William Harvey

William Harvey’s research resulted in a monumental scientific shift that overthrew a belief held for nearly 1,500 years. He found that blood circulates swiftly within the human body, propelled through a unified system of arteries and veins, backing his claim with experiments and reasoning.

To grasp Harvey’s groundbreaking work, we should revisit ancient Greece around 400 BCE. By then, the Hellenistic civilization had transitioned from mythology to logical reasoning. It was widely believed that humans comprised the same basic elements found in the universe: fire, water, air, and earth. These elements were present in food and drink, and digestion transformed them into bodily humors: blood, phlegm, yellow bile, and black bile.

Hippocrates, often called the father of Western medicine, asserted that good health hinged on a balance of these elements, with imbalances causing diseases. His ideas were central to Western medicine for half a millennium until Galen emerged. Born in today’s Turkey, Galen believed the body had three systems: the brain and nerves for sensation and thought; the heart and arteries for vital energy; and the liver and veins for nutrition and growth.

In Galen’s view, the liver produced blood from digested food, which then circulated around the body, nourishing it or turning into flesh. Despite some skepticism, his model remained dominant for around 1,500 years until William Harvey challenged and overturned it.

William Harvey was born on the 1st of April 1578 in Folkestone, England. By 16, he had secured a medical scholarship and later graduated from Cambridge University. A professor’s advice led him to Padua, Italy, where he learned from Hieronymus Fabricius, the discoverer of vein valves. Back in London, Harvey married the daughter of a leading physician, joined the Royal College of Physicians, and became the chosen doctor for King James I and Charles I of England.

Unlike luminaries like Johannes Kepler and Galileo Galilei who enhanced Copernicus’ findings, Harvey’s approach was revolutionary. He didn’t merely expand upon, refine, or better existing knowledge. Instead, he completely dismantled a prevailing dogma and introduced a new paradigm that stands unaltered to this day. His monumental discovery, highlighted in his 70-page work Anatomical Essay on the Motion of the Heart and Blood in Animals or De Motu, was released when he was 50.

Through few yet powerful observations, Harvey deduced the blood’s circulation. He measured the blood volume in the heart’s left ventricle and determined that if Galen’s model was accurate, the liver would need to produce a staggering 540 pounds (or 250 kg) of blood every hour. Such rapid production and consumption were implausible, pointing to blood circulation.

Further, Harvey demonstrated the existence of two distinct blood circulation loops: pulmonary and systemic. In a vivid experiment, he tightened a band around a person’s upper arm, making the forearm’s vein valves clearly visible. When he attempted to push blood down the forearm, it resisted. Pushing it up was easy, proving blood flowed towards the heart with the help of vein valves, ensuring one-way movement.

Harvey’s discoveries rank among the most monumental in medical history. They not only laid the foundation for physiology but also established the vital role of experimentation in medicine, paving the way for modern medical practices.