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The Infuence of Louis Pasteur

Louis Pasteur was one of the greatest scientists of the nineteenth century. Not only did his discoveries change some fundamental theories of science, but they also provided practical applications for society. It’s hard to imagine how science, medicine, the French economy, and many industries would have developed without him.

Pasteur, like many of history’s geniuses, was not a star student. He preferred fishing and art to class, and had the talent to become a great artist. His father, however; disapproved, so Pasteur studied science, with the hopes of becoming a professor at the local college. The headmaster of his college recognized Pasteur’s potential, and convinced his father to send him to Ecole Normale Supérieure, one of France’s best universities, that specialized in training students to be researchers.

After graduating with his bachelors degree, Pasteur began tutoring young students, and researching crystallographic, chemical, and optical properties of tartaric and racemic acid, in order to prepare for Ecole Normale Supérieure. Racemic acid was a newly discovered acid, formed during industrial processes, which experts of the time had found to have an identical chemical composition and structure to tartaric acid, which is formed in grape fermentation. Although it was believed that these acids were the same, because of the matching chemical composition, Pasteur refused to believe this due to their very different properties.

One of the properties that attracted Pasteur’s attention was that tartaric acid rotated polarized light, while racemic acid did not. He examined the crystals of the salts of both acids under his microscope. In doing so, it was found that the salt of racemic acid was made up of two types of crystals, that were mirror images of each other. Today this is referred to as right or left gloved. Pasteur performed an experiment in which he used a dissecting needle to separate the crystal shapes from each other. He then placed them in solution, and found that while one rotated polarized light to the left, the other rotated it to the right. It was also found that one crystal could be used as nutrition by micro-organisms. This proved that organic molecules with the same chemical composition could exist in different sterospecific forms, which would give them different properties. Thus began the science of stereochemistry.

Pasteur went even further with his analysis of the results, constructing the theory of molecular asymmetry. He believed that asymmetric molecules indicated living processes. Today we know this to be somewhat true, in that our bodies will burn only right gloved sugar, and is also selective in the form of animal proteins and amino acids used. This, however, was not recognized at the time, only the fact that the acids were different due to stereochemistry was accepted, and considered a significant breakthrough.

In 1845 Louis Pasteur became a master of science at Ecole Normale Supérieure. Three years later, after receiving his doctorate of philosophy he went to the University of Strasbourg to be a professor of Chemistry. Here he met and married the daughter of the universities rector, Marie Laurent. Pasteur was later invited to be the dean of science at the University of Lille. Here he reformed the school system, combining the teaching of theory and practice, something that is common today in many European school systems. In order to do this he commonly conducted tours of the large local factories for the students, and set up supervised practical courses. Pasteur also scheduled night classes, so that education could also be available to the young workmen of the city.

While serving as dean of science at the University of Lille, the father of one of his chemistry students asked Pasteur for help in solving some problems in the process of manufacturing alcohol through fermentation of beetroot. The brewers of wine, beer, and vinegar were facing very hard times, and up to this point the science community had offered them little help. Common problems included the sudden falling off of alcohol yields, the formation of lactic acid in the place of vinegar, unexpected changes in the quality and taste of beer, and the sudden souring and turning to vinegar of wine. The understanding of the fermentation process had come a long way form original alchemist beliefs, but there was still not enough knowledge to explain these occurrences.

When Pasteur began his research on fermentation, it was believed that sugar was the starting product, and could broken down into alcohol, carbon dioxide, and water. The process was thought to be driven by the presence of inherent unstabilizing vibrations. The vibrations could be transferred from a vat of finished wine to a new grape pressing in order to begin fermentation. Some believed yeast to be a product of the process, but were criticized for stepping backwards in scientific thought.

To begin his search for the answer to the brewing industry’s problem, Pasteur took his microscope to the factory. Through observation, it was found that when alcohol was produced, the yeast cells were plump, and budding, and that when lactic acid was produced rod like microbes were present along with the yeast. A chemical analysis of batches of the alcohol showed that amyl alcohol, and other complicated organic substances were formed, disagreeing with the prior belief that sugar was broken down in this process. Only some of the compounds rotated light. Due to his prior findings when investigating the differences between tartaric and racemic acid, Pasteur hypothesized and proved, that that living cells, the yeast, were the cause of alcohol formation form sugar, and it was the contamination of other microbes that caused the fermentation to sour. Through more observation, the micro-organisms responsible for either outcome in fermentation were identified. It was also found that heat would kill these living micro-organisms, preventing contamination and undesired outcomes through sterilization. A pure culture of desired micro-organisms could then be added to the sterile mash, allowing for a predictable fermentation.

Pasteur’s work in the area did not only provide a much needed solution for the brewing industry, but also offered the first explanation of fermentation based on experimentation. It also allowed for expanded shipment of beer and wine, because the process prevented deterioration. The process of sterilization by heat, is still commonly used today, known as pasteurization.

While working on the problem of fermentation, Louis Pasteur had been invited to the post of Director of Scientific Studies at Ecole Normale Supérieure. He accepted, and held the post while continuing his research. In the year 1867, however, he decided to give up the position in order to devote more time to research. Napoleon III decided to support him, and constructed a laboratory for him at the institution.

Following from his work on fermentation, Pasteur began research on spontaneous generation, a topic that divided many scientists of the time. He wondered if the microbes he discovered were always present in the atmosphere, or if they spontaneously generated. Through a simple experiment it was proven that spontaneous generation did not occur.

Previously Spallanzani had performed an experiment involving boiling broth, and sealing one container, and leaving another unsealed for a control. The sealed container did not develop micro-organisms, while the unsealed did. Critics claimed this proved nothing, as air was the “life force,” and necessary to produce new life. Pasteur set up a similar experiment, expect instead of sealing the broth form the air, he used a flask with a swan neck. The swan neck allowed air to have contact with the broth, but trapped all dust particles, preventing them from reaching the broth. The broth showed no evidence of micro-organisms, until Pasteur broke the swan neck, allowing dust particles to reach the broth. The results of this experiment supported the hypothesis that all living things come from other living things. This changed the way scientists viewed living organisms, and helped lay foundation for the development of the germ theory of disease.

The connecting step between the two was Pasteur’s work with silk worms. The department of Agriculture came to him, asking that he head a commission to discover a solution for the silk worm disease, that threatened to bring an end to the silk industry. This would have been disastrous, as the silk industry made up a major portion of the French economy. Pasteur moved to southern France, the center of silkworm breeding, and observed the worms. He found two diseases, and separated the worms into three groups, isolating the diseased worms from the healthy. In further experiments, it was found that the healthy worms became sick when nesting on leaves used by infected worms. It was also found that susceptibility varied on a variety of factors, including temperature, humidity, ventilation, sanitation, and food quality. Pasteur instructed silkworm farmers in methods of identification and separation, and moved on to work with the germ theory of disease.

In the past it had been believed that diseases were caused by curses, evil spirits, or night vapors. The germ theory of disease offered a new explanation, stating that germs were harmful microbes that existed in the environment and caused disease upon entry into an organism. The medical community recognized that diseases were accompanied by recognizable microbes, but for the most part would not agree that the microbes where the cause. Dr. Joseph Lister, a friend of Pasteur, began to systematically sterilize his medical equipment and use phenol solutions in operations, greatly reducing the occurrence of infection following surgery. This, however, was still a rare practice, sanity was not given much importance, nor was isolation. When many people in a hospital died of the same infection, it was common practice to close the ward, and send the living patients to other hospitals. The infection often followed these patients, and killed many more. Pasteur saw these problems in the medical community, and gave lectures emphasizing the importance in the avoidance of microbes in the avoidance of infection. In these lectures he spoke of both the importance of using only clean instruments, thoroughly washing hands between treating different patients, heating bandages to insure cleanliness. In 1873 Pasteur was elected a member of the Academy of Medicine, and many of these practices became common.

Pasteur took his knowledge of germ theory, and applied it to agriculture, developing vaccines for chicken cholera and anthrax. These vaccines were developed through weakening the microbe with heat, or a long period of time. A public test of the anthrax vaccine brought huge publicity to its development. The test showed the vaccine to work perfectly, as all of the test animals lived, and all of the control animals died. Many animals were vaccinated, saving the French economy large amounts of money. Supported by this success, Pasteur went on to identify and isolate microbes for a multitude of other diseases. One of his largest successes was his discovery of a rabies vaccine. Although few people actually died of this, it was a disease that had always been looked upon with fear and horror by the public. After much testing, it was found that the virus was present in the nervous system. A weakened form of the virus was obtained from dried nervous system tissue of an infected animal and used for inoculation. In 1885 this vaccine was first tested on a boy bit by a rapid dog, and was found to be successful. Three years later the Pasteur institute was established in Paris, so that research concerning the prevention and treatment of rabies might continue. Pasteur headed the institute, until he died in the September of 1895.

Pasteur devoted his life to science, transforming industry, medicine, and agriculture. He revolutionized the scientific method, by stepping outside of his laboratory, and observing micro-organisms in their national environment. Not only did he identify the causes of disease, or disorder, but he also found practical remedies. Pasteur’s combination of scientific theory and practice was behind his many successes, and caused him to be the most influential scientist of the nineteenth century.

Sources Used

Cohn, David V. “The Life and Times of Louis Pasteur.” Feb. 11, 1996.

Klein, Emily.

Miller, Kenneth R. And Joseph Levine. Prentice Hall Biology. Pearson Education Inc. Upper Saddle River, New Jersey. 2002.

Goetz, Philip ed. The New Encyclopedia Britannica. Macropedia, volume 25. 15th edition. Chicago. 1990.