrote that "Michael Villonovanus" had a knowledge of Galen "second to none." Servetus soon came to differ from Galen in the matter of pulmonary circulation. Galen had supposed aeration of the blood took place in the heart and assigned the lungs a fairly minor function. Servetus, by examining the wall of the heart and noting the size of the pulmonary artery, concluded that transformation of the blood, accomplished by the release of waste gases and the infusion of air, occurred in the lungs. It is not clear whether Servetus or a contemporary, unknown to Servetus, first made this discovery. Servetus was the first to publish. Although he only expressed the new knowledge as a lengthy metaphorical aside in his theological writing, he was the first person to record a modern understanding of pulmonary respiration.

In 1538 Servetus, as Villeneuve, got into trouble with the faculty of medicine, the Parlement of Paris, and the Inquisition for mixing astrology with medicine. Although he was acquitted by the Inquisition, the Parlement ruled that his published self-defense (Disceptatio Pro Astrologia) was to be confiscated and he was to desist from the practice of astrology. [To know more about this]

Servetus left Paris shortly thereafter, perhaps without a degree, to practice medicine in the area of Lyons. Around 1540 he became the personal physician of Pierre Palmier, Archbishop of Vienne.