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Redi's Experiment
Francesco Redi, first attacked the idea of spontaneous generation. Back then, maggots were believed to emerge spontaneously from rotting meat. To prove that spontaneous generation was wrong, he set up a controlled experiment like the one pictured. -
Needham's Rebuttal
In 1745, John Needham claimed that it was possible for spontaneous generation to occur and conducted an experiment to prove it.
Needham heated broth in a flask to its boiling point, to kill the microorganisms. Shortly after the broth cooled, he closed the flask. After a while, he observed living microorganisms in the broth, thus concluding that spontaneous generation was real and contradicting Redi's conclusions. -
Criticism from Spallanzani
Lazzaro Spallanzani, did not agree with Needham and conducted another heated broth experiment to prove the opposite.
Spallanzani filled a flask with broth and sealed it. Then, he boiled it to kill any microorganisms present.
After a while, the broth had no trace of life. When he opened the flask again, microorganisms grew again in the broth.
Spallanzani concluded that spontaneous generation was false and that microbes came from polluted air. -
Pasteur puts Spontaneous Generation to Rest
Louis Pasteur, recreated the experiment and left the system open to air. Later, he designed several vessels with curved necks pointing downwards. He filled one with broth, boiled it, and saw no life in the jar for a year. Then, he exposed it more directly to air and trapped particles, and observed life forms in the broth within days.
He reasoned the same as Spallanzani, that the pollution came from life forms in the air.