||Abstract: "Approximately 20% dry-matter content appears to be an accepted standard value for bacterial cells." P.755 left column top paragraph: "Reliable estimates of bacterial biomass (as carbon content) are essential to determine the quantitative importance of bacteria in many ecosystems. No reliable method for the direct determination of bacterial biomass is currently available. Useful estimates can be made, however, by converting bacterial biovolume into organic carbon (refs 3, 10, 11, 21). The conversion factor involved may be calculated from values for the buoyant density, the dry weight/wet weight ratio, and the carbon weight/dry weight ratio of bacterial cells. These values are seldom determined for each case, use being made of literature data obtained with other organisms for other purposes. Luria (primary source) states that about 20% is a reasonable average estimate of bacterial dry weight. Similar values have later been assumed to be valid for bacteria in general (refs 3, 10, 21)."