AbstractBy the “labeled mitoses” method of Quastler and Sherman and others, the cell cycle of the germinative zone cells of the bullfrog lens epithelium has been characterized. It has been shown that this cycle lasts approximately 83 days with the DNA synthetic phase enduring 100 hours and G2, 11 hours. G1occupies over 90 of the total time. the duration of mitosis itself has not been precisely determined. the length of the synthetic phase was corroborated by double labeling with c14and h3‐thymidine.When the temperature is raised by 6°c, from 24° to 30° the cycle is compressed by 40.When the nongerminative, central cells of bullfrog lens epithelium are activated (stimulated to undergo DNA synthesis and mitosis) by injury or throughin vitroculture, the length of the cycle also appears to decrease. in thein vitroexperiments the generation time, as judged by the period elapsing between two successive bursts of DNA synthesis involving the same cells, amounts to 177–190 hours at 24°c. by raising the temperature to 30°c the time from injury or isolation until the appearance of the first wave of mitosis is re
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