Abstract
Samples of mitotic L-cells [mouse fibroblast] were investigated after different preparation and staining procedures using the technique of pulse-cytophotometry. Most mitotic cells which should appear in the 2nd peak of the DNA histogram were disintegrated or separated into halves by pepsin pretreatment. The designation ''G2 + M'' for the 2nd peak is not correct for this preparative method. This should be taken into account in cell kinetic investigations performed after pepsin pretreatment.