Germ theory of disease
He also put some meat in a jar and covered it with gauze. Maggots were found on the gauze but not inside the jar. But when he placed meat in an open jar, maggots were found on the meat and inside the jar. Experiments like this proved that maggots come from flies who lay eggs, not from rotting meat. Later scientists would prove that diseases did not come from the air. Diseases are spread by infection.