Mitosis in the Mouse: A Study of Living and Fixed Cells in Tissue Cultures

1. Mitosis has been investigated in cultures of infant mouse tissues, in both living and fixed material. 2. Phase microscopy combined with serial photography was used to study the living cell. 3. The formation of chromosomes has been traced in the living cell from the intermitotic chromonemata and heterochromatic chromocentres. 4. Dividing cells can be recognized early in prophase and the duration of each phase of mitosis has been measured. 5. Curves of anaphase movement have been plotted; they are sigmoid as in amphibian cells. 6. The reconstruction of the daughter nuclei has been studied in detail in both living and fixed cultures. The chromosomes swell, then begin to lose their nucleic acid charge and to unravel into a web of fine threads. The nucleolar material can be identified in the living cell early in telophase; it appears as a diffuse system of lumps and strands occupying most of the nucleus and its direct transformation into the interphase nucleoli was followed in the film records. 7. The origin of polyploid nuclei by the mitosis of binucleate cells has been demonstrated. 8. Analysis of the film records showed that the average length of the intermitotic period is 12 hours.