Pasteur's work shows us that theories

The disproving of the notion of spontaneous generation. Pryor to this, there was the assumption that some life could spontaneously arise from nothing - such as the idea that maggots could appear from nowhere in a piece of rotten meat. In his experiment, Pasteur showed that while a piece of rotten meat attracted maggots, a piece of meat covered with a mesh just small enough to prevent flies from landing did not - indicating that flies had to deposit eggs for maggots to form. Also he developed the sterilization technique of pasteurization and invented a rabies vaccine.