In 1616, during a lecture that stunned a small audience of London scientists, William Harvey announced that the heart propels blood and that blood circulates throughout the body.
His findings seem obvious today, but they were revolutionary at the time. In those days, people believed fabulous notions about the heart and blood. Some thought the heart was the seat of "pneuma" or life force, that air flowed through the arteries and that the liver was the focal organ of the circulatory system. These ideas were strongly endorsed in medical and scientific circles.
William Harvey challenged the established view from within the establishment itself. Born in 1578 to a respectable family in Folkestone, a town in the English District of Kent, he earned a degree at Cambridge and then studied anatomy at the University of Padua in Italy—one of the foremost medical schools of the time. In 1602, at the age of 24, he opened his own medical practice in London. Within five years he was admitted to the Royal College of Physicians, and in 1615, at 37, he earned a prestigious appointment as a lecturer at the college. In 1618 he was appointed physician to King James I. For the next 40 years, Dr. Harvey gave lectures on medicine and anatomy.
It was from this position and carefully earned reputation that Dr. Harvey dared to utter his revolutionary ideas. Still, he would wait 12 years after his announcement to publish his findings. In 1628, publishing in Latin as was customary for academic works in those times, he printed a slender volume called Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (An Anatomical Treatise on the Movement of the Heart and Blood in Animals). It aroused a storm of criticism, and Dr. Harvey's medical practice declined considerably. Yet the book was irrefutable, a great example of the application of observation, experiment, and logical thinking in pursuit of the truth.
Dr. Harvey was unrelenting in his own dissections, but two discoveries made by others were keys to his work: that the veins had valves and that the heart did its work of pumping blood when it contracted.
Dr. Harvey began to see the light. The valves permitted blood to flow only in one direction. The heart worked like a pump. Still, to propose that the blood moved in a circle required a bold leap—there was still a gap in the circle that Dr. Harvey could not bridge. How did the blood travel from the arteries to the veins to make the return journey to the heart?
Four years after Dr. Harvey's death, the Italian anatomist Marcello Malpighi discovered the capillary vessels—the missing link whose existence Dr. Harvey had suspected, but which he could not find—using a new instrument called the microscope. Even before his death in 1657, however, Dr. Harvey's work had been accepted in scientific circles.