Pasteur's critics maintained that if putrefaction and fermentation be caused solely by microscopic organisms, then these must be found everywhere and in such quantities as to encumber the air. He replied that they were less numerous in some parts of the atmosphere than in others. To prove his contention he set out for Arbois with a large number of glass bulbs each half filled with a putrescible liquid. The necks of the bulbs had been drawn out and hermetically sealed after the contents had been boiled. In case the necks were broken (to be again sealed immediately), the air would rush in, and (if it held the requisite micro-organisms) furnish the conditions for putrefaction. It was found that in every trial the contents of a certain number of the bulbs always escaped alteration. Twenty were opened in the country near Arbois free from human habitations. Eight out of the twenty showed signs of putrefaction. Twenty were exposed to the air on the heights of the Jura at an altitude of eight hundred and fifty meters above sea-level; the contents of five of these subsequently putrefied. Twenty others were opened near Mont Blanc at an altitude of two thousand meters and while a wind was blowing from the Mer de Glace; in this case the contents of only one of the bulbs became putrefied.
While his opponents still professed to believe in the creation of organized beings lacking parents, Pasteur was under the influence of the theory of "the slow and progressive transformation of one species into another," and was becoming aware of phases of the struggle for existence hitherto shrouded in mystery. He wished he said to push these studies far enough to prepare the way for a serious investigation of the origin of disease.
He returned to the study of lactic fermentation, showed that butyric fermentation may be caused by organisms which live in the absence of oxygen, while vinegar is produced from wine through the agency of bacteria freely supplied with the oxygen of the air. Pasteur was seeing ever more clearly the part played by the infinitesimally small in the economy of nature. Without these microscopic beings life would become impossible, because death would be incomplete. On the basis of Pasteur's study of fermentation, his demonstration that decomposition is owing to living organisms and that minute forms of life spring from parents like themselves, his disciple Joseph Lister began in 1864 to develop antiseptic surgery.
Pasteur's attention was next directed to the wine industry, which then had an annual value to France of 500,000,000 francs. Might not the acidity, bitterness, defective flavor, which were threatening the foreign sale of French wines, be owing to ferments? He discovered that this was, indeed, the case, and that the diseases of wine could be cured by the simple expedient of heating the liquor for a few moments to a temperature of 50° to 60° C. Tests on a considerable scale were made by order of the naval authorities. The ship Jean Bart before starting on a voyage took on board five hundred liters of wine, half of which had been heated under Pasteur's directions. At the end of ten months the pasteurized wine was mellow and of good color, while the wine which had not been heated had an astringent, almost bitter, taste. A more extensive test—seven hundred hectoliters, of which six hundred and fifty had been pasteurized—was carried out on the frigate la Sibylle with satisfactory results. Previously wines had been preserved by the addition of alcohol, which made them both dearer and more detrimental to health.
In 1865 Pasteur was called upon to exercise his scientific acumen on behalf of the silk industry. A disease—pébrine—had appeared among silkworms in 1845. In 1849 the effect on the French industry was disastrous. In the single arrondissement of Alais an annual income of 120,000,000 francs was lost for the subsequent fifteen years. The mulberry plantations of the Cévennes were abandoned and the whole region was desolate. Pasteur, at the instigation of the Minister of Agriculture, undertook an investigation. After four or five years, in spite of repeated domestic afflictions and the breakdown of his own health, he arrived at a successful conclusion. Pébrine, due to "corpuscles" readily detected under the microscope, could be recognized at the moment of the moth's formation. A second disease, flacherie, was due to a micro-organism found in the digestive cavity of the moth. Measures were taken to select the seed of the healthy moths and to destroy the others. These investigations revealed the infinitesimally small as disorganizers of living tissue, and brought Pasteur nearer his purpose "of arriving," as he had expressed it to Napoleon III in 1863, "at the knowledge of the causes of putrid and contagious diseases."
Returning in July, 1870, from a visit to Liebig at Munich, Pasteur heard at Strasburg of the imminence of war. All his dreams of conquest over disease and death seemed to vanish. He hurried to Paris. His son, eighteen years of age, set out with the army. Every student of the Ecole Normale enlisted. Pasteur's laboratory was used to house soldiers. He himself wished to be enrolled in the National Guard, and had to be told that a half-paralyzed man could not render military service. He was obsessed with horror of wanton bloodshed and with indignation at the insolence of armed injustice. Trained to serve his country only in one way he tried, but in vain, to resume his researches. He retired to the old home town of Arbois, and sought to distract his mind from the contemplation of human baseness. Arbois was entered by the enemy in January with the usual atrocities of war. Pasteur accompanied by wife and daughter had gone in search of his son, sick at Pontarlier. The boy was restored to health and returned to his regiment the following month.
During this crisis Pasteur and his friends felt, as many English scientists feel in 1917, in reference to ignorance in high places. "We are paying the penalty," he said, "of fifty years' forgetfulness of science, and of its conditions of development." Again he speaks, as Englishmen to-day very well might, of the neglect, disdain even, of the country for great intellectual men, especially in the realm of exact science. In the same strain his friend Bertin said that after the war everything would have to be rebuilt from the top to the bottom, the top especially. Pasteur recalled the period of 1792 when Lavoisier, Berthollet, Monge, Fourcroy, Guyton de Morveau, Chaptal, Clouet, and other scientists had furnished France with gunpowder, steel, cannon, fortifications, balloons, leather, and other means to repel unjust invasion.
On the day after Sedan the Quaker surgeon Lister had published directions for the use of aqueous solutions of carbolic acid to destroy septic particles in wounds, and of oily solutions "to prevent putrefactive fermentation from without." He recognized that the earlier the case comes from the field the greater the prospect of success. Sédillot (the originator of the term "microbe"), at the head of an ambulance corps in Alsace, was a pioneer in the rapid transport of wounded from the field of battle. He knew the horrors of purulent infection in military hospitals, and regretted that the principles of Pasteur and Lister were not more fully applied.
After the war was over, Pasteur kept repeating his life-long exhortation: We must work—"Travaillez, travaillez toujours!" He applied himself to a study of the brewing industry. He did not believe in spontaneous alterations, but found that every marked change in the quality of beer coincides with the development of micro-organisms. He was able to tell the English brewers the defects in their output by a microscopic examination of their yeast. ("We must make some friends for our beloved France," he said.) Bottled beer could be pasteurized by bringing it to a temperature of 50° to 55° C. Whenever beer contains no ferments it is unalterable. His scrupulous mind was coming ever closer to the goal of his ambition. This study of the diseases of beer led him nearer to a knowledge of infections. Many micro-organisms may, must, be detrimental to the health of man and animals.