The Doctor's Secret (1934)

Bill Blake, a jovial con man is known to friends and his son as a travelling salesman, but in reality, operates a phony medicine show, complete with singing, a monkey, and audience shills. His son Ronnie has studied to become a doctor and internes at a nearby hospital. The boy's love interest is a nurse there, but his rival is anxious to expose his father as a market quack to ruin him.