The concept of spontaneous generation was disapproved by Louis Pasteur. He did this by boiling liquid with proteins and other nutrients in S-neck flasks and usual flask to eliminate all the microbes present. In the usual flask the liquid showed modifications when coming in contact with air, and in S-neck flask, there was no change, as microbes were not able to get within the S-neck flask.
When the S-neck was removed, a change in the liquid was observed as microbes were able to penetrate the liquid. Pasteur demonstrated that it was not the air itself, however, the particles present within it that exhibited microorganisms.