STUDIES ON LYMPHOCYTES

Some of the time parameters of the cell cycle in bovine thoracic duct lymphocytes have been estimated by analysing labeled mitoses curves, and by double labeling. The two methods gave similar estimates of T_s. Thus, T_s measured directly from labeled mitoses curves varied from 4 to 6 hr, while the estimates from double labeling were 4.8 and 4.5 hr. T _G measured directly from labeled mitoses curves was 5 hr, and estimates of T_G from the values of T_s ranged from 6.3 to 7.7 hr. The present data confirm the short generative cycle of large thoracic duct lymphocytes. Extracorporeal irradiation of the lymph (ECIL) had no detectable effect on the cell cycle or the fractional production rate of the lymphocytes. However, the calculated absolute production was reduced following ECIL, due to a decrease in the absolute number of cells present. The grain count over mitoses after ECIL was approximately one-half that found before ECIL.     

Interaction of the exr and lon Genes in Escherichia coli

Strains of Escherichia coli carrying the gene lon typically produced excess capsular polysaccharide, and were sensitive to ultraviolet light (UV) irradiation, thymine starvation, and nalidixic acid, forming long filaments after these treatments. Sensitivity was reduced by a number of posttreatments. In the presence of a second UV sensitivity gene, exr, some of these properties were suppressed: long filaments were not formed, the effect of lon on UV and nalidixic acid sensitivity was greatly reduced, and irradiation posttreatments gave an enhancement of survival characteristic of exr rather than lon strains. Production of capsular polysaccharide was not affected by the exr gene.     

Sodium Content of Community Water Supplies in California

The amount of sodium ion in water used for ingestion may be critical in effective use of a low sodium dietary regimen. Waters containing not over 20 mg of sodium per liter are provided for in the sodium restricted diets set forth by the American Heart Association. For diets containing more than 500 mg of sodium a day, waters of greater sodium content may be used if proper dietary adjustments are made.While assessment of the long-term average sodium content of a community water supply is difficult, the determined values for sodium lend to classification within range categories. The larger community water supplies in California are presented within several range categories of sodium content.The more commonly used water softeners add sodium to water. The sodium-restricted patient should be cautioned against their use. Similar consideration should probably be given to water supplies of retirement communities where the potential for disorders requiring sodium restriction is greater than in the general population.     

Cross-resistance relationships in Escherichia coli between ultraviolet radiation and nitrous acid

Zampieri, Antonio (Palo Alto Medical Research Foundation, Palo Alto, Calif.), and Joseph Greenberg. Cross-resistance relationships in Escherichia coli between ultraviolet radiation and nitrous acid. J. Bacteriol. 87:1094-1099. 1964.-A number of radiosensitive and radioresistant strains of Escherichia coli were tested for sensitivity to injury by nitrous acid. All the radioresistant strains, including 13 radioresistant mutants of strain S, B/r, Bpr5, and K-12, were found to be significantly more resistant to nitrous acid than were the radiosensitive strains S and B. The radioresistant mutants of strain S, Bpr5, and K-12 displayed similar responses to nitrous acid and were less resistant than was strain B/r. Strains B and S were indistinguishable on the basis of nitrous acid sensitivity. The survival curves of all strains examined were similar in shape to corresponding survival curves after ultraviolet radiation. The sensitivity to nitrous acid of the radiosensitive strains S and B, but not that of the radioresistant strains, was found to be greater on Tryptone medium than on Penassay medium, and greater on Penassay medium than on glucose-salts medium. Between 2 and 3% of the strain S survivors of nitrous acid treatment were radioresistant; 46 such radioresistant mutants were isolated and found to be identical in cross-resistance pattern with radioresistant types (R(3), R(4), or R(6)) previously described. The proportions in which these radioresistant types were found to occur were similar to those observed after selection by other radiomimetic agents.