From a history of the discovery of blood circulations

The discovery of blood circulations in 1628 by the English scientist William Harvey became one of the greatest scientific achievements of the 17th century. The emergence of new ideas about the motion of blood drew fierce criticism from the followers of Galen’s theory that had been dominating for 1.500 years. According to Galen, blood was formed in the liver from food and then entered the heart, from where it was carried by the arteries and veins to organs and tissues, and blood motion occurred in tides - back and forth. The description of venous valves by the Italian anatomist Heronymus Fabricius (or Girolamo Fabrizio), Harvey’s teacher, was an important fact that preceded the discovery of blood circulations. With experiments using venous ligation, Harvey was the first to prove that blood moved through the veins in the direction of the heart, and not vice versa. The most convincing evidence that the blood moved around in a circle was Harvey’s calculations of the speed of blood flow in a sheep. The calculations showed that in the course of half an hour, a quantity of blood equal to the weight of the animal passed through its heart, which excluded the possibility that the liver was involved in the formation of blood and could be explained only from the point of view of its circulation in the body. A progressive approach to solving the circulatory problem was Harvey’s inductive method based on observations and experiments. Despite convincing evidence for Harvey’s theory, it took almost 3 decades before his ideas received general acceptance. The new theory refuting the generally accepted ideas was approved not only thanks to the outstanding talent of Harvey, but also his great personal courage.