Discovery of the Circulation of the Blood

In his 1628 treatise De Motu Cordis, the English physician William Harvey demonstrated through dissection and quantitative reasoning, chiefly an estimate of how much blood the heart moves per hour, that blood circulates continuously through the body in a single closed system driven by the heart's own pumping action. This overturned the Galenic doctrine, dominant for some fourteen centuries, that the liver continuously manufactures blood which the body then consumes as fuel. Harvey's theory met sustained resistance from physicians trained in Galenic physiology and took decades to gain general acceptance. He could not observe the capillary vessels his closed-system theory logically required; Marcello Malpighi confirmed them under a microscope in 1661, four years after Harvey's death, completing the physical picture.