Researchers pushing their own bodies for science

In 1929, Werner Forssmann was a surgical trainee who wanted to learn about the heart. Unlike other wimpy doctors at the time, instead of learning about it from books or dead animals, he went for the more classic investigatory approach of "poke it with something."
Without any supervision, advice, or regard for that concept you call "survival," he cut a hole in his arm and pushed a catheter all the way up the limb and jammed it into his still-living heart.