THE modern discoveries Beyond all others, the chemist Pasteur deserves the credit of exploring this new world and revealing its lessons. Louis Pasteur was born at Dôle, France, on the 27th of December, 1822. His father was a tanner, who had served in Napoleon's armies. The son was taught at Besançon, and at the Normal School in Paris, and then at the Sorbonne, having already devoted himself to chemistry. He took his doctor's degree in 1847, and taught at Dijon, Strasburg, and Lille; but returned in 1857 to teach science in the Normal School. His researches in regard to fermentation first attracted general notice, and proved to be the foundation of all his later work. The great German chemist Liebig held that fermentation was a chemical change due to the action of oxygen of the air on fermentable substances. This opinion was universally accepted among chemists until Pasteur took up the study. He found that acetic fermentation is the work of a minute fungus which spreads over the surface of the liquid. He studied the deterioration of vinegar, wine and beer, revealed its cause, and showed the means of preventing it. What his opponents considered the ferments he proved to be the food of the ferments, which are always living plants and animalcules. He was thus brought to the question of spontaneous generation, which had been revived in the scientific world. The theory itself belongs to remote antiquity, and had been announced by Aristotle, who said, "All dry bodies which become damp, and all damp bodies which are dried, engender animal life." In this crude form the doctrine had been discarded except by the ignorant; but in a more plausible guise it had been accepted by the eminent naturalist Buffon. Finally, in 1858, another naturalist, Pouchet, claimed to have observed and proved by experiment the occurrence of the lowest forms of life without preceding germs. When Pasteur entered the field in opposition, the Academy of Sciences in 1866 formally censured the chemist for dabbling in biology, and rejected his dictum, "Life can only proceed from other life." But Pasteur took up the naturalist's experiments, and showed how each one was defective. When, as late as 1880, Dr. Bastian attempted to revive the doctrine with new experiments, Pasteur was again victorious, and the theory of spontaneous generation received its quietus. Tyndall said of Pasteur's experiments, "They have restored the conviction that life does not appear without the operation of antecedent life." But before this controversy was ended, Pasteur had been called by his former preceptor, the chemist J. B. Dumas, to attack a most serious practical problem. For some fifteen years a plague called pébrine had been epidemic among the silk-worms of France, and was destroying a great national industry. Each new supply of worms brought from foreign countries succumbed to the plague in a year or two. Dumas had investigated the disease without practical result, and in 1865 turned the task over to his pupil, whose future eminence he had already foretold. "But," said Pasteur, "I have never seen a silk-worm. "What of that? This plague threatens France; you are a Frenchman. I have failed; but you are younger. You must stop its progress." Pasteur went to a little cottage in Alais, among the Cevennes, in the silk-worm region. He soon reported, "This disease is caused by parasites; we must get rid of the worms which have parasites." Even the silk-raisers laughed at his diagnosis and the remedy proposed. Pasteur required the healthy moths to be isolated from the infected, and proved that then their eggs and larvæ would remain healthy. He discriminated also two diseases, pébrine and flacherie, and showed the necessary precautions for guarding against them. His practical success convinced the silk-growers and saved the great industry of southern France. Pasteur was in 1867 made professor of chemistry in the Sorbonne, and held the position until 1875, when he retired on account of impairment of his health. His years of severe labor had caused a paralysis of the left side, which thereafter affected his speech and motion. During his struggles he had received no public aid; but on his retirement he was pensioned by the French government, and other nations gave practical acknowledgment of the benefit of his labors to modern industry. He turned his attention next to the diseases of men and animals. Here he found new proofs of the germ-theory: animalcules, bacteria, bacilli, schizomycetes, are the cause of many diseases in man. "It is my conviction," said he, "that it is in the power of man to cause all parasitic maladies to disappear from the world. Such diseases can only be propagated by contagion. Therefore isolate the afflicted, and the well will remain well." For some years he directed his investigations to the discovery of a specific germ for each disease. Acting on this principle, he mastered chicken cholera, anthrax and other deadly diseases in beasts, and had marked success in regard to human diseases. The medical profession welcomed his discoveries, and in all parts of the world students set earnestly to work to develop bacteriology. Finally Pasteur made another announcement, which has |