Harvey explains blood circulation

William Harvey published his account of the heart and blood in 1628. He had studied medicine in Padua before working in London. An influential explanation held that blood was continually formed in the liver and consumed in the body. Harvey repeatedly observed beating hearts in living animals and compared their movements. He focused the investigation on a testable question: where does the blood pushed out by each contraction actually go?

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Harvey estimated the amount moved in a heartbeat and multiplied it across a period of time. Continuous consumption would demand implausibly large production of new blood, so blood must return. Ligature experiments compared changes in arteries and veins, while venous valves supported movement toward the heart. Quantitative reasoning, anatomy, and controlled interventions together made an outward arterial flow and returning venous flow intelligible as one circulation.

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Harvey inferred small connections between arteries and veins without seeing capillaries directly. Malpighi’s microscopic observations in 1661 supplied that part of the route. Circulation changed approaches to organ supply, bleeding, and the movement of medicines. Physiology increasingly examined continuous processes inside the body. Heart movements, valves, and vessels under ligatures also offered a set of observations that other teachers and researchers could repeat when testing the explanation.

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