14. Digestive System

The 3rd link (also embed), shows a 1956 TV adaptation of this famous story of St-Martin and Beaumont. 

This is the first time in history that the stomach's inner workings was observed directly.

 Beaumont (eventually called the "Father of Gastric Physiology") was the first to demonstrate that digestion was primarily a chemical process, rather than purely mechanical.

His experiments helped establish the scientific method in medical research.

On the opposite end, his research also raised questions about the ethics of using a living person for such experiments, which remain relevant in medical research today.