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This week’s honor goes to Louis Pasteur, the French biologist and chemist best known for his invention of pasteurization. Pasteur is a towering figure in the history of science for his groundbreaking discoveries, and his contributions have helped save or improve countless lives beyond his generation.

Here is a list of his major scientific contributions and the back stories behind them.

1. He discovered the existence of molecular asymmetry.

For a number of years, scientists had been puzzled about organic chemicals such as tartaric acid. A large number of natural organic substances had been found to rotate the plane of polarized light to the left or right, while the apparently identical substances made in the laboratory did not. Pasteur, who had made a study of polarized light for his physics thesis, discovered that molecules could exist in mirror-image forms; and his study demonstrated molecular chirality and even provided the first explanation of optical isomerism. Pasteur thus laid the foundation for stereochemistry and paved the way for crucial breakthroughs in chemistry, biochemistry, and pharmaceuticals.

2. He disproved “spontaneous generation”.

During Pasteur's time, people believed that microbes such as bacteria appeared due to "spontaneous generation,” meaning they thought the microbes randomly appeared out of nowhere. Pasteur did not believe this, so he conducted some experiments to show that no microbes ever grew in sterilized nutrient solutions, provided the air above the solutions was also sterilized. Pasteur thus disproved the “spontaneous generation” explanation, and was awarded the Alhumbert Prize in 1862 for his effort.

3. He invented pasteurization.

In 1854, Pasteur was appointed professor of chemistry and dean of the science faculty at the University of Lille. While working at Lille, he was asked to help solve problems related to alcohol production at a local distillery, and thus he began a series of studies on alcoholic fermentation. He further developed the germ theory to show that all fermentative processes were caused by living organisms, and found that fermentation could produce lactic acid, which makes wine sour. He then extended his research to include other liquids such as beer and milk, and finally came up with a simple solution to prevent the unwanted souring of these beverages, that is to heat the liquids up to 50–60 °C. This process came to be known as pasteurization.

4. He rediscovered anaerobiosis.

In 1857, aged 34, Pasteur returned to the École Normale in Paris as Director of Scientific Studies. Unfortunately, he was unable to acquire funding for his research and did not even get his own laboratory space. Undeterred, Pasteur personally paid for the conversion of part of the École Normale’s attic space to a laboratory and funded his own research work there. Shortly after, he rediscovered anaerobiosis and became the second person to discover anaerobiosis around 200 years after the Dutch scientist Antonie van Leeuwenhoek.

5. He helped save the French silk industry.

Around 1963, the French silkworm industry was being destroyed by an unknown, unstoppable disease. Despite knowing nothing about silkworms, Pasteur was repeatedly requested to investigate the problem and he finally accepted the task in 1965. He launched himself into the problem with enormous energy, working until his health broke from exhaustion. His wife, Marie, also launched herself into the work, growing the silkworms he needed for experiments and writing notes. Finally, after several years of research, Pasteur was able to save the silkworm industry through a method of prevention of contamination of healthy silkworm eggs. The method was soon employed by silk producers all over the world and is still used in silk producing countries today.

6. He created vaccines for rabies and anthrax.

Pasteur's first vaccine discovery was in 1879, with a disease called chicken cholera. After accidentally exposing chickens to the attenuated form of a culture, he demonstrated that they became resistant to the actual virus. Pasteur went on to extend his germ theory to develop causes and vaccinations for diseases such as anthrax, cholera, TB and smallpox. In 1885, Pasteur successfully administered the vaccine to a human being for the first time, to a young boy who was bitten by a rabid dog.



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