Pasteur, LOUIS, distinguished for his researches in chemistry and pathology, and more precisely for many discoveries in regard to bacteria, was born on 27th December 1822, at Dôle in the department of Jura. From the college of Arbois he passed to Besançon, and thence to the École Normale and the Sorbonne in Paris. After the completion of his preparatory studies he held various academic positions at Strasburg, Lille, and Paris, where in 1867 he became professor of Chemistry at the Sorbonne. From 1886 onwards the centre of his work was at the Pasteur Institute in Paris. His work was at first chemical. Following up well-known researches by Arago, Biot, and Mitscherlich, Pasteur discovered the facets on tartrate crystals and what are called left-handed tartrates. He also propounded the theory that 'molecular dissymmetry'—supposed to be expressed in the power which solutions of some organic substances have of causing a beam of polarised light to rotate—was characteristic of living matter and its products.
It is said that a German manufacturer of chemicals noticed that impure tartrate of lime fermented when dissolved and exposed in the sun, and that this prompted Pasteur to an investigation, the result of which was the discovery of a living ferment—a micro-organism comparable in its powers to the yeast-plant which Cagniard-Latour and Schwann had discovered in alcoholic fermentation. Pasteur was further able to show that the little organism would, in a solution of paratartrate of ammonia, select for food the 'right-handed' tartrates alone, leaving the 'left-handed,' although the difference between these is merely physical not chemical. Having got hold of a clue, Pasteur went on to show that other fermentations—lactic, butyric, acetic—are essentially due to organisms. He was naturally led to corroborate and extend Schwann's researches on putrefaction, which is also due to micro-organisms, and this path of investigation enabled him to make important practical suggestions in regard to the making of vinegar and the prevention of wine disease, as also to correct insufficiently careful experiments which were leading many to believe that spontaneous generation was demonstrable.
Prompted by his illustrious master Dumas, Pasteur next (1865) directed his inquiries to those diseases of silkworms by which the silk industry in France had been almost ruined. It is said that he had never before even seen a silkworm, though he knew the supposed disease-germs which had been demonstrated by previous investigations in the insect's blood. These he traced from egg to larva, from chrysalis to moth; and, as the pébrine disease is distinctly manifest in the adults, though it may be hidden in the young, the practical conclusion was plain that unhealthy moths should be rejected, and that all precautions should be taken to prevent infection. But Pasteur's work on the diseases of silkworms overstrained him, and in 1868 he was laid aside by paralysis. Soon, however, he was at work again, investigating beer as he had investigated wine, detecting the intruders which sometimes interfere with the life of the yeast-plant and spoil the brew. His researches began to come yet closer to human life, for he attacked the problem of splenic fever, the bacillus of which had been discovered by Davaine (1863), and skilfully traced from stage to stage by Koch (1876). Of Pasteur's investigations in this connection, that by which he showed that birds were not liable to fall victims to splenic fever, because the temperature of their blood is too high for the prosperity of the germ, may serve as a characteristic illustration. Passing from splenic fever to fowl cholera, Pasteur showed that it was possible to attenuate the virulence of injurious micro-organisms by exposure to air, by variety of culture, or by transmission through various animals. He thus 'tamed' the bacillus of splenic fever, and demonstrated by a memorable experiment that sheep and cows 'vaccinated' with he attenuated bacilli were protected from the evils of a subsequent inoculation with the virulent virus. Pasteur's subsequent researches in regard to Hydrophobia (q.v.) are discussed in that article, contributed to this work by himself. He wrote books on most of the special researches and discoveries by which he enriched science and benefited humanity. He died 28th September 1895, and was transferred from a temporary resting-place to a tomb in the Pasteur Institute on 26th December 1896.
See Lives of Pasteur (who was a devout Catholic) by his son-in-law (trans. 1885), Bournand (1896), Vallery-Radot, and Duclaux; and an English Life by Mr and Mrs Percy Frankland (1898). He contributed most of the article HYDROPHOBIA to this work.