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362 BCE
Aristotle proposed the spontaneous generation
The Greek philosopher Aristotle was one of the earliest recorded scholars to articulate the theory of spontaneous generation, the notion that life can arise from non-living matter. Aristotle proposed that life arose from non-living material if the material contained pneuma (“vital heat”). -
Redi's experiment
In this experiment, Redi put meat in three jars; he sealed one jar, left another open, and covered the third with gauze. He observed that maggots developed in the meat of the open jar and on the gauze of the corresponding jar, while no maggots developed in the meat of the sealed jar. In this experiment, Francesco Redi proved that insects are not born by spontaneous generation. -
Needham’s experiment
In 1745, John Needham conducted an experiment: he boiled meat broth to destroy pre-existing organisms and placed it in a container that was not properly sealed, because according to his theory, air was needed for this to take place.
Needham concluded that the microorganisms must have developed from the broths. Needham's findings supported the hypothesis of spontaneous generation of microorganisms. -
Spallanzani's experiment
Spallanzani doubted the results of the latest experiments supporting spontaneous generation that had been carried out in 1748 by John Needham. Regarding Needham's experiment, Spallanzani thought that the boiling had been insufficient and that the broth had not been properly sterilised. In addition, he suspected that the cork did not seal the flask hermetically. Spallanzani observed that there were no microorganisms in the sealed flasks and thus proved that spontaneous generation did not occur. -
Pasteur's experiments, conclusion and eliminated of theory of spontaneous generation
Pasteur used vessels with long, curved necks, into which he placed a broth that he had boiled for a few minutes. When removed from the heat, air entered through the neck, but the microbes were trapped in it, preventing them from contaminating the liquid and allowing it to be kept sterile indefinitely.
After a while, he observed that nothing grew in the broths, proving that the living organisms that appeared in the flasks without filters or long necks came from outside.