(b. Vienna, Austria, 14 October 1895; d. Pasadena, California, 24 May 1931)
Bělař, was the son of a jurist. While still a student he developed a strong interest in biology and carried out observations in his brother-in-law’s private laboratory. After graduation from gymnasium he studied zoology at the University of Vienna, specializing in protozoology, His studies were interrupted by service in the Austrian army during World War I. Bělař, resumed his studies at Vienna and obtained a Ph.D. in zoology in 1919. He then moved to Berlin, where he became an assistant in Max Hartmann’s department of protozoology at the Kaiser-Wilhelm-Institute (now the Max-Planck-lnstitute) at Berlin-Dahlem. Subsequently he was promoted lo scientific member of the Institute. He also taught a course in evolution at the University of Berlin, where he became professor in 1930. In 1929 he was invited by Thomas H. Morgan to serve as a visiting professor in the newly founded department at the California Institute of Technology. He was killed in an automobile accident.
A year after graduation from gymnasium, Bělař, published his first scientific paper, the description of a new species of protozoan that he called, in honor of his teacher, Prowazekia josephi, and its nuclear division. For many years after, his work was concerned with Protozoa, the central aspect being the nature of mitosis in that subkingdom. At the time he started his work, most zoologists believed that they could distinguish two types of cell division: “direct” or amitotic, in which the nucleus simply divided in two, and’ indirect,’ the mitotic division in which the chromatin appears organized into chromosomes that divide individually and are distributed equally to the daughter cells. It was assumed that direct division was more primitive and that most divisions in Protozoa, Algae, and Fungi were direct, while the more efficient mitotic mode evolved in higher animals and plants.
Through a careful study of cell division in living and stained preparations of several unicellular organisms, Belar demonstrated that all the divisions are actually mitotic. In this work he defined mitosis as involving the appearance of chromosomes and of an achromatic apparatus that may consist of spindle fibers, a centrosome, asters, and centrioles. He showed that most of the nuclear divisions previously described as amitotic are actually mitotic but are hard to recognize as such because the chromosomes are small numerous, and frequently hard to identify; the achromatic apparatus is highly variable; and the nuclear membrane does not break down. Bělař’s work on mitosis in unicellular organisms was summarized in his classical monograph Der Formwrechsel der Protistenkerne (1926). In this work he not only reviews his own work but also great amounts of published material, reinterpreting many aspects and testing them on his own preparations.
As a result Bělař makes it convincingly clear that the nuclear divisions of almost all Protozoans are mitoses. Only the division of the macronucleus of ciliates is admitted as being a direct division, and Bělař hints that he did not regard the ciliates as closely related to the other Protozoans. His book is not simply a compilation of published material; instead, the material is used to build up a consistent picture of the changes the nucleus undergoes during the cell cycle. His view that, in spite of many variations between different species and orders, the fundamental process is always the same is put forth with greatingenuity and critical understanding, and is completely convincing. The book has stood the test of time, and Bělař’s conclusions are still generally accepted.
His work on protozoan mitosis includes some important studies on the physiology of asexual reproduction and sexual processes in the heliozoan Actinophrys sol. These studies were suggested by Hartmann, the director of the laboratory at the Kaiser-Wilhelm-Institute, whose work centered on the physiology of sexual processes. In Actinophrys, Bělař studied both the cell division and the sexual process, in this case a type of autogamy. An encysted cell divides and the two daughter cells undergo a typical metosis. The meiosis is identical with that of an animal ovum, resulting in a gamete and polar bodies. The chromosomes, in this case, are very distinct though large in number. The two daughter cells (gametes) then fuse, reconstituting the diploid cell. In further experimentation Bělař discovered that the sexual process can be induced at any time by environmental conditions, such as starvation. Asexual reproduction by cell division, on the other hand, can go on indefinitely—in Bělař’s case for almost three years (at the rate of one to three divisions per day). Bělař pointed out that the problem of aging and death does not apply to Actinophrys because its life cycle is completely determined by environmental variables. Contrary to previous assumptions, based primarily on investigation of ciliates, continued asexual reproduction does not lead to aging.
Bělař next studied the mechanism of mitosis in the cells of higher plants and animals, particularly the formation and activity of the achromatic apparatus and its function in the separation of the chromosomes. His work was based on live observation of dividing cells, primarily spermatocytes of a grasshopper (Chorihippus) and mitosis in the hair cells of the anthers of the spiderwort, Tradescantia. In the spindle he distinguishes chromosomal fibers that are attached at one end to the centromere of the chromosomes and at the other end to the spindle poles. These fibers shorten considerably during anaphase and thus pull the chromosomes toward the spindle poles. The other component is the middle region of the spindle, which connects the two poles and in araphase lengthens and pushes the spindle poles further apart, thus aiding the further separation of the chromosomes attached to the poles. The action of the middle region was suggested by experiments in which dividing cells were put into hypertonic solutions. In this treatment the cytoplasm shrinks due to loss of water, finally forming a thin layer around the spindle. The spindle, on the other hand. lengthens considerably, particularly in anaphase cells. and frequently gets bent on itself because it meets the resistance of the reduced cytoplasm.
Bělař’s findings and conclusions formed the basis of later discussions of the nature of mitosis. Thereality of the spindle fibers and the longitudinal structure of the central spindle was in doubt for twenty years because, though quite conspicuous in fixed preparations, they cannot be seen in living cells. Belar supported their existence by indirect observations and conclusions. Only in 1953 was Inoue able to demonstrate their existence in living cells by means of polarization microscopy and to show the fibrous nature of the middle region. Since that time the picture has become more concrete by the employment of the electron microscope, which has shown both chromosomal fibers and central spindle fibers, and by biochemical studies of the behavior of tubulins, the main protein component of the spindle. The fibers of the middle region, which extend from one pole to the other, lengthen during anaphase, as Bělař envisioned; but it is now generally agreed that sliding of fibers against each other is probably the source of spindle elongation.
Bělař worked very hard, efficiently, and fast, and thus was able to accomplish much in his short life. He did not have graduate students or collaborators; all his publications bear only his name. He was very concerned with techniques and was admired for his ability to culture Protozoans. Belar was an excellent microscopist, using both stained and live preparations, and a superior draftsman; he did not only the drawings for his own papers but many drawings in the publications of his friends and colleagues as well. He was a pioneer in the use of photomicrography, particularly of living cells. He postulated that ideally every cell discussed in a paper should be shown both as a photomicrograph and as a drawing, since the photomicrograph is more objective while the drawing includes interpretation by the author.
Bělař had a very sharp and critical mind, and was famous and feared for his severe criticisms. He had little patience with inexact technique and sloppy thinking, and had the courage to attack even the most influential biologists of his time—for instance. Rudolf Flick, the head of the Anatomy Department in Berlin; the protozoologist Franz Doflein; the zoologist Alfred Kühn; and even his supervisor Hartmann, who complains about Bělař’s sharply critical remarks in the foreword he wrote for Bělař’s monograph on protozoan nuclei. But Belar used the same ruthless criticism against his own work and his earlier publications.
Besides his immersion in his work. Bělař shared aesthetic interests with in wife. Gertrud Bengelsdorff. He had great knowledge of the arts, and drew, sketched, and painted with watercolors. He was much attracted in his last two years by the charm and grandeur of the American landscape, particularly the desert and the mountains, which he spent much time sketching and painting.
Bělař’s significance in the history of cytology consists in the fact that he mercilessly destroyed many assumptions that were based on poor observations and wrong interpretations, and replaced them with carefully considered and solidly based ideas. Most of these are still valid, though superior methods have made them more concrete.
Bělař’s writings include “Untersuchungen an Actinophrys sol Ehrenberg I,” in Archiv für Protistenkunde, 46 (1923), 1–96; “Untersuchungen an Actinophrys sol Ehrenberg II,” ibid., 48 (1924), 371–434; Der Formwechsel der Protistenkerne, Ergebnisse und Fortschritte der Zoologie, no. 6 (Jena, 1926); “Die Technik der Zytologie,” in Tiber Péterfi, ed., Methodik der wissenschaftliche Biologie, II (Berlin, 1928); “Untersuchungen der Protozoen,” ibid., I (Berlin, 1928); “Die zytologischen Grundlagen der Vererbung,” in E. Baur and M. Hartmann, eds., Handbuch der Vererbungswissenschaften (Berlin, 1928); “Beiträge zur Kausalanalyse der Mitose II. Untersuchungen an den Spermatocyten von Chorthippus (Stenobothrus) lineatus Pans,” in Wilhelm Roux’s Archiv fü Entwicklungsmechanik der Organismen, 118 (1929), 359–484; “Mitotic Spindle Analyzed by Dr. Bělař in Lecture,” in The Collecting Net, 4 , no. 8 (1929), 8: and “Zur Teilungsautonomie der Chromosomen,” W. Huth. ed., in Zeitschrift fü Zellforschung und Mikroskopische Anatomie, 17 (1933), 51–66, a posthumous summary of Belar’s work at Pasadena on the eggs of the marine worm Urechis caupo. An obituary is Curt Stern. “Karl Bělař zum Gedächtnis.” in Naturwissenschaften, 19 (13 November 1931), 921–923.