Ascaris lumbricoides
The first crucial step in understanding the life cycle of the roundworm "Ascaris lumbricoides" was demonstrated by Grassi in a grotesque self-experimentation. To solve a century-old puzzle of how infection of roundworm is transmitted from one host to another, he ingested the roundworm eggs on 30 August 1879. He had obtained the eggs from a human corpse, which was heavily infected, upon autopsy on 10 October 1878. After twenty-two days, he found fresh eggs in his faeces. Thus proving that the roundworm is transmitted through direct ingestion from contaminated source.