Louis Pasteur: Greatest Achievements
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Louis Pasteur: Greatest Achievements
Louis Pasteur was one of the most important scientists of our time. The foundation of our knowledge about health and disease comes from the discoveries of this one man. He made many discoveries and solutions for problems of the every day life that are still in effect today.
Pasteur was born on December 27, 1822 in a little town called DÑ„le in the foothills of the Jura Mountains of eastern France. When he was five years old his family moved to Arbois where he grew up with his father, mother, and three sisters. While attending primary school Pasteur was only an average student. Some considered him to be slow because he worked so hard on an exercise problem to make sure that he had the right answer. While in high school Monsieur Romanet, Pasteurs principal, became interested in Pasteur and began to help him with his studies. With this encouragement Pasteur became a very good student. The principal suggested that he aim to attend Ecole Normale in Paris where he could become a professor at one of the great universities, however his father felt that this was far-fetched and preferred that Pasteur attend a more local school (Burton, 5-7).
Although his father had other plans for him, Pasteur had the opportunity to attend a preparatory school in Paris before going on to Ecole Normale, however when he got to Paris he became very homesick and his father soon arrived to take him home. After returning to Arbois Pasteur attended a local school named Besancon where he worked very hard and became one of the top students in his class. In 1842 Pasteur passed the admission tests to attend Ecole Normale however he was rated fifteenth of twenty-two candidates and this was not good enough to satisfy him. He continued to study and finally in 1843 Pasteur sailed through his admission tests and was awarded fourth place among the other candidates (Burton, 7-11).
Although Pasteur is sometimes considered to be the father of microbiology and immunology, he actually launched his career as a chemist who studied the shapes of organic crystals. Crystallography was just emerging as a branch of chemistry and his project was to crystalize a number of organic compounds. While working on this project he began to work with tartaric acid and racemic acid. Earlier these two acids had been determined to be identical, however Pasteur found that in solution they had a striking difference which was that tartaric acid rotated a beam of polarized light whereas the racemic acid did not. When looking at them under the microscope he found that the crystals of the tartaric acid were identical while the crystals of the racemic acid were of two types, almost identical but not quite. One type was mirroring the other the way the
right hand mirrors the left hand (Cohn, par. 6-8).
After discovering the different types of crystals, Pasteur then took a dissecting needle and separated the left and right crystals from each other under the microscope. He then showed that in solution one form rotated light to the left and the other to the right. This proved that organic molecules with the same chemical composition can exist in space in unique stereo specific forms. With this discovery Pasteur launched the new science of stereo chemistry. He proposed that asymmetrical molecules were indicative of living processes. Because of this we know today that proteins of higher animals are made up only of the amino acids that exist in the left-hand form. The mirror image right-hand amino acids are not used in human or animal cells. Just like our cells
only burn the right-hand form of sugar, not the left-hand that can be made in a test tube (Cohn, par. 9-10).
In 1856 Pasteur was approached with a problem by a Monsieur Bigo. Monsieur Bigo manufactured alcohol from beets and recently his beet juice had been spoiling instead of producing alcohol. Pasteur chose to look into the problem because it had something to do with the new concept of fermentation, which he had just become very curious about. To make alcohol the workers added yeast to a vat of fresh beet juice. Eventually the yeast formed a mold and then little bubbles appeared in the juice and it was said to be fermenting. If it was “healthy” then it would produce alcohol, but
sometimes it turned sour and Monsieur Bigo had to throw it away. Pasteur collected
samples of the juice and also deposits from the vats. After studying a large amount of his samples he began to notice a slight difference between the two. In the healthy fermentation there were round yeast globules and in the spoiled fermentation there were oblong yeast globules. He informed Monsieur Bigo to watch the yeast and to keep the oblong yeast globules out of the beet juice (Benz, 73-77).
This solved Monsieur Bigos problem however Pasteur was still very interested in the subject. A few scientists had said that fermentation was brought about by a living thing of some kind. Pasteur was inclined to agree because of the work that he did on crystals (Burton, 41). He went back to Monsieur Bigos factory and quickly found three clues that helped him solve the question of alcoholic fermentation. First, when alcohol was produced normally the yeast cells were plump and budding. However when lactic acid was formed small rod-like microorganisms were mixed with the yeast cells. Second, the analysis of the batches of alcohol showed that the amyl alcohol and other complex organic compounds were being formed during fermentation which proved that some additional processes must be involved. Third, some of these compounds rotated light which meant that they were asymmetric. Pasteur had already concluded that only living cells produced asymmetrical compounds. Therefore he concluded and was able to prove that living cells, the yeast, were responsible for forming the alcohol form sugar,
and that contaminating microorganisms turned the fermentations sour (Cohn, par. 18).
While Pasteur was creating controversy by his study in fermentation, there was
another debate going on in the scientific world over the concept of spontaneous generation. Pasteur became interested in the idea and although others warned him that it was unrewarding he began to conduct experiments with spontaneous generation. Based on his work in fermentation he concluded that the sources of yeasts and other microorganisms that were found during fermentation had to be brought in from the outside by a substance such as dust in the air. Pasteur went