SPONTANEOUS GENERATION

Hello Steemians, welcome to my blog once again. Today, I'll be talking about how the belief of spontaneous generation was disproved.

Introduction
Right from time, people always believed in Spontaneous Generation. The believe that living organisms could possibly develop from non-living thing/matter. In one of the instances, it was hypothesized that certain living things such as fleas could arise from dust. The belief that living things could evolve from nonliving matter was integrated by the ancient Greek philosopher Aristotle after he studied various compilation and works of earlier philosophers and this doctrine was taken as a scientific fact for close to two millennia. It was not until the mid-19th century that the theory of spontaneous generation was disproved.

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Experiments That Challenged And Disproved Spontaneous Generation

This theory was firstly disapproved by an Italian physician, Francesco Redi When he carried out several experiments on broth and decayed meat to show its ability to bring out maggots spontaneously. He placed the meat in three(3) containers. The first was left uncovered, the second was covered with paper and the last was covered with a fine gauze that would keep out flies. The following outcomes were discovered, files laid eggs on the first one and maggots were formed. The remaining two containers did not produce maggots spontaneously. However, after sometimes, Flies were attracted to the second one with a fine gauze and laid their eggs on it; then maggots were produced. Thus he proved that the evolvement of maggots from decayed meat resulted due to the presence of these fly eggs thereby proving that meat did not spontaneously generate maggots as previously hypothesized.

Similar experiments by other scientists helped in disproving the theory for larger organisms.

Leeuwenhoek's assertion on microorganisms however renewed the controversy. Some made proposal that microorganisms arose by spontaneous generation even though larger organisms did not. They made it known that boiled extracts of broth or meat gave rise to microbes after sitting for a while. Inarguably, these extracts are the front runners of the culture media still in use in many microbiology laboratories.

In 1748, the English priest John Needham recounted the outcome of his experiments on spontaneous generation. He boiled mutton broth in tightly stoppered flasks. Alas, many of the flask became cloudy and microorganisms were found to be present. Needham believed organic matter contained a vital force that could confer the properties of life in on nonliving matter.

Some years later, an Italian priest and naturalist named Lazzaro Spallanzani made improvement on Needham's experimental pattern by sealing the glass flasks that contained water and seeds. The sealed flasks were placed in a boiling water for about 40 minutes. No growth took place as long as he made sure the glass flasks remained sealed. He then proposed that the air carried germs to the culture media but also pointed out that external air might also be a requirement for the growth of animals already in the medium. The followers of Spontaneous Generation maintained that heating the air in sealed glass flasks possibly destroyed its ability to sustain life.

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Several other scientists made investigation in an attempt to counter such arguments. One of them was Theodore Schwann when he allowed air to enter a flask containing a sterile nutrient solution after passing the air through a red-hot tube. The flask still remained sterile. Subsequently,other scientists like Georg Friedrich Schroeder and Theodor von Dusch followed suit. However, they allowed air to enter a flask of heat sterilized medium after passing it through sterile cotton woo. No growth was observed in the medium even though the air has not being heated. Despite all these experiments, French naturalist Felix Pouchet made claim in 1859 to have carried out experiments absolutely proving that microbial growth could also occur without air contamination. Pouchet's claim however provoked Louis Pasteur to finally settle the matter of Spontaneous Generation.

Pasteur first filtered air through cotton and found that objects resembling plant spores have been trapped. If a piece of cotton was placed in sterile medium after air had been filtered through it, microbial growth occurred. After, he placed nutrient solution in flasks, heated the necks of those flasks in a flame and carved them out in a varieties of curves. The gooseneck flasks that he produced in this way had necks open to air. He then boiled the solution for some minutes and allowed it to cool. No growth was observed even though the flask contents were exposed to the air. Pasteur showed that growth did not occur because dust and germs had been trapped on the wall of the curved necks. When the necks were broken, growth started immediately. Pasteur experiment did not only solved the controversies surrounding spontaneous generation but also showed how to keep solutions sterile.

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Spontaneous Generation was dealt a final blow by the English physicist John Tyndall and the German botanist Ferdinand Cohn. Tyndall demonstrated in 1877 that dust did in fact carry germs and that if dust is kept absent, broth remained sterile even if it is exposed to air directly. During the course of his studies, he further provided evidences for the existence of exceptionally heat-resistant forms of bacteria. Working independently, Ferdinand discovered the heat resistant bacteria observed by Tyndall were species with the ability of producing bacterial endospores. Cohn was later of immense help as he played an instrumental role in establishing a system of classification for bacteria based on their morphological and physiological features.

Conclusion

Conclusively, all these early scientists/microbiologists not only disprove the theory of spontaneous generation but also contributed to the creation of microbiology. They all developed media for culturing microorganisms and methods for sterilizing media and maintaining their sterility. All these techniques are being used nowadays in understanding the role of microorganisms in diseases.

Thanks for reading, upvotes, comments and reesteems will be gladly appreciated.

Here is a link to my previous post on RNA world

References
Spontaneous generation

Redi's Experiment and Needham's Rebuttal

Louis Pasteur and the History of Spontaneous Generation