…He put the glass to his lips and drank at one gulp.  A cry followed; he reeled, staggered, clutched at the table and held on, staring with injected eyes, gasping with open mouth; and as I looked there came, I thought, a change – he seemed to swell – his face became suddenly black and the features seemed to melt and alter – and the next moment, I had sprung to my feet and leaped back against the wall, my arm raised to shield me from that prodigy, my mind submerged in terror.

“O God!” I screamed, and “O God!” again and again; for there before my eyes – pale and shaken, and half fainting, and groping before him with his hands, like a man restored from death – there stood Henry Jekyll!

What he told me in the next hour, I cannot bring my mind to set on paper. I saw what I saw, I heard what I heard, and my soul sickened at it; and yet now when that sight has faded from my eyes, I ask myself if I believe it, and I cannot answer. My life is shaken to its roots; sleep has left me; the deadliest terror sits by me at all hours of the day and night; and I feel that my days are numbered, and that I must die; and yet I shall die incredulous. As for the moral turpitude that man unveiled to me, even with tears of penitence, I cannot, even in memory, dwell on it without a start of horror. I will say but one thing, Utterson, and that (if you can bring your mind to credit it) will be more than enough. The creature who crept into my house that night was, on Jekyll’s own confession, known by the name of Hyde and hunted for in every corner of the land as the murderer of Carew…

Robert Louis Stevenson
The Strange Case of Dr. Jekyll and Mr. Hyde, 1886