If humoral theory was the map, bloodletting was the main road. Excess blood explained fever, flush, headache, and a dozen acute illnesses. Removing blood was supposed to cool the body and restore proportion. The practice was already old in 30 AD and would remain respectable in Europe until the nineteenth century. That longevity is a warning about how long a coherent error can live.
Three ways to take blood
Venesection (phlebotomy)
A lancet opened a vein, usually in the arm. The amount was judged by age, strength, season, and disease. Celsus notes that bleeding the young, the old, and the pregnant had once been forbidden, then became more common — he is not a mindless enthusiast. He still treats venesection as a general aid in many illnesses.
Leeches
Medicinal leeches did the measuring themselves. They were useful where a knife felt too bold, or where a local “drawing” was wanted rather than a stream from the elbow.
Cupping
A heated cup sucked skin upward. Dry cupping raised a bruise. Wet cupping added small cuts so blood entered the cup. The idea was to pull peccant matter to a chosen spot — including, in some recipes, toward the surface and out.
To let blood by incising a vein is no novelty; what is novel is that there should be scarcely any malady in which blood may not be let.
When they reached for the lancet
- Fevers and inflammations (hot, red, full pulse).
- Headaches thought to come from blood crowding the head.
- Sanguine excess — the person “too full.”
- Sometimes melancholy, on the theory that dark humors rode in the blood — a stretch even then, and cruel in the frail.
Location mattered in the more elaborate schemes: bleed here for the chest, there for the temples. The more precise the map, the more scientific it felt.
Why it seemed to work
A feverish patient may feel a brief coolness after losing blood. Many acute diseases end in a few days regardless. The physician who had done something dramatic was easy to credit. Failures could be narrated as “too little,” “too late,” or “the wrong day.” The theory was closed: it could not falsify itself.
The cost was real. Weak patients were made weaker. Wounds infected. Occasional deaths were absorbed into the same story. Celsus’s caution about children is the humane note in a dangerous habit.