The Citadel (1938)

Andrew Manson (Robert Donat), a young, enthusiastic doctor takes his first job in a Welsh mining town, and begins to wonder at the persistent cough many of the miners have. When his attempts to prove its cause are thwarted, he moves to London. His new practice does badly. But when a friend shows him how to make a lucrative practice from rich hypochondriacs, it will take a great shock to show him what the truth of being a doctor really is.