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The variability of Doppler ankle pressures was studied in 35 men with clinically stable claudication. An average of 6.8 measurements was obtained from each man. The mean range of ankle index was 0.18 with a mean standard deviation of 0.07. The brachial-ankle pressure gradient had a wider spread, with a mean range of 38 mm Hg and a standard deviation of 13.9. The amount of variation in a given patient was unrelated to mean blood pressure or mean ankle index. The results of this study show that the ankle index must change at least 0.15 before it can be considered significant. Based on the variability found, we recommend that multiple baseline determinations be obtained on patients who are to be followed longitudinally.

The relationship between termination of chromosome replication and cell division was investigated in Escherichia coli B/r. Synchronous cultures of E. coli B/r growing in glucose minimal medium or subjected to a nutritional shift-up were exposed to chloramphenicol, rifampin, mitomycin C, or nalidixic acid, and the ability of cells to divide in the presence of the inhibitors was measured. It was found that cell division became resistant to inhibitors of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) synthesis at approximately the same stage in the division cycle in all situations investigated. When the synchronous glucose-grown cultures were temporarily exposed to chloramphenicol early in the division cycle and then exposed to mitomycin C or nalidixic acid immediately after removal of chloramphenicol, the cells did not divide. In contrast, when DNA synthesis was inhibited by thymine starvation immediately after temporary exposure to chloramphenicol, cells divided. The results suggest that DNA chain elongation is completed in some cells in the absence of protein synthesis, but that additional steps involving specific RNA or protein synthesis, or both, may be required for processing the chromosomal structures to the form which is necessary for division. This processing, which normally occurs concurrent with DNA synthesis and is prevented by inhibitors of DNA synthesis, may trigger division. Alternatively, in the absence of protein synthesis, all aspects of chromosome formation may be completed, but final transcriptional events which are essential for division cannot take place until the complete synthesis of a critical amount of specific proteins.