HERBST, CURT ALFRED

(b. Meuselwitz, near Altenburg, Thuringia, Germany, 29 May 1899; d. Heidelberg, Germany, 9 May 1946)

embryology.

Herbst was the son of Heinrich Herbst, a manufacturer, and of Henriette Martin. He decided when young to become a biologist. In 1886 and 1887 he studied at Geneva with Carl Vogt, then went to Jena, where Ernst Haeckel was among his teachers. He was awarded the Ph.D. at Jena in 1889 under the sponsorship of Arnold Lang. He passed his examination magna cum laude; his dissertation was a morphological study of a myriapod. Scutigera coleoptrata.

Herbst became acquainted with Hans Driesch in 1887 while they were students at Jena. They were very close friends; Richard Goldschmidt describes Herbst as Driesch’s “alter ego.” Both Herbst and Driesch had independent means, and, slow to settle into academic life, they traveled widely together for a number of years. In 1889 they went to the Mediterranean for the Easter holidays. and from November 1889 through April 1890 they traveled to Ceylon, Java, and India. Herbst spent the summer of 1890 as an assistant to Lang in Jena, then briefly attended the Polytechnical Institute in Zurich to increase his knowledge of chemistry. Then his travels with Driesch continued—throughout Europe, Algeria and Tunis, Palestine, Syria and Greece, Scandinavia, Egypt (twice), and India (twice)—until Driesch married in 1899, and even shortly after. After attending the International Zoological Congress held at Berlin in August 1901, the Driesches and Herbst took the long way around to Naples, traveling through Russia and Turkestan for two months.

The voyagers did not abandon biological investigation for the pleasures of cosmopolitan travel. The latter were interrupted regularly by the performance of experimental investigations by both men on the development of marine eggs, occasionally at Trieste or Rovigno, more often at the zoological station in Naples. Herbst qualified as Privatdozent in zoology at Heidelberg in 1901, under the tutelage of Otto Bütschli. After several years as Privatdozent there, he became an assistant professor in 1906, and he succeeded Bütschli in the professorial chair of zoology in 1919. The Driesches settled in Hei delberg in 1900 and spent nineteen years there. In 1935 Herbst became emeritus professor, and he remained in Heidelberg for the rest of his life. He was strongly and openly anti-Nazi, and his later years were very difficult.

Herbst was elected to membership in the Heidelberg Academy of Sciences in 1919. From 1914 to 1919 he was corresponding member of the Kaiser Wilhelm Institute for Biology in Berlin-Dahlem. Beginning around 1914 there was discussion of Herbst’s becoming an assistant to Hans Spemann there, but the plans were not carried through.

Herbst was held in great respect by his contemporaries for his inventive studies in experimental embryology, and his work was of great influence in providing impetus for the development of this new form of investigation. In 1891, at Trieste, he began a series of investigations of the development of sea urchin eggs in seawater of altered composition. In 1889 G. Pouchet and Laurent Chabry, in France, had reported that sea urchin larvae developed abnormally in seawater from which calcium had been precipitated out by the addition of potassium or sodium oxalate. They observed that as a result of calcium deficiency in the medium, the skeletons of the larvae were defective or absent, and that when the calcareous skeletal rods were not present, the arms of the pluteus larvae in which they are normally located failed to form.

Pouchet and Chabry postulated a mechanical explanation, and thought that the arms failed to form because they were not pushed out by skeletal rods— as if they were normally pushed out by the skeleton in the way that a portion of glove might be pushed out by the protrusion of a finger. Herbst repeated the experiments in 1891 and confirmed their results, but he interpreted the effect differently, in terms of morphogenetic stimuli. He thought that the arms were absent because of the lack of the stimulus to growth that the rods would have exerted upon the cells that would have formed the arms.

Herbst published these experimental results and his interpretation of them in 1892. He continued to perform experiments that were related to them, directly or indirectly, until 1943. Herbst had diminished the which the embryos were maintained in the experiments described in 1892. He later (1900) extended this investigation to demonstrate that when cleaving sea urchin eggs or larvae were raised in calciumfree seawater, the cells completely separated from one another. At a time when important experiments involved blastomeres’ being separated from each other mechanically by shaking, or by other methods that could introduce serious experimental errors. this was a technical advance of great significance: the method remained useful for many decades.

Herbst not only removed ions from seawater, he also added them. He added calcium chloride, as well as other salts, to the seawater in which he maintained sea urchin embryos. He increased the ion concentration of sodium, potassium, or magnesium, which he knew to be normally present in seawater. He also added salts that increased the concentration of ions of lithium, cesium, or rubidium, all elements found in the same column of the periodic table as sodium and potassium.

The most interesting and surprising effects were those of increased lithium ion concentration. Some larvae maintained in seawater to which lithium salts had been added lacked skeletal rods and arms in the pluteus stage. In some of the gastrulas raised in this medium, the layer of blastula destined to invaginate within the cap that was to become ectoderm, to form the endoderm and the digestive system, instead turned outward to form an empty endodermal bag. These gastrulas, instead of gastrulating, “exogastrulated,” : Furthermore, in a number of the exogastrulas, the amount of the endoderm was considerably increased at the expense of the ectoderm.

This was a great blow to the doctrine of germ layer specificity, which was then so rigid that it threatened to stifle progress in embryology. Furthermore, since the endoderm is situated at the pole of the egg opposite to that where the ectoderm is located, the use of the lithium ion provided a method of altering the polar gradients of the egg. For decades it was applied, by followers of Herbst, to the most sophisticated morphological, physiological, and biochemical studies of polarity and gradients that embryologists have yet accomplished. Herbst’s studies on the effects of altered ionic constitution on development may be considered the first important steps in the origins of modern chemical embryology.

Later in his life Herbst became interested in the effect of such simple chemical substances as carbonic acid and dilute nitric acid on sex determination in Bonellia, a marine worm. In one of Hans Spemann’s Silliman Lectures on embryonic induction, begun at about the time he was awarded the Nobel Prize (1935), Spemann referred to the work of Herbst on Bonellia as supporting the concept of a chemical inductive stimulus. At the same time, Spemann drew attention to the possibility that’ the first inductions… were discovered, or even suspected, by… Herbst… in his theoretical discussions on the role of formative stimuli in animal development.’

As an outcome of his new interpretation of the results of the Pouchet-Chabry experiments. Herbst published (1894, 1895) two long articles on the significance of stimulus physiology for the causal interpretation of processes of animal development, and in 1901 his monograph on formative stimuli in animal development appeared. In these he extended the tropism theories of such plant physiologists as Julius von Sachs and Wilhelm Pfeffer to causal explanations of the growth and development of plants and animals. He first considered the effects of external stimuli on plant growth, then those of stimuli from one part of an organism upon the growth or development of another.

Herbst acknowledged that it was the pathologist Rudolf Virchow who had introduced the concept of formative stimuli. He adduced much evidence demonstrating the existence and actions of such stimuli, however, and because of his high standing among his contemporaries, his elaboration of the theory was widely known. Also, in his Analytical Theory of Organic Development (1894). Driesch had independently devoted considerable attention to contact and chemical induction and to releasing effects in development. Of particular importance was Herbst’s double interest in induction as a releasing effect, and in its evocation of the development of something qualitatively new and different from what would have been formed in the absence of the evoking influence. His emphasis on the actions and significance of morphogenetic stimuli provided strong support for the concepts of embryonic induction that have dominated embryological theory ever since.

Except in his association with Driesch, Herbst led a withdrawn life. He was socially aloof and, although amiable, he seemed unapproachable. He had few friends other than Driesch. He never married. In part because of his Saxon accent, he seemed a rather comic figure to his students; nevertheless, they greatly admired him for his knowledge and wisdom. One of Herbst’s seminars inspired an interest in experimental embryology on the part of Viktor Hamburger, later a codiscoverer of the nerve growth factor and a figure of enormous influence in the establishment of developmental neurobiology as a separate discipline during the latter half of the twentieth century. Walter Landauer, who under Herbst’s guidance wrote his doctoral dissertation on the effect of lithium ions on echinoderm hybridization, came to America in 1924 and became an influential innovator in the application of genetics and biochemistry to the study of vertebrate teratology.

Thus the work of Herbst, in terms of both technical advance and theoretical insight, greatly influenced the development of embryology and deserves far more attention than it has received.

BIBLIOGRAPHY

1. Original Works.Herbst’s monograph is Formative Reize in der tierischen Ontogenese (Leipzig, 1901). Articles related to work discussed in this article include “Experimentelle Untersuchungen über den Einfluss der veränderten chemischen Zusammensetzung des umgebenden Mediums auf die Entwicklung der Tiere. I. Teil, Versuche an Seeigeleiern,” in zeitschrift für wissenschaftliche Zoologie, 55 (1892), 446–518 “…II, Weiteres über die morphologische Wirkung der Lithiumsalze und ihre theoretische Bedeutung,” in Mitteilungen der zoologischen Station zu Neapel. 11 (1893), 136–220; “Über die Bedeutung der Reizphysiologie für die kausale Auffassung von Vorgangen in den tierischen Ontogenese, I,” in Biologisches centralblatt, 14 (1894), 657–666, 689–697, 727– 744, 753–771, 800–810; “Ueber die Bedeutung der Reizphysiologie für die kausale Auffassung von Vorgängen in der tierischen Ontogenese, II,” Ibid., 15 (1895). 721– 745, 753–772, 8007–805, 817–813, 849–855; “über das Auseinandergehen von FurchungS- und Gewebzellen in kalkfreiem Medium,” in Wilhelm Roux Archiv für Entwicklungsmechanik der Organismen, 9 (1900), 424–463; “Untersuchungen zur Bestimmung des Geschlechtes, I und II,” in Sitzungsberichte der Heidelberger Akademie der wissenschaften, math-Wiss. Ki.(1928), 1–19, and (1929), 1–43;’ …III, ’ in Naturwissenschaften, 20 (1932), 375–379;’ …IV, ’ in Wilhelm Roux arching für Entwicklungsmechanik der Organismen, 132 (1935), 337– 383;’ …V, ’ibid., 134 (1926), 313–330;’ …VI, ’ ibid., 135 (1936), 178–20;’…VII, ’ ibid., 136 (1937), 147–168;’…VIII, ’ ibid., 138 (1938), 451–464;’ …IX, ’ ibid., 139 (1939), 282–302;’ …X, ’ibid., 140 (1940), 252–and’ Die Bedeutung der Salzversuche für die frage nach der Wirkungsart der Gene, ’ ibid., 142 (1943), 319–378.

II. Secondary Literature.Because of the state of disorder in Germany at the time of Herbst’s death, no years later a brief, unsigned note about him appeared in Sitzungsberichte der Heidelberger Akademie der Wissenschaften, Jahreshefte 1943/55 (1959), 41–42, A short article about him by Hans Querner is in Neue deutsche Biographie, VIII (Berlin, 1969), 593. Hans Driesch, Lebenserinnerungen (Basel, 1951), describesDriesh and Herbst’s travels together; a few details about Herbst’s life are in Richard B. Goldschmidt, Portraits from Memory (Seattle, 1956); and in Georg Uschmann, Geschichte der Zoologie und der zoologischen Anstalten in Juna 1779–1919 (Juna, 1959). Hans Spemann, Embryonic Development and Introdution (New Haven, 1938), discusses Herbst’s work on 222–224, see also Frederick B. Churchill, “From Machine-Theory to Entelechy: Two Studies in Developmental Teleology,” in Journal of the History of Biology, 2 (1969), 1657–185; and Jane M. Oppenheimer. “Some Diverse Backgrounds for curt Herbt’s ideas about Embryonic Induction,” in Bulletin of the History of Medicine, 44 (1970), 241–250.

Valuable information about Herbst’s character and personality was provided by Hans Querner and Viktor Hamburger. I learned of the possibility that there was discussion of Herbst’s joining Spemann through the kindness of Klaus Sander of Freiburg, who had received photocopies of relevant documents held by the MaxP;amcl Gesellschaft zur Förderung der Wissenschaften E.V., Bibliothek und Archiv zur Geschichte.

Jane Oppenheimer