Pasteur Proves Germ Theory of Disease

French chemist Louis Pasteur (1822–1895) published definitive proof of germ theory in 1861, using his swan-neck flask experiments to disprove spontaneous generation and demonstrate that microorganisms cause fermentation and disease. Building on earlier work by Agostino Bassi and John Snow, Pasteur established that specific microbes cause specific diseases — the foundational principle of modern infectious disease medicine. His work directly inspired Lister's antiseptic surgery and laid the basis for Pasteur's own later development of vaccines for chicken cholera, anthrax, and rabies.