THE MITOTIC CYCLE 



Figure 6-1 is a diagrammatic description of the total mitotic cycle. 

 For the sake of simplicity it is divided into three segments, namely: a-b, 

 designated as active mitosis which includes prophase to telophase; 

 b-c, by definition covering that part of interphase during which various 

 synthetic activities are either known or assumed to be taking place; and 

 finally c-a, a segment termed ante phase, which represents that period 



Active 

 mitosis 



Figure 6-1. Diagrammatic Representation of the Mitotic Cycle in Tissues 

 of the Multicellular Organism. 



of interphase in which a cell has completed most, if not all, of the 

 synthetic processes necessary to make it competent or "ready" to enter 

 active mitosis. None of these segments are homogeneous either physi- 

 ologically or morphologically. Theoretically all stages of the mitotic cycle 

 could be subdivided, but for our present purposes, there is no point in 

 further fractionation. Experimental cytology has indicated that the three 

 major segments of the mitotic cycle are sufficiently different in their 

 metabolic characteristics to allow them to be studied separately. Each 

 one of these segments involves a number of problems peculiar to itself. 



138 / CHAPTER 6 



