Harvey studies the circulation of the blood

The story

Fourteen hundred years of mistakes about the human body

For more than fourteen hundred years doctors had followed the teachings of Galen, a Greek doctor who worked in Rome in the 2nd century AD. Galen thought that blood was produced all the time by the liver, from the food we eat, and that it then went around the body, where it was “used up” by the tissues, like wood in a fire. According to him the blood moved slowly back and forth, like water in the tide, but did not travel in a circle. He also thought that in the heart there were tiny invisible holes between the two halves, which let the blood through.

Galen had made many observations, but he had mostly dissected animals, because in Rome it was not allowed to open human bodies. For this reason some of his errors stood uncorrected for a long time. In the 16th century Andreas Vesalius, in Padua, began to correct them with human dissections, but on the movement of the blood the picture had not yet changed.

An English doctor in Padua

William Harvey was born in 1578 in Folkestone, in England. He studied at Cambridge and then at Padua, the most famous university in Europe for medicine, where his teacher was the anatomist Girolamo Fabrici d'Acquapendente. Fabrici showed him the valves of the veins, small flaps shaped like swallows' nests that let the blood pass in one direction only. Those valves, which made little sense in Galen's model, stayed in Harvey's mind.

Back in London, Harvey became an established doctor. He treated Kings James I and Charles I and taught anatomy at the Royal College of Physicians. With the king's permission he could also study the deer of the royal hunts. For many years he repeated experiments on animals of all kinds, from fish to snakes, from frogs to dogs, to see how the heart beat.

The sum that did not add up

Harvey made a simple and brilliant calculation. He worked out how much blood passes from the heart at each beat, and how many beats there are in an hour. Even with cautious estimates, the result was huge: much more than the weight of a person. It was not possible for the liver to make so much blood in an hour, nor for the body to use up so much. So it had to be the same blood all the time, going round in a circle: it leaves the heart through the arteries, reaches the tissues, comes back through the veins and enters the heart again.

To prove it he did experiments on himself and on others too. When an arm was tied tightly with a band, you could see the veins swell below the band and the arteries pulse above it. When you pushed the blood along a vein with your finger, you could see that it went only towards the heart and that the valves stopped it from going back.

A small and brave book

In 1628 Harvey published in Frankfurt, in Latin, a little book of only seventy-two pages, “De motu cordis”, “On the Motion of the Heart and Blood”. The book was printed on poor paper and with mistakes. Many doctors criticised it: they found it contrary to authors who had guided medicine for centuries. According to a biographer of the time, John Aubrey, after its publication Harvey lost many patients.

There was a gap: Harvey had not been able to see how the blood passed from the arteries to the veins, because the smallest vessels, the capillaries, are too thin for the naked eye. He imagined them, but could not show them. In 1661, four years after his death, the Italian Marcello Malpighi saw them with the microscope in the lungs of a frog. It was the missing confirmation.