"You have done something which is against Nature And Nature punishes."
In An Exchange of Souls (1911), a novel which greatly influenced Lovecraft's "The Thing on the Doorstep", Doctor Myas is obsessed with proving his theory that the soul and the body are separate entities. When Myas is found dead in his laboratory, his friend Compton begins to suspect that he may have succeeded - but at a terrible price...
The Octave of Claudius (1897) was the basis for the "lost" silent horror movie A Blind Bargain (1922), starring Boris Karloff. It involves another scientist, Dr Lamb, whose obsession is the acceleration of human evolution. Convinced that he can only achieve his aim by means of human vivisection, Lamb believes he has found a willing subject in the unfortunate Claudius, whom he has rescued from destitution. He promises Claudius eight days in which to fulfil his wildest desires, after which the young man must present himself for experimentation. Claudius readily agrees - but will a burgeoning love affair with a young woman change his mind?
These two novels by a master of the weird tale are linked by late-Victorian fears about the dangers of scientific enquiry beyond the bounds of conventional morality.