Dr. Cyclops

Dr. Cyclops is a 1940 Technicolor American science fiction horror film directed by Ernest B. Schoedsack, starring Thomas Coley, Victor Kilian, Janice Logan, Charles Halton, Frank Yaconelli, and Albert Dekker, and released by Paramount Pictures. It was nominated for an Academy Award for Best Visual Effects Farciot Edouart, Gordon Jennings at the 13th Academy Awards.

Insulted that they have traveled thousands of miles for nothing, they set up camp in Thorkels stockade, insisting that he tell them more about his research. While snooping around, Steve discovers the area is rich with pitchblende, an ore of uranium and radium. When he finds them looking around his laboratory, Thorkel becomes angry, but as he is outnumbered, reveals he is shrinking living creatures, among them a horse, using radiation piped from a radium deposit down a deep shaft. He invites them and his assistant Pedro Frank Yaconelli to examine his apparatus, then locks them inside his radiation chamber. With the information that Bill has provided, he is able to correct the flaw that has killed his prior specimens. When his victims awaken, they find they have shrunk to twelve inches tall.They flee from Thorkel, and then from Thorkels cat Satanus, from whom they are saved by Pedros dog Tipo, who is bewildered by his master now being smaller than him. Bullfinch is eventually coaxed into speaking with Thorkel, but the latter is not interested in negotiating, merely in measuring Bullfinch. When he discovers that Bullfinch is growing, he realizes that the effect is only temporary. He murders Bullfinch in cold blood and sets out to hunt the others down so that they cannot go to the authorities. ........

Source: Wikipedia