"It is absolutely necessary to conclude that the blood in the animal body is impelled in a circle, and is in a state of ceaseless motion; that this is the act or function which the heart performs by means of its pulse; and that it is the sole and only end of the motion and contraction of the heart."
William Harvey, Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (On The Motion Of The Heart And Blood In Animals), 1628
The year is 1600. Galileo Galilei is teaching mathematics at the University of Padua in Italy. He has held a post for the last eight years after spending time in Pisa. In ten years, he will hear of a new invention, the telescope, and constructing one of his own, Galileo will discover moons circling the distant planet of Jupiter. With these observations, he will shatter a belief held for nearly a millennium - that the earth is the center of the solar system. He would provide the empirical evidence of Nicholas Copernicus’s assertions that the planets, including the Earth, revolved around the sun. This ran counter to Ptolemy, the ancient Greek philosopher who was considered the authority on matters of astronomy. This paradigm shift would ultimately cause Galileo to run afoul of Church authorities. Unbeknownst to Galileo, a young Englishman, William Harvey, was also attending the University of Padua. After attending Cambridge University, Harvey had enrolled at the leading university of Europe for medicine. The medical faculty at Padua were some of the leading anatomical scholars. After nearly two decades of attending to the royal court in England, Harvey would publish a seventy-two-page book entitled Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, “On the Motion of the Heart and Blood in Animals,” in 1628. In his work, Harvey would shatter an old paradigm set forth by another ancient Greek, Galen, who was considered the authority on medicine for over a millennium. Through the use of empirical evidence, he would demonstrate the circulation of blood through the body. There is no evidence that Galileo and Harvey ever met while they resided at the University of Padua. Yet each would go on to fundamentally shift our understanding of the natural world.
Aelius Galenus, known as Galen, lived during the mid-2nd Century CE. He was the personal physician of Emperor Marcus Aurelius and a prolific writer on both medicine and philosophy. He was one of the few Classical authors whose work survived into the Medieval period of western Europe. His work became known throughout the Latin west mainly through Arabic translations. Along with Aristotle and Ptolemy, he would become one of the cornerstones of Medieval learning and Western thought. Galen proposed that the human body was comprised of three interconnected systems. The brain and nerves make up the nervous system responsible for thinking and sensation. The heart and arteries provide the body with energy or “vital spirit.” The liver and veins did nutrition. Blood originated in the liver produced by the foods we ingest. The veins carried this blood to the rest of the body by a tidal ebb and flow. Blood was constantly being consumed by the body and replaced by nutrients. Essentially there was no circulation of fluids. The right side of the heart was responsible for moving blood through this system. The job of the left side of the heart was to move blood into the lungs, where it gathered the “pneuma,” or spirit. The arteries then delivered this “pneuma”-rich blood to the rest of the body. Blood moved from one side of the heart to the other through pores in the septum.
Galen’s model would remain unchallenged in Europe for several centuries. However, the 8th through the 13th centuries are considered to be the “Golden Age” of Islamic science. Muslims made advances in optics, mechanics, chemistry, mathematics, astronomy, and medicine through experimental methods. Many of their innovations predated European “discoveries” by five hundred years. One of these Islamic polymaths was Ibn-al-Nafis, who lived in the early part of the 13th century. He based his views on observations while performing numerous dissections on both animals and humans. One of his works is the Commentary on Anatomy in Ibn Sina’s Canon. Ibn Sina, or Avicenna in Latin, was an early Persian thinker and philosopher who laid the foundation of Islamic medicine. As a physician, he exerted the same authority and influence that Galen did in the West. In his book, Ibn-al-Nafis challenged the established authority of both Galen and Ibn Sina. His observations led al-Nafis to reject Galen’s notion of pores in the heart’s septum to allow the mingling of blood. He could not see the pores and noted that the septum is thicker than elsewhere in the heart. Instead, al-Nafis hypothesized that blood entered the lungs from the pulmonary artery and circulated back into the left side of the heart via the pulmonary vein. Al-Nafis’s work remained largely unknown in the West until the early 20th century. He is now recognized as one of the earliest people to describe pulmonary circulation.
William Harvey was born in 1578 in Folkstone, Kent, England. His father was a wealthy merchant who could afford to provide his eldest child with an education. He attended a grammar school in Canterbury, where he received a classical education. In 1594, he attended Caius College at Cambridge, graduating in 1598. Dr. John Caius, the founder of the college, encouraged students to continue their medical studies abroad. For most, this meant any of the famed universities in the north of Italy. Of these, the University of Padua was the most prestigious, and it is here that Harvey chose to go at the age of twenty. Here at Padua, Harvey became exposed to the work of Andreas Vesalius and Harvey’s anatomy teacher Hieronymus Fabricius.
Andreas Vesalius was a Flemish physician and anatomist who lived in the early part of the 16th century. He was also a graduate of Padua, which had a long-standing reputation for its dissections. Vesalius did his own dissections, breaking with another tradition, and in true humanist fashion, he critically evaluated ancient texts, including Galen. Vesalius concluded that much of Galen’s anatomical knowledge derived from only animals and then applied them to the human form. In 1543, Vesalius published De humani corporis fabrica libri septem (“The Seven Books on the Structure of the Human Body”). As it is commonly referred to, the Fabrica was the most extensive and most accurate description of the human body ever done then. Vesalius determined, like al-Nafis, from his dissections that the heart had no pores as per Galen. He identified the four chambers of the heart: two ventricles and two atria. He also hypothesized that the heart's contractions are synchronous with the pulse in the arteries.
Hieronymus Fabricius was also a graduate of the University of Padua, and after a short stint as a private teacher, he became a professor of anatomy at Padua in 1565. He created the first public theater for doing anatomical dissections at the university. He investigated the development of the fetus and is often cited as the “Father of Embryology.” He also conducted studies concerning the digestive organs, eye, ear, and throat structures. But it would be his book, De venarum Ostiolis (”On the Valves of the Veins”), that would influence William Harvey’s work later on. In this work, published in 1603, Fabricius is the first to describe membranous folds within the veins. These semilunar-shaped folds he would label “valves.” Like Vesalius and other anatomists of the day, Fabricius did not move beyond the discovery and descriptions of organs. They had little interest in the actual physiology, which entailed the functions and uses of the organ within the body.
William Harvey graduated from the University of Padua in 1602. Two years after his return to England, he married Elizabeth Browne, the daughter of Queen Elizabeth I’s personal physician (who later became the physician to James I.) This marriage opened doors for Harvey and gained him access to the upper echelon of English Tudor society. In 1609, he was appointed to St. Batholomew’s Hospital where he established a successful medical practice. While here, he continued his studies into anatomy. By 1615 he was a lecturer at the College of Physicians. Then in 1618, he was appointed as the physician for King James I. Unfortunately, he was the target of rumors that accused him of poisoning the king and part of a larger Catholic conspiracy. It took the intervention of King Charles I to protect Harvey, and he was named Charles’s personal doctor.
In 1628, Harvey published his seminal work, Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, commonly known as the De Motu Cordis. In this book, which is in three parts, Harvey synthesizes the work of al-Nafis, Fabricius, Vesalius, and others. He marries anatomy and physiology by describing the organs themselves and how the entire circulatory system functions. By using descriptive and experimental science, Harvey demonstrated how blood circulates through the body by the action of a pumping heart. By doing so, he shattered Galen's model accepted by medical men for over a thousand years.
The first part focuses on the actions of the heart. Harvey had spent years vivisecting snakes and other reptiles because of their naturally slow heart rates. He noted changes in color and shape of the heart as the organ contracted or expanded. He showed that the heart fills the atria passively and then contracts actively to expel blood from the ventricles. He also pointed out how the cardiac valves prevent backflow into the heart’s chambers. He connected the arterial pulse and the contraction of the heart. In the second part, Harvey makes his major contribution to medical science. Questioning Galen’s assertion that the liver produced blood, Harvey used observations of deer hearts to calculate how much blood should be created. He discovered that the liver couldn't produce the quantities of blood required. But he went even further. Using his teacher Fabricius’s descriptions of the valves in veins, Harvey determined the direction of blood flow. Galen had stated that blood in the veins flows away from the heart. Harvey conducted experiments using tourniquets on the arms of farmhands to show that blood would flow from the hand toward the shoulder. The experiment was repeated with the neck, and he observed the blood flow from head to chest. He concluded that blood within the veins always flowed toward the heart. In the third part, Harvey describes blood flow from the heart and lungs. Without realizing it, he had rediscovered the work done by al-Nafis in the 13th century and confirmed the Islamic scientist’s hypothesis of pulmonary circulation. In this way, Harvey could map out the entire circuit in which blood traveled through the body. The heart, veins, and arteries make up a closed circulatory system in which the heart acts like a pump pushing the blood around the body. There was one missing piece. He could not account for how blood went from the arteries to the veins. It would take the invention of the microscope to enable the discovery of capillaries.
In his work The Structure of Scientific Revolutions, Thomas Kuhn states that “the decision to reject one paradigm is always simultaneously the decision to accept another, and the judgment leading to that decision involves the comparison of both paradigms with nature and with each other.” Scientific revolutions occur only if there is a sufficient model to replace the older one. The Ptolemaic model of the solar system and the Galenic model of the circulatory system survived as long as they did because there were no adequate models to replace them. Not until Galileo provided one for Ptolemy and William Harvey for Galen. William Harvey is regarded as the father of modern physiology. He is considered the first medical professional to utilize the power of observation, experimentation, and quantitative analysis in the application of medicine.
Further Reading
William Harvey: A Life in Circulation: Thomas Wright
Circulation: William Harvey's Revolutionary Idea: Thomas Wright