The germ-cell cycle in animals, by Robert W. Hegner.

Hegner, Robert

doi:10.5962/bhl.title.29344

Cited by 4 publications

(3 citation statements)

References 25 publications

(38 reference statements)

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“…23 Robert William Hegner (1880Hegner ( -1942, then assistant professor of zoology at the University of Michigan and later an international research leader in protozoology and parasitology at Johns Hopkins University, did the same in his textbook The germ-cell cycle in animals. 24 Similarly, the early development of Ascaris megalocephala as well as that of stem cells featured in a biological contribution by the Berlin anatomist Richard Weissenberg (1882Weissenberg ( -1974 to the Handbuch der Sexualwissenschaften of the sexologist Albert Moll (1862 -1939). 25 Weissenberg was a former assistant to Oscar Hertwig, who had been appointed director of the Anatomical -Biological Institute of Berlin University in 1888.…”

Section: Stem Cells In Embryology Around 1900mentioning

confidence: 99%

Ambiguous cells: the emergence of the stem cell concept in the nineteenth and twentieth centuries

Maehle

2011

Notes Rec. R. Soc.

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This paper elucidates the origins of scientific work on stem cells. From the late nineteenth century onwards, the notion of stem cells became customary in scientific communities of Imperial Germany. Adopting the term Stammzelle from Ernst Haeckel, Theodor Boveri was influential in introducing the concept in embryological studies and early genetics around 1900, describing a capacity of stem cells for self-renewal as well as differentiation. At the same time, blood stem cells were conceptualized by histologists such as Ernst Neumann and Artur Pappenheim in studies of physiological haematopoiesis and various forms of leukaemia. Furthermore, building on Julius Cohnheim's theory that tumours arise from ‘embryonic remnants’ in the adult body, pathologists aimed at identifying the cells of origin, particularly in the embryo-like teratomas. Embryonic stem cells thus assumed an ambiguous status, partly representing common heritage and normal development, and partly being seen as potential causes of cancer if they had been left behind or displaced during ontogeny. In the 1950s and 1960s experimental research on teratocarcinomas by Leroy Stevens and Barry Pierce in the USA brought together the strands of embryological and pathological work. Alongside the work of Ernest McCulloch and James Till at the Ontario Cancer Institute from the early 1960s on stem cells in haematopoiesis, this led into the beginnings of modern stem cell research.

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Section: Stem Cells In Embryology Around 1900mentioning

confidence: 99%

Ambiguous cells: the emergence of the stem cell concept in the nineteenth and twentieth centuries

Maehle

2011

Notes Rec. R. Soc.

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“…On April 19, the patient showed a marked improvement since starting work in the Constitution Clinic on Oct. 19,1928. He had indulged, however, in food that seemed to be putting unnecessary stress on his stomach.…”

Section: Pepticmentioning

confidence: 99%

The Man-Environment Unit and Peptic Ulcer

Draper¹

1932

Arch Intern Med

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“…A useful summary of the various forms of germ-track differentiators at present known is given by Hegner (1914 and). There appears to be nothing corresponding to the animal germ-track in the higher plants (see, however, footnote to p. 144).…”

Section: Chapmentioning

confidence: 99%

Cytology, with special reference to the metazoan nucleus, by W. E. Agar.

Agar¹

1920

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In general a cell is composed of two principal morphological constituents, the nucleus and the surrounding protoplasm, or better, cytoplasm, since some authors use the former word to include both cytoplasm and nucleus. This division of the cell constituents is quite sharp in all but the lowest organisms, the nucleus being delimited from the cytoplasm by a membrane except during a certain period of its division processes. In certain unicellular organisms (Protista), however, the word " nucleus " is inappropriate, since the material which composes this structure in the higher organisms is scattered through the cytoplasm as minute granules, or chromidia (see Chapter VI.). In other Protista both nucleus proper and chromidia are present (e.g. Diffltigia), while certain Bacteria are said to consist entirely of " nucleus." Even in multicellular organisms, both in Metazoa and Metaphyta, there are frequently minute bodies in the cytoplasm which are supposed by some cytologists to be derived from the nucleus, and to consist of true nuclear material, and therefore to be comparable to chromidia. A. THE CYTOPLASM The cytoplasm surrounding the nucleus includes a number of different structures of which the following are the most important : (i) The cytoplasm proper. (2) The cell membrane. (3) The centrosome. (4) Chondriosomes. (5) Metaplastic bodies. (i) The Cytoplasm Proper The living cytoplasm itself consists of a viscid, nearly transj:>arent substance, which often is clearly not homogeneous. Great difference of opinion exists as to its structure, chiefly owing to the fact that very Httlc I B nsnitn library N. C. State College attached to the spindle fibres. E, metaphase ; F, anaphase ; G, telophase ; H, nuclear and cell division complete, and daughter nuclei reconstituted. I MITOSIS 9 condensation ultimately form the relatively short and thick chromosomes of the later stages. Karyosomes, if present, since they are composed of chromatin, disappear, being used up with the rest of the chromatin in the formation of the chromosomes. If plasmosomes are present, they disappear either before or after the disappearance of the nuclear membrane (see below), apparently without participating in the formation of the chromosomes or playing any further part in the hfe-history of the nucleus. For some time after the thread formation, which starts in the early prophase, has proceeded or even been completed (by conversion of the entire chromatin content of the nucleus into filaments), the length of the threads is far greater than the circumference of the nucleus (Figs. 3, 6, 7, 8), and hence the nucleus is filled with a complicated tanglethe spireme of Flemming-in which it is impossible to discern how many separate filaments are present.. Numbers in thick type refer to pages on which figures will be found

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The germ-cell cycle in animals, by Robert W. Hegner.

Abstract: B. The Localization of the Keimbahn-Determinants, 235. C. The Fate of the Keimbahn-Determinants, 240. CHAPTER IX The Chromosomes and Mitochondria of Germ Cells 245 The Chromosome Cycle in Animals, 245. The Mitochondria of Germ Cells, 275.

Cited by 4 publications

References 25 publications

Ambiguous cells: the emergence of the stem cell concept in the nineteenth and twentieth centuries

Ambiguous cells: the emergence of the stem cell concept in the nineteenth and twentieth centuries

The Man-Environment Unit and Peptic Ulcer

Cytology, with special reference to the metazoan nucleus, by W. E. Agar.

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