Leaches produce enzyme that prevents blood cloth from forming. It also improves oxygenation. For some wounds, leaches would protect leg or arm from amputation.
* leeches
Leaching is a process in which you percolate a liquid (like water) through something, and it picks up chemicals and carries them out. Brewing coffee, for instance.
"Rationally designed" drugs do this now. An example: Exjade ;
Right but only because we know the mechanism of action and it's efficacy. It's also performed in a different manner to blood letting as a historical treatment.