(b. Tours, France, 5 April 1801; d. Rennes, France, 8 April 1860)
Both Dujardin’s father and grandfather were skilled watchmakers, originally in Lille, and Félix, who for a time trained in the trade, seems to have acquired some of his interests—as well as his remarkable manual dexterity—from them.
With his two brothers, Dujardin attended the classes of the Collège de Tours as a day pupil. He was originally attracted to art, especially drawing and design. His interest in science was apparently first aroused by a surgeon who was a friend of the family and who lent him some books on anatomy and natural history as well as Fourcroy’s Chimie. Chemistry became for a time Dujardin’s chief interest and, using a textbook by Thénard and some basic chemical reagents, he conducted simple experiments at home. Intending to study chemistry in the laboratories of Thénard and Gay-Lussac at Paris, he began to prepare himself for the entrance examination at the École Polytechnique. He persuaded his older brother to join him in these studies—particularly mathematics—and they both presented themselves for the examination in 1818. His brother succeeded, but Dujardin failed.
Discouraged by this failure, Dujardin went to Paris to study painting in the studio of Gérard, although he did not entirely forsake his scientific studies. In order to make a living, however, he soon accepted a position as a hydraulic engineer in the city of Sedan. He was married to Clémentine Grégoire there in 1823. Still restless, he returned to Tours, where he was placed in charge of a library. He began simultaneously to teach, especially mathematics and literature, and soon achieved sufficient success to give up his duties at the library. In his leisure, he pursued scientific studies of various kinds. His earliest publication, on the Tertiary strata and fossils of the Touraine area, were valuable enough to attract the attention of Charles Lyell1
When in 1826 the city of Tours decided to inaugurate courses in applied science, Dujardin was assigned to teach geometry. In 1829 he was asked to teach chemistry as well and was provided with liberal funds for the establishment of a laboratory. This gave Dujardin the opportunity to return to his initial interest in chemical research. He also pursued studies in optics and crystallography and found time for botanical excursions, which led in 1833 to the publication (with two collaborators) of Flore complète d’Indre-etLoire
About this time, the diversity of his interests began to trouble Dujardin. On the advice of Henri Dutrochet, he decided to specialize in zoology and left Tours for Paris in pursuit of this goal. For the next several years, he apparently supported himself and his family by writing for scientific journals and encyclopedias.
In 1839, on the strength of his work in geology, Dujardin was appointed to the chair in geology and mineralogy at the Faculty of Sciences at Toulouse. In November 1840 he was called to the newly established Faculty of Sciences at Rennes as professor of zoology and botany and dean of the faculty—a position that for several years embroiled him in disputes with his colleagues. The intensity of these disputes diminished somewhat after he gave up the deanship in 1842. Although he was nominated several times for more important positions in Paris, he seemed always to end up second in the voting. Convinced, with some justice, that he was being persecuted from all sides (his colleagues sought to undermine his authority by such tactics as spreading rumors about his sex life), Dujardin became almost a recluse and spent his final years at Rennes in quiet obscurity. Shortly before his death, he was elected corresponding member of the Académie des Sciences, twelve years after his name was first proposed.
From the beginning of his career in zoology, Dujardin seems to have perceived the importance of observing organisms in the living state. Having already traveled widely during his geological and botanical studies, he expanded his excursions in pursuit of living animal specimens. Some of this spirit is reflected in his rare but charming little book Promenades d’un naturaliste (Paris, 1838).
In the autumn of 1834 Dujardin went to the Mediterranean coast to study microscopic marine animals. It was this work that led him to suggest the existence of a new family, the Rhizopods (literally, “rootfeet”). This suggestion was based primarily on his careful examination of several living species belonging to a widely distributed group long known as the Foraminifera. The most obvious feature of these tiny organisms (especially in the fossil state) is a delicate multichambered shell, outwardly similar to the shell of such mollusks as the Nautilus, and they had consequently been classified as “microscopic cephalopods” by Alcide d’Orbigny in 1825. Although d’Orbigny’s classification was subsequently supported by the authority of Georges Cuvier, Dujardin rejected it because he was unable to see in the Foraminifera any evidence of the internal structure one ought to find in a mollusk. He perceived that the shell was only a secondary, external structure. By carefully crushing or decalcifying these delicate shells, he exposed a semifluid internal substance having no apparent structure.
As Dujardin observed the Foraminifera in their living state, he was struck by the activity of this contractile internal substance, which exuded spontaneously through pores in the calcareous shells to form pseudopodic rootlets. With equal spontaneity, these rootlets might then retract within the shell again. Dujardin became convinced that he was observing a special sort of amoeboid movement, in effect an amoeba within a porous shell. But pseudopodic rootlets could also be seen in microscopic animals having a less distinct casing than that of the Foraminifera, and Dujardin suggested that all such organisms should be joined in a new family to be called the Rhizopoda. According to this view, the Foraminifera, d’orbigny’s so-called “microscopic cephalopods,” were in truth merely rhizopods with shells (Rhizopodes á coquilles).
This work in systematics led Dujardin to conclusions of far greater significance. In particular he now denied the famous “polygastric hypothesis” of Christian Ehrenberg, the foremost protozoologist of the era. Ehrenberg had recently revived Leeuwenhoek’s view that infusoria were “complete organisms”; more specifically, that they possessed organ systems that imitated in miniature the general features of the organ systems of far more complex organisms, including the vertebrates. Like d’Orbigny, Ehrenberg enjoyed the support of Cuvier, and his theory was generally accepted. In his classificatory scheme, Ehrenberg placed several hundred species of infusoria in a new class, the Polygastrica (literally, “many stomachs”), in conformity with his belief that the globules or vacuoles which appear in most infusoria are tiny stomachs (as many as 200) connected together by an intestine. The strongest evidence for this belief came from experiments in which Ehrenberg had fed infusoria with various dyes (indigo and carmine, for example) and had then observed coloration of the “stomachs.”
Dujardin reported that this conception had troubled him for some time. Although he could see neither the intestine nor the anal and oral orifices that Ehrenberg had posited, the “stomachs” were clearly visible. “I would,” he wrote, “probably have lost courage and abandoned this research... if I had not fortunately found the solution to my problem in the discovery of the properties of sarcode.”
“Sarcode” (from the Greek word for flesh) was the name Dujardin gave to the structureless substance he had found within the Foraminifera and other rhizopods and that he had found to be in every sense comparable to the substance of the amoeba and other Polygastrica. “The strangest property of sarcode”, wrote Dujardin, “is the spontaneous production, in its mass, of vacuoles or little spherical cavities, filled with the environing fluid.” It was these spontaneously produced vacuoles (vacuoles adventives) that Ehrenberg had mistaken for stomachs. Far from being complex organs, they were a natural result of the physical properties of sarcode; vacuoles could be formed at any time, by a spontaneous separating out of a part of the water present in living sarcode.
Ehrenberg’s feeding experiments did not prove the existence of true stomachs, since the vacuoles did not become distended upon ingestion as might be expected of walled stomachs and only some of the vacuoles took on color, while others remained colorless. If they were stomachs, how could one explain “this choice of different aliments for different stomachs?” Dujardin thus rejected Ehrenberg’s theory “with complete conviction,” finding no reason to believe that his microscope and his sight were inferior to Ehrenberg’s, especially since in several infusoria he had seen essential details which had escaped the German observer.
Dujardin presented all this work in a memoir of 1835. Ehrenberg did not retract, however. When in 1838 he published his monumental work on the infusoria as complete animals, he took every opportunity to ridicule Dujardin. In 1841 Dujardin gathered his work together in a large but less pretentious treatise on the infusoria. In this work, which became the starting point for later attempts to classify the protozoa, Dujardin reasserted his views but treated Ehrenberg rather more fairly than Ehrenberg had treated him. The polemic between Dujardin and Ehrenberg stimulated great interest in the microscopic animals and focused attention on one of the most important and recurrent issues in the history of biology—the relation between structure and function. By 1870 this issue had been resolved at one level by the general acceptance of the protoplasmic theory of life, according to which the basic attributes of life resided in a semifluid, largely homogeneous ground substance (protoplasm) having no apparent structure.
Dujardin’s description of sarcode represents an important step toward this view. In his memoir of 1835, he wrote: “I propose to name sarcode that which other observers have called living jelly [gelée vivante], this diaphanous, glutinous substance, insoluble in water, contracting into globular masses, attaching itself to dissecting-needles and allowing itself to be drawn out like mucus; lastly, occurring in all the lower animals interposed between the other elements of structure.” Dujardin went on to describe the behavior of sarcode when subjected to various chemicals. Potash seemed to hasten its decomposition by water, while nitric acid and alcohol caused it to coagulate suddenly, turning it white and opaque. “Its properties,” wrote Dujardin, “are thus quite distinct from those of substances with which it might be confused, for its insolubility in water distinguishes it from albumen (which it resembles in its mode of coagulation), while at the same time its insolubility in potash distinguishes it from mucus, gelatin, etc.”
Because this is such a remarkably complete and accurate description of what would later be called protoplasm, some of Dujardin’s admirers have insisted that the German-directed (most especially by the histologist Max Schultze) substitution of “protoplasm” for “sarcode” represents “a violation of all good rules of nomenclature and justice.”2 If this attitude is meant to suggest that Dujardin was the rightful discoverer of the substance of life, one major objection can beraised; namely, that it ascribes to Dujardin’s work a broader interpretation than he himself seems to have given it. He did suggest, even in 1835, that sarcode was present in a number of animals more complicated than the infusoria (worms and insects, for example), and he did soon after recognize that the white blood corpuscles were also composed of sarcode. The identity between plant protoplasm and animal sarcode seems to have escaped him, however, and was emphasized instead by German workers, most notably Ferdinand Cohn and Max Schultze. Until this identity was recognized, the notion of a substance of life had little meaning. Perhaps Dujardin missed the identity because he never integrated his notion of sarcode with the concept of the cell.
Dujardin published memoirs on a variety of animals other than the infusoria, particularly the coelenterates, intestinal worms, and insects. In 1838 he described a rare species of spiculeless sponge, to which his name was later attached. He also considered the then disputed question whether sponges were animals or plants, and concluded that they were animals. In 1844, he published a major treatise on the intestinal worms, which laid the basis for much of the work done since in helminthology and parasitology.
At the time of his death, Dujardin was engaged in a major study of the echinoderms, although he was by then more interested in questions of broader biological significance. He regretted that this work on the echinoderms kept him from a proper investigation of the “division of germs,” of the species problem, and particularly from a new study on sarcode. This last point is especially interesting because by 1852 at least, Dujardin clearly recognized that the properties of sarcode led to an idea of great biological significance—the idea of “life as anterior to organization, as independent of the permanence of forms, as capable of making and defying organization itself.”3 It should be emphasized that Dujardin did not really deny all organization whatever to sarcode. Rather, he argued that its organization could not be compared to the definite structures observable in higher organisms. He seems to have had an almost prophetic vision of the importance of organization at the more subtle molecular level, and with the benefit of hindsight, E. Fauré-Fremiet makes a persuasive case for considering Dujardin a pioneer in the colloidal chemistry of protoplasm.4
Apart from this prophetic vision, perhaps the most appealing feature of Dujardin’s work is his consistent modesty and rigorous attention to methodology. He always recognized that his work might undergo significant modification through the efforts of later workers and rarely made a claim that was not supported by his own direct observations. In placing the bacteria among the animals rather than the plants, in failing to recognize the significance of the nucleus, and in considering spontaneous generation possible, Dujardin was in the company of most of his contemporaries. His close attention to microscopic method is particularly apparent in his Manuel de l’observateur au microscope (1843), but it also informs his major treatise on the infusoria, which contains a brief but suggestive sketch of the historical interrelationship between developments in microscopic technique and developments in knowledge about the microscopic animals.
The breadth of Dujardin’s early interests was crucial to his later success in protozoology. His artistic talent and training is evident in the many careful and beautiful plates with which his works are illustrated. His knowledge of optics allowed him to develop an improved method of microscopic illumination which bore his name and which can be considered an ancestor of the present condenser. Finally, his knowledge of physics and chemistry was important in enabling him to describe so completely and so accurately the properties of sarcode. It is easy to agree with Dujardin’s admirers that his work was improperly appreciated during his lifetime, and easy to understand why protozoologists still cite his work with admiration today.5
1. Charles Lyell, “On the Occurrence of Two Species of Shells of the Genus Conus in the Lias, or Inferior Oolite, near Caen in Normandy,” in Annals of Natural History, 6 (1840), 293; and Principles of Geology (9th ed., London, 1853), p. 236.
2. Yves Delage, La structure du protoplasma et les théories sur l’hérédité et les problèmes grands de la biologie générale (Paris, 1895), p. 19. See also L. Joubin, p. 10.
3. E. Fauré-Fremiet, pp. 261–262.
I. Original Works. Dujardin’s major works are “Recherches sur les organismes inférieurs,” in Annales des sciences naturelles (zoologie), 2nd ser., 4 (1835), 343–377; Histoire naturelle des zoophytes. Infusoires, comprenant la physiologic et la classification de ces animaux et la manière de les étudier à l’aide du microscope (Paris, 1841); and Histoire naturelle des Helminthes ou vers intestinaux (Paris, 1845).
A complete bibliography of Dujardin’s ninety-six published works can be found in Joubin (see below), pp. 52–57, while sixty-four of his papers are cited in the Royal Society Catalogue of Scientific Papers, II, 378–380.
Dujardin’s rich collection of manuscripts, including laboratory notes and more than 500 letters, many of which are from the leading scientists of the day, is preserved at the Faculty of Sciences in Rennes. This probably important collection remains largely untapped, although Joubin and E. Fauré-Fremiet have made some use of it.
II. Secondary Literature. The basic source is L. Joubin, “Félix Dujardin,” in Archives de parasitologie, 4 (1901), 5–57. At the time he wrote this paper, Joubin held the chair at Rennes once occupied by Dujardin, and it was his clear intention to bestow on his predecessor all the honor he had been denied in life. The attempt was marred by Joubin’s consistent and uncritical tendency to give Dujardin’s work an importance that only hindsight can provide.
Also on Dujardin, see Enrique Beltrán, “Felix Dujardin y su Histoire naturelle des zoophytes. Infusoires, 1841,” in Revista de la Sociedad mexicana de historia natural, 2 (1941), 221–232; “Notas de historia protozoologica. I. El descubrimiento de los sarcodarios y los trabajos de F. Dujardin,” ibid., 9 (1948), 341–345; and E. Fauré-Fremiet, “L’oeuvre de Félix Dujardin et la notion du protoplasma,” in Protoplasma, 23 (1935), 250–269.
More generally, see J. R. Baker, “The Cell Theory: A Restatement, History, and Critique. Part II,” in Quarterly Journal of the Microscopical Sciences, 90 (1949), 87–107; F. J. Cole, The History of Protozoology (London, 1926); G. L. Geison, “The Protoplasmic Theory of Life and the Vitalist-Mechanist Debate,” in Isis, 60 (1969), 273–292; Toward a Substance of Life: Concepts of Protoplasm, 1835–1870 (unpublished M.A. thesis, Yale University, 1967); and Arthur Hughes, A History of Cytology (London. 1959).
Gerald L. Geison