ATP is markedly affected by changes in environment and that fine struc- 

 ture, nuclear function, and osmotic balance are closely integrated (All- 

 frey and Mirsky, 1959). The correlation between the presence of a 

 negative electrical charge associated with the chromosomes and bio- 

 chemical activity of the nucleus has also been stressed by these same 

 workers. As pointed out by Stern (1956), it is obvious that disorganiza- 

 tion of the interphase nucleus at the onset of mitosis must have wide- 

 spread effects on cell activity. The morphological changes in the 

 chromosomes coincident with the development of prophase are well 

 known, and have already been described in detail in Chapter 5. It may 

 well be that the physical and chemical organization of the nucleus is so 

 radically altered at the onset of cell division that some of the metabolic 

 pathways which were operative during the premitotic period are either 

 greatly reduced in activity or made completely inoperative. The decrease 

 in oxygen consumption accompanying the onset of cell division and the 

 apparent lack of synthesis during the postprophase stages of mitosis 

 support this view. It is well known that marked changes in the appear- 

 ance of the cytoplasm occur during active mitosis. While the nature of 

 these changes is not completely known, it has been found that the 

 basophilic structures characteristic of the cytoplasmic membrane system 

 are altered at the onset of mitosis (Brachet, 1957). The recent electron 

 microscope studies of Porter and Machado (1960) have shown that 

 alterations in the structure and distribution of the endoplasmic reticulum 

 accompany the mitotic process in plant meristematic cells. These work- 

 ers suggested that the role played by the elements of the endoplasmic 

 reticulum during cell division may be passive relative to chromosome 

 movements in much the same sense that mitochondria and plastids are 

 apparently uninvolved. During mitosis in tissue culture cells and cleavage 

 in sea urchin eggs, the mitochondria lose their motility and fragment 

 into bead-like structures or granules which sometimes completely dis- 

 appear from view (Agrell, 1955; Chevremont and Frederic, 1952). 

 Reconstitution of the mitochondria apparently occurs during the terminal 

 stages of the mitotic process. On the basis of available evidence, it would 

 appear that oxidative processes are minimal during active mitosis and 

 that whatever metabolic activities are associated with this stage of the 

 mitotic cycle are most likely mediated through operation of a glycolytic 

 pathway. Further investigation of nuclear metabolism along lines similar 

 to those employed by the Allfrey group will undoubtedly yield many 

 new and interesting findings which hold promise of contributing signifi- 

 cantly to our understanding of the problem of cell division. 



MECHANICS AND PHYSIOLOGY OF CELL DIVISION / 159 



