(b Aurillac, Cantal, France, 24 June 1840; d. Paris, France, 2 May 1904)
Duclaux belonged to that group of physicists and chemists, still limited in the second half of the nineteenth century, who through their work increased our knowledge of living matter. It appears, however, that his lasting fame derives less from his discoveries than from the close ties that bound him to Pasteur and his followers throughout his adult life. He was, in fact, one of the first to believe in microbes, and the books he devoted to them have long remained the “gospel” of the new doctrine.
His father was bailiff of the court at Aurillac, where his mother ran a small grocery. As a child, his long walks through the beautiful Auvergne countryside gave Duclaux a taste for nature and poetry; and his parents’ example revealed to him the value of sincerity, simplicity, and perseverance.
In 1857, upon completing his classical education at the local collège, Duclaux left Aurillac and went to Paris to attend the special mathematics course at the Lycée St. Louis. Two years later he was accepted at both the École Polytechnique and the École Normale Supérieure; he chose the latter. In 1862 he became agrégé in the physical sciences and was then retained by Pasteur as his laboratory assistant (agrégé-préparateur) at the school. It was during this period that the discussions of the possibility or impossibility of spontaneous generation were at their liveliest. Pasteur maintained that the microscopic creatures responsible for fermentation came from parents similar to themselves. Nicolas Joly, Pouchet, and Musset asserted that, on the contrary, these creatures were born spontaneously in organic fluids. From time to time Dumas and Balard, members of the commission named by the Académic des Sciences to settle the question, came to the École Normale. Duclaux, who had already participated in the experiments of his mentor, now attended the debates. The impression they made on him showed him his true course in life.
Dissociated from Pasteur’s laboratory, an agrégé-préparateur faced an uncertain future. After defending his doctoral thesis in physical sciences in 1865, Duclaux decided to leave Paris. He became a teacher first at the lycée in Tours, then at the Faculty of Sciences at Clermont-Ferrand, in which city his mother, a widow since 1860, joined him. He was able to renew his collaboration with Pasteur, first at Pont-Gisquet, Gard, where the master was pursuing his work on silkworm diseases, and a little later at Clermont-Ferrand. The experiments—on fermentation—began in a makeshift laboratory set up by Duclaux and were repeated on a much greater scale at the Kuhn brewery in Chamalières, which is between Clermont-Ferrand and Royat. It is well known that these experiments were requested in order to revive the brewing industry.
New professional duties brought Duclaux to Lyons in 1873 and finally to Paris in 1878. In Paris he won a competition for the professorship of meteorology at the Institut Agronomique, and he was also given a lectureship in biological chemistry at the Sorbonne. He immediately used this opportunity to give a course in microbiology, the first of its kind anywhere.
His young wife, the former Mathilde Briot, succumbed suddenly to puerperal fever following the birth of their second son. To forget his grief, Duclaux threw himself into his work with even greater energy. He taught, experimented, and wrote; and he followed, day after day, Pasteur’s extraordinary series of accomplishments. These included the development of vaccines against fowl cholera, anthrax, swine fever, and, in 1885, against rabies. In 1888 the Institut Pasteur was founded in Paris on rue Dutot. Duclaux, who meanwhile had become titular professor at the Sorbonne, transferred his teaching activities to the Institut Pasteur. A little earlier, through his efforts a new monthly journal, the Annales de l’Institut Pasteur, was created to publish research in microbiology.
Beginning with this period, one may say that Duclaux’s life was almost inseparable from that of the Institut Pasteur. At the death of its brilliant founder in 1895, he took over its direction and in a few years made it into a sort of “scientific cooperative,” in which each scientist, while preserving the independence of his own ideas, worked toward a common goal. To the original buildings were added, at the beginning of the century, the Institut de Chimie Biologique and a hospital.
Duclaux became a member of the Académie des Sciences in 1888, of the Société Nationale d’Agriculture in 1890, and of the Académie de Médecine in 1894. In 1901 he married Mme. James Darmesteter (the former Mary Robinson), a woman remarkable for both her intelligence and her warmth. He had finally found familial happiness again, but this happiness did not last. In January 1902 he suffered his first stroke. Scarcely recovered, he began to write again for the Annales and in the spring of 1903 recommenced his lectures. But this was too much to demand of an overtaxed body. On the evening of 2 May 1904 Duclaux suddenly lost consciousness and died in the night. His place as director of the Institut Pasteur was assumed by one of his pupils from Clermont-Ferrand, Émile Roux. The latter had become well known for his research with Pasteur, his discovery of the diphtheria bacillus, and his development of a specific diphtheria antitoxin.
Duclaux’s scientific work is at once that of a physicist and that of a chemist. As a physicist he studied the phenomena of osmosis, of molecular adhesion, and of surface tension. As a chemist he concentrated especially on fermentation processes. In this area he was to some extent following up the work of Pasteur. As the years passed he was led to accord to enzymes (then called diastases) an increasingly important role in the phenomena of life. He devoted a long series of investigations to the respective roles played in the intestinal tract of men and animals by enzymes issuing from glands and by those liberated by microbes. He recognized that the microbes had no role in gastric and pancreatic digestion, which involve only juices released from the tissues. Microbial digestion does not begin until the intestine, but then rapidly becomes important. In a related area, Duclaux realized that microbes are indispensable in the formation in the soil of plant nutrients. Without microbes the earth is infertile, because the enzymes in the plant cells cannot leave the cells and thus cannot act outside the plant.
Milk provided Duclaux with a material ideally suited to the study of enzymes. In the first stage, through a great number of analyses, he was able to develop methods permitting the determination of the proportions of its constituents. In the second stage he studied the enzymes capable of modifying the constituents. The great importance of enzymes was shown in the transformation of milk into cheese. In this case, however, the active agents are of external origin. A cheese is in fact the result of microbial cooperation: “Each of the microscopic workers must act in its turn and stop at the right moment. Such a workshop is difficult to direct, and one may say that it has required the experience of centuries to obtain products whose taste and appearance are always the same” (Émile Roux, in Annales de l’Institut Pasteur, 18 , 337). Duclaux studied several types of cheese, but undoubtedly with particular relish the cheese from Cantal, one of the riches of his native area.
Duclaux the teacher was no less remarkable than Duclaux the researcher. His pupil Roux, recalling his days as a medical student at Clermont-Ferrand, wrote: “Duclaux presented a subject so clearly that everyone understood. His words were those of a scientist burning with the ‘sacred fire.’ He set thinking, to the point that when one had finished his course, he seemed to be there still” (ibid.).
In addition to his research papers Duclaux wrote a great many didactic works; and the critical reviews he published in the Annales remain models. It has been said of them that they display “the logic of the scientist and the style of the poet.... He could extract from a memoir... possible consequences that the author himself had not always suspected. How many ideas he explored; what new insights he lavishly bestowed. Duclaux sowed the high wind...” (Émile Roux, in Bulletin de l’Institut Pasteur, 2 , 369).
Duclaux was captivating, full of wit and verve. He was also a just man with a passionate soul. He dreamed of a universal brotherhood under the banner of science—“the common fatherland,” as he used to say, “where one could have passions without having hatreds.” But he was not oblivious to what was happening outside his laboratory. On several occasions his devotion to the truth led him to enter into political conflicts. In particular he took a very active part in the campaign that finally forced the reinstatement of Captain Dreyfus.
I Original Works. A complete list of Duclaux’s scientific publications appears in Annales de l’Institut Pasteur, 18 (1904), 354–362.
Among his most important books are Ferments et maladies (Paris, 1882); Le microbe et la maladie (Paris, 1886); Cours de physique et de météorologie (Paris, 1891), a published version of his course at the Institut Agronomique; Traité de microbiologie, 4 vols. (Paris, 1891–1901); Principes de laiterie (Paris, 1892); Le tail, études chimiques et microbiologiques (Paris, 1894); Pasteur, histoire d’un esprit (Paris, 1896), which contains the frequently cited phrase, “Chemistry has taken possession of medicine, and will not let go” and L’hygiène sociale (Paris, 1902).
II. Secondary Literature. On the life and works of Duclaux, two articles by Émile Roux are classics: “Notice sur la vie et les travaux d’Émile Duclaux,” in Annales de l’Institut Pasteur, 18(1904), 337–362; and “Émile Duclaux,” in Bulletin de l’Institut Pasteur, 2 (1904), 369–370. A biography, La vie d’Émile Duclaux, was written by his second wife, Mary Darmesteter Duclaux (Paris, 1906).