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Wednesday, June 27, 2007

Tyndall’s Experiment


After Pasteur, John Tyndall, an English Physicist and a passionate follower of Pasteur established an important fact that was overlooked by Pasteur. He discovered the presence of “spores” of different microbes in air & in certain organic infusions. Since the spores are more resistant to heat, the organic infusions are often not sterilized after heat treatment giving rise to controversy in favor of spontaneous generation theory. He established that even after prolonged heating of 5½ hr the spores are not killed. So he mentioned that all bacteria have two phases, one thermo-labile phase (destroyed after 5mins of heating) and one thermo-stable phase. His views were supported by a German Botanist Ferdinand Cohn, who also like Tyndall worked with hey bacteria. Since hey is not a very good source of nutrient the bacteria are starved & as a result endospores are produced (spores are dormant phase of bacteria, fungi, lower plants & protozoa to survive the harsh environmental condition. They may also be called reproductive cells as favorable condition gives to the following organisms).

Friday, June 8, 2007

Swan-neck flask of Pasteur



This led to one of the most famous experiment of microbial history, the “Swan-neck flask” experiment by Pasteur. Please refer the figure for the shape of the flask. Now organic infusion inside the flask was made sterile by heating. Indeed there was no microbial growth in the organic infusion as the microbes cannot ascend the bent neck of the flask. But when the neck is broken or the sterile liquid becomes densely populated with microorganisms. Pasteur’s experiments made it clear that the living organisms are evenly distributed throughout the atmosphere. Thus "Germ Theory" was established and gained over "Spontaneous generation" theory.

Friday, June 1, 2007

One of the most important things Pasteur able to do was to demonstrate that air does contain microscopically observable “organized bodies”. What he did was to pass air through a tube plugged with guncotton (served as a filter). He then removed the guncotton & dipped in alcohol and ether mixture. The sediment thus obtained was examined under microscope. It was found that the mixture contains many small, round bodies besides organic matter. These bodies were believed to be the microorganisms everybody was talking about. He then performed two additional experiments which fully proof the fact that of the presence of microorganisms in air. First he passed heated air through preheated organic infusion to find that there is no growth. And 2nd he placed a piece of germ-laden guncotton a well heated airtight organic infusion to find that growth is appearing through these is as air supply. Thus he proved successfully the presence of microbes in air.
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