I've always been impressed by what Barry Marshall did.
For years it was common knowledge that ulcers were caused by stress, spicy food, and excess acid. A "bland diet" was the prescribed palliative care for ulcers. There was no cure. And ulcers could - and often did - lead to stomach cancer.
Dr. Marshall thought that that the bacterium H. pylori might be the cause. But the idea that bacteria could thrive in the acidic environment of the stomach was thought to be ridiculous.
So he tested the theory by drinking a solution of H. pylori and giving himself ulcers.
He had a biopsy taken on himself to prove it was the bacteria, and then cured himself with a course of antibiotics - the same way ulcers are cured today.
Ulcers are not a chronic disease any more, and stomach cancer has become rare.
http://discovermagazine.com/2010/mar/07-dr-drank-broth-gave-...