For some reason I had assumed that bloodletting wasn’t very common in the Middle Ages, but my current reading about medieval medicine has set me right. Even in the early Middle Ages it was far from unusual.
Bloodletting is a logical consequence of accepting that illness is caused by an imbalance of the humours. As medical texts from the Greek and Arabic-speaking worlds were translated into Latin from the twelfth century onwards, it became even more important as one of the physician’s many skills. Bloodletting was carried out by both surgeons and physicians, even though it was technically a surgical procedure.
One of the purposes of bloodletting was to allow the physician to make a diagnosis. An instruction book, probably written by Maurus of Salerno in the twelfth century, told the physician what to look for in the blood he collected from his patient. The physician was to examine it before, during and after coagulation. He was to look for viscosity, hotness or coldness, greasiness, taste, foaminess and speed of coagulation. You’ll note that this required him to do a bit more than just look at the blood.
The main purpose of bloodletting was to treat diseases by restoring balance between the humours. All the four humours were present in blood, so an excess of one of them could be removed by drawing off some blood.
The most common place for bloodletting was the arm, in which there were three major veins: the cephalic, the median and the basilic. If the diagnosis was that the patient was melancholic, however, a vein in the forehead was more likely to be cut. The veins in the thumb were associated with pains in the head and the vein between the ankle and the foot was linked to diseases of the genitals.
There were detailed instruction books available to physicians telling them how to tie the arm to prepare the vein and how to make the cut. There were also instructions about how to avoid nerves and arteries near the site of the incision. The manuals also told them how to limit the bleeding when they were finished.
The patient’s diet before and after the bloodletting was important, as were the seasons of the year, the phases of the moon and the time of day when the procedure was carried out. Charts like the one above, which showed where on the body cuts should be made for bloodletting, often included diagrams of astrological influences on the patient. Each sign of the zodiac had power over a specific part of the body and the diseases that affected it. In the fourteenth century, physicians would consult an astrological table to find out when there was a favourable alignment in the heavens for the exact procedure they were proposing. Knowing where the moon was in relation to the signs of the zodiac meant that the physician knew where to cut, since the moon and the other planets drew the humours to different parts of the body. The physician had to examine astrological tables and calendars to hand before he could decide what to do.
There were other things to think about as well. Was it better to remove a lot of blood in one go or to make a number of incisions over a period of time? Should the blood be taken from the afflicted area or from the opposite side of the body to encourage the blood to move away from the site of the disease?
Most medieval practitioners were aware of the risks associated with bloodletting. They were advised that blood should not be taken from small children, pregnant women, the old or the weak. Although they didn’t know what caused it or what it really was, they also knew about the risk of infection. They didn’t know how to prevent it, though, and there was little they could do once a cut became infected.
Despite this, some people had regular bloodlettings. In the late twelfth century, Peter the Venerable, Abbot of Cluny, wrote a letter to a medical expert asking for help with an illness of long-standing and mentioned that he had put off his bi-monthly bloodletting. He was obviously someone who believed in the preventative efficacy of bloodletting, which was a common practice for those wealthy enough to be able to look after their health. Blood was a warm and wet humour, and bloodletting could make the patient cooler and drier, ready to face a hot summer.
Leeches were also used for bloodletting, but very rarely. I couldn’t even find them listed in the indices of the reference books I used.
Sadly, despite its popularity, bloodletting achieved nothing other than, in some cases, weakening the patient. It was many centuries, however, before the practice was challenged.
Medieval Bodies by Jack Hartnell
Medieval and Early Renaissance Medicine by Nancy G. Siraisi