The Monk Basin and Bloodletting


Bloodletting was common among many ancient cultures: Greece, Egypt, and Mesopotamia. Islamic medicine preserved and developed the medical knowledge of the classical period and the main traditions of Hippocrates, Galen, and others including the practice of bloodletting. Al-Jazari designed four apparatus for measuring the quantity of blood drawn. Al-Jazari devices are unprecedented and resemble water clocks and automata rather than medical tools.

The Monk Basin for measuring amount of blood during bloodletting.

How does it work?

The monk basin mechanism is quite similar to the mechanism of the Water Clock of the scribe. I bring the original drawing of the mechanism in parallel to the drawing made by Donald R. Hill, The book translator with my captions. The technical explanation, as always, will be colored in blue, so anyone who is not interested in pulleys or balancing weight can skip those bits.

The monk is standing in the center of the basin with a flat rim. He holds a staff in his hand pointing downward. The rim is numbered between 1 and 120 dirhams (درهم) about 360 milliliters. The monk is positioned on the main pulley which is attached to two ropes through two small pulleys. On one end there is a float and the other is attached to a balancing weight. Before the beginning of the bloodletting, two dirhams of water (approximately 6 milliliters) are poured for two purposes:

  • It wets the walls and reduces surface tension so that blood flows more smoothly
  • It sets the float to the starting point and zeros the staff position.

As bloodletting begins, the blood flows through the holes into the reservoir. As a result, the float goes up and releases rope through the pulley, the weight continues to pull down, and the large pulley rotates with the monk staff indicating the amount collected so far.



Bloodletting was a common medical treatment in ancient times, but it received substantial reinforcement from Galen, the Court physician of the Roman Emperor Marcus Aurelius. Galen’s understanding of anatomy and medicine was influenced by the then-current theory of humorism, also known as the four humors – black bile, yellow bile, blood, and phlegm.  Excess of black bile was understood to cause depression or melancholy. Phlegm, or mucus, was thought to be associated with a low level of energy and emotion, as preserved in the word “phlegmatic.” Yellow bile was connected to aggression, but Glen believed that blood is the dominant of the four. It was assumed to be produced exclusively by the liver and was associated with enthusiastic, active, and social nature. To balance one temperament or health, Galen created a complex system that showed how much blood must be shed, based on the patient’s age, status, season, and weather. He believed that “excess” blood symptoms are fever and a headache. Bloodletting location was specific to disease: vein or intravenously, close or far from the affected body part. As the problem was more serious, more blood was shed. High Fever demanded enormous amounts of bloodletting. Galen theories dominated Western medical science for more than 1,300 years. Understanding the function of the heart and the circulation of blood was obtained by surgery of cadavers in the 16th century. Amazingly it didn’t stop the practice of bloodletting till the 19th century when significant evidence regarding the damage caused by the procedure was accumulated.

It’s interesting that you can still find the remains of Galen theory in our language – for example, melancholy is literally “black bile” in Greek ((μελας, melas “black”, χολη, kholé “bile”).  In the medieval time, Islamic medical knowledge was the most advanced in the world, it combined the knowledge of the ancient Greek, Persian traditions and the ancient Indian tradition of Ayurveda. Rebirth of Western medicine was based mainly on texts in Arabic. In addition to preserving the knowledge, there were significant advancements including initial understanding, at least in part, of the blood circulation by Ibn al-Nafis which pre-dates William Harvey, by ~ four hundred years. It did not help to stop the bloodletting.

Maimonides, Rabbi Moshe Ben Maimon, beyond being the most prolific and influential Torah scholars of all generations, was an exceptional philosopher and physician who wrote (surprisingly?) about alcohol, exercise, and hygiene in a way that fits our current medical information. He did not reject bloodletting but added a few reservations, probably from his experience:

“A man should not accustom himself to let blood regularly, nor should he do so unless he is in great need of it. He should not let blood in hot days or rainy days but in Nisan ( a month on the Jewish the calendar ~ March-April) and a little in Tishrei (the first month of the Jewish year ~ September) and after fifty (years) will not let blood. One will not let blood and enter the bath on the same day, nor will he let blood and go on a journey or in the following day. He would eat and drink less than he is used to and rest at the day of bloodletting.”

Mishne Torah (I could not find a proper translation to English, so this is a literal translation by me)

Al-Jazari and Bloodletting

Two things jump immediately:

  • The first is the device choice. It seems it would be much easier to measure the blood in a bowl or a vessel with scale than the extravagant solution al-Jazari chose. The next post on the “Basin of the Two Scribes” will elaborate on this point.
  • The second point is the monk. The fact that a Muslim engineer chose a Christian monk surprised me.

To the best of my knowledge of Islam, as a rule, does not support abstinence and seclusion and considers it a sin. The multinational society in Diyarbakir in the 12th century included Christians, was it the responsibility of monks to let blood?

I could not find any direct information, but in 1163 the Church issued a church order which forbade monks and priests from bloodletting, claiming the Church despises (no less!) the procedure. It was part of a ban on scientific investigation, so we cannot suspect the Church of medical progress. Since a decree was warranted, we can assume that this was rather common and the al-Jazari’s device is reflecting that. In response to the order, the barbers began to offer a variety of medical services including bloodletting, pulling teeth and even surgical operations like amputations. It is hard to imagine a haircut or a shaving following a surgery. The pole with stripes that mark a barbershop even today:

The barbershop pole originated from the practice of bloodletting in medieval days. The top bowl represents a basin for leeches, where the bottom bowl represents the basin where blood was collected. The striped pattern is red for blood, white for the bandages and blue perhaps for the veins (?) The last part is not very convincing, but I did not find a better one. There are claims that barbers used to hang bloody towels or bleeding bandages on the pole


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