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Francesco Redi
Redi tested the idea that maggots arose spontaneously by placing meat in three jars: one open, one sealed, and one covered with gauze. Maggots only appeared in the open jar where flies could access the meat. This showed that maggots came from fly eggs, not from the meat itself. -
John Needham
Needham boiled chicken broth, sealed it, and observed microbial growth. He argued that boiling killed all life, so the reappearance of microbes supported spontaneous generation. However, his experiments were flawed due to insufficient boiling, leaving microbial spores alive. -
Lazzaro Spallanzani
Spallanzani extended Needham’s work by boiling broth for longer and sealing the flasks. No microbial growth occurred in sealed flasks, but critics argued that sealing prevented the "vital force" in the air from entering. Spallanzani concluded microbes came from the air, not spontaneously. -
Louis Pasteur
Pasteur used swan-neck flasks to allow air in but trap airborne particles. No microbial growth occurred unless the flask neck was broken, allowing particles to contaminate the broth. This experiment definitively proved that microorganisms originate from existing microbes, not spontaneous generation.