William Harvey and the Circulation of the Blood (1628)

William Harvey’s discovery of the circulation of the blood, published in 1628 in his short Latin book De Motu Cordis (“On the Motion of the Heart”), showed that the heart is a pump driving the same blood around the body in a continuous circuit. Harvey, an English physician working in London, overturned a theory that had dominated Western medicine for some 1,400 years. His use of experiment, observation and simple calculation made the book a landmark not only of medicine but of the scientific method itself.

Background: Galen’s model of the blood

Until the seventeenth century, European and Islamic medicine largely followed the second-century Greek physician Galen. In his system the liver turned digested food into blood, which flowed out through the veins to nourish the body and was consumed in the process. A different kind of blood, mixed with “vital spirit” drawn from the air, filled the arteries.

Galen believed that some blood seeped from the right side of the heart to the left through invisible pores in the thick wall, or septum, between the two ventricles. The heart’s main active movement was thought to be its expansion, drawing blood in, rather than its contraction.

Cracks had already appeared in this picture. The Arab physician Ibn al-Nafis, working in Cairo, had argued in the thirteenth century that blood passes from the right to the left side of the heart through the lungs. In the sixteenth century Michael Servetus and Realdo Colombo described the same pulmonary transit, and Andreas Vesalius, whose great anatomy book is covered in the article on the Fabrica of 1543, doubted that the septum had pores. Harvey’s own teacher, Hieronymus Fabricius, published a description of the valves in the veins in 1603, but did not grasp their purpose.

Harvey’s career

William Harvey was born on 1 April 1578 in Folkestone, Kent, the eldest son of a prosperous yeoman. He studied at the King’s School, Canterbury, and Gonville and Caius College, Cambridge, and then went to the University of Padua, then Europe’s leading medical school. There he studied under Fabricius and received his doctorate in 1602. Padua had a permanent anatomical theatre, opened in the 1590s, where students crowded around steep wooden galleries to watch dissections. The university’s tradition of careful anatomy, going back to Vesalius, and Fabricius’s interest in comparing the organs of different animals shaped Harvey’s whole approach to research.

Back in London, Harvey became a Fellow of the College of Physicians in 1607 and physician to St Bartholomew’s Hospital in 1609. In 1615 he was appointed Lumleian lecturer in anatomy and surgery for the College, and his surviving lecture notes from 1616 already describe the movement of blood in a circle. In 1618 he became one of the physicians to King James I, and he later served Charles I.

Harvey was not a quick publisher. He continued to test his ideas for about a dozen years before printing them, dissecting and experimenting on a wide range of animals and repeating his demonstrations before colleagues at the College of Physicians. This long delay reflected both caution and his awareness that the idea would meet strong resistance from colleagues trained in Galen.

The experiments

Harvey spent years observing the hearts of living animals: dogs, pigs, snakes, frogs, fish, even shrimps and insects. Cold-blooded animals were especially useful, because their hearts beat slowly enough to watch each stage. He concluded that the heart’s active phase is contraction, called systole, when it hardens and pushes blood out, and that the pulse felt in the arteries is caused by this push.

He followed the flow of blood through the heart and the great vessels. Blood entering the right side of the heart passes through the lungs to the left side and is then driven into the aorta and out to the body. The valves of the heart allow it to move only in one direction.

His most famous demonstrations used the human arm. A very tight bandage above the elbow stopped the blood in the arteries, so the hand became cold and pale while the artery above the bandage swelled. A looser bandage, which allowed arterial blood in but blocked the veins, made the veins below it swell. Blood was clearly entering the arm by the arteries and leaving it by the veins.

By pressing on a vein and stroking along it, Harvey showed that blood could be pushed towards the heart but not away from it. The valves Fabricius had described were one-way gates, directing blood back to the heart. De Motu Cordis illustrated these experiments with its only figures, engravings of an arm with its veins.

The quantitative argument

Harvey added a striking argument from numbers. Even if the left ventricle expels only a small part of what it holds at each beat, he reasoned, the heart beats more than a thousand times in half an hour. Using deliberately cautious estimates, the total pumped in that time is far more blood than the whole body contains, and far more than could be made from the food a person eats.

The only possible conclusion was that the same blood must return to the heart again and again. In Harvey’s words, the blood moves in a kind of circle. The argument was simple, but using measurement and arithmetic in physiology was new and powerful.

Modern figures bear him out. An adult heart at rest pumps roughly five litres of blood a minute, about the total volume of blood in the body, so the whole supply passes through the heart roughly once a minute. Harvey’s own estimates were far lower than this, which made his conclusion all the more secure: even on the most cautious assumptions, the blood could not be made fresh and consumed as Galen had taught.

De Motu Cordis (1628)

Harvey published his findings in 1628 as Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (“An Anatomical Exercise on the Motion of the Heart and Blood in Animals”). It was a slim book of 72 pages, printed in Frankfurt by William Fitzer, probably so that it could be sold at the city’s international book fair. Harvey dedicated it to King Charles I, comparing the heart to the king as the source of life in his kingdom.

The book is short and carefully argued, building step by step from observation to conclusion. Harvey framed his discovery in the language of Aristotle, whom he admired, describing the circular motion of the blood as fitting the perfection of the circle in nature.

Reception and controversy

Reactions were divided. Some physicians accepted Harvey’s view quickly, but many defended Galen. The most prominent opponent was Jean Riolan the Younger, the leading anatomist in Paris, to whom Harvey replied in two published letters in 1649. The French philosopher René Descartes accepted the circulation in his Discourse on Method of 1637, although he wrongly explained the heart’s motion as caused by heat.

According to the antiquarian John Aubrey, Harvey’s medical practice suffered after the book appeared, because some thought him eccentric. The claim cannot be tested, but it shows how radical the idea seemed at first.

During the English Civil War Harvey stayed loyal to Charles I. He was present at the Battle of Edgehill in 1642, and his London lodgings were ransacked, destroying papers and notes. In 1645 he became Warden of Merton College, Oxford, the royalist capital. In 1651 he published a major work on reproduction, De Generatione Animalium. He died at Roehampton on 3 June 1657 and was buried at Hempstead in Essex.

By the time of his death the circulation was widely accepted among anatomists. The missing link, the tiny vessels connecting arteries and veins, was supplied in 1661, when the Italian anatomist Marcello Malpighi observed capillaries in the lungs of a frog through a microscope.

Legacy and myths

Harvey’s work became the foundation of modern physiology and changed the understanding of everything from the pulse to the spread of poisons. It made possible later experiments with injections and blood transfusion, attempted in England and France in the 1660s, and influenced the experimental culture of the Royal Society.

Myth: Harvey immediately ended bloodletting. He did not. Bloodletting remained common medical practice for about two more centuries, because doctors fitted it into new theories.

Myth: Harvey discovered everything about circulation alone. He built on Padua’s anatomical tradition and on earlier work on the lungs and venous valves. His achievement was to bring the evidence together and demonstrate a complete circuit.

Timeline

• 1578, 1 April: William Harvey born in Folkestone, Kent.
• 1602: Harvey receives his medical doctorate at Padua.
• 1603: Fabricius publishes his study of the valves in the veins.
• 1609: Harvey becomes physician at St Bartholomew’s Hospital, London.
• 1616: Harvey’s lecture notes describe the circulation of the blood.
• 1628: De Motu Cordis published in Frankfurt.
• 1649: Harvey replies to his critic Jean Riolan.
• 1657, 3 June: Harvey dies at Roehampton.
• 1661: Malpighi observes capillaries, completing the picture.

Why it matters

Harvey replaced a theory based on authority with one based on experiment, measurement and careful reasoning. His discovery that the heart pumps blood in a circuit underlies modern medicine, from blood pressure to surgery, and his method became a model for the new sciences of the seventeenth century.