In 1628, the English physician William Harvey created a sensation by publishing a radical new view of how the body uses blood. Until then, doctors had relied on the 1,300-year-old teachings of Galen, a Greek physician, who claimed that blood was created by the liver and then consumed by living tissue. In contrast, Harvey argued that the amount of blood is fixed, and constantly circulates round the body, being refreshed by passing through the lungs and other organs.
Harvey's revolutionary view implied that blood supply was limited - casting grave doubt over widely-used practices such as 'blood-letting'. After sometimes bitter criticism, Harvey's claims were confirmed and he is now regarded as one of the founders of modern medicine.
But historians have since found that Harvey's revolutionary ideas about the circulation of the blood had already been discovered over 400 years earlier. The 13th-Century Arab physician Ibn al-Nafis showed that the construction of the heart contradicted Galen's claims, and argued that there must be tiny blood vessels allowing blood to circulate. Now called capillaries, their existence was confirmed only in the 17th Century. Unfortunately for al-Nafis - and countless patients - his pioneering work remained unknown in Western Europe until the early 20th Century.
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