William Harvey

By Lin Yue

Every physician before him knew the blood moved. None of them knew it came back. William Harvey, born in 1578 in Folkestone, England, studied at Cambridge and then at Padua — in the very anatomical theater where Vesalius had once wielded the knife, under Fabricius, who had discovered the valves in the veins without understanding them. Harvey returned to London, became physician to St. Bartholomew's Hospital and then to two kings, James I and Charles I, and spent his spare years doing something no one had thought to do: he measured.

The argument of De motu cordis — On the Motion of the Heart and Blood, published in Frankfurt in 1628 — is the first great quantitative argument in biology. Harvey estimated the volume of blood the heart expels with each beat, multiplied by the heart rate, and showed the result was absurd: in half an hour the heart pumps more blood than the entire body contains, more than the liver could possibly manufacture from food in Galen's scheme. The blood could not be consumed by the tissues; it had to return. It had to circulate. With ligatures on the arm he demonstrated the one-way valves in the veins, showing blood flows toward the heart in veins and away from it in arteries. The heart was a pump; the body was a closed hydraulic circuit.

He was wrong about one link — he never saw the capillaries connecting arteries to veins; Malpighi would find them with the microscope four years after Harvey's death — and he clung to some Aristotelian notions of the heart's innate heat. It didn't matter. The quantitative method was the revolution: Harvey had done for physiology what Galileo was doing for physics, replacing qualitative essences with numbers that forced a conclusion.

The establishment resisted, as establishments do; the young embraced him. He lived through the English Civil War, saw his house looted and his manuscripts on generation scattered, and died in 1657 of gout and grief. But by then every medical student in Europe learned the circulation. Galen's thirteen-century reign over the body ended not with a better theory but with arithmetic.

Impact on civilization

Harvey's discovery of the blood's circulation founded modern physiology by introducing quantitative reasoning into biology — the first time measurement, not authority, decided a question about the living body. It destroyed the Galenic system of ebb-and-flow blood production and replaced it with the heart-as-pump and the closed circuit, making modern cardiology, hematology, and transfusion medicine conceivable. His method — estimate, calculate, conclude — became the template for experimental life science. Every blood pressure cuff, every bypass operation, every unit of transfused blood descends from the arithmetic of De motu cordis.