Effects of x-ray exposures of 8, 16, 32, 64, 128, 512, and 1024 R on mitosis in hanging-drop preparations were determined by repeated observations of selected prophase cells before and at short intervals after irradiation. Prophase was subdivided into eight microscopically distinguishable stages: very-early, early, initial-middle, intermediate-middle, terminal-middle, initial-late, intermediate-late, and terminal-late. With one exception, cells treated at intermediate- or terminal-late prophase with any of the doses were neither delayed nor reverted. After 8 to 16 R nearly all cells from early to initial-late prophase are delayed in reaching prometaphase, but none reverts. After 32 to 64 R all cells in early to initial-late prophase are delayed and most revert; after 128 to 1024 R nearly all revert. Delay or reversion is preceded by a postirradiation inertia, during which the cell progresses mitotically at an almost normal rate for a short time. Duration of inertia is inversely related to dose. The degree of reversion depends on the exposure; at 128 R and greater, all cells that revert go back to early prophase. The relations of the G1, S, and G2 periods of the mammalian cell to the morphologically defined stages of the cell cycle of the acridian neuroblast are considered.

This content is only available as a PDF.
You do not currently have access to this content.