Discovery of Circulation of Blood

Galen was a Greek physician born around AD 130 in Pergamum, Asia Minor now part of Turkey. He lived for more than 80 years until his death in AD 217. At that time Pergamum was one of the most affluent cities in the Greek speaking part of the Roman Empire.

View_of_ancient_Pergamon in modern day Turkey where galen lived

Reconstruction of Pergamon

Galen was the son of Aelius Nicon, a wealthy architect and farmer. When Galen was 16 his father was visited in a dream by Asclepius, the Greek god of healing. In the dream Asclepius told Nicon to encourage his son to study medicine. From that time onwards Galen’s education was steered towards medicine, a vocation sanctioned by the Gods.

The ancient greek galen made some discoveries about the circulation of the blood


Galen studied medicine at Corinth in Greece and Alexandria in Egypt. Moving back to Pergamun he became chief physician to the gladiators for five years from AD 157. Thereafter he moved to Rome where he became a leading medical authority. Such was his reputation that he served as physician to two emperors including Marcus Aurelius and Commodus.

Galen was a prolific writer and is most remembered today for his skill at dissection and his understanding of the structure of the human body.

Given how Roman citizens treated slaves and gladiators as worthless and expendable, it is somewhat surprising that the dissection of human corpses was banned at that time.

  • Given these circumstances how did Galen learn human anatomy?
Gladiators fighting from the Zliten mosaic

Gladiators fighting 

Most of Galen’s dissection work was carried out on monkeys, pigs and dogs. However he did manage to carry out a few dissections on human bodies, describing in his writings how he was able to dissect the corpses of hanged criminals and bodies washed out from a flooded cemetery.

Although his anatomical experiments on animals led to a better understanding of the nervous and respiratory systems, the conclusions Galen reached about the functioning of the human circulatory system were way off the mark.

Galens open ended vascular system showing air and blood in the arteries and pores in the heart

He believed that blood was constantly being manufactured in the liver. It was then carried by open-ended veins throughout the body and deposited in tissues to provide nourishment. The function of the lungs, left side of the heart and arteries was to deliver fresh air, remove waste products and cool the body.

Explanation of Galen and how he viewed the circulation of blood round the body

Galen also made reference to imaginary ‘pores’ in the interventricular septum between the right and left ventricles through which blood could pass, completely avoiding the lungs. It was in the interventricular septum that Galen believed air was mixed with blood.

Galens imaginary pores in the interventricular septum

Galen’s views on the circulation of blood were to go largely unchallenged for more than 1,500 years until the arrival of Vesalius in the 16th century.

Vesalius and the circulation of the blood

Vesalius was born in Brussels on 31st December 1514 into a family of physicians. His grandfather, Everard van Wesel, had been Royal Physician to Emperor Maximilian; his father Anders van Wesel had served as pharamist to Emperor Maximilian and then to King Charles V.

Vesalius was encouraged to continue in the family tradition. Before learning medicine he was obliged to learn Latin and Greek, languages which he studied in a Roman Catholic religious community in Brussels.

Next he enrolled to study medicine at the University of Louvrain (Leuven) in Belgium before moving to Paris in 1533 to continue his medical training.

Portrait of Vesalius holding dissection of human arm

At that time Paris was at the center of a revival of Galenism; it was in Paris that Vesalius first became interested in human anatomy. However his studies were interrupted by war between France and the Holy Roman Empire and in 1536 he was forced to return to Louvrain to complete his medical degree.

gallowsHis fascination with human anatomy was such that, in the Autumn of 1536, he stole a body from a gibbet outside Louvrain to take home and dissect.

After graduating Vesalius moved to the University of Padua in Italy where he became a teacher in the Faculty of Medicine. His study of human anatomy was ably assisted by the Judge Marcantonio Contarini who supplied Vesalius with a constant supply of bodies of executed criminals for Vesalius and his students to dissect.

As a teacher Versalius insisted on performing his dissections himself, explaining to his students directly the significance of what he was dissecting.

Vesalius De humani corporis fabrica libri septem fronticepiece showing versalius dissecting a corpse to his students

This direct method of teaching was in stark contrast to the prevailing attiude of the day in which professors used to employ surgeons to carry out dissections while the learned professors would direct proceedings from a safe distance.

In 1543 Vesalius published his magnum opus on human anatomy entitled De Humani Corporis Fabrica Libri Septem (On the Fabric of the Human Body in Seven Books). John Stephen of Kalkar, a respected pupil of renaissance artist Titian, was probably the main illustrator for Versalius’s masterwork.

The Fabrica, as it became known, not only contained detailed diagrams showing the circulatory system…

De Humani Corporis Fabrica

…but many other diagrams of the human body. These diagrams included images of a skeleton and….

Vesalius De humani corporis fabrica 1543 Skeleton leaning on a spade

… the exterior muscle structure.

muscles of the body from De humani corporis fabrica by versalius

The Fabrica underlined the importance of accepting the evidence of your own eyes rather than relying on facts handed down by previous generations.

Vesalius was instrumental in making the study of human anatomy respectable although there remained a lingering disquiet about the unsavory business of dissecting dead humans.

heart in de humani corporis fabrica

Heart in De Humani Corporis Fabrica

Versalius became physician to Philip II of Spain

Phillip II

Having made his mark on medical research Vesalius abandoned his academic career at the age of 29. His motives for abandoning such an illustrious career at such a young age remain unknown. Was he tired of the constant criticism meted out by die hard Galenists or did he want to practice medicine instead of teaching it?

Whatever his motives for quitting his next move was to serve as physician to two kings- Charles V and Phillip II of Spain. In 1564 Vesalius obtained permission from King Phillip II to go on a pilgrimage to Jerusalem. On the way back from the Holy Land the ship Vesalius was traveling in ran aground on the Isle of Zante. Versalius became ill and died in October 1564, aged 50.

Circulation of the blood- from Vesalius to William Harvey

Gabriele Falloppio who discovered the fallopian tubes


There exists a well documented lineage linking Versalius to William Harvey.  William Harvey, the first person to accurately explain how blood circulates round the body, built on the wisdom and knowledge of two Italians, Gabrielle Falloppio and Girolamo Fabrizio.

Fabricius believed that valves of the veins slowed down flow of blood from the liverGabriele Falloppio (also known by his latinised name Fallopius) had been a student of Vesalius’s at the University of Padua. Fallopius enjoyed a successful medical career and in 1551 rose to become Professor of Anatomy. It was Falloppio who discovered the fallopian tubes which still bear his name.

Fallopius taught Girolamo Fabrizio ( also known as Fabricius). Fabricius succeeded Fallopius as Professor of Anatomy after Fallopius died in 1562.

Girolamo Fabrizi d'Acquapendente also known as fabricius first described the values in the veins


One of Fabricius’s most important contributions to medicine was to provide an accurate description of valves in the veins.  Fabricius believed that the role of the valves in the veins was to slow down the flow of blood from the liver allowing time for blood to be absorbed by tissues of the body. Like Galen more than 1,300 years previously, Fabricius believed that blood was manufactured in the liver and dispersed throughout the body to provide nourishment to the tissues.

In his 1603 work De Venarum Ostiolis (On the Valves of the Veins) Fabricius illustrates the anatomical structures of veins and valves in the veins.

De Venarum Ostiolis from 1603 by Fabrizio showing the valves of the veins.

William Harvey and circulation of the blood

William Harvey was born in Folkestone in Kent, England on 1st April 1578. He was the eldest son of a yeoman farmer and was educated at the prestigious King’s School in Canterbury. After leaving school Harvey moved to Caius College in Cambridge where he studied the Classics, Rhetoric and Philosophy.

Caius College shown in the 17 th century where William Harvey studied

Caius College

William Harvey who discovered the circulation of the blood

William Harvey

Following the completion of his degree he moved to Padua to study medicine where he was taught by none other than Fabricius. It is amazing to think that while Harvey was a student in Padua Galileo occupied the Chair of Mathematics.

Harvey graduated as a Doctor of Medicine in Padua in 1602 after which he moved back to England. In 1604 he married Elizabeth Browne; Elizabeth’s father Lanceleot was very well connected having been physician to Queen Elizabeth I.

Harvey enjoyed a distinguished medical career. He became a physician at St Batholemew’s Hospital in London before being appointed physican to King James I followed by King Charles I.

It was in his spare time that Harvey researched the circulation of the blood. He published his seminal work De Motu Cordis et Sanguinis in Animalibus (On the Motion of the Heart and Blood in Animals) in 1628. Harvey was meticulous in his research- he had to be to fend off the many defenders of Galenism.

The following is a summary of some aspects of Harvey’s research:

He (partially) proved that blood enters limbs through arteries and returns along veins

Harvey carried out two experiments to prove that blood enters limbs through arteries returning along veins.

In his first experiment he used a tight ligature to compress the arteries and veins of one arm. This tight compression just above the elbow resulted in a loss of a pulse to the wrist.

Tight ligature employed by William Harvey compressing both veins and arteries

The section of artery below the elbow became engorged with blood following each systole. (A systole is the phase of heartbeat when the heart muscle contracts and pumps blood into the arteries.)

Harvey next employed a ligature of medium tightness; since arteries lie deeper inside the arm than veins the effect was to compress the veins but not any of the arteries.

diagram showing arteries and veins of forearm. Arteries lie deeper in the arm than veins

By employing a ligature of medium tightness blood was still able to flow down the arm through the arteries but unable to flow back up the arm through the veins.

William Harveys experiment with a ligature of medium-tightness

With this type of ligature a pulse in the wrist could be felt; it was the hand that now became swollen with blood. The veins below the ligature also became swollen whereas the veins above the ligature were not filled with any blood.

Based on these observations Harvey concluded that blood enters the arm by means of arteries and leaves by means of veins.

  • So how did Harvey think blood entered veins from arteries?

He had no way of knowing. The capillaries, those connections between arteries and veins, could not be seen with the naked eye and Harvey was completely unaware of their existence. So small are the capillaries that blood cells often have to travel through them in single file.

William Harvey wa unable to see with the naked eye capillaries through which blood cells pass through in single file

Given the lack of evidence for the existence of capillaries Harvey could only surmise that blood passes from arteries to veins through some sort of direct connection (anastomoses) or porous skin that is permeable to blood.

Harveys and Galens views about the existence of capillaries compared

The definitive proof for the existence of capillaries would have to wait until 1661…

Malpighi discovered how arteries and veins are connected by capillaries

… when Italian biologist Marcello Malpighi discovered their existence with the help of a microscope.

Marcello Malpighi discovered the existence of capillaries under a microscope

Measuring the capacity of the heart

Diagram of William Harveys closed circulatory systemHarvey measured the capacity of the heart and estimated that it pumped out 260 liters of blood each hour . His estimate was inaccurate but good enough to prove a point. (The human heart actually pumps out between 300 and 420 liters of blood hourly)

Harvey thought it highly improbable that the liver could continuously manufacture such copious quantities of blood- blood supposedly manufactured from nutrients provided by digested food. Harvey calculated that if 1 liter of blood weighs the equivalent of 1.06 liters then 260 liters of blood would weigh a massive 276 kgs- a total greater than the combined weight of three people!

Based on these findings Harvey reached the conclusion that the liver could not continuously manufacture blood; there simply had to be another reason to explain why the heart pumped out so much blood.

Harvey’s explanation was both radical and innovative; blood circulated round the body in a single loop continually returning to the heart to provide the quantity of blood required for each heartbeat.”It is matter of necessity that the blood perform a circuit, that it return to whence it set out”. The function of the heart was to keep “the blood in the animal body mov(ing) around in a circle continuously and that action or function of the heart is to accomplish this by pumping. This is only reason for the motion and beat of the heart.”

Harvey illustrated his explanation by pointing out how the entire body suffers after a snake bite to the foot. This would be impossible unless there was some means to convey blood around the body.

The function of venous valves

Harvey used a series of ligature experiments….

William Harvey De Motu Cordis et Sanguinis in Animalibus showing ligatures

….to prove how venous valves prevent the backflow of blood traveling from the periphery of the body towards the heart.

diagram showing venal valve preventing reverse backflow

In De Motu Cordis Harvey described an ingenious experiment in which a medium-tight ligature was attached to the arm above the elbow. The fist was repetitively clenched and then opened. This caused blood to be pumped into the hand along the arteries.

Figure 1 of De Motu Cordis shows distended veins in the forearm and the position of valves

The pressure from the ligature allowed blood to continue flowing to the hand along arteries whilst at the same time preventing any blood returning towards the heart along veins. As a consequence the veins become swollen with small bulges appearing along the veins at regular intervals. These bulges were the venal valves.

A finger was then pressed into the vein next to the valve at point ‘M’.

Figure 2 of De Motu Cordis shows that if a vein has been milked centrally and the peripheral end compressed, it does not fill until the finger is released.

Another finger (not shown ) was used to push blood along the vein from point ‘M’ to just beyond the venal valve at point ‘O’.

After the finger at point ‘O’ was lifted off, with pressure of the finger on the venal valve at point ‘M’ still maintained, no blood flowed into the vein from the direction of point ‘G’.

This simple experiment illustrated how venal valves only allow blood in veins to flow in one direction- the direction of the heart.

William Harvey’s legacy

Herman Boerhaave


In some ways Harvey was a modern scientist. He realized that observation, while key to the scientific method, must be followed by the formulation of a hypothesis. The validity of that hypothesis (that bloods circulates in a continuous loop round the body) required proof from repetitive, directed experiments. Harvey was heavily influenced in his approach by the tradition of experimental science that blossomed in 17th century Padua.

So comprehensive were Harvey’s findings about the circulation of the blood that early in the 18th century the illustrious Hermann Boerhaave, Professor of Medicine at Leyden, declared that nothing that had been written before Harvey was worthy of consideration any more. The conclusions of De Motu Cordis about the circulation of the blood were unassailable.

To end on a quote from Galileo:


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