Galen and Humoral Theory

Anna Marie Eleanor Roos. Scientific Thought: In Context. Editor: K Lee Lerner & Brenda Wilmoth Lerner. Volume 1. Detroit: Gale, 2009.


The Greek physician Galen of Pergamum (AD 129-c.216) was the first major systematizer of medical practice and theory in the ancient world. His work had its basis in the ideas of his predecessor Hippocrates of Cos (460-375 BC) as well as Platonic, Aristotelian, and Stoic philosophy.

As Galen persuasively argued that medicine was both an art and a science, and promoted the idea that health was the result of a balance between the soul, mind, and body, his work was extremely influential. Galenic medicine dominated science for 1,300 years, and some of his precepts were still in use in the 1800s. After the fall of the Roman empire in the fifth century AD, Galen’s writings were preserved by Arab scholars and retranslated into Latin in the eleventh century. Galenic works served as the basis for university medical study until the discoveries of the Italian anatomist Vesalius (1514-1564) in 1543. This article will analyze the roots of Galenic medicine, explore its principles based upon bodily humors or fluids, and demonstrate the influence it held until the Renaissance.

Historical Background and Scientific Foundations

Galen was born in Pergamum, an important center of research and medicine in the ancient world. His father, Nicon, was a wealthy architect and had the means to provide his son with a fine and wide-ranging education, including exposure to the four major philosophical schools at the time: the Platonists, the Aristotelians, the Stoics, and the Epicureans. Galen drew from this wide variety of thought to formulate the direction and development of his medical theories, beginning medical school at the age of sixteen in Smyrna, Corinth, and Alexandria.

Galen was probably trained to dissect cadavers in Egypt, writing that Alexandrian physicians “instruct their pupils with the aid of autopsy.” While the Greek world had a taboo against human dissection, Egyptian practices of organ removal, embalming, and preserving the body during mummification meant there were fewer obstacles to autopsies for medical study. The pharaohs also allowed dissection on criminals that had been executed. Galen would later perform extensive dissections in Greece on Barbary apes and pigs to avoid Greek religious prohibitions.

In 157, Galen returned to Pergamum and became a physician to the local gymnasium, where his patients were largely gladiators. The wounds they received in gladiatorial combat gave Galen the experience to experiment and create a method to promote the healing of tendon injuries. Since most of his time was spent setting broken bones and repairing flesh wounds, he also improved his knowledge of anatomy. In 162, due to civil unrest in Pergamum, he moved to Rome to start a new medical practice, where he ultimately became personal physician to both the Emperor Marcus Aurelius (121-180) and Aurelius’s son Commodotus. Marcus Aurelius wrote masterpieces of Stoic meditations, which may have influenced Galen’s incorporation of the Stoic philosophy in his medical works. During this period, Galen wrote an extensive corpus of medical treatises of which approximately 20,000 pages survive.

Galen and the Art and Science of Medicine

When any scientific discipline is forming, a variety of different “schools” or opinions will coexist until one theory or paradigm dominates. When Galen began his practice, Greek medicine was dominated by three main schools of thought: the rationalists (sometimes known as the dogmatists), the empiricists, and the methodists.

The rationalists thought that reason should be used to understand causes of disease, health, and physiology and to create medical theory. They believed reason and conjecture were more important than experience in medical practice. In other words, a conceptual philosophical structure within which to interpret and explain nature was more important than observation.

The empiricists, directly opposed to the rationalists, were largely anatomists from Alexandria. They believed that direct observation of the patient and his or her symptoms were the basis of medicine, and that theories were largely useless and ineffective. Galen himself had keen powers of observation. As Vivian Nutton notes in her article “Logic, Learning, and Experimental Medicine,” Galen “had a sharp eye, wherever he traveled, noting the variety of wheat growing in northern Greece, the fighting habits of weasels, and the annoying behavior of young children, some of whom, he commented ruefully, seem to have been born naughty.”

In the first century AD, the Methodist sect emerged. These physicians criticized both the elaborate theories of the rationalists and the empiricists’ claim that a successful physician must have lengthy experience to be effective. They proposed instead that medical treatment could be carried out on the basis of a few simple rules that could be mastered in six months.

Galen synthesized the works of these three schools, claiming that both reason and experience were important to the practice of medicine. His writings were designed to be part of a larger curriculum, a system of medicine with a cohesive course of study. Galen’s works ranged from abstract works of reason, logic, and philosophy to therapeutically precise treatises on anatomy, pharmacology, and fevers.

Medical studies began with a course of philosophy. As Galen himself stated, philosophy consisted of natural philosophy (what we now think of as science), logic (reasoned, step-by-step arguments), and ethics (what is good and bad). This distinguished a true physician from false doctors or quacks.

The study of natural philosophy or science gave the doctor insight into bodily processes. Logic allowed him to make good judgments, to understand the underlying cause of diseases, and to make diagnoses (identification) and prognoses (predict outcomes) of a specific illness. An understanding of ethics was important not only to the doctor, but to the patient, as Galen believed the patient was responsible for regulating their emotions and moral actions to promote good health and to balance body and soul.

After the medical student studied philosophy, he would turn to the more specific science of the body, which was learned by observation and dissection. This was the basis of practical applications or methods in diagnosis, drugs, and treatments. As an example of his practical advice, Galen wrote in his On the Art of Healing:

When you meet the patient, you study the most important symptoms without forgetting the most trivial. What the most important tell us is corroborated by the others. One generally obtains the major indications in fevers from the pulse and the urine. It is essential to add to these the other signs, as Hippocrates taught, such as those that appear in the face, the posture the patient adopts in bed, the breathing, the nature of the upper and lower excretions … presence or absence of headache … prostration or good spirits in the patient, … [and] the appearance of the body.

Galen, Hippocrates, and the Humors

Galen believed that the best example of a philosopher-physician was the Greek Hippocrates of Cos (c.460-c.377 BC), whose premise that the body should be treated as a whole, as well as his accurate description of diseases such as pneumonia and epilepsy, were valued by Galen. The Hippocratic Oath, still taken today by physicians, reflects Galen’s belief that doctors must adhere to a code of medical ethics.

In particular, Galen relied upon the Hippocratic treatise On the Nature of Man, which stated that good health relied on the balance of four humors or bodily fluids: phlegm, blood, yellow bile, and black bile. The humors nourished the body, provided the material for sperm, and in pregnancy, for the fetus.

Phlegm was a general term for any colorless or whitish secretion (except semen and milk), and could include mucus, lymph fluid, saliva, pus, cerebrospinal fluid, or sweat. The brain was the organ associated with phlegm, most likely due to the color and consistency of brain tissue. Yellow bile was thought to be the fluid found in the gallbladder and black bile from the liver, but either fluid could be present in vomit or feces. The humor of blood was more complex. It was believed to consist of a mixture of blood with a smaller amount of the other three humors, which were produced as part of the bodily manufacture of the blood. Taking a blood sample therefore was a means to ascertain if the proportions of humors in the body were balanced.

Humoral balance was also influenced by one’s complexion or temperament. There were four basic complexions, each caused by the dominance of one humor. The sanguineous personality resulted from the predominance of the blood and had a lively and cheerful temperament. Sanguine people also tended to have florid complexions from an excess of blood. The melancholy personality resulted from a surfeit of black bile, and melancholics were thought to be dark in skin and hair tone and prone to depression and worry. The phlegmatic dominated by the phlegm humor was calm, slow, and prone to watery swellings in the body. Cholerics with a surfeit of yellow bile were energetic and quickly prone to anger.

The humors were to the human body what the elements were to the common matter of the earth, and each humor had its own counterpart among the ancient Greeks’ concept of the elements of earth, water, air, and fire. Each humor also was related to a principal area of the body.

If a person was too emotional, it was thought he had an “overactive” heart due to too much blood. Humoral balance could then be restored by therapeutic bloodletting via leeches or lancet. The vein was manually perforated by the doctor and sometimes many shallow cuts were made. When the patient felt faint, and was considered to be “calmer” due to the purgation of the excess humor, the bleeding was stopped. Bleeding was also done if another humor was too predominant, as the pure humor blood contained a smaller amount of the other humors.

Humoral balance could also be achieved via diet or herbal remedies, using a treatment of opposites. For instance, if there was an overabundance of cold and moist phlegm, the physician would give the patient remedies associated with hot and dry yellow bile. Usually these remedies were in the form of herbs or poultices of crushed minerals, or even amulets thought to carry hidden or occult principles.

So, if a patient had a disease like scrofula (a form of tuberculosis that caused watery-looking swellings of the lymph nodes under the neck), the Galenic physician would conclude the patient had too much phlegm, which had upset their humoral balance. He would prescribe a course of bleeding and perhaps a “hot and drying” substance like mustard or a poultice of mustard seed. If the patient was wealthy, the Galenic physician might cast a gold amulet for her to wear; as the metal gold was associated with the hot and fiery sun, the gold would “dry out” the patient who had overly moist and cold humors.

Galen also thought the humors could affect a patient’s physical appearance and even their character, and he subsequently taught a “science” of physiognomy, which claims that a person’s physical features indicate their internal character, tendencies, and intelligence. Historians have speculated that when Galen was studying medicine in Smyrna, he read De Physiognomonia, a second-century handbook of physiognomy by the physician Polemo of Laodicea.

Galen applied physiognomy to his doctrine of the humors. He postulated that the humors of the body were directly related to the temperament. For instance, excess dryness of the humors was associated with wisdom, and moistness with madness. A choleric person, quick of temper, tended to have red hair. A sanguineous person had blonde hair and was happy and easygoing. Galen also thought that humoral balance was reflected in personality. As Evans has indicated, one who had balanced humors was kind, affectionate, humane, and prudent, of good color, between a smooth and hairy skin, and between a dark and light complexion.

Galen the Anatomist

As part of his belief that empirical observation was crucial to the study of medicine, Galen did extensive dissections, claiming to have done one every day. Dissecting Barbary apes and pigs, as well as other animals (including an elephant) to avoid Greek taboos on human dissection, Galen made many discoveries—and a few mistakes—when he analogized too closely between animal and human anatomy. Nutton notes that “Galen’s anatomy of the womb is that of a dog, his positioning of the kidneys that of a pig, and his anatomy of the brain—the result of some delicate work with the knife—that of a cow or goat.”

That said, Galen made important contributions to the understanding of neural function and created a theory of blood circulation that dominated medicine until the discoveries of English physician William Harvey (1578-1657) in the seventeenth century. At each vertebra in the spine, Galen tied or cut the spinal cord to see the effect on the animal. In this manner, he discovered the nerves of the larynx and how the vagus nerve in the chest cavity regulates breathing and the function of the diaphragm.

Galen also developed a theory of nutrition and blood circulation via the knowledge he attained through dissection. He postulated that food was digested in the stomach where it was turned into blood, providing nutrition for the body. A small amount of blood went through a septum or hole he mistakenly thought was between the ventricles of the heart. As Nutton has remarked, Galen thought:

In the left ventricle, mixed with air drawn in from the lungs, [blood] was transformed into arterial blood, which as it flowed in the arteries gave life and energy to the body. A tiny fraction of this blood underwent a third transformation in [a bundle of nerves at the base of the brain], the rete mirabile to become “psychic pneuma” in the brain. This pneuma, or spirit, operating in the channels of the nerves, was the agent of sensation that transmitted perceptions to the brain. It was also the means whereby the reasoning part of the soul in the brain could control the rest of the body and instigate voluntary action.

Galen in Western Europe

After their predominance in Roman culture, Galen’s vast amount of writings ultimately became appreciated and preserved by the Muslim world. After the Western half of Roman empire fell in the fifth century AD, a good deal of Greek and Roman medical knowledge was temporarily lost in Western Europe. The eastern half of the Roman Empire continued as the Byzantine Empire with a capital at Constantinople (present-day Istanbul in Turkey). Here, Greek and Roman medical knowledge survived and was transmitted via trade, doctors, and wandering scholars to distant regions of Syria, Iraq, Iran, North Africa, and Egypt, spreading throughout the Arabic Empire.

The Arab empire’s zenith was between the eighth and thirteenth centuries, its territory stretching from Spain to central Asia. Islamic doctors and natural philosophers translated Galen into Arabic, commenting upon and improving his work. As Lindberg has noted, “only two or three of Galen’s works were available in Latin before the eleventh century, whereas Hunayn ibn Ishaq (AD 809-873) listed 129 Galenic works known to him in Baghdad, forty of which he claimed personally to have translated into Arabic.” Arabic physicians combined Galen’s tenets with their own medical literature, producing encyclopedic works that greatly influenced Western medicine in the later Middle Ages such as the Almansorof Rhazes (ca. 930), and the Canon of Medicine by Avicenna (980-1037). The Muslims also established schools and universities in Mespotamia, Egypt, Spain, and Jerusalem, translating and preserving ancient Greek and Roman texts.

Twelfth-century Christian crusades to the Middle East began to transfer Muslim scientific knowledge back to the West via southern Italy and Spain. This recovery of Greek and Roman knowledge in Western Europe, as well as the establishment of towns and trade routes with the Middle East in the twelfth century, led to the rise of medieval universities in Paris, Bologna, and Oxford. Curricula included Galen’s writings; his works were taught at the medical school in Salerno in Southern Italy from the eleventh century. Constantine the African (c.1020-1087), a Benedictine monk who had close ties with the Salerno medical school, translated works of Hippocrates and Galen from Arabic to Latin, which was the language of scholarship in the Middle Ages.

Galen’s doctrine of the humors and individual complexion or temperament was important to medieval medicine. Health was also believed to be influenced by the “non-naturals,” which included air, food, drink, sleep, activity, rest, and state of mind, a reflection of Galen’s belief in a balance between body and mind in the preservation of health. Medieval practitioners continued to bloodlet and administer purges and cathartics to restore the humoral balance, as well as using herbal remedies based on folk medicines. From the twelfth century onward, new translations of works by Galen and his Arabic commentators such as Avicenna helped organize pharmacological knowledge.

Medieval doctors also followed Galen’s emphasis on urinalysis and the examination of the pulse. Galen believed that urine (as well as blood) could reflect the degree of humoral balance in the body as well as the state of the liver. Charts were created to demonstrate the connection between colors of urine and illness.

Galen’s insistence on knowledge of anatomy had a lesser influence on medieval medicine, as most treatments (whether dietary, bleeding, or herbal) did not require a high degree of anatomical knowledge. Surgery, usually confined to setting bones, pulling teeth, performing lithotomies (incisions to the bladder) for bladder stones, and lancing boils tended not to be performed by university-educated physicians, but by barber-surgeons who learned their craft via observation and performing the procedures, not by studying Galen’s anatomical works.

That said, Galen’s extensive corpus of anatomical works handed down from the Arabs could not be ignored, and autopsies and human dissection were performed at the University of Bologna in the late thirteenth century. By the fourteenth century dissection became part of the regular medical curriculum at Padua and Bologna. However, the medical students themselves did not do the dissections; rather the instructor read from Galen’s anatomical work, and an assistant demonstrated the parts of the body to the audience. Medieval medical universities made the entirely reasonable assumption that Galen had been correct in his anatomical studies, and they were largely right. However, as anatomical practice was revived and improved, it would only be a matter of time before Galen’s mistakes came to light.

The Corrective Work of Andreas Vesalius

Andreas Vesalius (1514-1564) was a Belgian anatomist and physician. A graduate of the Universities of Louvain and Paris, he became a lecturer on surgery at the University of Padua. Eventually he served as court physician to Charles V, Holy Roman Emperor, as well as Philip II, King of Spain.

In his De Humani Corporis Fabrica (Fabric of the human body, 1543), Vesalius illustrated the results of his anatomical studies, which were not only the most thorough and accurate to date, but corrected Galen’s past errors. Vesalius did not, however, attack Galen or Galenic doctrines except as he felt the facts necessitated such actions, and limited his criticism to Galenic anatomy.

Vesalius did not, as is often asserted, challenge Galen’s humoral medicine. Vesalius did, however, realize that Galen based most of his work on animal dissections and offered corrections in the Fabrica. Vesalius realized the lower jaw of humans consisted of one bone, the mandible, not two as Galen had asserted. Vesalius also discovered the human heart was four-chambered, and that major blood vessels such as the vena cava had their origins in the heart, not the liver as Galen had claimed.

The most important correction that Vesalius made was his discovery that there were no pores or passageways between the ventricles of the heart as Galen claimed. This was important, because the pores had been necessary to Galenic anatomy; they provided a route from the pulmonary artery, which Galen called the “arterial vein,” to the pulmonary vein (or “venal artery”). Galen believed that air reached the heart through this passageway.

The lack of the interventricular septum or pores meant that the Galenic model for blood circulation was flawed; research eventually led to the correct explanation in the seventeenth century by William Harvey. Vesalius’s work, which also gave the fullest anatomical description of the brain to that point and had anatomical illustrations that set the current standard, eventually superseded the Galenic anatomical model.

The Survival of Humoral Theory

Despite the replacement of Galen’s anatomy, his humoral theory survived in medicine in some cases until the nineteenth century, often with unfortunate results. American physician Benjamin Rush (1746-1813) used bleeding to treat sufferers of Philadelphia’s Yellow Fever epidemic in the 1790s; President George Washington (1732-1799) died as the result of overenthusiastic bloodletting and other misguided treatments. Patients continued to be given purges to restore humoral balance into the 1800s. In his article “The Origin of Species and the Origin of Disease: A Tale of Two Theories,” Wilbur L. Bullock comments:

On the assumption that humoral imbalance was often related to too much of a poison or poisons, weird concoctions were used as purgatives and/or emetics. At times treatment was based on the objective of neutralizing such poisons by medication with another poison. Hence mercurous chloride (calomel) became a most popular form of therapy, even into the nineteenth century. Often both calomel and bleeding were used on the same patient!

John Duffy, in his book Sword of Pestilence: The New Orleans Yellow Fever Epidemic of 1853, has shown that the chorus of a song which followed the yellow fever epidemic in New Orleans in 1653 made reference to humoral theory and the use of calomel:

And when I must resign my breath, Pray let me die a natural death And bid the world a fond farewell Without one dose of calomel!

Modern Cultural Connections

It was not until the firm establishment of the germ theory of disease by Pasteur and Koch in the nineteenth century that the role of microscopic pathogens in causing ailments was understood and humoral medicine declined. The rise of psychology and psychiatry in the nineteenth century also gradually replaced the idea of the complexion or temperament in humoral medicine. Yet there is little doubt that Galen was a predominant figure in the history of medicine.