Captive Wild Woman (1943)

Dr. Sigmund Walters, an expert in glandular research, becomes convinced that his experiments involving lower animal species cannot succeed, so he arranges to have a very intelligent female gorilla kidnapped from the circus and brought to his lab. Using the glands of a patient and the brain of his faithful nurse, he performs transplant surgery on the intelligent simian. When the ape morphs into exotic and sexy Paula Dupree, the experiment seems to be s success. She even finds a place for herself at her old circus assisting lion tamer Fred Mason. Unfortunately when aroused by desire and jealousy over the affections of Mason, her delicate metabolism breaks down, and she regresses to her ape form.