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Redi's experiment
Francesco Redi, an Italian physician and poet, made the first serious attack on the idea of spontaneous generation in 1668. At that time, it was widely held that maggots arose spontaneously in rotting meat. To achieve his goal of proving spontaneous generation to be wrong, he set out a controlled experiment such as the one described in this figure: -
Spallanzani experiment
Spallanzani did not agree with Needham’s conclusions. Spallanzani poured broth into flasks and sealed them. Next, he boiled the flasks for a long time, to kill present microorganisms. After some time, the broth did not have any trace of life. However, once he unsealed the flask, microorganisms rapidly grew in the broth. Spallanzani concluded that spontaneous generation was false and microbes came from contaminated air. -
Needham’s rebuttal
In 1745, an English clergyman called John Needham claimed that spontaneous generation could occur and performed what he considered the definitive experiment. Needham briefly heated broth to its boiling point, to kill microorganisms, and poured it into flasks. Soon after the broth cooled, he sealed them.
After some time, he observed living microorganisms in the sealed broth, thus concluding that spontaneous generation was a fact and contradicting Redi’s conclusions. -
Pasteaur experiment
He subsequently designed several bottles with S-curved necks that were oriented downward. He placed a nutrient-enriched broth in one of the swan-neck bottles, boiled the broth inside the bottle, and observed no life in the jar for one year. Then broke off the top of the bottle or tilted the flask, exposing it more directly to the air and trapped particles, and noted life forms in the broth within days. He reasoned that the contamination came from life forms in the air, not a supposed life force.