The Effects of X-Rays on the Mitotic Activity of Mouse Epidermis

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Abstract
Mice of CF1 strain, 6-8 wks. old, were exposed to 250-KVP x-rays at the rate of 50 r/min., and autopsied at diff. times after exposure. Sections of epidermis of the ear were stained with Mayer''s hematoxylin, and cells in mitosis in a given number of fields outlined by a Whipple disc were counted. The number of cells in the field was detd. for animals of the strain and age used so that the final value of the mitotic index can be expressed as mitoses/100,000 cells. A variation from field to field gives an error of 1-2% not found when individual cells are counted. The larger numbers examined by the field method compensates for this error by reducing the over-all statistical error. Since x-ray dosage to 325 r does not significantly change the number of cells per field, the method is valid for mouse skin after irradiation. The change in mitotic index over a range of 5 to 325 r was studied. In animals receiving 35 to 325 r, the minimum point of mitotic activity is <1 mitosis/100,000 cells. This is reached less than 2 hrs. after exposure. The time for the index to return to normal varies from 5 hrs. at 35 r to 6 days at 325 r. Over-compensation is evident at 325 r, with mitotic activity more than double that of normal on the 8th day after irradiation. Mitotic activity of mouse skin is highly sensitive to x-rays. The best index of damage is the time for the mitotic index to return to normal. It is postulated that the degree of depression of mitotic activity may serve as an index of tissue damage at very low dosages.

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