The Effect of X-Radiation on the Yoshida Ascites Tumor I. Inhibition of Mitosis by a Single Irradiation"

The ascites tumors are particularly well suited to radiobiological research. Since the cells float and grow freely in an ambient medium, there is no stroma to be damaged and thus complicate the in terpretation of radiation effects on the tumor cells. If radiation is carried out at an early stage of tu mor growth, there is such a small volume of ascitic fluid that adequate diffusion of oxygen and nu trients to the cells may be assumed. Furthermore, it is possible to remove small aliquots of fluid con taining tumor cells repeatedly from the same ani mals without apparent harm to host or tumor. Thus, the same tumor may be followed throughout its life span in the same host, both before and after radiation. Yoshida ascites tumor1 cells in their free state resemble monoblasts. The solid tumor has the histological appearance of reticulum-cell sarcoma. Although the origin of the tumor is uncertain, it is probably derived from the reticuloendothelial sys tem (31, 32). This paper will describe the first discernible ef fect of x-radiation on the Yoshida tumor, the in hibition of mitosis. An attempt will be made to explain this phenomenon and to determine which cells of the irradiated population have been af fected.