For over a thousand years, doctors in Europe depended on Galen. Galen represented the pinacle of Hellenic medicine. He experimented, for one thing: he invented the process of taking patients’ pulses, demonstrated that the kidneys produce urine, and explored the role of nerves in keeping animals alive. But he didn’t understand the role of the heart in blood circulation and didn’t, in fact, understand blood circulation at all. Numerous inaccuracies crept into his work, some possibly due to his philosophical beliefs and some due to his practice of dissecting not human corpses but those of pigs, sheep, and apes. Galen’s mistakes were generally obvious to anyone with a cursory knowledge of human anatomy, but scientific experimentation simply fell out of medical science. Some naturalists recorded the world around them, but until 1543, the way a European doctor learned about medicine was through reading Galen and Galenists like Mondino who had themselves relied upon Galen as an authority, even when Galen’s claims contradicted what they saw. When Andreas Vesalius published his On the Fabric of the Human Body (De humani corporis fabrica libri septem), the first modern anatomy text, he was putting an end to that forever.
Vesalius wrote in his introduction, "As soon as the custom ended of training boys in dissection, as an immediate and inevitable consequence they learned less well, since the training they were accustomed to commence in childhood was abolished." Vesalius had mastered the art of dissection, trusted in what he saw, and was determined to use all his rhetorical skill to put an end to milennia of medical ignorance. The effect on a society where learning descended from scriptural authority or the scholarship of antiquity was pronounced:
[H]e destroyed the foundation of the whole teaching of Galenism and of the belief in its authority, and pointed out the way for the free investigation of nature. However, the numerous followers of Galen began a bitter struggle against the daring investigator, and even the medical school of Padua turned against him. Jacobus Sylvius called him a madman and declared that an advance beyond the knowledge of Galen was impossible, and that Galen had not erred, but probably the human body had changed since then. Bartholomew Eustachus of Rome declared he would rather err with Galen than accept the truth from the innovator. His enemies even sought to prevent his appointment as physician to the emperor and spread slanders, so that Vesalius, depressed by his troubles, threw a large part of his manuscript and works into the fire.
Shielded from the backlash to his work by Emperors Charles V (to whom the only known color copy of De humani corporis was presented) and Phillip II, his immensely powerful patrons, Vesalius was largely left to his work. He stripped down Latin, insisted that doctors perform their own dissections, and disseminated hundreds of anatomical illustrations (executed by apprentices in Titian’s workshop, many of the engraved wood blocks survived until the twentieth century) throughout Europe. The idea of anatomical studies flourished; medical illustration and later anatomical models (link via The Eyes Have It) and medical photography (link via Speckled Paint) became a fixture in medical education. The idea that medical students should perform dissections took root as well. Belief in bodily resurrection meant that the cadavers used were generally those of executed criminals, but by the nineteenth century, demand for bodies was outstripping the supply that the hangman could supply. Graverobbing came into vogue; the famed "ressurectionist" team of Burke and Hare took a further step, ensuring a constant supply of corpses for Edinburgh’s medical students by suffocating a stream of victims in 1827 and 1828.
A contemporary account holds that Vesalius was himself accused of murder (for dissecting a man whose heart had not yet stopped beating), contemporary scholarship regards this as a malicious invention. Ideas, however, are another matter. Vesalius helped usher in the Age of Reason, the Europe of Galileo and Newton, by the claim that people should believe their own eyes and not what they read. The concept of studying and classifying the world around one through direct observation, rather than through a filter of classical scholarship, wouldn’t go away; natural philosophy led to the study of biology and thus to John Gould‘s depiction of Mr. Darwin’s curious finches. Medieval thought was still alive until Vesalius and his fellow humanists took up the knife.