Ehrenberg, Christian Gottfried

(b. Delitzsch, near Leipzig, Germany, 19 April 1795; d. Berlin, Germany, 27 June 1876)

biology, micropaleontology.

Ehrenberg’s father, Johann Gottfried Ehrenberg, was a municipal magistrate in the small city of Delitzsch; his mother, Christiane Dorothea Becker, was the daughter of an innkeeper. She died when Ehrenberg was thirteen years old. At the age of fourteen he entered school in Schulpforta, near Naumburg, a Protestant boarding school with a high level of instruction and a classical-philological orientation. In 1815, after passing his final examination, Ehrenberg, at his father’s request, began to study theology in Leipzig. He then changed to medicine, however, and during his five semesters in Leipzig also attended J. C. Rosenmüller’s lectures on anatomy and Schwägrichen’s lectures on botany and zoology.

In 1817 Ehrenberg continued his medical studies at the University of Berlin, where in 1818 he passed the state medical examination. He studied under Christoph W. Hufeland, K. A. W. Berends, and K. F. von Graefe and was especially influenced by Karl Rudolphi and Heinrich Link, who encouraged his botanical and zoological studies and stimulated his interest in microscopical technique. With the presentation of a botanical dissertation, “Sylvae mycologicae Berolinensis,” he was made a doctor of medicine in November 1818. This work not only depicts some 250 species of fungi found in the vicinity of Berlin (including sixty-two described for the first time) but it also demonstrates the constancy of the fungi species and their origin from seeds, which was still disputed. In a specialized work on the Syzygites megalocarpus (1819) he described for the first time the copulatory process among the molds and provided still further proofs of the sexual generation of the mushrooms in the essay De mycetogenesis epistola (1821).

These fundamental microscopical investigations led Ehrenberg to reject the then dominant view that spontaneous generation (generatio aequivoca) was possible in principle and that “lower” organisms, among which algae and fungi were grouped, could originate directly out of a basic inorganic substance, that is, water and slime. A major portion of Ehrenberg’s lifework, above all the later microscopical research, was directed toward the clarification of this question. In the context of this problem, it becomes understandable why throughout his life Ehrenberg placed so much weight on demonstrating the constancy of species even among the lower organisms. Through his research on fungi, Ehrenberg became acquainted with Nees von Esenbeck, the president of the Deutsche Akademie der Naturforscher Leopoldina, of which Ehrenberg had become a member in 1818. His acquaintance with Adelbert von Chamisso was also a result of his botanical studies. While preparing the material from his expeditions, Ehrenberg was able to observe the generation of the lichen.

Ehrenberg’s scientific career took a decisive turn in 1820 when he was presented with the opportunity to participate in the archaeological expedition of Count Heinrich von Menu von Minutoli, who planned to travel in Egypt. With a friend from his student days, Wilhelm Hemprich, Ehrenberg joined this expedition, which was advocated by Alexander von Humboldt (then residing in Paris) and by Heinrich Lichtenstein, the director of the university’s zoological museum. The expenses of Ehrenberg and Hemprich were financed primarily by the Prussian Academy of Sciences, which also gave the instructions for the expedition. The two men were first to study thoroughly the natural history collections in Vienna and to consult scientists residing in that city. Therefore, in June 1820, Ehrenberg traveled from Berlin to Vienna and then to Trieste, where the party boarded ship for Alexandria on 5 August. The journey led through the Libyan desert to Cyrenaica, to Fayum in 1821, toward the Nile to Dongola, and to the shores of the Red Sea (in 1823) and yielded an unexpectedly large body of scientific results. Of the animal species alone, 3,987 (34,000 individual zoological objects) were sent to the collections of the Berlin Zoological Museum, which in that period were under the supervision of Heinrich Lichtenstein. As for botany, 46,000 plant specimens representing approximately 3,000 species were collected. The poor organization of the journey and its insufficient financing resulted in a considerable loss of time and many privations. Many members of the expedition became seriously ill. Ehrenberg’s companion Hemprich fell victim to a fever in Massawa shortly before the end of the trip in 1825. Ehrenberg was forced to halt the journey ahead of schedule, without being able to explore the interior of Abyssinia; however, he had already made the littoral observations that were to make him famous as a zoologist. In his work on the coral polyps of the Red Sea (1834), he presented the first exact investigations on the anatomy, nourishment, and growth of the corals, and in individual works (published mostly in Poggendorf’s Annalen der Physik) he explained the causes of the coloring of the Red Sea and the composition of the dust of trade winds. He also made drawings, based on microscopical studies, of numerous marine animals (mollusks, echinoderms, medusae, and electric rays) in situ; examined vertebrates for endoparasites; and made anatomical and embryological observations on insects, crabs, and spiders. In accordance with the scientific instructions given by the Berlin Academy, the collecting was not confined to plants and animals but also included rocks, fossils, and geographic measurements, as well as historical and ethnographic data and materials, among which were six manuscripts of ancient Arab physicians.

At the beginning of December 1825, Ehrenberg landed again in Trieste, the only survivor of an expedition that had lost nine members, including Hemprich. After his return Ehrenberg, originally humorous and joyful, experienced further disappointments that spoiled his enjoyment of the scientific utilization of this unusual and very productive journey. Even before his return his collections were decimated through the sale of the duplicates, and some of the boxes were damaged during quarantine, resulting in the destruction of their contents; consequently, of the originally immense series of forms of each species, only a fraction was still usable. Moreover, labels and sketches were missing, and Ehrenberg could hardly put the collections in order by himself.

Although in 1826 he published the plan for a comprehensive work (in the journal Hertha, pp. 92–94), the first section of which was to contain an account of the expedition, and the second, illustrated descriptions of the individual plants and animals, neither portion was completed, even though draftsmen paid by the state aided in preparing the material. The description of the journey and the first parts of the Symbolae physicae, dealing with animal and bird descriptions, appeared in 1828. Moreover, individual results obtained on the expedition had been reported since 1826 in the sessions of the Berlin Academy of Sciences by its members Alexander von Humboldt, Heinrich Lichtenstein, Heinrich Link, Karl Rudolphi, and Christian Weiss.

In July 1827, Ehrenberg was elected a member of the Berlin Academy of Sciences, having already become, on 24 March of that year, an assistant professor at the University of Berlin. In these years Ehrenberg obtained financial aid and scientific support through the influential Alexander von Humboldt, who in May 1827 left Paris to settle permanently in Berlin. He persuaded Ehrenberg to participate in a scientific expedition to Siberia financed by Czar Nicolas I. Ehrenberg used this opportunity not only to collect botanical and zoological specimens but also to undertake geological and paleontological studies, and to make microscopical observations on the Infusoria (or, as they were then called, animalcules). Humboldt’s eight-month journey, in which, besides Ehrenberg, the Berlin mineralogist Gustav Rose took part, went from St. Petersburg and Moscow to Nizhni Novgorod (now Gorki), up the Volga to Kazan and to Ekaterinburg (now Sverdlovsk), and form there into the northern Urals. On the return journey, based in Astrakhan, they navigated the Volga and the Caspian Sea, where Ehrenberg, in addition to gathering fish for the St. Petersburg, Paris, and Berlin museums, made observations on living plankton.

Following his return home in 1831, Ehrenberg married Julie Rose, the niece of Gustav Rose and the daughter of Johannes Rose, a businessman and the consul in Wismar. After her early death (1848) he was married again, in 1852, this time to Karoline Friederike Friccius, sister-in-law of the chemist Eilhard Mitscherlich. From his first marriage he had one son, Hermann Alexander, and four daughters. The eldest daughter, Helene, married the botanist Johannes Hanstein, and another married the chemist Karl Friedrich Rammelsberg; the youngest daughter, Clara, aided her father in his scientific research.

When in 1833 Johannes Müller was appointed successor to the late Karl Rudolphi, Ehrenberg was disappointed in his hope of being named to the chair of comparative anatomy, which would have allowed him to use the zootomical collections (including the material he himself had contributed) unhindered by questions of competence. As a result of Alexander von Humboldt’s vigorous intercession, a strengthening of Ehrenberg’s academic standing was sought, and in 1839 he was given a full professorship in “Methodologie, Enzyklopädie und Geschichte der Medizin.” Ehrenberg did not, however, view this teaching post in terms of an active role. Generally, he hardly functioned as a university teacher, although as a member of the Berlin Academy of Sciences he had the right to lecture at the university even without a teaching appointment.

Ehrenberg’s lifework consisted mainly of specific research, which he carried out at the Berlin Academy. It was recognized through his election to the Académie des Sciences of Paris (1841), his appointment as secretary of the Mathematics-Physics Section of the Berlin Academy of Sciences (1842), and by the award of the Order of Merit (1842), in which Alexander von Humboldt’s opinion was important.

The scientific work that Ehrenberg undertook in Berlin following his return from the Russo-Siberian expedition was at first still related to the observations he had made on the Middle Eastern journey, especially those from the Red Sea. Included in this category are the publications on Hydrozoa and mollusks, especially the works on the coral polyps of the Red Sea (1831–1834); contributions to the knowledge of the physiology of the coral polyps in general and those of the Red Sea in particular, including an essay on the physiological systematics of these animals (1832); the medusae of the Red Sea (1834, 1835); marine phosphorescence (1835); the development and structure of the gastrotricha and rotatoria (1832); and the first reports on the so-called animalcules (Infusoria), the group that later absorbed Ehrenberg’s interest. Already in 1828 and in 1830 he had given lectures at the Berlin Academy on the organization, systematics, and geographical relations of the Infusoria, which were soon followed by a series of papers entitled “Zur Erkenntnis der Organisation in der Richtung des kleinsten Raumes” (from 1832). Ehrenberg first treated this theme in monograph form in 1838, in Die Infusionsthierchen als vollkommene Organismen, in which he also presented a detailed historical sketch on the investigation and significance of this heterogeneous class of animals and elucidated the method of study underlying his microscopical researches. Although in all these works Ehrenberg utilized primarily observations and specimens from his Middle East expedition, he nevertheless almost always completed them with comparative material from the Baltic Sea and North Sea or from the Russo-Siberian expedition.

All Ehrenberg’s individual observations were viewed in the light of a fundamental conception held consistently since his student years: this consisted of examining the theory, revived by Leibniz in the eighteenth century, of the existence of a “chain of being” (scala naturae) in nature. One of the bases for this theory was the various levels of organization among organisms, combined with the ideas that there exist gradual transitions in structure and performance from the mineral kingdom to man, that transformations from “lower” into more highly organized creatures still take place everywhere in nature, and that the lowest organisms can emerge spontaneously out of inorganic matter. These theories, which were earnestly discussed until the middle of the nineteenth century, were based mainly on that little-investigated group of organisms that Cuvier had united in the fourth class of his “radial animals.” The five classes of the “radial animals” were, according to Cuvier, echinoderms, entozoa, medusae, polyps, and Infusoria; and they were considered to be simple organized animals, as opposed to the divisions within the vertebrates, mollusks, and arthropods. From the beginning of his research Ehrenberg strove to investigate the inner organization of the animals of these five classes and particularly to provide a new, systematic grouping for the Infusoria, a task to which he was led in large part by the use of the microscope.

In his opinion, all animals possess with an equal degree of completeness the important organs of life, e.g., nervous and vascular systems, muscles, and digestive and sexual organs. Through comparative anatomical investigations. Ehrenberg examined Cuvier’s five classes for the presence of these organs. In order to ascertain the nervous capacity of the echinoderms and medusae, he employed, on the advice of Alexander von Humboldt, galvanic currents as stimuli. In exploring the structure of the digestive organs he utilized, beginning in 1833, food colored with indigo or carmine. He carried out an extensive series of studies of this type with the Infusoria in particular. At the time this group still included such heterogeneous organisms as bacteria, all single-celled animals, the many-celled rotatoria, and several worms. Ehrenberg did not yet separate the manycelled animals from the single-celled ones, a concept that became current in systematic zoology only after 1850; rather, he believed that he could demonstrate the presence of complete organ systems in singlecelled animals. This was for him an important argumentment against spontaneous generation and the “chain of being.”

In spite of a critical, inductive research method, Ehrenberg succumbed to an optical error, especially when he consciously renounced microscopical magnifications of greater than 300. His error was similar to that of the pioneers of the microscope in the seventeenth century, like Leeuwenhoek and Swammerdam, who considered the indistinct structures in the egg and the sperm to be complete organisms and on these grounds derived the preformation theory. The basis for the correction of Ehrenberg’s errors was set out only in 1863, with the union of protozoology and cytology. In his later years Ehrenberg could no longer accept the more correct perceptions of Felix Dujardin (his most vehement opponent), Theodor von Siebold, Max Schultze, and others, since they did not concern an individual error but called into question the entire conception of his system of the animal kingdom.

As a systematist Ehrenberg proceeded from Cuvier, but he had rejected both the latter’s graduated hierarchy of the more highly and thoroughly organized animals and his classification of man among the mammals. His own system, which he proposed in 1836 in the sketch of the animal kingdom according to the principle of a single type reaching down to the monad, set man (Kreis der Völker) as a systematic category in contrast with the animals (Kreis der Tiere). He based this procedure on the “capacity for mental development” (geistigen Entwicklungsfähigkeit) of the human race, and even for the classification of the animals he employed social behavior as the most important taxonomic characteristic. This conception remained limited to its time and later hindered Ehrenberg’s acceptance of the Darwinian theory of evolution.

So much the greater, then, is the importance of the continuation of the studies on single-celled marine and fossil animals, with which Ehrenberg completed his pioneering achievements. With the microscope he discovered single-celled fossils that built up geological strata; he gave exact descriptions of and discriminated among the shells and skeletons of freshwater and marine animals, thereby becoming the founder of microgeology and micropaleontology in Germany. His collection of samples, containing many types, along with his manuscripts and correspondence, are still available for study in the Museum für Naturkunde in Berlin.

Through his worldwide marine investigations Ehrenberg was invited to participate in oceanographic research projects of international importance. Thus he influenced the instructions, drawn up by Humboldt, for James Ross’s Antarctic expedition (1839– 1843)and for the Novara expedition (1857–1859) and worked on the deep-bottom samples of the American researchers Silliman, L. W. Bailey, and M. F. Maury; the latter, beginning in 1853, provided him with material taken from depths of 10,000–12,000 feet. These results made possible L. Brooke’s invention of the deep-sea lead, for the employment of which on German ships such as the Arkona and the Thetis (1860–1862) and the Nymphe (1865–1868) Ehrenberg tirelessly campaigned. Finally, the Gazelle expedition (1874–1876) was equipped with this device, but Ehrenberg did not live to see the results. Even the investigation of the sea bottom served Ehrenberg in his refutation of the theory of spontaneous generation, which had again come under discussion from the standpoint of the theory of evolution, through the hypothetical prehistoric organism Bathybius haeckeli.

In his lifetime and until the present, Ehrenberg has been reproached for not completing the utilization of the collections assembled on his Middle East expedition, for not accepting the findings of cytology and of the theory of evolution, and for not correcting his errors. The first stemmed both from technical problems, extending to a lack of scientific organizational ability, and from his very exact and laborious method of working, which aimed at comprehensive analysis. Moreover, the results were embedded in a philosophical system that presupposed the spiritual origin and constancy of the world order and therefore resisted materialistic and evolutionary interpretations. His method was based on the comparative anatomy and morphology of the first half of the nineteenth century; in these areas, as a pioneer of microscopy, he employed polarized light and pursued a comparative microscopical anatomy—with outmoded optical means. He expressed the program of his life and his research in a youthful letter (1821) to Nees von Esenbeck: “Until now my favorite pursuit has been neither naked systematizing nor unsystematic observation, and whenever time and circumstances, together with my ability, allow it, I prefer getting down to the grass-roots level” (Stresemann, “Hemprich und Ehrenberg. Reisen zweier naturforschender Freunde...,” p. 42). In later years he considered only purely empirical knowledge to be valid; the lasting merit of his description and classification of the fossil protozoans stems from this position.

BIBLIOGRAPHY

I. Original Works. Ehrenberg’s writings include Reisen in Aegypten, Libyen, Nubien und Dongola, I, pt. 1 (Berlin, 1828), not completed; Symbolae physicae (Berlin, 1828–1845): Aves, pts. 1–2 (1828–1829), Mammalia, pts. 1–2 (1828–1832),Evertebrata excl. Insecta, pts. 1–2(1829–1831), Insecta, pts. 1–5 (1829–1845), none of the divisions completed; “Ueber die Natur und Bildung der Corallenbänke des rothen Meeres und über einen neuen Fortschritt in der Kenntnis der Organisation im kleinsten Raume durch Verbesserung des Mikroskops von Pistor und Schiek,” in Abhandlungen der Preussischen Akademie der Wissen-schaften zu Berlin (1832), pp. 381–438; “Ueber den Mangel des Nervenmarks im Gehirn der Menschen und Thiere, den gegliederten röhrigen Bau des Gehirns und über normale Krystallbildung im lebenden Tierkörper,” in Annalen der Physik, 28 , no. 3 (1833); Ueber die Natur und Bildung der Coralleninseln und Corallenbänke im rothen Meere (Berlin, 1834); Das Leuchten des Meeres. Neue Beobachtungen nebst Übersicht der Hauptmomente der geschichtlichen Entwicklung dieses merkwürdigen Phänomens (Berlin, 1835); Die Akalephen des rothe Meeres und den Organismus der Medusen der Ostsee erläutert und auf Systematik angewendet (Berlin, 1836), which contains the first draft and a review of his system; Beobachtung einer auffallenden bisher unerkannten Structur des Seelenorgans bei Menschen und Tieren (Berlin, 1836); “Ueber das Massen verhältnis der jetzt lebenden Kiesel-Infusorien...,” in Abhandlungen der Preussischen Akademie der Wissenschaften zu Berlin (1836), pp. 109–136; Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben der Natur (Leipzig, 1838), with an atlas and 64 colored copperplates; “Über noch zahlreich jetzt lebende Tierarten der Kreidebildung,” in Abhandlungen der Preussischen Akademie der Wissenschaften zu Berlin (1839), pp. 81–174; “Kieselschaligen Süsswasserformen am Wasserfall-Fluss im Oregon” and “Mikroskopisches Leben in Texas,” in Monatsberichte der Akademie der Wissenschaften zu Berlin (1848–1849), pp. 76–98; “Über das mikroskopische Leben der Galapagos-Inseln,” ibid. (1853), pp. 178–194; “Über die erfreuliche im Grossen fördernde Teilnahme an mikroskopischen Forschungen in Nord-Amerika,” ibid., pp. 203–220; “Über die seit 27 Jahren noch wohl erhaltenen Organisations-Praparate des mikroskopischen Lebens,” in Abhandlungen der Preussischen Akademie der Wissenschaften zu Berlin (1862), pp. 39–74, with three color plates; “Über die wachsende Kenntnis des unsichtbaren Lebens als felsbildende Bacillarien in Californien,” ibid.(1870), pp. 1–74, with three plates; “Uebersicht... über das von der Atmosphäre getragene organische Leben,” ibid. (1871), pp. 1–150; “Nachtrag zur Übersicht der organischen Atmosphärilien,” ibid. (1871), pp. 233–275, with three plates; “Mikrogeologische Studien über das kleinste Leben der Meeres-Tiefgründe aller Zonen und dessen geologischen Einfluss,” ibid. (1873), pp. 131–398, with twelve plates; and “Fortsetzung der mikrogeologischen Studien als GesammtÜbersicht der mikroskopischen Paläontologie gleichartig analysierter Gebirgsarten der Erde, mit specieller Rücksicht auf den Polycistinen-Mergel von Barbados,” ibid. (1875), pp. 1–225.

Unpublished travel diaries, MSS, and letters on his journeys to the Middle East and Siberia are in the archives of the Berlin Academy of Sciences, and original drawings are in the library of the zoological museum (Museum für Naturkunde) of Humboldt University, Berlin.

II. Secondary Literature. Biographies of Ehrenberg are Clara Ehrenberg, Unser Elternhaus. Ein Familienbuch (Berlin, 1905); Johannes von Hanstein, Christian Gottfried Ehrenberg (Bonn, 1877); and Max von Laue, Christian Gottfried Ehrenberg. Ein Vertreter deutscher Naturforschung im neunzehnten Jahrhundert (Berlin, 1895), with portrait and bibliography.

On specific aspects of Ehrenberg’s work, see H. Engel, “Het Levenswerk van Christian Gottfried Ehrenberg,” in Microwereld, 15 (1960), 19–32; Gerhard Engelmann, “Christian Gottfried Ehrenberg, ein Wegbereiter der deutschen Tiefseeforschung,” in Deutsche hydrographische Zeitschrift22 (1969), 145–157; Siegmund Günther, “Chr. G. Ehrenberg und die wissenschaftliche Erdkunde,” in Deutsche Rundschau für geographische Statistik, 17 (1895), 529–538; A. von Humboldt, “Bericht über die naturhistorischen Reisen der Herren Ehrenberg und Hemprich,” in Hertha (1827), 73–92; Otto Koehler, “Christian Gottfried Ehrenberg,” in H. Gehrig, ed., Schulpforta und das deutsche Geistesleben (Darmstadt, 1943), pp. 58–68; Erwin Stresemann, “Hemprich und Ehrenberg. Reisen zweier naturforschender Freunde im Orient, geschildert in ihren Briefen aus den Jahren 1819–1826,” which constitutes Abhandlungen der Deutschen Akademie der Wissenschaften zu Berlin, Klasse für Math, und allg. Naturwiss. (1954), no. 1, with a portrait; “Hemprich und Ehrenberg zum Gedenken. lhre Reise zum Libanon im Sommer 1824 und deren ornithologische Ergebnisse,” in Journal für Ornithologie, 103 (1962), 380–388: and Sigurd Locker, “Mikrofossilien aus der Sammlung Christian Gottfried Ehrenberg,” in Wissenschaftliche Zeitschrift der Humboldt-Universität zu Berlin, Math. Naturwiss. Reihe., 19 , no. 2–3 (1970), 186–189.

There is no comprehensive assessment of Ehrenberg’s importance in micropaleontology and geology. Unpublished letters and MSS in these areas are included in the micropaleontological collection of the Museum für Naturkunde, Berlin.

Ilse Jahn