Chemist, founder of physio-chemistry, father of bacteriology, inventor of bio-therapeutics; born at Dole, Jura, France, 27 December, 1822; died near Sevres, 28 September, 1895. His father was a poor tanner who moved to Arbois when his son was but two months old. Pasteur received his early education at the College Communal of Arbois, but paid little attention to his books, devoting himself to fishing and sketching. For a time it seemed as though he would become a painter. When science was reached in the course he grew interested. He received his degree at Besancon and then in order to devote himself to science went to Paris to study under Dumas, Balard, and Biot. His father helped him, but he had to support himself partly by his own labours. His first original work was done on crystals. Mitscherlich announced that two tartaric acids, apparently identical in chemical qualities and in crystalline form, acted differently in solution toward polarized light. Refusing to accept this dictum, Pasteur demonstrated that the crystals thought to be similar were different, and explained the seeming inconsistency.

His discovery attracted wide attention. As a result he devoted himself to the study of what he called dissymmetry, pointing out that inorganic substances are not dissymmetrical in their crystallization, while all the products of vegetable and animal life are dissymmetric. He concluded that there was some great biological principle underlying this. As the result of his discovery he was made (1848) professor of physics at the Lycee of Dijon; three months later he became deputy professor of chemistry at the University of Strasburg, and full professor in 1852; in 1854 dean and professor of chemistry at the new University of Lille; in 1856 the English Royal Society conferred on him the Rumford Medal for researches on the polarization of light with hemihedrism of crystals; in 1857 he became director of scientific studies at the Paris Ecole Normal, in 1863 professor of geology and chemistry at the Ecole des Beaux Arts, in 1867 professor of chemistry at the Sorbonne, where he remained till 1889, when he became the Director of the Pasteur Institute, founded in his honour.

His early chemical studies led him to the investigation of fermentation and putrefaction, which he showed were due to living germs of various kinds. From this the demonstration that spontaneous generation does not take place was but a step. He showed that in highly-organized material, if the living germs are all destroyed, and if further access of germs be prevented, even though air may be allowed free access, fermentation or putrefaction does not take place. A piece of cotton wool, or a mere bending of the neck of the flask to keep germs from entering, is sufficient after sterilization to keep organic solutions quite sterile. The study of fermentations led Pasteur to studies in vinegar, wine, and beer. As the result of his successful investigation of ferments he was asked by the Empress Eugenie whether he would not now devote himself to the organization of great manufacturing industries for the benefit of France. He replied that he considered it quite beneath the dignity for a scientist to give up his time to commerce, and while he was willing that others should take advantage of his discoveries he wanted to push on to further scientific work.

This was a fortunate decision. His successful investigations led the French Government to appeal to him to study the silk-worm disease. This had produced such ravages in the silk industry in France that the end of it seemed not far off. Many expedients and supposed remedies had been tried. Fresh silk-worms had been brought from China on a number of occasions, but they succumbed to the disease, or their progeny became affected by it. Nothing availed and the case seemed hopeless. Pasteur found the silk-worm had been suffering from two diseases, pebrine and flacherie, and that the spread of these diseases could be prevented by careful segregation of healthy worms from those diseased. The announcement seemed too good to be true and was scouted. Pasteur demonstrated its absolute truth and his practical ability by taking charge of the villa of the French Prince Imperial, where the silk industry had been ruined. At the end of the year the sale of cocoons gave a net profit of 26,000,000 francs (over $5,000,000).