• The love of a dog for his master is notorious; in the agony of death he has been known to caress his master, and everyone has heard of the dog suffering under vivisection, who licked the hand of the operator; this man, unless he had a heart of stone, must have felt remorse to the last hour of his life.

    "The Descent of Man". Book by Charles Darwin, volume I, chapter II: "Comparison of the Mental Powers of Man and the Lower Animals", p. 40, 1871.