The Professor's Secret (1908)

Acting on the Darwin theory, that man descended from a monkey, a scientist experiments towards turning man back to the monkey stage. He inoculates a number of persons with the preparation and after the subjects reach their homes the reversing process begins, and they become monkified. Their antics are uproariously funny. The scientist is unable to turn them back to human beings again, so they are collected in a large cage and places on exhibition. Here they are visited by an ape dressed in human attire. (Moving Picture World)