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951.
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The regulation by substrate induction of the acetohydroxy acid isomeroreductase was studied in Escherichia coli. Induction was inhibited by chloramphenicol and rifampin. The addition of rifampin resulted in a decay of the capacity to form isomeroreductase. This was attributed to the breakdown of the isomeroreductase messenger, which had a half-life of about 45 sec at 37 C. Induction of isomeroreductase was enhanced by including glucose in the medium. This effect was shown to be due in part to the lowering of the pH of the medium, which presumably made inducer entry more rapid.  相似文献   
954.
955.
Albert's method, of staining diphtheria cultures consists of staining a fixed smear for one minute (some laboratories stain for five minutes) with a solution containing toluidine blue and malachite (or methyl) green, washing with water, and applying Albert's iodine for one minute. This procedure is discussed and criticized, and in addition the mechanism of the stain is elucidated. Also, the procedure which involves staining a fixed smear for one minute with Loeffler's alkaline methylene blue solution is discussed and criticized.

To overcome the objections to the above staining methods, a different method is proposed. This consists of staining a fixed smear with an acid solution of toluidine blue, washing with water, applying Albert's iodine for one minute, washing with water, and finally applying a safranin solution for 15-20 seconds. The theoretical basis for this method is presented.  相似文献   
956.
The transition from larval to adult pigmentary patterns during metamorphosis of wild-type. burnsi, and kandiyohi R. pipiens is described. Larval fusiform epidermal melanocytes form a pattern that exactly corresponds to the adult spotting pattern. It is concluded that the larval epidermal pattern expresses a “prepattern” in the larval tissue for the adult pattern. This “prepattern” is visible in kandiyohi, but not in burnsi, tadpoles. The role of the extracellular environment in pigmentary pattern determination is discussed. Gradual changes in all chromatophore densities accompany larval development, while abrupt changes accompany metamorphic climax. There is a net increase in all chromatophore densities by the completion of metamorphosis. Kandiyohi density changes differ quantitatively but not qualitatively from those of wild type. In both wild type and kandiyohi, differentiation of many new dermal melanophores in presumptive spot regions effects expression of the adult spotting pattern. The relative roles of chromatophore differentiation and mitosis in pattern expression, and the hormonal control thereof, are discussed.  相似文献   
957.
The effects of mammalian gonadotropins, methyltestosterone and partially purified salmon gonadotropin on spermiation and oocyte maturation were studied in adult grey mullet. Methyltestosterone was a potent spermiating agent in both prespawning and spawning trials. The most effective dose was 5 mg/100 g body weight. Human chorionic gonadotropin (HCG) was moderately effective at a dose rate of 20 IU/100 g body weight. Both hormones blocked resorption of milt in captive animals. The HCG, FSH/LH combination, Synahorin+mullet pituitary homogenate, and partially purified salmon gonadotropin were equally effective, at the doses used, in inducing oocyte maturation and preventing onset of atrophy before completion of vitellogenesis. Atrophy occurred in all experimental fish at mean oocyte diameter of 750 μ. The significance of this finding is discussed. (Oceanic Institute Contribution No. 98).  相似文献   
958.
959.
Mirror carp were infected with Ichthyophthirius multifiliis (Fouquet) under standardized conditions. The size and number of parasites at selected sites on the body were recorded during the course of the infection. Initial exposure to 40 mature parasites resulted in a mild infection with 100% recovery after 18 days. Recovered fish did not appear to be carriers of the parasite. Exposure to 400 parasites resulted in 100% mortality between 22–25 days. The growth rate of the parasite was linear. Parasites were more numerous in the dorsal surface of the fish than in the lateral or ventral surface. The increase in parasite numbers during the disease was greater in the gills than in the skin.  相似文献   
960.
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