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William Harvey. Coloured portrait of the English physician William Harvey (1578-1657) sitting in a chair. Harvey is considered the founder of modern physiology for his work on the circulation of the blood. Until his research, popular belief followed the Greek physician Galen's view that blood oscillated back and forth in the vessels. His experiments showed that the heart was a muscle and acted as a pump. Through dissection he saw that the valves joining the heart's two upper and lower chambers permitted blood flow in only one direction and that blood moved around the body in a closed loop.
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