Louis Pasteur

(History of the World: The 19th Century)

Article abstract: Pasteur, by his pioneering work in crystallography, 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.

Early Life

Louis Pasteur was born in Dôle on December 27, 1822, but he grew up in Arbois, a nearby and smaller town in which 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 Revolution 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 which 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.

Pasteur, as he continued his research on crystallography, 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....

(The entire section is 2465 words.)