William Harvey and the Circulation of Blood (1628)

WILLIAM HARVEY AND THE CIRCULATION OF BLOOD (1628)

Look at the veins in your arm. Can you see the blood moving in them? Probably not. You can feel your pulse or your heartbeat, but you can't really see where the blood is moving, or why. It was the genius of William Harvey (1578-1657)--physician to Kings James I and Charles I--that he was able to clearly and thoroughly described the action of the heart, and the ways in which blood is moved through the body. Harvey showed how the heart's left ventricle pushed "fresh" blood through the arteries of the body, and when the "spent" blood returned the right ventricle sent it through the pulmonary artery to the lungs to be reoxygenated. He also discovered the function of the valves in the veins, which prevent blood from flowing backward (away from the heart).

• This put Harvey at odds with the accepted theory: the Greek physician Galen (129-216 CE) thought that the heart produced heat, and the lungs cooled the blood like a radiator.

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(Image courtesy Wikimedia Commons; CTTO)