In the early 17th century, before the scientific method began its ascendancy in the Western world, the Englishman William Harvey described how the blood circulates through the human body, solving a mystery that had stumped scientists for centuries.
Only Harvey, who assiduously tested his theories on living animals, figured out that blood circulates throughout the entire body.
He published his thesis in 1628, as On the Motion of the Heart and Blood in Animals. His discovery is considered one of the most important achievements in medical history.
Harvey introduced the "experimental and observational approach" to scientific inquiry, the British medical historian P.M. Dunn writes in an article for the Archives of Disease in Childhood.
In addition to his revolutionary work on blood, Harvey also advanced our understanding of human reproduction. His practice extended to obstetrics, and he was interested in and knowledgeable about birth.
Harvey's 1651 book On the Generation of Animals, published with the stunning essay "On Parturition," debunked the idea that embryos were fully formed at conception, and advanced the theory of epigenesis, which held correctly that a chick, for example, grew all its various parts from a single cell.
Harvey also addressed labor, advising birth attendants to let nature take its course rather than to intervene unnecessarily. Harvey's tract was the first original work on obstetrics written by an Englishman. Aside from these famous works, the rest of his prodigious writing has been lost.
What remains is "truly remarkable when judged against the ignorance of the times and the prevalent reliance on ancient authority," Dunn writes of Harvey.