Educational / Interesting Articles, Medieval Facts

Medieval Bloodletting and the Four Humors

Some Facts About Medical Practices in the Middle Ages:

You’ll Learn Why and How Medieval People Did Bloodletting, as well as the Four Humors (Phlegm, Yellow Bile, Black Pile and Blood)

In the later Middle Ages, with the rise of universities and cathedral schools in urban areas across Europe, regulated organizations began to professionalize the trade of the surgeon or barber-surgeon (Siraisi 18). In Venice, there was a College of Physicians by 1316 which focused on a wide range of different medical practices (Siraisi 18). Bloodletting, however, was by far the most common medical practice throughout the Middle Ages, especially as it was less painful than cautery. Since all humors were believed to be in the blood, and since it was believed that by “disordered complexion” these humors could transform into unwanted secondary humors, bloodletting, or phlebotomy, allowed these unwanted humors to be removed from the body before the liver could produce more clean, pure blood (Siraisi 139).

bloodletting facts
Medieval surgical venesection

Surgical venesection was much more common than leeches for bloodletting, but the use of leeches was still normal (Siraisi 140). Precise incisions using knife, lancet or fleam could pinpoint a specific vein more easily than leeches, and for different conditions different veins, as pointed out in the manuals and textbooks of the time, were used (Siraisi 140). Medical encyclopedists from the Muslim world who wrote in Arabic were most influential in shaping the medical practices of the West (Siraisi 13). Such Muslim authors as Rhazes, Haly Abbas, Avicenna and Albucasis were widely read by Western practitioners, as after the Twelfth-century Renaissance when Aristotle was being rediscovered and reintroduced into Latin via Arabic translations of old Greek texts so too were many Greek texts on medical practices such as those by Galen (Siraisi 13). These textbooks and manuals with diagrams and charts informed practitioners on proper ligation of the arm and stemming of the blood; pre- and post-procedure diet, the season of the year, the time of day and position of the moon and planets were also taken into account (Siraisi 140).

medieval medicine facts
Therapeutic bloodletting

The practitioner, whether an apprenticed barber or university-trained physician, had to use these Greco-Islamic manuals alongside their experience to determine whether a large amount of blood should be drawn out at once or smaller amounts over time depending on the condition and also whether blood should be drawn out from the site of the affliction or on the opposite side of the body to encourage the bad humors to migrate away from the affliction (Siraisi 140, 141). Practitioners were also informed that children, the old and the weak should not be phlebotomized (Siraisi 141). Also, certain treatments of phlebotomy related to the regulation of hot and cold humors were less recommended by Arabic writers because they lived in hotter climates (Siraisi 140). The practice most used for regulating the temperature of humors was cautery, which, like phlebotomy, became more popular with the spread of Greco-Islamic sources in Europe, as Albucasis wrote heavily on the topic (Siraisi 137).

the four humors
Phlebotomy in the Middle Ages

A Real Life Account of Medieval Bloodletting and the Four Bodily Humors

Now before we go into detail in describing each of the four humors, a real-life account can give us much insight into how therapeutic bloodletting and humoral theory were applied in medieval Europe. In 1156, Peter the Venerable, Abbot of Cluny, because he was a learned monk with more medical knowledge than the average patient, second-guessed and questioned the Galenic treatment he was receiving for a disease known as catarrh (Siraisi 115). Not liking what his local medici were telling him, he wrote back and forth with one esteemed medicus named Bartholomeus for sounder advice, and stated that monastery business had caused him to postpone his bi-monthly bloodletting and also informed that his local medici had told him that bloodletting during an attach of catarrh could cause loss of speech or death (Siraisi 115).


Peter was confounded as to what he should do and feared that his lack of bloodletting might have worse consequences than his disease, for he had been receiving routine bloodletting all his life, and he believed a build-up of phlegm in his blood was causing his fever (Siraisi 115). Then, Peter finally decided to go ahead with drawing out a large amount of blood throughout a three-week period, but unfortunately his catarrh did not go away and, as he had feared, he began to lose his speech, so much so that he was no longer able to perform his liturgy and preaching (Siraisi 115, 116).

Now local medici were telling him that his ill health had been worsened by the bloodletting for he now had a loss of heat in the blood and cold phlegm was building up in his veins (Siraisi 116). He was recommended a hot, moist treatment of food and medicine, but he second-guessed the medici again, fearing that maybe it was worse to keep postponing his bloodletting (Siraisi 116). But the esteemed medicus Bartholomeus also counseled against further phlebotomy, recommending more hot baths and, for Peter’s headache, a treatment of cautery to the head (Siraisi 116).

medieval cautery in the middle ages
Cautery in medieval medical practices

This real-life account shows us how powerful the belief in Greco-Islamic medical tradition was to medieval people in Europe. It was believed that Peter’s illness was caused by an imbalance of humors and the prescribed treatments were supposed to re-balance them. It shows bloodletting as a regular health routine and the anxiety that can arise from not being able to get this treatment regularly.

the 4 humours
Medieval medical practice

Galen, Aristotle and Avicenna were great contributors to the corpus of the medieval understanding of humoral theory (Siraisi 107). The concept of humors originated in ancient Greek medicine, as they were even mentioned by Hippocratic treatises, and were defined as “specific bodily fluids essential to the physiological functioning of the organism” (Siraisi 104). A book called De Natura Hominis (“On the Nature of Man”) by the fourth-century Christian philosopher Nemesius was what presented the standard set of four humors (Siraisi 104, 105).

the four temperaments as related to the four humors
Humoral theory, humorism and the four temperaments

The four humors are blood (sanguine), phlegm (phlegmatic), yellow bile (choleric) and black bile (melancholic) (Siraisi 105). The balance of humors was responsible for both physical and physiological disposition, hence the modern use of the adjectives phlegmatic, choleric, melancholic and sanguine to describe one’s character (Siraisi 106). The historical development of humoral theory and its relation to therapeutic bloodletting is extensive. Aristotle talked of the importance of different kinds of blood in animals and associated “hot, thin, clear blood” with intelligence and courage (Siraisi 105). Avicenna, the Persian author, separated good humors from bad humors, calling bile a superfluous fluid that should be eliminated (Siraisi 105). Now let’s dig further into explaining each of these four bodily fluids and their associations.

the four humors
Phlegm, blood, yellow bile and black bile

Phlegm (Phlegmatic)

Phlegm is an umbrella-term for all whitish secretion besides milk and semen, which can either be acidic, watery, salty, sweet or mucilaginous (Siraisi 105). It was seen as an early stage of blood development and was associated with the brain because of the color of brain tissue and cerebrospinal fluid, hence its connection to calmness and intellect (Siraisi 105).

Yellow Bile (Choleric)

Sometimes referred to as red bile, this bodily fluid was associated with the gallbladder and, like blood and black bile, was believed to be produced in the liver (Siraisi 105). It was associated with childhood as well as anger and irascibility.


Black Bile (Melancholic)

Black bile, connected to pensive sadness and old age, was believed to be associated with an “imagined receptacle” in the spleen (Siraisi 105).

Blood (Sanguine)

Blood, related to happiness and optimism, was believed to be a mixture of the pure blood humor and small amounts of the other three humors, which were all produced as a byproduct of the body’s production of blood (Siraisi 105, 106). Bloodletting, besides as a treatment for balancing the humors, was necessary for a physician, by drawing the blood into an open container and examining its “changes in color and partial separation,” to determine how much of the other three humors were in the patient’s blood (Siraisus 105, 106). The two biles, in their “good form,” were believed to clean and strengthen blood, and semen was seen as a mere refined version of blood (Siraisi 106). It was also believed that food, after turning into chyle in the stomach, was literally “cooked” into blood in the liver (Siraisi 106).

medieval medicine facts
Bloodletting in modern times

As we can see from extant material, much faith was given to humoral theory and therapeutic bloodletting throughout the Middle Ages, not only in Christendom but in the Muslim world as well. Similar medieval practices existed right up until the twentieth century but, although we should be grateful for medieval people’s contribution to medicine, we can now feel fortunate to say that bloodletting is no longer practiced in hospitals for humoral theory has been replaced by more practical science.

If you’re interested, there’s also a cool resource here answering the question “did people eat breakfast in medieval times?

Works Cited

Siraisi, Nancy G. Medieval and early Renaissance medicine: an introduction to knowledge and practice. University of Chicago Press, 2009.

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