(b. St. Mandé, France, 23 July 1845; d. at sea, March 1892)
Although little is known of Fol’s immediate family, he was descended from Gaspard Fol, a religious refugee who left Touraine to settle in Geneva in 1590. His father was rich, and one of his brothers became a prominent art scholar and curator of the Musee Fol, which he founded in Geneva; a cousin, Auguste Fol, was a watchmaker and director of Geneva’s Caisse Hypothécaire from 1882 to 1891.
Fol himself always retained a strong attachment for Geneva. He received his early education at the Gymnasium there, where his interest was turned toward natural science by Edouard Claparède and F. J. Pictet. On Claparède’s recommendation, he went on to study medicine and zoology at the University of Jena. Two of his teachers there were Gegenbauer and Haeckel, both of whom influenced him strongly. In the winter of 1866–1867 Fol joined Haeckel on an extended trip to the western and northern coasts of Africa and the Canary Islands; several collecting trips inland confirmed his enthusiasm for natural history.
In 1867 Fol began to study medicine at Heidelberg (and later at Zurich and Berlin as well); he took the M.D. in 1869, with a thesis on the anatomy and development of Ctenophora. On his return to Geneva in 1870 he continued his zoological researches in preference to practicing medicine and spent several winters collecting and studying marine invertebrates. He married a Mlle. Bourrit in the early 1870’s.
In addition to his study on the Ctenophora, Fol worked on the embryology of Mollusca and made microscopic studies of fertilization, cell division, and early embryonic growth. In the 1870’s little was actually known about the nature of fertilization and especially about the role in this process of such organelles as the nucleus and centrosome. It had been observed that the nucleus disappeared shortly before the onset of mitosis and that the centrosome and the mitotic spindle appeared by late prophase, but was the spindle system composed of the remains of the nucleus or was it produced by the centrosome? What was the function of the spindle, and what was the function of the chromatin bodies (chromosomes) within the nucleus? Was the sperm nucleus or the centrosome necessary to fertilize the egg, or were they both necessary to fertilization? And did the sperm contribute anything material to the fertilized egg, or was it simply an agent to development?
Among the many theories formulated to answer some of these questions were those of Oscar Hertwig, who noted that immediately after fertilization two distinct nuclei could be seen in the egg cell. From this he concluded that one nucleus had come from the sperm and one from the egg, and went on to theorize that the two nuclei fused and that all the nuclei in all the cells of the developing organism were therefore the descendants of this first fused pair. His inferences were open to dispute, however, and it was pointed out in criticism that he had not actually seen the sperm penetrate the egg. Moreover, some thought the germinal vesicle (the egg nucleus) to be a separate and autonomous cell within the larger cell.
Fol pursued the same line of investigation as Hertwig, apparently quite independently. In two papers, one presented in 1877 and the other in 1879, Fol showed that in sea urchins the egg nucleus is not a separate cell but rather an important structural and functional part of the ovum; that during maturation of the egg three daughter nuclei are cast off as polar bodies so that the mature ovum contains only one nucleus; and that sperm actually penetrates the egg. He made the last observation in 1877 and was thus able to provide more conclusive evidence than Hertwig’s about the relationship between the two gametes at the moment of fertilization. Like Hertwig, Fol suggested that the daughter nuclei in all the cells of a growing embryo are descended from the original sperm-and-egg fusion pair.
At the time when Fol and Hertwig were carrying out their studies, the hereditary function of the nucleus was not suspected. Their emphasis on nuclear continuity during maturation of the gametes and during subsequent cleavage was, however, an important step in the understanding of this function. Fol himself did not go on to speculate that the nucleus was the vehicle of heredity; while he reaffirmed the idea of nuclear continuity, he also denied the purity of the fundamental nuclear components; that is, he did not believe that the nucleus had a special structure of its own whereby it could preserve hereditary information from one generation to the next. Fol did not characterize fertilization primarily as the fusion of the sperm-and-egg nuclei; rather, he considered the male nucleus to be a degeneration product of sperm components in contact with egg cytoplasm.
Fol’s embryological work emphasized the structural and morphological aspects of fertilization by focusing attention on the material organelles (such as the nucleus); work done prior to his and Hertwig’s was physiological in design. His investigations enabled later workers (including T. H. Boveri, August Weismann, and E. A. Strasburger) to clarify the actual hereditary function of the nucleus.
Fol conducted these researches while simultaneously engaged in an academic career. In 1876 he had declined the offer of a chair of comparative anatomy at the University of Naples; two years later he accepted a titular professorship (without pay) in comparative embryology and teratology at the University of Geneva. In addition to his work on sea urchins he applied himself to a wide variety of zoological problems and collected a great deal of material on the comparative embryology of invertebrates. He spent winters in Villefranche, near Nice, where in 1880 he established, at his own expense, a marine laboratory in an abandoned quarantine station; summers he gave courses in parasitology and general zoology at the university.
In 1882, when the International Congress on Hygiene was held in Geneva, Fol became greatly excited by the work of Louis Pasteur and Robert Koch. During the next year he made microscopic studies of various bacteria and, at the request of the city officials, made a detailed analysis of the Geneva water supply. At the same time he became an avid photographer and began to experiment with applying photographic techniques to his microscopic researches. He was founder of the Geneva Photographical Society and published articles in the Revue suisse de photographie. He also founded the Recueil zoologique suisse.
A somewhat unpredictable and eccentric person, Fol became involved in quarrels with some other members of the university and resigned in 1886 to retire to Villefranche. At the time of his teaching appointment he had given his laboratory there to the French government, which had appointed Jules Barrois to be its director. On his return, the government made Fol a codirector; and there he continued his studies on embryology, cytology, histology, and invertebrate zoology. He further collaborated with Eduard Serasin on a study of the penetration of light into seawater.
His last important microscopic research was a study of the centrosome. In 1889 Rádl had predicted, on strictly a priori grounds, that the centrosomes, like nuclei, would be found to unite at fertilization; by this theory, each gamete would contribute two centrosomes, the product of the fusion dividing to form the two poles of the mitotic spindle. In a paper of 1891, “Le quadrille des centres,” Fol again used sea urchins in an experiment that confirmed Radl’s prediction. He showed that each gamete contributed either two centrosomes, or one centrosome that divided immediately after fertilization; the daughter centrosomes then united in such a way that one from the male parent always joined one from the female parent (the movements involved in this pairing reminded Fol of the distribution of cards in the eighteenth-century game of quadrille and thus gave him his paper’s title). The paper became somewhat notorious and brought Fol under attack from both Boveri and Hertwig, who agreed with each other that centrosomes were not permanent cell organelles. At a slightly later date, Boveri and E. B. Wilson made specific studies of sea urchins and could observe nothing to substantiate the idea that the centrosomes actually congregate and fuse after fertilization; subsequent investigators also proved Fol wrong.
While working full-time at Villefranche, Fol also made several short collecting trips to the western Mediterranean. Ever since his trip with Haeckel in the 1860’s, however, he had wished to make a longer expedition. In 1891 he was given a commission by the French government to lead an expedition to the coast of Tunisia to study the distribution of sponges; he set off with a two-man crew in a new yacht, the Aster, on 13 March 1892. Although the boat was rumored to have reached the port of Benodet a few days later, the expedition was never heard from again.
Fol received many honors in his lifetime, including the Legion of Honor for establishing the Villefranche laboratory. He belonged to a number of scientific societies, including those of Moscow and Belgium and the Leopoldina-Carolina.
I. Original Works. An excellent bibliography is that by Maurice Bedot, cited below. A few of Fol’s most crucial papers are “Le premier développement de l’oeuf chez les Géryonides,” in Archives des sciences physiques et naturelles, 2nd ser., 48 (1873), 335–340; “Sur le commencement de I’hénogénie chez divers animaux,” ibid., 58 (1877), 439–472; “Recherches sur la fécondation et le commencement de I’hénogénie chez divers animaux,” in Mémoires de la Société de physique et d’histoire naturelle de Genève, 26 (1878), 89–250; and “Le quadrille des centres, un épisode nouveau dans l’histoire de la fécondation,” in Archives des sciences physiques et naturelles, 3rd ser., 25 (1891), 393–420.
II. Secondary Literature. The only available biographical sketch of Fol is Maurice Bedot, “Hermann Fol: sa vie et ses travaux,” in Archives des sciences physiques et naturelles, 31 1894), 1–22, which also includes a complete bibliography of Fol’s writings from 1869 to 1891. A discussion of Fol’s contributions may be found in Arthur Hughes, A History of Cytology (London, 1959), pp. 61–63, 70, 82–83; and William Coleman, “Cell, Nucleus, and Inheritance: An Historical Study,” in Proceedings of the American Philosophical Society, 109 (1965), 124–158, esp. 138–139.
Garland E. Allen