THE EFFECT OF A MEDIUM DOSE (430 ROENTGENS) OF X-RAY IRRADIATION ON RESTING CELLS OF THE LIVER

The mitotic activity of regenerating liver cells after a single dose (430 r) of x-ray irradiation was studied. In every group of the experimental animals (white rats), the mitotic activity (mitotic index) and the number of abnormal mitotic figures were determined. The results indicated that resting cells irradiated a short time before mitotic activity showed reactions similar to those of cells irradiated during mitotic activity. The disturbances in the irradiated mitotically active cells were only quantitatively different from those in the irradiated resting cells. The disturbances in the irradiated resting cells depended upon the time interval between the irradiation and the beginning of mitotic activity stimulated by partial hepatectomy. It was found that the shorter the time interval, the more pronounced were the disturbances and the more similar they became to those of irradiated mitotically active cells. Conversely, the longer the time interval between the irradiation and the beginning of mitotic activity, the less pronounced were the disturbances and the more similar they became to those of the non-irradiated control cells. A discussion is presented as to whether or not the lesions of resting cells caused by a single medium dose of x-ray irradiation are reversible, and whether such lesions are only brought to light by the process of mitosis or whether the process of mitosis renders it possible for these lesions to develop.