There was a movie, black & white I think, that took place in the jungle. A mad scientist was working with a radiation source in a deep well . He used this to shrink about 6 of his workers. They were locked in small containers for study. The scientist found out that they were starting to grow again so he was killing them off one by one as they realized that they were growing too. They escaped and were determined to stop the scientist by trying to kill him. Eventually they killed him and only 2 or thee survived.
What was the name of this movie? I think the title contained the letter "X" in it, like Doctor X or The X factor.