(15,16). RESULTSVitamin A supplementation resulted in prominence of lipocytes without significantly altering the light microscopic appearance of paraffin-embedded material. The total amount of collagen estimated by determination of hepatic hydroxyproline was the same in rats supplemented with vitamin A and rats not supplemented, the collagen concentration increasing in CC14-treated animals from 1.00 mg to 1.71 mg of hydroxyproline per g of dried, defatted tissue at the end of 6 weeks, and from 1.17 mg to 5.03 mg of hydroxyproline after 12 weeks. Light and electron microscopy After 1 or 2 weeks' duration of the experiments, the livers displayed centrolobular necrosis with steatosis in the surrounding parenchyma. The necrotic area contained, besides macrophages, conspicuous numbers of lipocytes, as shown by many Phosphin-3R-positive fat droplets imparting a fading vitamin A autofluorescence. Lipocytes were also recognized in 1 ,um thick sections and under the electron microscope. They were far more conspicuous, and indeed presented a striking appearance, after vitamin A supplementation (Fig. 1), when the cells appeared larger and contained a greater number of fat droplets, the latter imparting a strong vitamin A autofluorescence. They were intermixed with pigmented macrophages containing granules giving a yellow, nonfading autofluorescence, presumably of lipofuscin. Fibroblasts were not conspicuous in the necrotic area in the first 2 weeks.In animals treated for longer periods, connective tissue septa linking central zones with each other were observed after 6 weeks; after 12 and 24 weeks, the septa extended to the portal
Amicronucleate (strain W) and micronucleate (strain HAM 3) Tetrahymena pyriformis have been studied by light and electron microscopy. Numerous interphase and individually‐sectioned organisms in division stages have been examined. In macronuclei of the amicronucleate organisms (strain W) the time of division is characterized by a rather marked chromatin condensation, by morphological changes in nucleoli, and by the presence of dense granules. In macro‐nuclei of the micronucleus‐possessing organisms (strain HAM 3) little alteration of the interphase morphology is observed at division. Mitochondrial changes and an increase in the amount and complexity of the endoplasmic reticulum are observed in division in the amicronucleate strain. These results show that macronuclear division is more complex than a simple “pinching‐in‐two” and that loss of the micronucleus may alter the mitotic events of the macronucleus.
PLATES 113 Am) 114In our description of the mitochondrion of Paramecium aurelia and Paramecium bursaria (4), it was stated that "the undifferentiated mitochondrion in Paramecium is interpreted to consist of a compact mass of twisted tubules, the walls of which are made up of at least two kinds of substances (based on density differences in the photographs)." Since then more evidence confirming • this aspect of mitochondrial structure in Paramecium aurelia has been gathered by us, and this basic type structure has been recognized in sections of mito~ chondria of other Protozoa in our and other laboratories. Furthermore, sections of mitochondria of Metazoa as well as plants show, in addition to plates and folds, a range of structure that includes tubules very similar to those of the protozoan mitochondrion, indicating that a rigid concept of mitochondrial structure that excludes this type is incorrect. Materials and MethodsThe materials were two kinds of ciliate Protozoa as indicated below, rat kidney, and the ovotestis of Helix. These were prepared by fixation in 1 per cent 0sO4, pH 7.4, sectioned in methacrylate by a glass blade at a thickness of 0.025/z, and mounted on carbon membranes. The EMU-2 and the EMU-3A models were used. RESULTSParamecium aurelia.--The section (Fig. 1) is evidence, in addition to that presented before (4), demonstrating that in this cell the mitochondrion is a mass of tubules. Again, the clear circles and ovals (transversely sectioned tubules) are bounded by an electron-dense material. These in turn are surrounded by a less electron-dense material that forms the continuum of the mitochondrion. Several of the tubules (at points indicated by the arrows) open to the cytoplasm.Euplotes patella.--The mitochondrion of this hypotrichous ciliate (Fig. 2) presents the same aspect in section as that of Paramecium. Here again the two kinds of material are clearly evident--the electron-dense material immediately surrounding the clear lumens, and the less dense material between and * Work performed under the auspices of the United States Atomic Energy Commission. 341J.
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