The Mitotic Index and Interphase Processes

The mitotic index of a cell population, defined by Champy as the per mille proportion of the population in any mitotic stage, has long been regarded as an important criterion of the growth and multiplication of tissues. It is commonly measured in fixed and stained specimens, and therefore represents the stage of the material at the time of fixing only. However, cells grown in tissue culture may be observed and photographed for a considerable period before any measurement is made; such observations, which have been reported elsewhere (Walker & Yates, 1952a, b), show that some cytochemical results may require reinterpretation.