FREQUENCY DISTRIBUTION OF STAGES OF THE CELL CYCLE OF MOUSE ASCITES TUMORS FOLLOWING IN VIVO AND IN VITRO LABELING WITH TRITIATED THYMIDINE

Ehrlich Ascites tumor cells aspirated from the peritoneal cavity of mice bearing 7-10-day-old tumors when incubated for 1 hour at 37 °C in medium 199 containing tritiated thymidine at a concentration of 4 μc/ml. yielded labeling indices and frequency distribution of stages of the cell cycle similar to those obtained when the same mice received a single intraperitoneal injection of 100 μc of the label and the cells were harvested 1 hour later. Analysis of stages of the cell cycle by the combined techniques of DNA cytophotometry and cellular autoradiography (direct method) yielded a frequency distribution of S, G2, M, and G1, similar to those of other investigators with the labeled metaphase curve (indirect) method.