The Strange Case of Dr. Jekyll and Mr. Hyde

"The most racking pangs succeeded: a grinding in the bones, deadly nausea, and a horror of the spirit that cannot be exceeded at the hour of birth or death. Then these agonies began swiftly to subside, and I came to myself as if out of a great sickness. There was something strange in my sensations, something indescribably new and, from its very novelty, incredibly sweet. I felt younger, lighter, happier in body; within I was conscious of a heady recklessness, a current of disordered sensual images running like a millrace in my fancy, a solution of the bonds of obligation, an unknown but not an innocent freedom of the soul. I knew myself, at the first breath of this new life, to be more wicked, tenfold more wicked, sold a slave to my original evil; and the thought, in that moment, braced and delighted me like wine. I stretched out my hands, exulting in the freshness of these sensations; and in the act, I was suddenly aware that I had lost in stature. . . ."
The novella's impact is such that it has become a part of the English language, with the very phrase "Jekyll and Hyde" coming to mean a person who is vastly different in moral character from one situation to the next.