what did john Needham conclude from his test of Redi's findings
One very important point to note here is that Pasteur did not seek to find an answer to the broad question, "Has spontaneous generation occurred?" Rather, as any good scientist, he limited his scope to a very narrow piece of the picture: "Is it possible for spontaneous generation to occur given the conditions under which Needham (and others) claims it will occur," the "life force?" Interestingly, in 1936, when Alexander Ivanovich Oparin, a Russian scientist, published , in which he described hypothetical conditions which he felt would have been necessary for life to first come into existence on early Earth, some scientists found it difficult to acknowledge that under the very different conditions which Oparin was proposing for early Earth, some form of "spontaneous generation" might indeed have taken place.
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In 1861, Louis Pasteur presented evidence that would virtually put an end to the debate. He designed an experiment similar to Spallanzani's, however, Pasteur's experiment implemented a way to filter out microorganisms. Pasteur used a flask with a long, curved tube called a swan-necked flask. This flask allowed air to have access to the heated broth while trapping dust containing bacterial in the curved neck of the tube. The results of this experiment were that no microbes grew in the broth. When Pasteur tilted the flask on its side allowing the broth access to the curved neck of the tube and then set the flask upright again, the broth became contaminated and in the broth. Bacteria also appeared in the broth if the flask was broken near the neck allowing the broth to be exposed to non-filtered air. This experiment demonstrated that bacteria appearing in broth are not the result of spontaneous generation. The majority of the scientific community considered this conclusive evidence against spontaneous generation and proof that living organisms only arise from living organisms.
In 1765, Italian biologist and priest Lazzaro Spallanzani, set out to demonstrate that microbes do not spontaneously generate. He contended that microbes are capable of moving through the air. Spallanzani believed that microbes appeared in Needham's experiment because the broth had been exposed to air after boiling but before the flask had been sealed. Spallanzani devised an experiment where he placed the broth in a flask, sealed the flask, and removed the air from the flask before boiling. The results of his experiment showed that no microbes appeared in the broth as long as it remained in its sealed condition. While it appeared that the results of this experiment had dealt a devastating blow to the idea of spontaneous generation in microbes, Needham argued that it was the removal of air from the flask that made spontaneous generation impossible.
What was John Needham's hypothesis based on …
A few years later (1765 - 1767), Lazzaro Spallanzani, an Italian abbot and biologist, tried several variations on Needham's soup experiments. First, he boiled soup for one hour, then sealed the glass flasks that contained it by melting the mouths of the flasks shut. Soup in those flasks stayed sterile. He then boiled another batch of soup for only a few minutes before sealing the flasks, and found that microorganisms grew in that soup. In a third batch, soup was boiled for an hour, but the flasks were sealed with real-cork corks (which, thus, were loose-fitting enough to let some air in), and microorganisms grew in that soup. Spallanzani concluded that while one hour of boiling would sterilize the soup, only a few minutes of boiling was not enough to kill any bacteria initially present, and the microorganisms in the flasks of spoiled soup had entered from the air.
Needham maintained that while spontaneous generation did not ..
In 1745 - 1748, John Needham, a Scottish clergyman and naturalist showed that microorganisms flourished in various soups that had been exposed to the air. He claimed that there was a "life force" present in the molecules of all inorganic matter, including air and the oxygen in it, that could cause spontaneous generation to occur, thus accounting for the presence of bacteria in his soups. He even briefly boiled some of his soup and poured it into "clean" flasks with cork lids, and microorganisms grew there.
John Needham 1668: According to ..
He thought he disproved spontaneous generation, but his critics argued that all living things need air and that was the reason why no maggots formed in the sealed jar.
John Needham Meath Broth is boiled for ..
An Italian priest, Lazzaro Spallanzani, was not convinced, and hesuggested that perhaps the microorganisms had entered the broth fromthe air after the broth was boiled, but before it was sealed. To testhis theory, he modified Needham's experiment - he placed the chickenbroth in a flask, sealed the flask, drew off the air to create apartial vacuum, then boiled the broth. No microorganisms grew. Proponents ofspontaneous generation argued that Spallanzani had only proven thatspontaneous generation could not occur without air.