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Biomedical subjects

D W FAWCETT

Publications and source records attributed to D W FAWCETT.

At least 37 records · Page 2Linked to original sources
PubMed1956

Electron microscope observations on intracellular virus-like particles associated with the cells of the Lucké renal adenocarcinoma.

The common renal adenocarcinoma of the leopard frog was studied in thin sections with the electron microscope. Approximately a third of the tumors examined were found to contain spheroidal bodies of uniform size and distinctive morphology that are believed to be virus particles. These consist of hollow spheres (90 to 100 mmicro) having a thick capsule and a dense inner body (35 to 40 mmicro) that is eccentrically placed within the central cavity (70 to 80 mmicro). Virus particles of this kind occur principally in the cytoplasm but occasionally they are also found in the nucleus and in the extracellular spaces of the tumor. The intranuclear inclusion bodies that are visible with the light microscope are largely comprised of hollow, spherical vesicles with thin limiting membranes. These are embedded in a finely granular matrix. A few of the thin walled vesicles contain a dense inner body like that of the cytoplasmic virus particles. This suggests that they may be immature virus particles. The inclusion bodies are believed to be formed in the course of virus multiplication but they usually contain very few mature virus particles. Bundles of dense filaments and peculiar vacuolar inclusions also occur in the cytoplasm of the tumor cells. These seem to be related in some way to the presence of virus but their origin and significance remain obscure. These findings are discussed in relation to previous work suggesting that the Lucké adenocarcinoma is caused by an organ-specific filtrable agent. It is concluded that the "virus particles" found in electron micrographs of the tumor cells may be the postulated tumor agent. On the other hand, the possibility remains that the particles described here are not those that are causally related to the tumors.

Carcinoma, Renal Cell↗
PubMed1956

The fine structure of chromosomes in the meiotic prophase of vertebrate spermatocytes.

The prophase chromosomes of the first meiotic division in pigeon, cat, and man contain a central structure or core consisting of a pair of dense fibrils (450 A) that are parallel to one another and equidistant from a delicate linear region of increased density midway between them. These parallel strands are present early in prophase and the chromosomes seem to arise by congregation and organization of the chromatin granules around them. They have not been observed in mitosis or in other stages of meiosis.

Animals↗
PubMed1956

An electron microscope study of spermatid differentiation in the toad, Bufo arenarum Hensel.

The differentiation of the spermatids of Bufo arenarum has been described from a study of electron micrographs of thin sections of testis. The development of the acrosome from the Golgi complex takes place in much the same manner as in mammalian spermatogenesis but no acrosome granule is formed. A perforatorium is described for the first time in this species. It is formed by a convergence of dense filaments that arise between the nuclear membrane and the head cap. During maturation of the spermatid the chromatin undergoes striking physicochemical alterations. Fine chromatin granules uniformly dispersed in the karyoplasm are replaced by larger and larger aggregates and these ultimately coalesce to form a very dense sperm head. Two centrioles of cylindrical form are situated very near the base of the sperm head. The longitudinal fibrils of the tail flagellum take origin from one, and the dense fibrous substance of the undulating membrane is closely related to the other. Phase contrast cinematographic observations on the swimming movements of living toad sperm, when considered in relation to the fine structural components of the tail, suggest that there is a contractile component in the undulating membrane as well as in the axial fibrils. The differences in the structure of mammalian and amphibian sperm tails are discussed in relation to differences in the character of their movements.

Acrosome↗
PubMed1955

Studies on the fine structure of the mammalian testis. I. Differentiation of the spermatids in the cat (Felis domestica).

The differentiation of cat spermatids was studied in thin sections examined with the electron microscope. The Golgi complex of the spermatid consists of a central aggregation of minute vacuoles, partially surrounded by a lamellar arrangement of flattened vesicles. In the formation of the acrosome, one or more moderately dense homogeneous granules arise within vacuoles of the Golgi complex. The coalescence of these vacuoles and their contained granules gives rise to a single acrosomal granule within a sizable membrane-limited vacuole, termed the acrosomal vesicle. This adheres to the nuclear membrane and later becomes closely applied to the anterior two-thirds of the elongating nucleus to form a closed bilaminar head cap. The substance of the acrosomal granule occupies the narrow cleft between the membranous layers of the cap. The caudal sheath is comprised of many straight filaments extending backward from a ring which encircles the nucleus at the posterior margin of the head cap. Attention is directed to the frequent occurrence of pairs of spermatids joined by a protoplasmic bridge and the origin and possible significance of this relationship are discussed.

Acrosome↗
PubMed1954

Cytological and pharmacological observations on the release of histamine by mast cells.

Experimental solutions known to affect mast cells or to cause liberation of histamine from the tissue were introduced into the peritoneal cavity of rats. Samples of the peritoneal fluid were withdrawn at intervals afterward and assayed for histamine and the condition of the mast cells was subsequently ascertained by microscopic examination of stained spreads of the mesenteries. Intraperitoneal injection of distilled water caused osmotic disruption of the mast cells and the appearance of an appreciable amount of histamine in the peritoneal fluid. Injection of Tyrode solution alone was not particularly damaging to the mast cells and little or no histamine was released. Injection of Tyrode solution containing compound 48/80 resulted in extensive release of granules from mast cells and the appearance of large amounts of histamine in the fluid. Solution of 48/80 failed however to cause histamine release when injected into rats whose subserosal mast cells had previously been destroyed. A series of increasing doses of compound 48/80 had a graded morphological effect upon mast cells and resulted in a graded increase in the amount of histamine that appeared in the peritoneal fluid. It is unlikely therefore that this compound acts by simply lysing the plasma membrane. It is concluded that mast cells in the rat are extraordinarily rich in histamine which is liberated under conditions which cause mast cells to release their granules. The histamine set free by the potent histamine liberator, compound 48/80, appears to come principally from the tissue mast cells.

Animals↗