Blood Circulation: from Greeks to Harvey

Two thousand years ago, the Greeks thought that blood moved backwards and forwards in the blood vessels rather like waves on a beach. They also believed that blood was gradually used up by the body, and that new blood was made from food, water and air. In 1628, William Harvey, an English doctor who worked at St Bartholomew’s Hospital in London, published a famous book about the heart.

Doctors in Harvey’s day were taught the Greek ideas about blood. They were not expected to study the heart and blood vessels for themselves. It was enough to hear about the Greek ideas and to glance at a few dissected bodies, Harvey was the first doctor to make a really careful study of the heart and blood vessels for himself. He was able to show that the Greeks were wrong. The blood moves in one direction only through the heart and blood vessels. The heart acts as a pump to keep the blood moving.

Harvey discovered the circulation of the blood. He worked out how much blood was pumped out of the heart each minute. He also showed that this was far more than could be made from the food and water taken in. This helped to support his idea that blood moves round the body continuously, and that it is not used up. Harvey was unable to see the smallest blood vessels, which we now call capillaries, but he knew that they must be there. However, soon afterwards in 1661, an Italian scientist named Malpighi used a microscope to examine the lungs of a frog. He was able to see the capillaries. Blood passes from the arteries through the capillaries to the veins. The last link in Harvey’s discoveries about blood circulation was now in place.