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Francesco Redi conducted an experiment with meat in jars, some of which were sealed and some of which were left open. He observed that maggots only appeared in the open jars, suggesting that they arose from eggs laid by flies. -
John Needham conducted an experiment with boiled beef broth, which he then sealed and observed the appearance of microorganisms. Needham believed that the microorganisms arose spontaneously from the non-living matter. -
Lazzaro Spallanzani repeated Needham's experiment but boiled the broth for a longer period of time and sealed the flask with an airtight seal. Spallanzani observed that no microorganisms appeared in the broth, even after several months of observation, while Needham's experiment had allowed for the entry of microorganisms from the air. -
Louis Pasteur conducted a series of experiments using swan-necked flasks that allowed air to enter but prevented the entry of microorganisms. Pasteur observed that the broth in the flasks remained sterile, even after long periods of time, demonstrating that microorganisms do not arise spontaneously from non-living matter but rather come from pre-existing life.