[crich70]

Originally Posted by John A. A. Logan

The Heart of a Dog, by Mikhail Bulgakov, might qualify (or might not, as the dog is involved in a strange experiment!) (published 1925) -

"A rich, successful Moscow professor befriends a stray dog and attempts a scientific first by transplanting into it the testicles and pituitary gland of a recently deceased man. A distinctly worryingly human animal is now on the loose, and the professor's hitherto respectable life becomes a nightmare beyond endurance. An absurd and superbly comic story, this classic novel can also be read as a fierce parable of the Russian Revolution."

Spoiler:

Sounds like the author based part of the idea on some experiments that people did in the late 19th and early 20th centuries. Some used parts of monkey glands on humans thinking that the substances produced by the glands would help retard the aging process. It's also part of the rational of A.C. Doyle's story "The Creeping Man."