A new antibiotic U-58, 431 has been isolated from the fermentation broth of Streptomyces helicus DIETZ and Li, sp. n. (UC-5837) and the structure of this antibiotic, namely, 6-amino-3, 4, 5, ...8-tetrahydro-4, 9-dihydroxy-3-methyl-5, 8-dioxo-1, 4-ethano-1H-2-benzopyron-7-carboxamide has been determined by X-ray crystallography. The antibiotic inhibits a variety of Gram-positive and Gram-negative bacteria in vitro. However, it is toxic to mice and does not protectexperimentally infected animals when administered at the maximum tolerated dose.
Antibiotic U-24,544 is a new agent isolated from the culture broth of a streptomycete strain. The antibiotic inhibits a variety of gram-positive and gram-negative bacteria in vitro, but is ...ineffective in treatment of experimental bacterial infections in mice. It is fairly cytotoxic in mammalian cell cultures and remarkably nontoxic in mice.
Steffimycin B, an anthracycline, has been isolated from cultures of Streptomyces elgreteus by solvent extraction and purified by silica gel chromatography. NMR and mass spectroscopy indicate the ...presence of a methoxyl group in the sugar moiety of steffimycin B not found in steffimycin, a related antibiotic. Steffimycin B is not active against bacteria in experimentally infected animals, but has shown some potential antitumor activity in an in vitro screen. Further testing is in progress.
Difficulties encountered by younger children in doing arithmetic word problems have been attributed to their lack of understanding of the underlying logico-mathematical problem structure. It is ...argued that presentational structure, ie, effects of wording, is also important. Reusser's situation problem solver (1990) models problem solving with emphasis on linguistic & situational components. A review of the research shows that word problems are more readily solved when they are concretely tied to the real world, when they are explicit about states of possession rather than requiring inferences, when they mirror the real-world order of initial state-transfer-resulting state, & when narrative perspective is kept constant. Word problems simultaneously tap into students' understanding of language, situations, & mathematics, & must be viewed in that light. 2 Tables, 2 Figures, 37 References. L. Lagerquist
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