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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 Dфle 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, Pasteur’s 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 Bigo’s 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 Bigo’s 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 on to conduct experiments that destroyed every argument supporting the spontaneous generation theory. He proved that the skin of the grapes toward the beginning of the grape harvest was the source of the yeast. Drawing grape juice from under the skin with sterile needles gave juice that would ferment. Covering the grape arbors with a wrap to keep off contaminating dust gave grapes that would not produce wine (Cohn, par. 26).

The other experiment that proved his argument was the use of the swan-neck flask. In this experiment he placed fermentable juice in a flask and after sterilization the neck was heated and drawn out of the tube taking a gentle downward then upward arc, resembling the neck of a swan. The end of the neck was then sealed and as long as it remained sealed the juice did not change. If the flask was opened by taking off the end of the neck the air would enter, however the dust would become trapped on the wet

walls of the neck. Under these conditions the fluid would remain forever sterile proving

that air alone could not stimulate the growth of microorganisms. If the flask was tipped

and allowed to touch the walls then it was contaminated and immediately microorganisms would begin to grow (Cohn, par. 27).

In 1858 the grape-growing winemakers of France were beginning to have problems with their wine In some cases their wine was becoming cloudy and flat, and in others it was becoming very bitter. He began to study the fermentation of wine over the next few years and saw the diseases of the wine were coming up again and again. He then began a systematic study of the wine diseases and set up a laboratory and the grape growers were happy to supply Pasteur with a sample of their wine to test. He began to see that the flat tasting wine had not only yeast but also little oblong globules of his lactic acid fermentations. In the acid wine there was a very different microorganism called mycoderma aceti. Pasteur knew from previous studies that this organism changed the alcohol in wine to acetic acid. The bitter wine also had its own characteristic organism as well as the oily wine (Burton, 75).

Pasteur’s question now was how to keep the microorganisms from getting into the wine. This was going to be difficult because he had to find a way to kill the harmful organisms without harming the taste of wine. He first tried antiseptics but they did not satisfy him. Then he hit on the idea of using heat. By experimenting he learned to

hold the temperature between fifty and sixty degrees Celsius (122 to 140 degrees

Fahrenheit) for a few minutes. A higher temperature would spoil the taste, and a lower

temperature would not have killed the harmful microorganisms. He then began to design equipment so the wine makers could heat their wine safely and efficiently. The following year he obtained a patent for his method but he freely gave the use of it to all wine makers. His only reason for getting the patent was so that others could not exploit or monopolize his discovery. It took a number of years for the wine makers to be completely convinced that heating could protect their wines without harming the taste. Eventually they accepted the process and it was also adopted to kill disease-carrying microorganisms in milk, butter, cheese, and other foods. Pasteurization is now the familiar word for the process in many different languages (Burton, 76-77).

The word about Pasteur making the discovery that the wine diseases were being caused by the entry of a certain microorganism spread and doctors in England began to systematically sterilize their instruments, bandages and spraying phenol solutions in their operating rooms. This reduced infections following surgery to incredibly low numbers. By 1875 many doctors were beginning to realize that some diseases were accompanied by specific microorganisms, however the body of medical opinion was unwilling to concede that the serious diseases such as cholera, diptheria, scarlet fever, childbirth fever, syphilis, and small pox could ever be caused by these microorganisms (Benz, 133-137).

As Pasteur walked through the hospitals he became increasingly aware that the

spread of infection was spread by the doctors and hospital attendants from the sick patients to the healthy patients. In a famous speech Pasteur made in front of the Academy of Medicine in Paris he stated “This water, this sponge, this lint with which you wash or cover a wound, may deposit germs which have the power of multiplying rapidly in the tissue...If I had the honor of being a surgeon....not only would I use none but perfectly clean instruments, but I would clean my hands with the greatest care...I would use only lint, bandages, and sponges previously exposed to a temperature of 1300 to 1500 degrees.” This eventually became the rule of antiseptic medicine and surgery (Benz, 138-141).

The final success of Pasteur’s research was the development of the vaccine for rabies, or hydrophobia as it was also known. The treatments for the victims were known as cauterizing the bite wound with a red-hot poker. Pasteur and his colleague Roux initially tried to transfer the infection by injecting healthy dogs with the saliva from rabid animals. The results were variable and unpredictable. They later recognized that the active agent was in the spinal cord and brain and because they were unable to detect the specific microorganism, they applied extracts of rabid spinal cords directly to the brains of dogs. This produced rabies every time within a few days. The treatment plan

to develop immunity to rabies was to inject under the skin of a dog the least potent

preparation of minced spinal cord, followed every day for the next twelve days with a

stronger and stronger extract. At the end of this time the animal was completely resistant to bites of rabid dogs and failed to develop rabies even if the most potent of extracts were applied directly to the brain (Nicolle, 192-194).

Although he had figured out a way to keep the dog from contracting rabies, he was very unsure of trying this in a human. Pasteur was not comfortable with the fact that he had not found the actual microorganism that cause rabies. However a nine year old boy named Joseph Meister came to Pasteur in 1886. He had been bitten by a rabid dog so many times he could hardly walk. Pasteur was very uncertain about treating the young boy, however after consulting his colleagues he agreed to treat him. Despite Pasteur’s fears, the boy made a full recovery (Nicolle, 199-200).

After making his discovery about rabies his health began to deteriorate and he suffered from paralysis on his left side from a serious stroke. This made his work in the laboratory extremely difficult. Pasteur died in 1895 after suffering from additional strokes. Pasteur was a great man with a great mind. Because of his many discoveries there are many people that owe him their lives. Without his brilliance the medical sciences would be at a complete loss today.

Works Cited

Benz, Francis E.. Pasteur Knight of the Laboratory. New York, New York: Dodd, Mead and Company, 1938. 73-141.

Burton, Mary June. Louis Pasteur Founder of Microbiology. New York, New York: Franklin Watts, Inc., 1963. 5-77.

Cohn, David V.. “The Life and Times of Louis Pasteur.” University of Louisville School of Dentistry. 11 Feb. 1996. 45 pars. 7 Mar. 2004.

Nicolle, Jacques. Louis Pasteur The Story of His Major Discoveries. New York, New York: Basic Books, Inc., 1961. 192-200.