HARKER: But professor, vampires only exist in ghost stories.... and he brought some of it with him. Get it?
HELSING: The vampire, Mr. Harker, is a thing that lives after its death by drinking the blood of the living. It must have blood or it dies. Its power lasts only from sunset to sunrise. During the hours of the day, it must rest in the earth in which it was buried.
- From the screenplay for Dracula, 1931