THE BIOLOGY BOOK
Harvey’s De motu cordis
Galen (c. 130–c. 200), William Harvey (1578–1657), Marcello Malpighi (1628–1694)
In 1628, William Harvey published a heretical paper, De motu cordis et sanguinis (On the motion of the heart and blood), in which he proposed that blood was pumped by the heart in one direction through a closed system from arteries to veins and was then returned to the heart. Harvey based his theory not on speculation but on dissections and physiological experiments conducted on multiple species of living and dead animals and in human subjects. A critical piece of the puzzle was his observation that the valves present in the veins permitted blood to flow in only a single direction, toward the heart.
Why was Harvey reluctant to delay widely publicizing this concept, replete with convincing experimental evidence, years after first introducing it in his public 1615 Lumleian Lecture? His explanation challenged Galen’s teachings of blood flow, promulgated 1,400 years earlier, which had been accepted as dogma by all authoritative scientists and physicians ever since. According to Galen, blood originated in the liver, after being formed from food. It then passed between the two lower chambers in the heart through invisible pores and was consumed by the organs of the body, serving as a nutrient. Blood was utilized at the same rate it was being produced. Based on his data and analysis, Harvey determined this to be a mathematical impossibility.
Harvey was the well-respected court physician to King James I and his son King Charles I, both of whom encouraged and supported his research. But by challenging the authority of Galen, the seventy-page De motu cordis generated controversy and animosity, particularly in Continental Europe, for some twenty years after it was published. An important missing link in Harvey’s explanation was how blood flowed from the arteries to veins. He postulated the presence of capillaries, a fact validated by Marcello Malpighi in 1661.
De motu cordis is now considered to serve as the foundation for our understanding of the heart and cardiovascular system and among the most important publications in the history of biology and medicine. Called the father of modern physiology, Harvey was the first to supplement simple observation with experimental methodology and quantification.
SEE ALSO: Pulmonary Circulation (1242), Leonardo’s Human Anatomy (1489), Scientific Method (1620), Placenta (1651).
During the course of his medical practice, William Harvey, shown in this engraving, examined four women accused of witchcraft. Notwithstanding the societal pressure upon him to discover suspicious body marks as evidence of their guilt, he provided testimony leading to their exoneration.