Louis Pasteur

French bacteriologist

• Born: December 27, 1822
• Birthplace: Dôle, Jura, France
• Died: September 28, 1895
• Place of death: Villenueve-l'Étang, near Saint Cloud, France

Through his pioneering work in crystallography, Pasteur established the discipline of stereochemistry (left-handedness and right-handedness in organic structures). He spent the bulk of his career founding modern microbiology and making exciting discoveries in immunology and bacteriology—a field that he virtually created.

Early Life

Louis Pasteur (PAHS-tewr) grew up in Arbois, a small town near the town of his birth. There, his father, Jean-Joseph, a veteran of Napoleon I’s army, operated a tannery. His mother, Jeanne-Étiennette Roqui, was a gardener’s daughter. The best portraits of his parents were done in pastels by young Louis himself, who was an excellent artist. He, like them, was of medium height and dark-haired with a high forehead. His nearsightedness was said to have enhanced his ability to see small details close up. In his maturity, he wore the beard and mustache of most males of his time.

Louis was a late bloomer, and his grades in school were only slightly above average. He attended the Collège d’Arbois, and late in his career there, he became inspired and desired to enter the prestigious École Normale Supérieure in Paris. He left Arbois in 1838 and entered Barbet’s preparatory school in Paris but became so homesick that his father had to bring him home. In 1839, Louis enrolled in the Collège Royal at Besançon, in his home province of Franche Comté. Away from home but not far from it, the young scholar partially supported himself with a student assistantship and received his bachelor of science degree in 1842. Although accepted to the École Normale Supérieure, Pasteur believed that he was not yet ready to enter, and thus he spent a year at Barbet’s preparatory school before finally matriculating in the fall of 1843.

Pasteur did well at the École Normale Supérieure, passing high on the teachers’ examination in 1845 and quite high in his comprehensive exams the following year. In 1847, he received his doctorate in chemistry and soon found employment as a professor, first at the University of Dijon, where he taught physics for a semester, and then at the University of Strasbourg, where in 1849 he obtained a position in the chemistry department. It was also in Strasbourg that Pasteur met Marie Laurent, the twenty-two-year-old woman whom he soon made his wife. Their marriage lasted a lifetime and produced five children, although three of the daughters died early from typhoid. Throughout his life, Pasteur was politically conservative except for a youthful involvement in the revolutions of 1848, and he was a thoroughgoing supporter of the Second Empire under Napoleon III. Indeed, he received considerable grants and recognition from the emperor and empress personally.

Life’s Work

As early as 1848, Pasteur was publishing his work on crystals, which he had begun for his doctoral research. Working with tartaric acid, he searched for the solution as to why one form of the acid twisted to the right the light rays passing through it, while another form (paratartaric or racemic acid) did not rotate the plane of the light rays.

The two forms of the acid were chemically identical, but Pasteur discovered that racemic acid had crystals that were either left-handed or right-handed—each the mirror image of the other. Using tweezers, he laboriously hand-separated the dried crystals into left and right piles. Then he dissolved each pile and found to his satisfaction that the left-handed crystal solution rotated light rays to the left and the right-handed to the right. When the two solutions were then mixed in equal amounts, no rotation occurred—the mixture was optically inactive. This breakthrough established Pasteur’s reputation as a scientist, because it opened the door to stereochemistry, a new way of studying the molecular composition of substances. Pasteur had begun to understand dissymmetry, which characterizes not only organic forms but most inorganic forms as well.

As he continued his research on crystallography, Pasteur moved to the University of Lille, where he served as a dean as well as a professor from 1854 to 1857. While at Lille, Pasteur was approached by a man seeking expert help in explaining why some of his vats of sugar-beet juice, which he was fermenting prior to distilling alcohol from the mash, had been going bad. Pasteur had been urged by his superiors to serve practical ends as well as pure science, and, as it happened, Pasteur’s own research into the composition of organic molecules had caused him to want to know how fermentation modified those molecules. Pasteur was eager to use the sugar-beet industry as a laboratory.

The scientist examined the vats and took samples. Under his vertically mounted microscope, Pasteur detected small, round globules of yeast from the “good” samples but found that the “bad” ones contained rodlike microorganisms, bacilli. He assumed that the yeasts, which he observed multiplying by budding, were the cause of fermenting beet sugar into the desired alcohol, but the rods were a mystery.

After considerable effort, he succeeded in formulating a soup in which he was able to culture the bacilli. After introducing only a few of the rods into the sterile solution, he saw them multiply into millions of vibrating germs. They were alive, and they were what crowded out the yeast and transformed the sugar into lactic acid—the acid of sour milk. Pasteur wrote a paper on his discovery entitled “Mémoire sur la fermentation appellée lactique” (memoir on the fermentation called lactic), which was published by the French Academy of Sciences in 1857. This paper was hailed as the initial proof that germs cause fermentation.

Pasteur’s article of 1857 was the second great stride of his career, and as a result he was called to Paris and made director of scientific studies at the École Normale Supérieure. His elevated post, however, did not provide him with his own laboratory, so he created one for himself in two rooms in the attic. There he proceeded to demonstrate the extreme complexity of the processes involved in alcoholic fermentation. Chemists had previously expressed the conversion of sugar into ethyl alcohol and carbonic acid by means of a simple, inorganic formula, but Pasteur detailed the complex role of brewer’s yeast in digesting the sugar into a number of compounds, of which alcohol was only the most important.

Continuing his work on microbes, Pasteur found that some bacteria required the absence of oxygen in order to survive, whereas others needed oxygen to live. The former he termed “anaerobic,” and he named the latter “aerobic”—nomenclature used by science to the present day, as Pasteur was the first to bring to scientific and public attention the two different kinds of bacteria. Antoni van Leeuwenhoek and Lazzaro Spallanzani had earlier observed anaerobic bacteria but had failed to attract much notice to the discovery.

Pasteur then conducted a lengthy experiment on the canning of food, a process discovered by his fellow countryman François Appert in the time of Napoleon I. Pasteur showed conclusively that the heating of sealed containers killed the microbes that caused fermentation and putrefaction. That was the secret of food preservation. He explained that microbes are necessary for decomposition of organic matter into its inorganic components and that without such microbes all the plants and animals that had ever lived would have their dead remains choking the surface of the planet.

Pasteur also proved that microbes came only from other microbes, that life came from life, and that there was no spontaneous generation. Leeuwenhoek two hundred years earlier had disproved spontaneous generation, but few had been willing to listen. Pasteur was so insistent that he forced people to pay attention. To illustrate that microbes can be carried through the air, Pasteur and his assistants exposed many sterile cultures briefly to the air of a deep basement in Paris, the surface-level air in Paris, the air of a vineyard on a hill of the Jura Mountains, and finally the air high on the slopes of Mont Blanc. Pasteur found that the higher and more rural the area the lower the percentage of cultures that were contaminated. The only low-lying location that had pure air was the nearly draft-free deep cellar in Paris.

Next Pasteur and his chief assistant, Émile Duclaux, set up a makeshift field laboratory in Pasteur’s hometown of Arbois. Wine producers in the area had been having difficulty, as their output was sometimes ropy, acid, oily, or bitter. Looking through his microscope, Pasteur startled the vintners by correctly pronouncing what was wrong with each sample without tasting it. To prevent the spoilage, Pasteur recommended a treatment that came to be known as “pasteurization”—heating the wine, once fermentation was complete, to a certain temperature below boiling and holding it there for a specified period of time. The temperature could be lower if the time were lengthened and vice versa. When farmers objected to cooking their wine, Pasteur explained that the natural acidity of their product made it less hospitable to germs and that the required temperature was really quite low. Milk, beer, cider, and other liquids could be similarly preserved, and Pasteur designed special equipment for commercial pasteurization.

One of Pasteur’s former professors, J. B. Dumas, begged Pasteur to investigate a disease of silkworms, pébrine, a blight that was devastating a main industry in south central France. Between 1865 and 1870, Pasteur spent several months of each year in and around Alais (modern Alès), the center of the nation’s silk culture. Pasteur’s confusion about what ailed the silkworms was compounded, as he eventually discovered, by the fact that the worms were suffering not from a single disease but from two different microbial infections.

Before he attained a breakthrough in the silkworm diseases, however, Pasteur suffered a cerebral hemorrhage in October, 1868, at the age of forty-five. Many thought that he would surely die; his left side was completely paralyzed. However, he regained partial use of his left side, and he walked, though with a severe limp. He depended on his assistants to do much of the manipulation required by his experiments, but his mind remained keen, and he never relinquished control over his laboratories. He had finished the rescue of the silk industry by 1870.

Pasteur, whose name was a household word in France and who had greatly assisted the French sugar-beet, wine, vinegar, silk, and beer industries, moved comparatively late in his career into the field of immunology. He confirmed the work of Robert Koch in Germany, who had discovered the complete life cycle of the anthrax bacillus, the cause of the animal (and sometimes human) disease anthrax, but he greatly desired to outdo the German. After considerable experimentation with animals, Pasteur announced that he had invented a vaccine, composed of weakened bacilli, which if injected into an animal would confer immunity against anthrax.

It was something Koch had never done. Skeptical French veterinarians in 1881 challenged Pasteur to a dramatic public experiment to test the immunization. Pasteur’s assistants cautioned against accepting, as the vaccine had not been field-tested and a public failure could be devastating. Pasteur was adamant, however, and they caught the train for Pouilly-le-Fort, a village near Melun, southeast of Paris. Twenty-four sheep, one goat, and six cows were immunized, it was hoped, by Pasteur’s assistant, the physician Émile Roux, with two injections of serum twelve days apart. Two weeks later, those animals and an equal-sized control group of animals were injected with a powerful culture of anthrax bacilli. All the immunized animals survived; all the others died; France went wild with the news.

Pasteur next turned to conquer rabies, probably motivated by childhood memories of an attack on his town by a rabid wolf. Sucking foam from the mouths of caged mad dogs, Pasteur and his men never found a responsible microbe, as hydrophobia is caused by a virus—something too small to be seen with a light microscope—but the scientists made a vaccine and used it successfully on animals. Then a mother brought in her son, bitten by a mad dog and sure to die. Pasteur ordered the child inoculated, and the child lived. Soon others came, even from distant Russia and the United States, and, except where too much time had elapsed, the cure was effective.

It was fitting climax to a brilliant career. On his seventieth birthday, a great celebration was held to honor Pasteur. Pasteur’s son had to deliver his father’s speech, in which Pasteur said that it gave him immense happiness to “have contributed in some way to the progress and good of humanity.”

Significance

Louis Pasteur is best known for his work in bacteriology, a field that he virtually founded. His discoveries contributed greatly to the control and treatment of cholera, diphtheria, tetanus, tuberculosis, and other diseases. His studies of the transmission of infection also contributed to the development of antiseptic procedures in surgery. His discovery of vaccines to prevent anthrax and other diseases of animals had an enormous impact not only in France but also worldwide. Although less widely known than his contributions to immunology, Pasteur’s pioneering researches in crystallography were of fundamental importance. Among the many great scientists of the nineteenth century, Pasteur stands in the first rank.

Bibliography

Compton, Piers. The Genius of Louis Pasteur. New York: Macmillan, 1932. A readable and thorough account of Pasteur’s life and contributions, this book has several interesting photographs of people, places, and events in his life.

Cuny, Hilaire. Louis Pasteur: The Man and His Theories. Translated by Patrick Evans. London: Souvenir Press, 1965. This book provides detail without being overwhelming. Cuny’s explanations of the technical aspects of Pasteur’s work are readily comprehensible to the layperson.

Debré, Patrice. Louis Pasteur. Translated by Elborg Forster. Baltimore: Johns Hopkins University Press, 1998. Comprehensive study of Pasteur’s life and work written by a French immunologist who describes his subject as “a living symbol, embodying both science and France.” Debrée describes the scientific details of Pasteur’s experiments in simple, understandable language.

De Kruif, Paul. Microbe Hunters. New York: Pocket Books, 1950. Although more superficial than the full-length biographies, this book has two exquisitely entertaining chapters on Pasteur that convey the excitement inherent in making scientific breakthroughs that result in saving lives and industries.

Dubos, René. Louis Pasteur: Free Lance of Science. Translated by Elizabeth Dussauze. New York: Charles Scribner’s Sons, 1976. This book is thorough and gives a good perspective on Pasteur. Includes a large photographic section.

Duclaux, Émile. Pasteur: The History of a Mind. Translated by Erwin Smith and Florence Hedges. Philadelphia: W. B. Saunders, 1920. Reprint. Metuchen, N.J.: Scarecrow Press, 1973. Written by a man who studied and worked under Pasteur, this book provides many insights into Pasteur’s thinking. Duclaux deals exclusively with Pasteur’s professional life and not with his personal life, and gives a balanced treatment with proper credit to Pasteur’s rival researchers.

Geison, Gerald L. The Private Science of Louis Pasteur. Princeton, N.J.: Princeton University Press, 1995. Revisionist and controversial biography based upon Geison’s extensive study of Pasteur’s unpublished correspondence, lecture notes, and workbooks, Geison found significant differences between Pasteur’s public positions and private records, concluding that some of Pasteur’s experiments were tainted by lies and scientific, if not moral, misconduct.

Vallery-Radot, René. The Life of Pasteur. Translated by R. L. Devonshire. Mineola, N.Y.: Dover, 1960. This is the standard biography of Pasteur and was written by Pasteur’s son-in-law. The book provides many quotations from documentary sources and gives an inside look at Pasteur, his life and his work.