In this narrated segment, Lois Letchford introduces William Harvey, the 17th‑century English physician who proved that blood circulates continuously around the body driven by the heart’s pump. Letchford outlines Harvey’s education—Cambridge, then Padua under Fabricius— and explains the prevailing Galenic doctrine that the liver produced blood and that tiny pores in the heart allowed its passage. She details Harvey’s logical critique of Galen, highlighting the absurd volume of blood the old model required, and describes his key experiments: using a tourniquet to show arterial back‑pressure and dissecting the heart to refute the pore theory. Harvey concluded that blood moves in two closed loops (pulmonary and systemic) via arteries and veins. The segment notes his 1628 publication of a 72‑page treatise, the fierce backlash from the medical establishment, and the eventual triumph of his ideas, underscoring the importance of challenging entrenched theories.
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Hello, I'm Lois Letchford, author of the book Reversed: A Memoir, and reading from the book Eureka! of Scientists Who Changed the World. This week I'm reading about William Harvey. He was an Englishman who lived from 1578 to 1657. Check it out on a timeline. Harvey's discovery that the blood circulates around the body in a system powered by the pumping of the heart spelled the end for the medical theories of Galen, which had for nearly 1,500 years stifled progress in medicine. William Harvey was born in Kent. He took his first degree in Cambridge University, then studied medicine In Italy at the University of Padua, and so you can read more about him. He studied under Fabricius. Fabricius's specialty was studying of the veins, and the book was published in 1603. He announced his discovery that the veins had little valves in them. This discovery. Was to provide a major clue to Harvey. And then we'll learn a little bit about Galen. In the 2nd century, Galen taught that the liver manufactured blood from digested foods and sent it round the body through veins. Much of it was turned into flesh at the body's peripheries. Some went to the heart's right side, then passed through minute pores through the heart's dividing wall. to the left side before being launched, now laden with some sort of vital spirit to refresh the muscles, nerves, and brain. Through observing the actions of a heart, Harvey realised that Galen's model would require the liver to manufacture some 540 pounds, 200 kilos, of blood Daily. Clearly an absurdity. The only credible alternative was that the body contained a limited amount of blood that was constantly being circulated around the body by the pulsing of a heart. Harvey realised the valves Fabrius had discovered in the veins controlled the flow in those vessels. The blood in them could flow only Toward the heart. He concluded that the heart must pump blood around the body through the arteries, and the veins served as vessels to bring the blood back to the heart. To demonstrate this point, he devised an experiment that took advantage of the fact that arteries are buried much deeper in the flesh than the veins. Check it out in your arm. He applied a tourniquet to a patient's arm and saw how the arteries to the right side of the tourniquet bulged as the blood backed up in them. When the tourniquet was loosened a little so the blood was free to flow through the arteries, the veins in the same arm were still constricted, and now it was in them that the blood backed up on the side of the tourniquet. Away from the heart. Through dissection— dissection is the cutting up— Harvey showed that Galen's idea of microscopic pores letting blood pass from one side of the heart to the other was a fantasy. He correctly deduced that blood circulation via 2 loops, a smaller one that passes through the lungs and a larger one that consists of a system of arteries. spreading all through the body, getting even smaller, and a complementary system of veins that returns the blood to his heart. His book— his— he published his conclusions in book form in 1628. Harvey's little book, just 72 pages long, appalled the medical establishment because it dared to challenge Galen, a revered authority for centuries. Distinguished physicians published sturdy rebuttals, and Harvey's medical practice suffered grievously. Harvey just let them bluster, sure the truth would triumph sooner rather than later, as indeed it did. So it does take challenging current theories to create new ideas. Keep thinking, Keep sharing, hit like, and hit subscribe, and find out more about people who changed the world.
