Roundworm Puzzle

To solve a century-old puzzle of how roundworm infection transmitted from one host to another, 19th-century Italian doctor Giovanni Grassi self-ingested the roundworm eggs. He obtained the eggs from a human corpse, which was heavily infected with roundworms. After a month, he experienced stomach discomfort and found fresh eggs in his feces. He thus proved that the roundworm transmitted through the fecal matter of humans and was also the first person to demonstrate the direct life cycle of the roundworm.