Original: In 1861, Louis Pasteur performed a series of experiments which demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media.
Simplified: Yet it was not until 1861 that Louis Pasteur performed a series of careful experiments. With these experiments, Pasteur proved that organisms such as bacteria and fungi do not appear in nutrient-rich media of their own accord in non-living material.