The Return of Doctor X

The Return of Doctor X also billed as The Return of Dr. X is a 1939 American science fictionhorror film directed by Vincent Sherman and starring Wayne Morris, Rosemary Lane, and Humphrey Bogart as the title character. It was based on the short story The Doctors Secret by William J. Makin. Despite supposedly being a sequel to Doctor X 1933, also produced by Warner Bros., the films are unrelated.

A pair of bizarre murders occur wherein the victims are drained of their rare blood type. Reporter Walter Garrett Wayne Morris consults with his friend Dr. Mike Rhodes Dennis Morgan which leads them to Rhodes former mentor, hematologist Dr. Francis Flegg John Litel. Flegg is initially unhelpful but when Garrett and Rhodes notice a striking resemblance between Fleggs strange assistant, Marshall Quesne Humphrey Bogart and the late Dr. Maurice Xavier, they confront Flegg. Flegg admits that he used scientific methods to bring Xavier back from the grave and employed a synthetic blood formula to sustain his life. However, the formula is unstable, and therefore, QuesneXavier must seek out human victims with a rare blood type featured in the formula in order stay alive.

Source: Wikipedia