M. Bigo’s son, who studied in Pasteur’s laboratory, has summed up in a letter how these accidents of manufacture became a starting point to Pasteur’s investigations on fermentation, particularly alcoholic fermentation. “Pasteur had noticed through the microscope that the globules were round when fermentation was healthy, that they lengthened when alteration began, and were quite long when fermentation became lactic. This very simple method allowed us to watch the process and to avoid the failures in fermentation which we used so often to meet with.... I had the good fortune to be many times the confidant of the enthusiasms and disappointments of a great man of science.” Young Bigo indeed remembered the series of experiments, the numerous observations noted, and how Pasteur, whilst studying the causes of those failures in the distillery, had wondered whether he was not confronted with a general fact, common to all fermentations. Pasteur was on the road to a discovery the consequences of which were to revolutionize chemistry. During months and months he worked to assure himself that he was not a prey to error.
In order to appreciate the importance of the ideas which from that small laboratory were about to inundate the world, and in order to take account of the effort necessitated to obtain the triumph of a theory which was to become a doctrine, it is necessary to go back to the teachings of that time upon the subject of fermentations. All was darkness, pierced in 1836 by a momentary ray of light. The physicist Cagniard-Latour, studying the ferment of beer called yeast, had observed that that ferment was composed of cells “susceptible of reproduction by a sort of budding, and probably acting on sugar through some effect of their vegetation.” Almost at the same time the German doctor Schwann was making analogous observations. However, as the fact seemed isolated, nothing similar being met with elsewhere, Cagniard-Latour’s remark was but a curious parenthesis in the history of fermentations.
When such men as J. B. Dumas said that perhaps there might be a sequel to Cagniard-Latour’s statement, they emitted the idea so timidly that, in a book On Contagion published at Montpellier in 1853, Anglada, the well known author, expressed himself thus—
“M. Dumas, who is an authority, looks upon the act of fermentation as strange and obscure; he declares that it gives rise to phenomena the knowledge of which is only tentative at present. Such a competent affirmation is of a nature to discourage those who claim to unravel the mysteries of contagion by the comparative study of fermentation. What is the advantage of explaining one through the other since both are equally mysterious!” This word, obscure, was to be found everywhere. Claude Bernard used the same epithet at the Collège de France in March, 1850, to qualify those phenomena.
Four months before the request of the Lille manufacturer, Pasteur himself, preparing on a loose sheet of paper a lesson on fermentation, had written these words: “What does fermentation consist of?—Mysterious character of the phenomenon.—A word on lactic acid.” Did he speak in that lesson of his ideas of future experiments? Did he insist upon the mystery he intended to unveil? With his powers of concentration it is probable that he restrained himself and decided to wait another year.
The theories of Berzelius and of Liebig then reigned supreme. To the mind of Berzelius, the Swedish chemist, fermentation was due to contact. It was said that there was a catalytic force. In his opinion, what Cagniard-Latour believed he had seen, was but “an immediate vegetable principle, which became precipitated during the fermentation of beer, and which, in precipitating, presented forms analogous to the simpler forms of vegetable life, but formation does not constitute life.”
In the view of the German chemist Liebig, chemical decomposition was produced by influence: the ferment was an extremely alterable organic substance which decomposed, and in decomposing set in motion, by the rupture of its own elements, the molecules of the fermentative matter; it was the dead portion of the yeast, that which had lived and was being altered, which acted upon the sugar. These theories were adopted, taught, and to be found in all treatises on chemistry.
A vacancy at the Académie des Sciences took Pasteur away from his students for a time and obliged him to go to Paris. Biot, Dumas, Balard and Senarmont had insisted upon his presenting himself in the section of mineralogy. He felt himself unfit for the candidature. He was as incapable of election manœuvres as he was full of his subject when he had to convince an interlocutor or to interest an audience in his works on crystallography. (These works had just procured the bestowal on him of the great Rumford medal, conferred by the London Royal Society.) During this detested canvassing campaign he had one happy day: he was present on February 5, 1857, at the reception of Biot by the Académie Française.
Biot, who had entered the Académie des Sciences fifty-four years earlier, and was now the oldest member of the Institute, took advantage of his great age to distribute, in the course of his speech, a good deal of wise counsel, much applauded by Pasteur from the ranks of the audience. Biot, with his calm irony, aimed this epigram at men of science who disdained letters: “Their science was not the more apparent through their want of literary culture.” He ended by remarks which formed a continuation of his last letter to Pasteur’s father. Making an appeal to those whose high ambition is to consecrate themselves to pure science, he proudly said: “Perhaps your name, your existence will be unknown to the crowd. But you will be known, esteemed, sought after by a small number of eminent men scattered over the face of the earth, your rivals, your peers in the intellectual Senate of minds; they alone have the right to appreciate you and to assign to you your rank, a well-merited rank, which no princely will, no popular caprice can give or take away, and which will remain yours as long as you remain faithful to Science, which bestows it upon you.”
Guizot, to whom it fell to welcome Biot to the Académie, rendered homage to his independence, to his worship of disinterested research, to his ready counsels. “The events which have overturned everything around you,” he said, “have never turned the course of your free and firm judgment, or of your peaceful labours.” On that occasion the decline of Biot’s life seemed like a beautiful summer evening in the north, before nightfall, when a soft light still envelops all things. No disciple ever felt more emotion than Pasteur when participating in that last joy of his aged master. In Regnault’s laboratory, a photograph had been taken of Biot seated with bent head and a weary attitude, but with the old sparkle in his eyes. Biot offered it to Pasteur, saying: “If you place this proof near a portrait of your father, you will unite the pictures of two men who have loved you very much in the same way.”