I didn't remember, if I ever knew, that Jack London had written a science fiction novel until I read the boingboing post on it.
Jack London (1876-1916) was an American author best known for his novels Call of the Wild and White Fang and his short story "To Build a Fire". The Scarlet Plague was written in 1912 and first published in London Magazine. You can listen to it here and read it online here, here or here, among other places.
The story takes place in 2073, sixty years after an uncontrollable epidemic, the Red Death, has depopulated the planet. James Howard Smith is one of the few survivors of the pre-plague era left alive in the San Francisco area, and as he realizes his time grows short, he tries to impart the value of knowledge and wisdom to his grandsons.
The picture at the top of the post is from Wikipedia.