Louis Pasteur’s father was a somewhat slow, reflective man; a little melancholic, not communicative; a man who lived an inner life, nourished doubtless on the memories of the part he had played on a larger stage than a tannery affords. His mother, on the other hand, was active in business matters, hard-working, a woman of imagination, prompt in enthusiasm.
Before Louis Pasteur was two years old, his parents moved first to Marnoz and then to a tannery situated at the entrance to the village of Arbois; and it was Arbois that Pasteur regarded as his home, returning in later life year after year for the scanty absence from his laboratory that he annually allowed himself. Trained at the village school, he repeated with his father every evening the task of the day. He showed considerable talent, and his eagerness to learn was fostered by the interest taken in him by M. Romanet, principal of the College of Arbois. At sixteen he had exhausted the educational resources of the village; and, after much heart-searching and anxious deliberation, it was decided to send the young student to Paris to continue his studies at the Lycée Saint-Louis. It was a disastrous experiment. Removed so far from all he knew and loved, Louis suffered from an incurable home-sickness, which affected his health. His father hearing this, came unannounced to Paris, and with the simple words, ‘Je viens te chercher,’ took him home. Here for a time he amused himself by sketching the portraits of neighbours and relatives, but his desire to learn was unquenched, and within a short time he entered as a student at the Royal College of Franche-Comté at Besançon. This picturesque town, situated only thirty miles from Arbois, was within easy reach of his home; and, above all, on market days his father came thither to sell his leather.
At eighteen Pasteur received the degree of Bachelier ès Lettres, and almost immediately was occupied in teaching others; but Paris, although once abandoned, was again asserting its powers of attraction, and by the autumn of 1842 he was once more following the courses at the Lycée Saint-Louis. He also attended the brilliant lectures of Dumas at the Sorbonne, and vividly describes the scene: ‘An audience of seven or eight hundred listeners, the too frequent applause, everything just like a theatre.’ At the end of his first year in Paris he achieved his great ambition, and succeeded in entering the École Normale, and entering it with credit.
For the last year or two Pasteur had been studying mathematics and physics; at the École Normale he especially devoted himself to chemistry. Under the teaching of Dumas and of Balard his enthusiasm redoubled, and he passed his final examinations with distinction. Balard was indeed a true friend. Shortly after the end of his career at the École Normale, the Minister of Public Instruction nominated Pasteur to a small post as teacher of physics at the Lycée of Tournon. But banishment from Paris meant banishment from a laboratory. Balard intervened, interviewed the Minister, and ended by attaching Pasteur to his staff of assistants.
It must always be remembered that Pasteur was trained as a chemist—was, in fact, a chemist. In afterlife he attacked problems proper to the biologist, the physiologist, the physician, the manufacturer; but he brought to bear on these problems, not the intellect of one trained in the traditions of natural science, medicine, or commerce, but the untrammelled intelligence of a richly-endowed mind, ‘organized common sense’ of the highest order. After the legal, there is, perhaps, no learned profession so dominated by tradition, by what our fathers have taught us, as the medical; and the advances in preventive medicine which will ever be connected with Pasteur’s name owe at least something to the fact that he was unfettered by any traditions of professional training or etiquette. Passing from the diseases of the lowest of the fungi to those of a caterpillar, a fowl, a sheep, until he reached those of man himself, it must be acknowledged that he approached the art of healing along an entirely new path.
His first researches were purely chemical—‘On the Capacity for Saturation of Arsenious Acid,’ ‘Studies on the Arsenates of Potassium, Soda, and Ammonia’—but he had been early attracted to the remarkable observations of Mitscherlich and others on the optical properties of the crystals of tartaric acid and its salts. Ordinary tartaric acid crystals, when dissolved in water, turn the plane of polarized light to the right; but another kind of tartaric acid, called by Gay-Lussac racemic acid, and by Berzelius paratartaric acid—as M. Vallery-Radot remarks, the name does not matter, and each is equally terrifying to the lay mind—leaves it unaffected. In spite of the different actions of the solutions of these two acids on light, Mitscherlich held their chemical composition to be absolutely identical.
This set Pasteur thinking. He repeated the experiments. On examining the crystals of sodium-ammonium salt of racemic acid, he noticed that certain facets giving a degree of asymmetry were always found on the crystals of the optically active salts and acids. On examining the crystals of the racemic acid, he did not find, as he had expected, perfect symmetry; but he saw that, whilst some of the crystals showed these facets to the right, others showed them to the left. In fact, sodium-ammonium racemate consisted of a mixture of right-handed and left-handed crystals, which neutralized one another as regards the polarization of light, and were thus optically inactive. With infinite patience Pasteur picked out the right from the left handed crystals, and investigated the action of their solutions on polarized light. As he expected, the one sort turned the plane of polarization to the left, the other to the right. A mixture of equal weights of the two kinds of crystals remained optically inactive. ‘Tout est trouvé!’ he exclaimed; and rushing from the laboratory, embraced the first man he came across. ‘C’était un peu comme Archimède,’ as his biographer gravely remarks.
His work immediately attracted attention. Biot, who had devoted a long and strenuous life to the problems of polarization, was at first sceptical, but, after a careful investigation, was convinced. Pasteur began to be talked about in the circle of the Institute.
In the midst of these researches Pasteur’s mother died suddenly, and her son, overwhelmed with grief, remained for weeks almost silent and unable to work. Shortly after this we find the old longing revived, and Pasteur sought at any cost some post near Arbois, somewhere not quite out of the reach of those he loved. Besançon was refused him, but at the beginning of 1849 he replaced M. Persoz as Professor of Chemistry at Strasbourg.
The newly-appointed Rector of the Academy of Strasbourg, M. Laurent, had already gained the respect and the affection of the professoriate. He and his family were the centre of the intellectual life of the town. Within a few weeks of his arrival Pasteur addressed to the Rector a letter, setting forth in simple detail his worldly position, and asking the hand of his daughter Marie in marriage. The wedding took place on May 29, 1850, and there is a tradition that Pasteur, immersed in some chemical experiment, had to be fetched from the laboratory to take his part in the ceremony at the church. Never was a union more happy. From the first Madame Pasteur, animated by the spirit of the Academy of Science, which always prints ‘Science’ with a capital letter, not only admitted, but approved the principle that nothing should interfere with the laboratory; whilst, on his side, Pasteur always flew to his wife to confide in her first of all any new discovery, any new advance he had made in his researches. During the five years passed at Strasbourg Pasteur continued to work on the borderline between chemistry and physics. His work on the polarization of light of the tartaric acid crystals led him into the question of the arrangement of the atoms within the molecule. ‘Il éclaire tout ce qu’il touche!’ exclaimed the once sceptical but now convinced Biot; and it is hardly too much to say that his researches were the starting-point of the new department of physics which, under the name of stereo-chemistry, has attained vast developments during the last quarter of the past century. These researches were rewarded by the French Government, which in 1853 conferred on him the ribbon of the Legion of Honour, and received the recognition of our own Royal Society, which rewarded him in 1856 the Rumford medal.