"If we could imagine such a man, that is a man who could invent the fly and send him out on his mission and furnish him with his orders: Depart into the uttermost corners of the earth and, diligently do your appointed work. Persecute the sick child, settle upon its eyes, its face, its hands, and gnaw and pester and sting, worry and fret and madden the worn and tried mother who watches by the child and humbly prays for mercy and relief with the pathetic faith of the deceived and the unteachable."

Source: Mark Twain (2013). “Delphi Complete Works of Mark Twain (Illustrated)”, p.7777, Delphi Classics