In the history of science war is no mere interruption, but a great stimulating influence, promoting directly or indirectly the liberties of the people, calling into play the energy of artisan and manufacturer, and increasing the demand for useful and practical studies. In the activities of naval and military equipment and organization this influence is obvious enough; it is no less real in the reaction from war which impels all to turn with new zest to the arts and industries of peace and to cherish whatever may tend to culture and civil progress. Not infrequently war gives rise, not only to new educational ideals, but to new institutions and to new types of institution favorable to the advancement of science. As we have already seen, the Royal Society and Milton's Academies owed their origin to the Great Rebellion. Similarly the Ecole Polytechnique, mother of many scientific discoveries, rose in answer to the needs of the French Revolution. No less noteworthy was the reconstruction of education under the practical genius of Napoleon I, the division of France into académies, the founding of the lycées, the reëstablishment of the great Ecole Normale, and the organization of the Imperial University with new science courses and new provincial Faculties at Rennes, Lille, and elsewhere. With all these different forms in which the influence of war makes itself felt in the progress of science the life and career of Louis Pasteur (1822-1895), the founder of bacteriology, stood intimately associated.
He was born at Dôle, but the family a few years later settled at Arbois. For three generations the Pasteurs had been tanners in the Jura, and they naturally adhered to that portion of the population which hailed the Revolution as a deliverance. The great-grandfather was the first freeman of Pasteur's forbears, having purchased with money his emancipation from serfdom. The father in 1811, at the age of twenty, was one of Napoleon's conscripts, and in 1814 received from the Emperor, for valor and fidelity, the Cross of the Legion of Honor. The directness and endurance of the influence of this trained veteran on his gifted son a hundred fine incidents attest. In 1848—year of revolt in the monarchies of Europe—the young scientist enrolled himself in the National Guard, and, seeing one day in the Place du Panthéon a structure inscribed with the words autel de la patrie, he placed upon it all the humble means—one hundred and fifty francs—then at his disposal.
It was in that same year that Pasteur put on record his discovery of the nature of racemic acid, his first great service to science, from which all his other services were to proceed. As a boy he had attended the collège at Arbois where his teacher had inspired him with an ambition to enter the great Ecole Normale. Before reaching that goal he took his bachelor's degree in science as well as in arts at the Besançon college. At Paris he came in contact with the leaders of the scientific world—Claude Bernard, Balard, Dumas, Biot.
J. B. Biot had entered the ranks of science by way of the Ecole Polytechnique and the artillery service. In 1819 he had announced that the plane of polarized light—for example, a ray passed through Iceland spar—is deflected to right or left by various chemical substances. Among these is common tartaric acid—the acid of grape-juice, obtained from wine lees. Racemic acid, however, which is identical with tartaric acid in its chemical constituents, is optically inactive, rotating the plane of polarized light neither to the right nor the left. This substance Pasteur subjected to special investigation. He scrutinized the crystals of sodium ammonium racemate obtained from aqueous solution. These he observed to be of two kinds differing in form as a right glove from a left, or as an object from its mirror-image. Separating the crystals according to the difference of form, he made a solution from each group. One solution, tested in the polarized-light apparatus, turned the plane to the right; the other solution turned it to the left. He had made a capital discovery of far-reaching importance, namely, that racemic acid is composite, consisting of dextro-tartaric and lævo-tartaric acids. Biot hesitated to credit a mere tyro with such an achievement. The experiment was repeated in his presence. Convinced by ocular demonstration, he was almost overcome with emotion. "My dear boy," he exclaimed, "I have loved the sciences so much my life through that that makes my heart jump."
Pasteur began his regular professional experience as a teacher of physics in the Dijon lycée, but he was soon transferred to the University of Strasburg (1849). There he married the daughter of the rector of the académie, and three years later became Professor of Chemistry. In 1854 he was appointed Dean of the Faculty of Sciences at Lille, a town then officially described as the richest center of industrial activity in the north of France. In his opening address he showed the value and attractiveness of practical studies. He believed as an educator in the close alliance of laboratory and factory. Application should always be the aim, but resting on the severe and solid basis of scientific principles; for it is theory alone which can bring forth and develop the spirit of invention.
His own study of racemic acid, begun in the laboratories of Paris, and followed up in the factories of Leipzig, Prag, and Vienna, had led to his theory of molecular dissymmetry, the starting point of modern stereo-chemistry. It now gave rise on Pasteur's part to new studies and to new applications to the industries. He tried an experiment which seems almost whimsical, placing ammonium racemate in the ordinary conditions of fermentation, and observed that only one part—the dextro-rotatory—ferments or putrefies. Why? "Because the ferments of that fermentation feed more easily on the right hand than on the left hand molecules." He succeeded in keeping alive one of the commonest moulds on the surface of ashes and racemic acid, and saw the lævo-tartaric acid appear. It was thus that he passed from the study of crystals to the study of ferments.
In the middle of the nineteenth century little was known of the nature of fermentation, though some sought to explain by this ill-understood process the origin of various diseases and of putrefaction. Why does fruit-juice produce alcohol, wine turn to vinegar, milk become sour, and butter rancid? Pasteur's interest in these problems of fermentation was stimulated by one of the industries of Lille. He was accustomed to visit with his students the factories of that place as well as those of neighboring French and Belgian cities. The father of one of his students was engaged in the manufacture of alcohol from beetroot sugar, and Pasteur came to be consulted when difficulties arose in the manufacturing process. He discovered a relationship between the development of the yeast and the success or failure of the fermentation, the yeast globules as seen under the microscope showing an alteration of form when the fermentation was not proceeding satisfactorily. In 1857 Pasteur on the basis of this study was able to demonstrate that alcoholic fermentation, that is, the conversion of sugar into alcohol, carbonic acid, and other compounds, depends on the action of yeast, the cells of which are widely disseminated in the atmosphere.
In this year of his second great triumph Pasteur was appointed director of science studies in the Ecole Normale, from which he had graduated in 1847. Two years later the loss of his daughter by a communicable disease—typhoid fever—had a great effect on his sensitive and profound mind. Many of his opponents, it is true, found Pasteur implacable in controversy. Undoubtedly he had the courage of his convictions, and his belief that, for the sake of human welfare, right views—his views won by tireless experiment—must prevail, gained him the name of a fighter. But in all the intimate relations of life his essential tenderness was manifest. Like Darwin he had a horror of inflicting pain, and always insisted, when operations on animals were necessary in the laboratory, on the use of anæsthetics (our command of which had been greatly advanced by Simpson in 1847). Emile Roux said that Pasteur's agitation at witnessing the slightest exhibition of pain would have been ludicrous if, in so great a man, it had not been touching.
A few months after his daughter's death Pasteur wrote to one of his friends: "I am pursuing as best I can these studies on fermentation, which are of great interest, connected as they are with the impenetrable mystery of life and death. I am hoping to make a decisive advance very soon, by solving without the least lack of clearness the famous question of spontaneous generation." Two years previously a scientist had claimed that animals and plants could be generated in a medium of artificial air or oxygen, from which all atmospheric air and all germs of organized bodies had been precluded. Pasteur now filtered atmospheric air through a plug of cotton or asbestos (a procedure which had been followed by others in 1854), and proved that in air thus treated no fermentation takes place. Nothing in the atmosphere causes life except the micro-organisms it contains. He even demonstrated that a putrescible fluid like blood will remain unchanged in an open vessel so constructed as to exclude atmospheric dust.