Until 1628 few Europeans disputed the teachings of Galen, an accomplished Greek physician and scholar. Galen lived in the second century A.D., and his teachings would come to dominate European medicine and scholarship for centuries.
Galen’s massive contributions to medicine cannot be denied. He was the first to identify the physiological difference between veins and arteries. He also disproved a 400-year-old theory that arteries conveyed not blood but air throughout the body (the name artery comes from this original idea: The Greek arteria means “that which conveys air”). By the 16th and 17th centuries scientific methods had evolved, making it easier for new scientists to challenge the old ones. Galen’s theories were sitting ducks, waiting for a physician like Englishman William Harvey to take them down.
Galen taught that there are three main interconnected systems in the body: the brain and nerves; the heart and arteries; and the liver and veins. According to Galen, dark, venous blood formed in the liver and then traveled through the veins throughout the body to deliver nourishment and build and maintain tissues. Some blood would come into contact with air in the lungs and go to the heart. From there, this bright red blood went to the brain to form “pneuma,” a substance responsible for sensation and feeling.
According to Galen’s theory, the blood did not return to the liver or the heart. Instead, it would be consumed by the body, which meant that it needed to be constantly replenished. Sometimes the liver might produce too much blood, and the body became imbalanced, leading to illness. Galen’s cure was bloodletting, as drawing off the excess fluid would restore equilibrium.
Other scientists had discovered the true nature of circulation centuries before Harvey. One of the main manuals of Chinese medicine, written 2,600 years ago, stated that “all of the blood in the body is pumped by the heart, completes a circle and never stops moving.” In the 13th century the Arab doctor Ibn an-Nafis described so-called “small circulation” in which blood circulated only from the heart to the lungs and back without reaching other parts of the body.
In 16th-century Europe Galen’s teachings were beginning to be challenged. The Spanish physician Michael Servetus argued that the venous blood was purified in the lungs before returning to the heart. Out of respect for, or fear of, the Galenic tradition, however, this philosopher and doctor did not describe the pathways through which the blood circulated. His contemporary the Belgian anatomist Andreas Vesalius demonstrated in the 1500s the flaws in Galen’s anatomical description of the heart, but he did not challenge the rest of his teachings.
Harvey and the Heart
The growing skepticism of Galen’s work had a great influence on William Harvey, who was born in Folkestone, England, in 1578. The son of a farmer, Harvey showed great promise as a child, and his father encouraged his studies. As a young man he studied at the King’s School in Canterbury and at Cambridge University. He completed his medical education at the University of Padua in 1602. He returned to England and began practicing medicine and teaching. In 1607 he became a fellow of the Royal College of Physicians, and in 1609 he was appointed physician to St. Bartholomew’s Hospital in London. Harvey’s star continued to rise: In 1618 he became the royal physician, serving both James I and his successor, Charles I.
Through his teachings and observations, Harvey began to develop a new theory to explain how blood flowed through the body. He applied rigorous standards to his research and only accepted conclusions as proven when they were based on evidence from repeated experiments. He collected data from phlebotomies (drawing blood from a vein) and palpitations of arterial aneurysms (abnormal dilation). He conducted thorough research, including numerous dissections of human beings and as many as 40 animal species. Harvey pored over the results before compiling them and publishing his groundbreaking Exercitatio anatomica de motu cordis et sanguinis in animalibus (On the Motion of the Heart and Blood in Animals) in 1628. Harvey’s small volume—about 70 pages long—became a gigantic milestone.
In this book (first published in Latin, and then in English 25 years later) Harvey laid out the evidence supporting his case that blood moved throughout the body in a circle. His strongest evidence was that it would be impossible for the body to replenish the amount of blood it would consume under Galen’s theories. He arrived at this conclusion by calculating the total volume of blood that moves through the body in an hour and showed that it was too high for the body to replenish. Therefore, the amount of blood in the human body must be constant and in perpetual motion.
Harvey’s observation of beating animal hearts showed him how the heart, not the liver, functions as the engine for the circulatory system: “It must therefore be concluded that the blood in the animal body moves around in a circle continuously and that the action . . . of the heart is to accomplish this by pumping.” The action of the heart moved blood out through the arteries to the body and then back to the heart through the veins.
Because Harvey’s work challenged the accepted ideas of the time, it was greeted with a mix of interest, skepticism, and hostility. In England many were intrigued by his writing and persuaded by his science. King Charles I saw the academic value of his work, but some conservative doctors leveled accusations of quackery at him, causing his private practice to suffer. In Europe his discoveries were not embraced, and detractors included leading writers of the period. While Molière and Boileau supported Harvey’s views, Descartes—who initially accepted blood circulation—rejected the idea that the heart pumped the blood. Despite initial resistance, Harvey’s theory of circulation was widely accepted by the time of his death in 1657 at age 79.
Paradoxically, the growing acceptance of Harvey’s work on circulation was not adopted by practicing physicians right away. Traditional remedies (such as enemas and purgatives) were based on Galen’s idea of human physiology, but doctors still applied them to patients. Bloodletting, in particular, remained a popular treatment for illness; even Harvey supported its use. A half century after Harvey’s death, the French king Louis XIV was still accepting traditional treatments. Throughout his life, the king was treated with 2,000 purgatives, hundreds of enemas, and 38 bloodlettings.
Professionally, Harvey remained in service to the royal family and was sent on several diplomatic missions to Europe. He largely retired from public life in 1645, but he did continue his medical research into the human body with a focus on reproduction. While his work on circulation is certainly his greatest achievement, he also produced the pioneering work Exercitationes de generatione animalium, or On Animal Generation, on embryology in 1651. The last years of his life were spent in poor health, as he suffered from gout, kidney stones, and insomnia before dying from a stroke.
In life Harvey had been unable to prove the connection between veins and arteries, but four years after his death, another scientist would build on Harvey’s legacy. Marcello Malpighi (1628-1694) revealed the passages that connected the venal and arterial systems. Using a microscope, he discovered minuscule vessels, the capillaries, the missing piece of the puzzle.