Servetus Describes the Circulatory System Summary

  • Last updated on November 11, 2022

Servetus was the first person to publish his findings on how blood circulates from the heart, through the lungs, and then back to the heart, and how breathing has a function other than the cooling of the blood. His theories and discoveries marked major breakthroughs in the history of medicine and human anatomy and physiology and differed dramatically from the Aristotelian thought of his day.

Summary of Event

Michael Servetus was convicted of heresy, condemned to death, and burned at the stake along with his books on October 27, 1553. Born Miguel Serveto in Villanueva de Sixena, Spain), in 1511, he received an education in law and mathematics. Later, he occupied himself with geography and astronomy and developed a strong interest in biblical studies before undertaking work as an editor of medical works. Medicine;France Servetus, Michael Calvin, John Harvey, William Champier, Symphorien Andernach, Johann Guenther von Champier, Symphorien Guenther von Andernach, Johann Calvin, John Harvey, William Servetus, Michael

As a literary assistant influenced by Symphorien Champier, founder of the medical faculty at Lyon, Servetus quickly distinguished himself in the field of medicine. He later returned to Paris in 1536 to study medicine. As part of his studies, Servetus took part in anatomical dissections, which was key to his later insights. His proficiency in anatomy was praised by the professor of anatomy, Johann Guenther von Andernach, who said that Servetus was second to none in his knowledge of Galen.

During the Renaissance, the study of medicine relied on, primarily, the interpretation of the Greek and Latin texts of such figures as the Greek physician Hippocrates (c. 460-c. 377 b.c.e.) and the Roman physician Galen (129-c. 199). Although Servetus supported the medical views of Champier, a well-known Galenist, and while he expressed an acceptance of Galenism, his scholarly reflection allowed him to question strict Galenic ideas regarding the functions of the arterial and venous systems, and, in particular, the movement of blood from the left to the right side of the heart through pores in the septum.

Servetus formulated his concept of pulmonary circulation for the first time in 1546, contradicting Galen’s misconceptions involving the functions of the lungs, and he accepted theories declaring the existence of pores in the septum separating right and left ventricles. Servetus stated that blood could only pass from the right ventricle to the left by means of the pulmonary artery and the lungs. This significant discovery in human physiology was incorporated into a manuscript of Servetus’, one on theological ideas called Christianismi restitutio Christianismi restitutio (Servetus) (1553; partial translation, 1953), which was his final work. In the hope that his treatise would bring about a return to Christianity in its original form, Servetus sought but failed to find a willing publisher, primarily because his work incorporated heretical religious views involving the Trinity and opposition to the sacrament of infant baptism. Servetus, however, secretly agreed to print the manuscript in 1553 at his expense. A draft of the work was sent in 1546 to the Reformer of Geneva, John Calvin, who became Servetus’s main enemy. The book was criticized vehemently from the moment of its release and its theories and claims led to Servetus’s execution.

Undeniably, the small section of Servetus’s ill-fated treatise that contained a detailed description of the pulmonary circulatory system constituted a significant anatomical breakthrough. Not only did Servetus describe the circulation of blood in the heart and the lungs accurately, his work heralded the declaration of the existence of general blood circulation, which was to be fully described seventy-five years later by the English physician William Harvey.

Servetus’s description of pulmonary circulation, however, was not an exercise in human anatomy alone. In addition, the work was theological. Servetus discussed the Holy Spirit, but he also argued, controversially, that there was a physiological basis to the principle of life. The principle of life was traditionally believed to be manifested in the form of a soul or vital spirit. Aristotle and Galen believed the heart to be the source of what was called animal heat, that blood circulated to warm the body, and that respiration’s function was to cool the blood. Galenic thought, however, acknowledged that the vital spirit circulated in blood and originated in the liver. Servetus calculated that the soul of a human being was instilled during the first respiration at birth; the infant’s first breath started the circulation of blood.

Servetus argued also for the existence of a “triple spirit” in humans: natural (specifically located in the liver and in the veins), vital (situated in the heart and arteries), and animal (seated in the brain and in the nerves). To explain how these parts of the spirit were joined together, Servetus reasoned that the vivifying factor resided in blood, which, because it constituted a moving component, connected all parts of the body. His idea was similar to the Hebrew conception that the soul resides in blood and originates from the “breath of lives.” This conformed in large measure with Galen’s teaching regarding the pneuma, that is, the soul or spirit.

Because Servetus had extensive knowledge of anatomical dissection, he could observe firsthand and thus describe the course of blood in the heart and the lungs precisely. Although he maintained Galenic thoughts on the origin of blood in the liver, Servetus amended Galen’s claims that blood passes through orifices in the middle partition of the heart; Servetus had observed that in the heart, the primary movement of blood from right to left did not occur by way of the heart partition because it lacked orifices. This septum was not, according to Servetus, permeable to blood. Instead, he postulated that blood passed from the right ventricle to the left by means of a complex device, or communication joining the pulmonary artery with the pulmonary vein through a system of vessels by way of the lungs. Consequently, he figured that blood passed through the lungs to aerate, that is, to supply blood with oxygen through respiration; it was obvious to him that respiration was a physiological phenomenon. Yet he considered it also to be an aspect of divine process. Servetus’s ideas were influenced by two significant foundations of Renaissance thought: the Bible and Galenism.


The consequences of Servetus’s discovery of the pulmonary circulation of blood are wide-ranging, and few figures in medicine can compare in stature and significance. In his final work, Christianismi restitutio, Servetus’s description of the pulmonary circulation system linked oxygen, the air humans breath, with life.

He showed that there were capillaries in the lungs and in the brain that join the veins with the arteries and perform special functions. This discovery was a critical one.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Bainton, Roland H. Hunted Heretic: The Life and Death of Michael Servetus, 1511-1553. Boston: Beacon Press, 1960. A landmark study on the career and heresy trial of Servetus, and the theological debates with Calvin.
  • citation-type="booksimple"

    xlink:type="simple">Bainton, Roland H. “Michael Servetus and the Pulmonary Transit.” Bulletin of the History of Medicine 7 (1938): 1-7. A short but helpful discussion of the major medical discovery made by Servetus. This article is especially useful for those interested in Servetus as a physician.
  • citation-type="booksimple"

    xlink:type="simple">Cunningham, Andrew. The Anatomical Renaissance: The Resurrection of the Anatomical Projects of the Ancients. Brookfield, Vt.: Ashgate, 1997. This important study of the history of anatomy emphasizes work that addressed Galenic anatomy and the importance of ancient science to Renaissance thinkers generally.
  • citation-type="booksimple"

    xlink:type="simple">Goldstone, Lawrence, and Nancy Goldstone. Out of the Flames: The Remarkable Story of a Fearless Scholar, a Fatal Heresy, and One of the Rarest Books in the World. New York: Broadway Books, 2002. Examines the life, death, and writings of Servetus. Useful for detailing the growth of literacy, Renaissance scholastic doctrine, and theological inquiry.
  • citation-type="booksimple"

    xlink:type="simple">Hillar, Marian, and Claire S. Allen. Michael Servetus: Intellectual Giant, Humanist, and Martyr. New York: University Press of America, 2002. An authoritative analysis of Servetus as a scholar, inquisitive experimenter, philosopher, and Christian reformer.
  • citation-type="booksimple"

    xlink:type="simple">O’Malley, Charles Donald. Michael Servetus: A Translation of His Geographical, Medical, and Astrological Writings, with Introductions and Notes. Philadelphia: American Philosophical Society, 1953. Provides useful translations of Servetus’s nontheological works, including selections from Christianismi restitutio.

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Categories: History