Abstract
Summary
1. The numbers of resting and dividing cells in the cortex of the mouse thymus were significantly reduced 24 hours after a single total-body dose of 400 r gamma rays followed by an injection of colchicine. Increase in the number of mitoses between 52 hours and 3 days postirradiation preceded the rise in the number of cells. The greatest number of mitoses (20.4%) appeared on the 5th day after exposure. 2. The fluctuations in the number of resting and dividing cells after irradiation in the medulla followed no regular pattern. 3. The evidence presented supports the view that the cells repopulating the thymic cortex after irradiation arise in situ.
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