In 1874 the Government conferred upon Pasteur a life annuity of twelve thousand francs, an equivalent of his salary as Professor of Chemistry at the Sorbonne. (He had received appointment in 1867, but had been compelled by ill-health to relinquish his academic functions.) The grant was in all respects wise. Huxley remarked that Pasteur's discoveries alone would suffice to cover the war indemnity of five milliards paid by France to Germany in 1871. Moreover, all his activities were dictated by patriotic motives. He felt that science is of no country and that its conquests belong to mankind, but that the scientist must be a patriot in the service of his native land.
Pasteur now applied his energies to the study of virulent diseases, following the principles of his earlier investigations. He opposed those physicians who believed in the spontaneity of disease, and he wished to wage a war of extermination against all injurious organisms. As early as 1850 Davaine and Rayer had shown that a rod-like micro-organism was always present in the blood of animals dying of anthrax, a disease which was destroying the flocks and herds of France. Dr. Koch, who had served in the Franco-Prussian War, succeeded in 1876 in obtaining pure cultures of this bacillus and in defining its relation to the disease. Pasteur took up the study of anthrax in 1877, verified previous discoveries, and, as we shall see, sought means for the prevention of this pest. He discovered (with Joubert and Chamberland) the bacillus of malignant edema. He applied the principles of bacteriology to the treatment of puerperal fever, which in 1864 had rendered fatal 310 cases out of 1350 confinements in the Maternité in Paris. Here he had to fight against conservatism in the medical profession, and he fought strenuously, one of his disciples remarking that it is characteristic of lofty minds to put passion into ideas. Swine plague, which in the United States in 1879 destroyed over a million hogs, and chicken cholera, also engaged his attention.
Cultures of chicken cholera virus kept for some time became less active. A hen that chanced to be inoculated with the weakened virus developed the disease, but, after a time, recovered (much as patients after the old-time smallpox inoculations). It was then inoculated with a fresh culture supposed sufficient to cause death. It again recovered. The use of the weakened inoculation had developed its resistance to infection. A weakened virus recovered its strength when passed through a number of sparrows, the second being inoculated with virus from the first, the third from the second, and so on (this species being subject to the disease). Hens that had not had chicken cholera could be rendered immune by a series of attenuated inoculations gradually increasing in strength. In the case of anthrax the virus could be weakened by keeping it at a certain temperature, while it could be strengthened by passage through a succession of guinea-pigs. There are of course many instances where pathogenic bacteria lose virulence in passing from one animal to another, the human smallpox virus, for example, producing typical cowpox in an inoculated heifer. These facts help to explain why certain infections have grown less virulent in the course of history, and why infections of which civilized man has become tolerant prove fatal when imparted to the primitive peoples of Australia.
Pasteur's preventive inoculation for anthrax was tested under dramatic circumstances at Melun in June, 1881. Sixty sheep and a number of cows were subjected to experiment. None of the sheep that had been given the preventive treatment died from the crucial inoculation; while all those succumbed which had not received previous treatment. The test for the cows was likewise successful. Pasteur thought that in places where sheep dead of anthrax had been buried, the microbes were brought to the surface in the castings of earthworms. Hence he issued certain directions to prevent the transmission of the disease. He also aided agriculture by discovering a vaccine for swine plague.
When Pasteur at the age of fifteen was in Paris, overcome with homesickness, he had exclaimed, "If I could only get a whiff of the old tannery yard, I feel I should be cured." Certainly every time he came in contact with the industries—silk, wine, beer, wool—his scientific insight, Antæus-like, seemed to revive. All his life he had preached the doctrine of interchange of service between theory and practice, science and the occupations. What he did is more eloquent than words. His theory of molecular dissymmetry, that the atoms in a molecule may be arranged in left-hand and right-hand spirals or other tridimensional figures corresponding to asymmetrical crystals, touches the abstruse question of the constitution of matter. His preventive treatment breathes new life into the old dictum similia similibus curantur. The view he adopted of the gradual transformation of species offers a new interpretation of the speculations of philosophy in reference to being and becoming and the relation of the real to the concrete. Yet Pasteur felt he could learn much of value from the simplest shepherd or vine-dresser.
He was complete in the simplicity of his affections, in his compassion for all suffering, in the warmth of his religious faith, and in his devotion to his country. He thought France was to regain her place in the world's esteem through scientific progress. He was therefore especially gratified in August, 1881, at the thunders of applause which greeted his appearance at the International Medical Congress in London. There he was introduced to the Prince of Wales (fondateur de l'Entente Cordiale), "to whom I bowed, saying that I was happy to salute a friend of France."
Pasteur's investigation of rabies began in this same year. Difficulty was found in isolating the microbe of the rabic virus, but an inoculation from the medulla oblongata of a mad dog injected into one of the brain membranes (dura mater) of another dog invariably brought on the symptoms of rabies. To obtain attenuation of the virus it was sufficient to dry the medulla taken from an infected rabbit. The weakened virus increased in strength when cultivated in a series of rabbits. Pasteur obtained in inoculations of graded virulence, which could be administered hypodermically, a means of prophylaxis after bites. He conjectured that in vaccinal immunity the virus is accompanied by a substance which makes the nervous tissue unfavorable for the development of the microbe.
It was not till 1885 that he ventured to use his discovery to prevent hydrophobia. On July 6 a little boy, Joseph Meister, from a small place in Alsace was brought by his mother to Paris for treatment. He had been severely bitten by a mad dog. Pasteur, with great trepidation, but moved by his usual compassion, undertook the case. The inoculations of the attenuated virus began at once. The boy suffered little inconvenience, playing about the laboratory during the ten days the treatment lasted. Pasteur was racked with fears alternating with hopes, his anxiety growing more intense as the virulence of the inoculations increased. On August 20, however, even he was convinced that the treatment was a complete success. In October a shepherd lad, who, though badly bitten himself, had saved some other children from the attack of a rabid dog, was the second one to benefit by the great discovery. Pasteur's exchange of letters with these boys after they had returned to their homes reveals the kindliness of his disposition. His sentiment toward children had regard both to what they were and to what they might become. One patient, brought to him thirty-seven days after being bitten, he failed to save. By March 1 Pasteur reported that three hundred and fifty cases had been treated with only one death.
When subscriptions were opened for the erection and endowment of the Pasteur Institute, a sum of 2,586,680 francs was received in contributions from many different parts of the world. Noteworthy among the contributors were the Emperor of Brazil, the Czar of Russia, the Sultan of Turkey, and the peasants of Alsace. On November 14, 1888, President Carnot opened the institution, which was soon to witness the triumphs of Roux, Yersin, Metchnikoff, and other disciples of Pasteur. In the address prepared for this occasion the veteran scientist wrote:—