Vesalius, Harvey and the New Medicine

The Scientific Revolution transformed the study of the human body as well as the stars. For centuries medicine relied on Galen, a second-century physician whose anatomy was based largely on dissecting animals. In 1543 Andreas Vesalius published On the Fabric of the Human Body, using careful human dissection and detailed illustrations to correct many of Galen's errors. In 1628 the English physician William Harvey demonstrated that blood circulates continuously, pumped by the heart, rather than being constantly made and consumed as Galen taught.

Harvey used experiments and simple arithmetic about how much blood the heart moves to make his case. Microscopes then revealed new worlds: Robert Hooke described 'cells' in 1665, and Antonie van Leeuwenhoek observed single-celled organisms in the 1670s. These advances encouraged the Enlightenment belief that direct observation, not inherited authority, should guide practical knowledge that could improve human lives.