Estimation of growth rate from the mitotic index.

The growth rate of a eukaryotic population dividing at a constant rate can be estimated from the equation, t(m)/g ln 2 = ln (1 + R), in which t(m) is the time required for mitosis, g is the generation time, and R is the fraction of cells undergoing mitosis. Values for t(m) and R can be determined by direct microscope examination of the population. The validity of the derived equation has been checked with an exponentially growing culture of a prokaryote, Escherichia coli, in which chloramphenicol was administered to inhibit protein synthesis. Cells having enough protein completed the division process whereas the rest of the population was inhibited. From the plot of the growth curve before and after administration of chloramphenicol, t(m) and R were estimated. The calculated and actual growth rates were almost identical.