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Francesco Redi
He made the first serious attack against spontaneous generation. At that time, it was widely held that maggots arose spontaneously in rotting meat.
In spite of his well-executed experiment, the belief in spontaneous generation remained strong and even Redi continued to believe it occurred under some circumstances. The invention of the microscope only served to enhance this belief. -
John Needham
An English clergyman, 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. -
Lazzaro Spallanzani (the year is approximate)
An Italian priest, Spallanzani, didn't agree with Needham’s conclusions, however, and performed hundreds of carefully executed experiments using heated broth. -
Louis Pasteur's
In a lecture , Pasteur articulated “Omne vivum ex vivo” (“Life only comes from life”). In this lecture, Pasteur recounted his famous swan-neck flask experiment stating: “life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment”. To Pasteur’s credit, it never has. -
Louis Pasteur
The french scientist, re-created the experiment and left the system open to air. 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. He then broke off the top of the bottle or tilted the flask, exposing it more directly to the air and trapped particles, and saw life forms in the broth within days. He reasoned that the contamination came from life forms in the air, not a supposed “life force”.