We have William Harvey (1578-1657) to thank for the discovery of our blood circulation. With this experiment (taken from his book of 1628) he showed that blood inside our veins is constantly flowing back towards the heart. By putting pressure at different valves along a vein in the arm ("Figura 1"), it’s possible to stop the flow of blood towards the body ("Figura 2") but impossible to ‘push’ blood out towards the hand ("Figura 3"). Releasing pressure from near the hand, allows the blood to rush back into the empty space ("Figura 4") proving the flow is one way. Although he lacked the technology to prove it, Harvey also theorised a method for transfer of blood from arteries to veins – completing its circuit back to the heart. Four years after his death, Harvey was proven correct when Marcello Malpighi discovered blood capillaries in the surface of a frog’s lung.
Written by John Ankers
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