NUCLEAR DIVISION AS OBSERVED IN LIVE BACTERIA BY A NEW TECHNIQUE

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Abstract
Stages of division in Escherichia coli and Bacillus cereus are shown with phase contrast photo-micrographs. High concentrations of gelatin (20-27% for E. coli, 28-35% for B. cereus) in brain heart infusion broth in-creased the contrast within the cells. A drop of a 2 to 4-hour-old gelatin-broth culture at 37[degree] C was mounted between a cover slip and slide for observation of nuclear changes during growth of the cells. The bright high phase contrast objective (N. A. = 1. 25) of the Spencer phase microscope was superior to the bright medium and the B minus objectives for these observations. Areas of lowest refractive index in the cells have the same position and configurations as stained nuclei. Certain nuclear figures consistently reoccur, but even photographic sequences made at intervals of 0. 5 minute did not provide conclusive evidence either for a mitotic or for an amitotic pattern of nuclear division.