RABL, CARL

(b. Wels, Oberösterreich, Austria, 2 May 1853; d. Leipzig, Germany, 24 December 1917)

anatomy, comparative embryology, cytology.

Rabl’scontemporaries saw him primarily as a zoologist whose anatomical studies encompassed many facets of morphology and whose researches in comparative embryology clarified various aspects of developmental history; but his role in the development of the chromosome theory of inheritance remains outstanding, It was Rabl who first clearly expressed the concept of the continuity of the chromosomes throughout cellular division. The idea of the individuality of the chromosomes, suggested by Edouard van Beneden and given its fullest definition in the basic work of Boveri, was fundamental to the understanding of the mechanism of heredity within the cell.

The son of Carl Rabl, a physician, Rabl entered the Gymnasium at Kremsmünster, intending to study medicine. He early showed a preference for natural history and was especially attracted to zoology and comparative anatomy. Books on biological aspects of man’s place in nature became his favorites. But, most of all, Ernst Hacekel’s Natürliche Schöpfungs-geschichte fired his enthusiasm, for in Germany that period was marked by fascination with Darwin’s theory of evolution. Long before he finished his Gymnasium course in 1871, Rabl had resolved to study under Haeckel at Jena; but instead he studied medicine for two years at Vienna. Disappointed by the lack of stimulus or encouragement, he attended lectures and dissected both in the anatomical rooms and at home, meanwhile reading the works of Haeckel and Darwin.

In the fall of 1873 Rabl transferred to the University of Leipzig to work under the zoologist Rudolf Leuckart, a happier experience, and managed to visit Jena and meet Haeckel. During the Easter vacation of 1874 he was already engaged in research on the early development of gastropods, which he planned to continue during the summer at Jena. He studied there under Haeckel in the summers of 1874 and 1875 and in the latter year published the first of several papers on his investigations in developmental biology. The general direction of his work was deeply influenced by Haeckel, who communicated his scientific enthusiasms and in later years remained his friend and correspondent. But Haeckel tended to broad theorizing, as Rabl recognized; returning to Vienna in 1875, he came under the tempering influence of another great teacher, the physiologist Ernst Brücke, who insisted on extremely careful observation in his histological studies and firmly placed fact before theory.

Rabl’s zoological interests had caused him to take longer than usual to complete his medical course; finally, in 1882, he received his degree at Vienna, then became a prosector at the anatomical institute there, assisting Karl Langer. In addition to lecturing to medical students and carrying out special studies of vertebrate developmental anatomy, Rabl published a remarkable and carefully illustrated monograph on cell division, “Über Zelltheilung,” in Morphologisches Jahrbuch (1885). He continued this work when he was appointed in 1885 to teach anatomy at the Ferdinand University in Prague, where in 1886 he attained the rank of ordinary professor.

While at Prague, Rabl served a term as the dean of his faculty, and he was rector of the Ferdinand University in 1903–1904. In 1891 he had married Marie Virchow, daughter of the pathologist Rudolf Virchow; but although they had many friends and Rabl was esteemed by his colleagues at Prague, he felt that he would be happier at a German university and accepted the chair at Leipzig as successor to Wilhelm His in 1904. At Leipzig, Rabl reorganized and improved the teaching of anatomy, expanding the facilities and research collections, and directed the anatomical institute until his death.

As Haeckel’s student Rabl had begun investigations into the formation of the germ layers in the young embryo. Soon he was going back to early cleavage and to the structure of the egg cell itself. Over the years he returned to the formation of the germ layers and especially of the mesoderm and its derivatives. The various organs of which he traced the origins were not, however, followed merely to chronicle in detail their separate morphological histories; rather, they were examples that would lead, through induction, to general laws. Rabl was convinced that the events of cell division were precisely determined and that embryological development was a mechanism in which the final position of each cell in the body had been predetermined, a conclusion he reached independently of His, but one similarly opposed to epigenetic explanations. The cell was to Rabl a complex and bilaterally differentiated and symmetrical organism; he stressed its polarities, and he concluded that the unsegmented egg already contained differentiated protoplasmic particles.

During the period when the new science of cytology was making known the course of cell division and was revealing that the chromosomes were halved lengthwise, to be distributed equally to the daughter cells, Rabl published his detailed description of the process, beautifully illustrated with his own drawings. In this study (1885) he maintained that the chromatinstaining filaments in the nucleus, later called the chromosomes, must actually persist through inter- phase even though, for a time, they seemed to disappear. “It is inconceivable,” he wrote, “that in the resting cell no trace of this arrangement should exist any more.” He had concluded, following his determination in studies of salamander larvae, that the organization of the cell must remain through division; that there was a constancy in the number of chromosomal filaments characteristic of a given tissue; and that a numerical law applied to each kind of cell. The significance of the continuity of the chromosomes for the understanding of the process of cell division soon became evident, and the important individuality of the chromosomes was shown in 1887 and afterward in the work of Boveri. Although Boveri acknowledged Rabl’s contribution, embryologists in later years took sides in an unfortunate priority dispute—for, as one colleague put it, Rabl regarded the theory of the continuity of the chromosome as “his exclusive intellectual property.”

Besides his work on the cell, Rabl’s numerous special investigations included the development of the heart in amphibians, the formation of the lens of the vertebrate eye, and cranial segmentation, skeletal derivation, and the origin of the paired extremities. His contributions to morphology were widely cited by other comparative anatomists. Still, Rabl was no systematist, despite his careful working out of detail; rather, he sought to make a general application of his findings in a theory of development.

BIBLIOGRAPHY

I. Original Works. A curious but invaluable assessment of Rabl’s ideas and the aims of his research is provided by his “critical analysis” of the work of his colleague Edouard van Beneden, a critique requested in the latter’s will. It was to have been written by Rabl and Walther Flemming, who predeceased van Beneden, and became an entire volume that even included some new work by Rabl: “Edouard van Beneden und der gegenwärtige Stand der wichtigsten um ihm behandelten Probleme,” in Archiv für mikroskopische Anatomie …, 88 (1915), 1–470. Rabl’s paper on the cell, “Über Zelltheilung,” in Morphologisches Jahrbuch, 10 (1885), 214–330, was followed by an essay on the same subject addressed to Kölliker, “Über Zelltheilung,” in Anatomischer Anzeiger, 4 (1889), 21–30. Rabl’s inaugural lecture at the University of Leipzig, Uper “Organbildende Substanzen” und Hire Bedeutung für die Vererbung (Leipzig, 1906), outlines his researches and views, and defines problems of the day in regard to the cell, heredity, and embryonic development. Developmental studies include “Die Ontogenie der Süsswasser-Pulmonaten,” in Jenaische Zeitschrift fur Naturwissenschaft, 9 (1875), 195–240; “Ueber die Entwicklungsgeschichte der Malermuschel,” ibid., 10 (1876), 310–394; “Über den Bau und die Entwicklung der Linse,” in Zeitschrift fur wissenschaftliche Zoologie, 63 (1898), 496–572; 65 (1899), 257–367; 67 (1900), 1–138; and others listed in the obituaries cited below.

II. Secondary Literature. See A. Fischel, “Carl Rabl,” in Anatomischer Anzeiger, 51 (1918), 54–79; Hans Held, “Nekrolog auf Carl Rabl,” in Berichte Über die Verhandlungen der Sachsischen Gesellschaft der Wissen-schaften zu Leipzig, math.-phys. Kl., 60 (1918), 363–380; and F. Hochstetter, “Carl Rabl,” in Wiener klinische Wochenschrift, 31 (1918), 196–200; and his obituary notice in Almanach der Akademie der Wissenschaften in Wien, 69 (1918), 260–274. Georg Uschmann, Geschichte der Zoologie und der zoologischen Anstalten in Jena 1779–1919 (Jena, 1959), 130–133, 167, and plate 41 , describes Haeckel’s influence on Rabl’s work and their continuing relationship and correspondence.

Gloria Robinson