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Redi's Experiment
There were some biologists who thought that there were some forms of life that are more simple, and they generated by spontaneous generation. This theory was rejected for some animals that had more complex forms, but there was doubt about animals such as insects, because their reproductive cycle was unknown. -
Redi's Experiment
In Redi's experiment, there were 6 flasks of fresh meat. Two of the bottles were not covered, this caused the meat to attract flies and some time later the maggots appeared. Then there were two other flasks that were hermetically covered so that flies could not enter, so that maggots were not produced. And finally, there were two other flasks covered with porous gauze. The smell of the meat attracted the flies, which stay on the gauze and that's where the maggots were generated. -
Conclusion of Redi's Experiment
So Redi arrived at the conclusion that flies are necessary to produce more flies, because his experiment showed that they do not generate spontaneously from the meat. -
Criticism from Spallanzani
Lazaro Spallanzeni did not agree with Needham's conclusions, so he wanted to make experiments using hot broth. He filled 4 flasks with broth. One flask was open, and it became turbid and microbes were found. The second flask was closed and they found again that it was turbid and that there are microbes. In the third flask, which was opened and boiled, the same thing happened again. And finally, in the fourth flask, which was closed and boiled, no microbes were found and the broth was not turbid. -
Spallanzani's Conclusion
Spallanzani came to the conclusion that microbes are not formed from nowhere, because if not all the flasks would have microbes. -
Needham's rebuttal
John Needham made an experiment where he boiled broth with vegetable or animal matter. He wanted to kill all the microbes, so he sealed the flasks, and after a few days he observed that the broth had become turbid and that in a single drop there were many microscopic creatures.
Needham said that new microbes must come about spontaneously. But probably what he did wrong was not to boil the broth sufficiently to kill all the microbes. -
Louis Pasteur's Experiment
Louis Pasteur prepared a broth and picked up two long necked flasks. One of the flasks was left with a straight neck, and the other flask was folded to make an "S" shape. He boiled the broth in the flasks to kill any living matter that may be in the liquid. He then allowed the broths to stand at ambient temperature and exposed to the air.
Weeks later, Pasteur saw that the straight necked flask was turbid and discolored, and in contrast, the "S" shaped flask was unchanged. -
Louis Pasteur's Conclusion
He arrives to the conclusion that in the straight-necked flask the germs could fall down and arrive to the broth. But on the other hand, in the S-shaped flask the germs did not arrive to the broth and that is why their color never changed. This means that the germs can only come from other germs.