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INVENTORS AND INVENTIONS
Louis Pasteur
PASTEURIZATION PROCESS

Throughout human history, physicians have struggled with the problem of determining what cause diseases. In the mid‐19th century, many people believed in Miasma, the concept that disease was caused by polluted air. However, the milestone work leading to understanding the causes of diseases was not made by a doctor, but by a chemist, Louis Pasteur. Pasteur destroyed the widely held myth of spontaneous generation as the cause of diseases, thus setting the direction for modern biochemistry and biology.

Louis Pasteur was born on December 27, 1822, in Dole, Jura, France, and grew up in the nearby town of Arbois. As a child, Pasteur showed an interest in chemistry, and the headmaster of the local college convinced Louis and his father that Louis should try to enter the École Normale Suprieure in Paris, a highly regarded French university specifically created to train students for university careers in science and the arts. Pasteur began his successful journey as a scientist in the École Normale.

When Pasteur was 26 years old, crystallography was a new branch of chemistry. One of his first projects while working at the École Normale was attempting the crystallization of tartaric acid, an organic acid that exists in the sediments of fermenting wine. A second acid, paratartaric acid or racemic acid, was also found in the sediment in wine barrels. At the time of the beginning of his studies, science had already determined that tartaric and paratartaric acids had identical chemical compositions; however, tartaric acid rotated a beam of polarized light passing through it to the right, and paratartaric acid did not rotate the light at all. Pasteur was determined to find out what caused this difference. Upon microscopic examination, Pasteur discovered that the paratartrate crystals comprised two types of optically asymmetric crystals, one being the mirror image of the other.

Pasteur then performed one of the more elegant procedures in the annals of chemistry experimentation. He separated the left and right paratartrate crystal shapes from each other with a dissecting needle to form two collections of crystals. When placed in solution, one form of the crystal rotated light to the left, the other to the right. This showed that organic molecules having the same chemical composition can have two different stereospecific forms. He concluded that this molecular asymmetry was one of the mechanisms of life, in that living organisms only produce molecules of one specific orientation, and these molecules are always optically active. He also found that fermenting solutions contained optically active compounds, which led him to surmise that fermentation was a biological process performed by microorganisms, or germs. This hypothesis, designated the germ theory, was used by Pasteur as a foundation for his experiments that positively demonstrated the existence of microorganisms and their effect in the fermentation process. The germ theory was the basis of his work in the large‐scale brewing of beer and wine, the pasteurization of milk, antiseptic operations on humans, and in curing contagious diseases since he also discovered that the blood of diseased humans contained increased amounts of germs. He, and later other scientists, discovered that manipulation of infection agents in test tubes could be used to immunize humans and animals against diseases caused by germs.

Pasteur later began teaching at Strasbourg University, where his studies on molecular asymmetry continued. While at Strasbourg, Pasteur married the university rector’s daughter, Marie Laurent, with whom he spent the rest of his life. In 1854, Pasteur became Dean and Professor of Chemistry at the Faculty of Sciences in Lille, France. This was a blue‐collar town, with numerous factories and distilleries. The Minister of Public Instruction of Lille encouraged the university faculty to conduct work and studies that would assist the industries of the surrounding countryside.

Pasteur took this advice to heart, taking his students on tours of the local factories and advising managers of his availability to help solve their problems. Thus, in 1856, M. Bigot, the father of one of his chemistry students, called upon Pasteur to help overcome problems in the manufacture of alcohol by fermentation of beetroot. Bigot’s problem was that his fermentations, instead of producing alcohol, yielded lactic acid.

At that point in time, chemistry was just starting to take root as a true scientific discipline, wrenching itself from the work of the alchemist. The chemical processes involved in living animals were slowly being discovered, and the chemist Lavoisier had showed, among other things, that sugar, the initial product of the fermentation process, could be broken down into alcohol, CO₂, and H₂O by placing a sugar solution on a heated plate of platinum. In addition, Wöhler had amazed the scientific community by synthesizing urea, demonstrating for the first time that organic compounds, previously believed only to be synthesized by living animals, could be produced in a test tube. Pasteur’s previous work on crystals also led to the routine discovery of the internal structure and analysis of complex organic compounds.

Given this environment in 1856, fermentation, which was used in the production of wine, beer, and vinegar, was thought to be a process involving the chemical breakdown of sugar into the desired molecules based upon the existence of destabilizing vibrations in the molecules. It was known at the time that yeast cells existed in the fermenting vats of wine, and had been recognized as living organisms, but they were believed to be a product of fermentation or catalytic agents that infuse the ingredients that allow fermentation to take place. Ridicule befell those few biologists who had concluded that yeast was the cause of, and not the result of, fermentation. Also, at that time, the scientists of the community were not providing much assistance to the wine, beer, and vinegar producers, who were facing serious economic downturns directly related to the fermentation processes. Yields of alcohol fell off, wine grew sour or turned to vinegar, and vinegar, when desired, ended up as lactic acid instead. Most importantly, the quality and taste of beer was prone to change from vat to vat, making quality control impossible.

Into this world came Louis Pasteur, entering Mr. Bigot’s factory with his microscope. Pasteur found that when alcohol was produced normally, the yeast cells were plump. However, when lactic acid would form instead of alcohol, rod‐like microbes were mixed with the yeast cells. He also found that amyl alcohol and other complex organic compounds were formed during the fermentation process, which could not be explained by the simple catalytic breakdown of sugar shown by Lavoisier. Pasteur concluded that some additional processes must be involved. Also, based on his earlier work on crystallography, he found that some of the compounds rotated light, and were, therefore, asymmetric. His early work had shown that only living cells produced asymmetrical compounds, and thus he extrapolated his findings to determine that living cells—yeast—were forming the alcohol from sugar, and that other microorganisms contaminated the fermentation, and turned the fermentation sour.

Over the next several years, Pasteur isolated and then identified specific microorganisms that led to both abnormal and normal fermentations in wine, beer, and vinegar production. He determined that if wine, beer, or milk were heated to moderately high temperatures for a short period of time and then cooled, living microorganisms could be killed, thereby sterilizing (later known as pasteurizing) the fermentation batches and preventing their degradation. Thus, if microbes and yeasts in pure cultures were added to sterile fermentation masses and air was prevented from entering the vats by sealing them, predictable fermentation would follow.

Pasteur’s earlier work on crystallography, chemistry, and optics led him to formulate the theory that asymmetric molecules are the result of living forces, and his work developed the new science of stereochemistry. In his work on fermentation, he demonstrated that each type of fermentation is caused by the existence of a specific microorganism or ferment, which is a living organism that can be studied through cultivation in a sterile medium. This is the basis of microbiology today.

Following his work in fermentation, and his discovery that the living microorganisms could be controlled to prevent the spoliation of products, Pasteur went on to a successful career as a chemist, with several major discoveries to his name. For example, he debunked the theory of spontaneous generation, which held at that time that microbes could be generated spontaneously from spoiling matter. Through his work on fermentation, he proved that microorganisms found during fermentation and putrefaction came from the outside, such as from dust in the air, and destroyed every theory that supported the spontaneous generation argument. He also concluded that microscopic beings are generated from parents similar to themselves.

Pasteur went on to research and cure a devastating disease among silkworms that was destroying the French silk industry. He also discovered the germ theory of disease and the use of vaccines in humans to prevent those diseases. It was only through the teachings of Pasteur, Lister, and others that antiseptic medicine and surgery began saving many lives. Pasteur also made major advances in dealing with anthrax, rabies, and the use of vaccines in humans.

While experimenting with biochemical agents for use against an increasing rabies infection epidemic in France, Pasteur discovered that contagions were the cause of disease. He also identified different germs that were present in the human body during illness. With this information, he found the causes of several diseases, and also discovered how to protect uninfected people through the use of vaccines that he ultimately developed. Pasteur made successful vaccines for diphtheria, tetanus, anthrax, chicken cholera, silk worm disease, tuberculosis, and the plague. In 1858, he proved garlic could be used as an antibacterial agent, which he ultimately gave to people who were seriously ill or had developed plague. His work on sterilization in medical procedures was slow to be adopted by many hospitals, but during his lifetime he spent much of his time working in hospitals with doctors trying to find ways to sterilize the equipment and the rooms in which operations were performed.

In 1885, Pasteur was working on experiments with rabies vaccines involving dogs, but had not used the vaccine on humans because he was afraid of unanticipated results and his inability to isolate the substance causing rabies. However, as in the development of all significant scientific discoveries and inventions, fate played its hand. A 9‐year‐old, Joseph Meister, appeared in Pasteur’s laboratory on July 6, 1886, with his mother. The young boy had been bitten by a rabid dog, and he could hardly walk. Pasteur, up to that time, had successfully treated 40 dogs, but had never used his vaccine on a human. Pasteur then consulted with many of his physician colleagues, and with much hesitation and reluctance treated the youth with his vaccine. Joseph Meister recovered, and lived a long and healthy life. Following this, people bitten by rabid dogs in many countries, including Russia and the United States, came to Pasteur for treatment. Newspapers reported these treatments and cures with overwhelming interest, making Pasteur a legend. Funded by public and governmental funds, the Pasteur Institute was created in Paris, initially to treat victims of rabies. Eventually, other Pasteur Institutes were built, including three in the United States, to treat rabies and other diseases.

The treatment of rabies was the last major project of Louis Pasteur. At the age of 46, he suffered a serious stroke, and his general health began failing. After suffering additional strokes, he died in 1895.