Galen, William and the Heart

Aelius Galenus  (Galen)

Galen was a 2nd century physician who was the first to do proper dissections on animals and look in detail at the circulatory system including the heart, the veins and the arteries. He was the first to realise that there is a difference between venial and arterial blood.However his views were flawed in that he assumed that the venial blood originated in the liver and that the arterial blood originated in the heart and that they were not connected.

William Harvey

 William Harvey was one of the first people to study the circulatory system in detail since Galen over 1000 years ago. Harvey conducted many detailed experiments on a variety of animals. From these experiments he concluded that it was a closed system in which the heart continuously pumped blood round in a loop. He also did basic calculations on how much blood the heart pumped in a day to conclude it was impossible that the liver could produce that amount of blood that was being pumped. He calculated the liver had to produce 540 pounds of blood every day a ridiculous quantity. He theorised about the existence of capillaries, however because of a lack of decent microscopes that were only available a few hundred years later, he could not prove the existence of them.