Bloodletting was used in many medical traditions for centuries, especially within systems that interpreted illness through bodily balance. In European medicine, it became closely associated with humoral theory, in which blood was one of several substances thought to require regulation.
Why the practice seemed plausible
Within humoral medicine, fever, inflammation and other signs could be interpreted as evidence that the body was out of balance. Removing blood therefore appeared to fit the prevailing theory. The practice was reinforced by medical training, classical authority and the difficulty of separating treatment effects from the natural course of illness.
Why it declined
Bloodletting did not disappear because of one experiment or one discovery. Its decline reflected broader changes in clinical observation, pathological anatomy, statistics, physiology and later microbiology. As doctors became better able to link symptoms to specific disease processes, a general treatment based on removing blood became less defensible for most conditions.
Some modern medical procedures still involve removing blood for specific indications, but these should not be confused with historical bloodletting based on humoral theory.
The history is useful because it shows how a treatment can remain credible inside a coherent theoretical system even when later evidence changes the underlying model.
