William Harvey: The Father of Modern Physiology (Part 2)
So, we’ll let’s take a quick look at some of the other people who contributed to cardiac knowledge!
The earliest known writings on the circulatory system are found in the Ebers Papyrus (16th century BCE), an ancient Egyptian medical papyrus containing over 700 prescriptions and remedies, both physical and spiritual. In the papyrus, it acknowledges the connection of the heart to the arteries. The Egyptians thought air came in through the mouth and into the lungs and heart. From the heart, the air travelled to every member through the arteries. Although this concept of the circulatory system is only partially correct, it represents one of the earliest accounts of scientific thought.
Because blood pools in the veins after death, arteries look empty. Ancient anatomists (as far back as the Egyptians) assumed they were filled with air and that they were for transport of air because they based their understanding of physiology solely upon the observation of anatomy of a cadaver. We’ll discuss this more later.
Ayurveda medical texts from 600 BCE present knowledge of circulation of vital fluids through the body. Sushruta the ancient Indian physician credited with writing this text also presents knowledge regarding the arteries.
The valves of the heart were discovered by a physician of the Hippocratean school. However their function was not properly understood then. It is possible that Harvey read about these in the Hippocratean works since they were available to him at Padua. But it is more likely that this was an idea he was exposed to by his contemporaries.
Herophilus was a Greek physician deemed to be the first anatomist. He was the first scientist to systematically perform scientific dissections of human cadavers. He recorded his findings in over nine works, which are now all lost. Through dissections, Herophilus was able to deduce that veins only carried blood. After studying the flow of blood, he was able to differentiate between arteries and veins. He noticed that arteries pulsed or rhythmically throbbed. He worked out standards for measuring a pulse and could use these standards to aid him in diagnosing diseases. But he thought that the pulse was a property of the artery itself and did not realize that it was caused by fluid moving through it. He also incorrectly believed that air moved through the arteries.
Along with fellow physician Herophilus, Erasistratus founded a school of anatomy in Alexandria, where they carried out anatomical research. He is credited for his description of the valves of the heart, and he also concluded that the heart was not the center of sensations, but instead it functioned as a pump. Erasistratus was among the first to distinguish between veins and arteries. He believed that the arteries were full of air and that they carried the “animal spirit” (pneuma).
Galen knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart’s motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.
Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through ‘pores’ in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created ‘sooty’ vapors were created and passed to the lungs also via the pulmonary artery to be exhaled. His theories became widely accepted.
Avicenna or Ibn Sīnā was a Persian polymath who is regarded as one of the most significant thinkers and writers of the Islamic Golden Age. Avicenna’s corpus includes writings on astronomy, alchemy, geography and geology, psychology, Islamic theology, logic, mathematics, physics and poetry. Avicenna “correctly wrote on the cardiac cycles and valvular function”, and “had a vision of blood circulation” in his Treatise on Pulse. Avicenna provided the first correct explanation of pulsation.
Ibn Al-Nafis was educated in jurisprudence, literature and theology. He was the first to describe pulmonary circulation. In addition, Ibn al-Nafis had an insight into what would become a larger theory of the capillary circulation. He stated that “there must be small communications or pores between the pulmonary artery and vein,” a prediction that preceded the discovery of the capillary system by more than 400 years.
Harvey could have encountered Al-Nafis writings (and this is debated by historians). In 1344 Kazrouny wrote a copy of Al-Nafis’s work and then returned to Damascus. In 1500, Andrea Alpago returned to Italy after studying in Damascus. In 1547 Alpago makes reference to Al-Nafis’s work in his publications. Alpago’s work was published in Venice during its rule over Padua. Harvey arrived at Padua in 1597. This sequence of events means that Harvey could have been exposed to Al-Nafis’s ideas regarding how the heart worked.
In 1553, Michael Servetus posed that the heart sent blood to the lungs and that while in the lungs it mixed with air before returning to the heart. This not only accurately described pulmonary circulation, but it addressed the basic concept of the physiology. He was a Spanish theologian, physician, cartographer, and Renaissance humanist. He was a polymath versed in many sciences: mathematics, astronomy and meteorology, geography, human anatomy, medicine and pharmacology, as well as jurisprudence, translation, poetry and the scholarly study of the Bible in its original languages.
Cesalpino was an Italian physician, philosopher and botanist. Cesalpino also did limited work in the field of physiology. He theorized a circulation of the blood. However, he envisioned a “chemical circulation” consisting of repeated evaporation and condensation of blood, rather than the concept of “physical circulation” popularized by the writings of William Harvey. Cesalpino described the movement of blood to be “more like a circulation than an oscillation” before Harvey proposed his ideas of circulation.
In 1603, Hieronymus Fabricius ab Acquapendente published a work clearly describing the valves in the veins and showing that they hinder the flow of blood away from the heart. Fabricius was a pioneering anatomist and surgeon known in medical science as “The Father of Embryology.” Harvey was one of his students at Padua. Thus, it is clear that he was a strong influence on Harvey’s ideas and that Fabricius’s theories would be known to Harvey.
Realdo Colombo was an Italian professor of anatomy and a surgeon at the University of Padua between 1544 and 1559. Had clearly described a theory on pulmonary circulation. It is likely that his work was still present and available for Harvey to view when he went to Padua in 1597.
And there was Vesalius who had also been at Padua. His work was both detailed and accurate. It would also have been readily available to Harvey as a student at Padua. Vesalius had done detailed anatomical work on the heart and circulatory system. He had then posed several theories as to the purpose and functions for the parts that he was seeing.
There are others who researched the heart and other places it has been documented. But these are the ones most likely to have influenced Harvey’s work. Because nothing is ever written in a vacuum. This book is important both for the explanation of the complete circulation and for the experimental, quantitative and mechanistic methodology which Harvey introduced. He looked upon the heart, not as a mystical seat of the spirit and faculties, but as a pump analyzable along mechanical lines.
He also measured the amount of blood which it sent out to the body. He observed that with each beat two ounces of blood leave the heart; so that with 72 heart beats per minute, the heart throws into the system 540 pounds of blood every hour. Where could all this blood come from? The answer seems to be that it is the same blood that is always returning.
Moreover, the one-way valves in the heart, like those in the veins, indicate that, following the pulmonary circulation, the blood goes out to all parts of the body through the arteries and returns by way of the veins. The blood thus makes a complete closed circuit. As Harvey expressed it, “There must be a motion, as it were, in a circle.”
There was, however, one stage in the circulation which Harvey was not able to see – that in which the veins and arteries lose themselves by subdivision into the tiny capillary vessels. Harvey believed that the blood was soaked into the body from the arteries and then seeped out again into the veins. He did not predict that they were a connected system. It was in 1660, three years after Harvey’s death, that Marcello Malpighi saw (through a microscope) the blood moving in the capillaries of a frog’s lung, and thus supplied the missing link in Harvey’s proof of the circulation of the blood.
De Motu Cordis was published in 1628 which he dedicated to King Charles I. He published the book in Frankfurt which was the host to an annual book fair which allowed an immediate dispersion of the work which was part of why it carried so much influence. Harvey’s book inevitably and historically came into conflict with Galen’s teachings and the publication of his treatise De Motu Cordis incited considerable controversy within the medical community. Some doctors affirmed they would “rather err with Galen than proclaim the truth with Harvey.”
Harvey finally put to rest some of the errors Galen had made so many years earlier. Yet Galen did not get everything wrong. Some of his teachings were useful. At one point Galen had to flee from Rome because his methods threatened the careers of Rome’s quack physicians. Ironically, in correcting Galen’s mistakes about blood and circulation, Harvey himself ran into trouble with Europe’s latest crop of quack physicians, who were making great use of Galen’s worthless blood letting methods. While not forced to flee for his life, Harvey’s own medical practice declined because of the barrage of criticism he took from physicians.
After the first chapter, which simply outlines past ideas and accepted rules regarding the heart and lungs, Harvey moves on to a fundamental premise to his treatise, stating that it was extremely important to study the heart when it was active in order to truly comprehend its true movement; a task which even he found of great difficulty, as he says:
“…I found the task so truly arduous… that I was almost tempted to think… that the movement of the heart was only to be comprehended by God. For I could neither rightly perceive at first when the systole and when the diastole took place by reason of the rapidity of the movement…”
This idea of stressing the importance of observation while in action is a radial game changer. This brings back the idea of vivisections and all the reasons that they were considered as viable options for learning how the body works. The point that Harvey was stressing is that seeing the body while it was functioning removes much of the guess work that we make when we see it in passivity. Consider the error of believing that arteries were filled with air that lasted for so long. This error lasted because our understanding was based upon the death rather than the living. The story of understanding the function of the heart clearly paints the picture of the importance of considering the manner in which research is performed. It is easy to assume that the best practice is being used, but the research story on the heart cautions us to constantly question the way we do things.
So, how do we ethically achieve research on the living?
To overcome the ethical challenges he faced, Harvey performed his research of animals. This presented other difficulties that he was well aware of being present in Galen’s work. So, how does one avoid applying inaccurate information observed in animals to humans? Harvey got all of his anatomical research from human cadavers. Then he observed the heart in action during the vivisections a numerous types of animals. His theory was that if the hearts in all the animals worked the same, it was likely that our heart work that way as well.
It is tempting to view Harvey, with his quantitative experiment and his model of the heart as a pump, as someone who supported or was inspired by the new mathematical and mechanical ideas of the 17th century, which played significant roles in the scientific revolution of the time. However, there is a need for considerable caution here. Harvey did quantify blood flow, but his quantification is very approximate, and he deliberately used underestimates to further his case. This is very different from the precise quantification leading to the mathematical laws of someone like Galileo. It was important that Harvey saw the heart as a pump, but he saw it as an organic pump, rather than as a mechanical pump. He also interpreted the blood as having an irreducible life force of its own. Harvey was deeply and bitterly opposed to the mechanical philosophy of French mathematician and philosopher René Descartes as well as to any purely mechanical conception of the human body.
Descartes believed that all material bodies, including the human body, are machines that operate by mechanical principles. In his physiological studies, he dissected animal bodies to show how their parts move. He argued that, because animals have no souls, they do not think or feel; thus, vivisection, which Descartes practiced, is permitted. He also described the circulation of the blood but came to the erroneous conclusion that heat in the heart expands the blood, causing its expulsion into the veins.
Harvey was very much influenced by the ideas of Greek philosopher Aristotle and the natural magic tradition of the Renaissance. His key analogy for the circulation of the blood was a macrocosm/microcosm analogy with the weather system. A macrocosm/microcosm analogy sees similarities between a small system and a large system. Thus, one might say that the solar system is a macrocosm and the atom is a microcosm. The Renaissance natural magic tradition was very keen on the idea of the human body as a microcosm. The macrocosm for Harvey was the Earth’s weather cycle. Water was changed into vapour by the action of the Sun, and the vapour rose, was cooled, and fell again as rain. The microcosm was the human body, where the action of the heart was supposed to heat and change the blood, which was cooled again in the extremities of the body. Harvey says (and compare the earlier quote concerning the king) that:
So the heart is the beginning of life, the Sun of the Microcosm, as proportionably the Sun deserves to be call’d the heart of the world, by whose vertue, and pulsation, the blood is mov’d, perfected, made vegetable, and is defended from corruption and mattering; and this familiar household-god doth his duty to the whole body, by nourishing, cherishing, and vegetating, being the foundation of life, and author of all.
This was critical to Harvey. How could arterial blood be rapidly, efficiently, and consistently converted into venous blood (and vice versa) within one system? This was a key question, which prompted Harvey to draw on his macrocosm/microcosm analogy. It also should be noted that much of his terminology for change was drawn from the alchemy of his time. Harvey was very much a man of the later Renaissance—not a man of the scientific revolution and its mechanical nature.
And as a side note: go back and read that quote. Sounds like poetry. You’ll never read a medical text that is written like that now!
Harvey’s ideas were eventually accepted during his lifetime. It did confront the prevailing paradigm of Galen, which dominated thought of the time, and was of significant importance in overcoming that pernicious influence. Harvey’s work was attacked, notably by Jean Riolan in Opuscula anatomica (1649), which forced Harvey to defend himself in Exercitatio anatomica de circulations sanguinis (also 1649) where he argued that Riolan’s position was contrary to all observational evidence. Harvey was still regarded as an excellent doctor.
There is a lust in man no charm can tame: Of loudly publishing his neighbor’s shame: On eagles wings immortal scandals fly, while virtuous actions are born and die. -William Harvey
Robert Fludd, a colleague at the College of Physicians was the first to accept Harvey’s circulatory model, and Rene Descartes also accepted the discovery of the circulation of the blood but disagreed with Harvey’s explanation for the movement of the heart. Leyden University was the first to accept Harvey’s views on the continent, but in many schools it was a further half century before his work was fully appreciated. By the beginning of the eighteenth century, Hermann Boerhaave, the great Dutch teacher of medicine in Leyden, stated that nothing written before Harvey was any longer worthy of consideration.
Even so, Harvey’s work had little effect on general medical practice at his time, bloodletting, based on the prevailing Galenic tradition, was a popular practice, and continued to be so even after Harvey’s ideas were accepted. Harvey’s work did much to encourage others to investigate the questions raised by his research, and to revive the Muslim tradition of scientific medicine expressed by Nafis, Avicenna, and Rhazes.
All we know is still infinitely less than all that remains unknown. -William Harvey
References and Further Reading:
- Brainy Quote
- Online Encyclopedia
- Britannica: William-Harvey
- Britannica: al-Razi
- Britannica: Aristotle
- Britannica: Rene Descartes
- Britannica: Ibn-an-Nafis
- New World Encyclopedia: William_Harvey
- Kids Britannica: William Harvey
- Famous Scientists: William Harvey
- Today in Science History: Harvey William
- Goodreads: William Harvey and the Mechanics of the Heart
- Goodreads: William Harvey
- Wikipedia: Michael Servetus
- Wikipedia: Andrea Cesalpino
- Wikipedia: Marcello Malpighi
- Wikipedia: Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus
- Wikipedia: William Harvey
- Wikipedia: Realdo Colombo
- Wikipedia: Andreas Vesalius
- Wikipedia: Ebers Papyrus
- Wikipedia: Circulatory System
- Wikipedia: Sushruta
- Wikipedia: Ayurveda
- Wikipedia: Avicenna
- Wikipedia: The Canon of Medicine
- Wikipedia: Galen
- Wikipedia: Pneuma
- Wikipedia: Erasistratus
- Wikipedia: Herophilos
- Wikiquote: William Harvey
- William Harvey and the discovery of the circulation of the blood
- History Learning Site: William Harvey
- The Famous People: William Harvey
- Galileo Rice Catalog: Harvey
- Encyclopedia: William Harvey
- Citizendium: William Harvey: Works
- Citizendium: William Harvey
- Science Museum: William Harvey
- The Embryo Project Encyclopedia: William Harvey
- Biographies: Harvey
- Science World: Harvey
- NNDB: Harvey
- Prezi: Harvey
- Soft School: William Harvey Facts
- On The Motion Of The Heart And Blood In Animals
- William Harvey and the Discovery of the Circulation of Blood
- The Birth of a Scientific Revolution and Modern Physiology
- Discoveries in Medicine: Harvey