Fourth Lateran Council c. 18
No cleric may decree or pronounce a sentence involving the shedding of blood,nor carry out a punishment involving the same, or be present when such punishment is carried out. If anyone, however, under cover of this statute, dares inflict injury on churches or ecclesiastical persons, let him be restrained by ecclesiastical censure. A cleric may not write or dictate letters which require punishments involving the shedding of blood; in the courts of princes this responsibility should be entrusted to laymen and not to clerics. Moreover no cleric may be put in command of mercenaries or crossbowmen or suchlike men of blood; nor may a subdeacon, deacon or priest practice the art of surgery, which involves cauterizing and making incisions; nor may anyone confer a rite of blessing or consecration on a purgation by ordeal of boiling or cold water or of the red-hot iron, saving nevertheless the previously promulgated prohibitions regarding single combats and duels.