William Harvey

English physician, physician to King James I and King Charles I. In his 1628 treatise Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (An Anatomical Study of the Motion of the Heart and of the Blood in Animals), Harvey demonstrated through direct dissection and quantitative reasoning that blood circulates continuously through the body in a single system driven by the heart's pumping action, overturning the centuries-old Galenic doctrine that the liver continuously manufactures blood which the body then consumes. The finding met considerable resistance from physicians trained in Galenic physiology and took decades to become the accepted account. Harvey could not observe the capillary connections his theory required; Marcello Malpighi confirmed them under a microscope in 1661, four years after Harvey's death.