Francesco Redi was an italian doctor and one of the first to disprove the idea of spontaneous generation.
Spontaneous generation is the idea that organisms originate directly from nonliving matter, or "life from nonlife." During his time the common belief was that abiogenesis (a-not, bio-life, genesis-origin) occurred.
Redi's problem: where do maggots come from? Redi realized that when meat was left out in the open that flies would come around and that maggots would eventually appear on the meat. He knew the flies were able to come around due to their ability to fly. Maggots however did not have this ability.
Redi hypothesized that maggots came from flies.
To test this idea Redi put meat into three separate jars. The first jar was left open so that flies could easily access the meat. The second jar was covered with sack cloth, so that the flies could not get in direct contact with the meat, but could still be around the meat. The third jar was completely sealed from the outside.
From his experiment Redi found that in the first jar, where flies were able to directly land on the meat, the maggots appeared on the meat. In the second jar, where the flies could only land on the sack cloth, the maggots began to appear on the the sack cloth. Finally, in the third jar, that was completely sealed, Redi observed that no maggots appeared on the lid of the container or on the meat.
From Redi's experiment it was concluded that spontaneous generation was not occurring. He observed that the maggots were appearing where the flies were able to land. Redi concluded that the maggots arose from eggs laid by the flies.
