A method for the scrutiny of live mammalian cells in culture and for the measurement of their proliferative ability after x-irradiation.

A method is described for the observation of live mammalian cells in culture with an incubated phase-contrast microscope. A sample of plated cells may be watched and their respective capacities to form a colony measured by daily cell counts. The method has first been used to make direct estimations of the plating efficiency of the diploid line of Syrian hamster fibroblasts, BHK 21 C13, and then to observe the response of synchronous samples of these cells to 220 kV X-rays. A dose of 1.4 Gy given in Gl has no immediate detectable effect on cell or unclear morphology, and cell capacity to reach post-irradiation mitosis in unimpaired apart from delay. In contrast, after this mitosis is completed, descendant cells from some mitoses retain a normal form and clonogenic capacity, whereas the cells from other mitoses show varying degrees of abnormality and produce either slow-growth or stop-growth (micro-) colonies.