Sir Humphry Davy's Researches chemical and philosophical: chiefly concerning nitrous oxide (1800), pp. 556 and 557 (right), showing how nitrous oxide relieves pain during surgery.
An anaesthetic (anesthetic) is a substance that either stops pain, or causes the user to sleep.There are two types: general anaesthesia causes a reversible loss of consciousness. Local anaesthetic cause a loss of sensitivity (and pain) on a local area.