The control of cell division 



Robinow, C. F. (1949). Addendum in The Bacterial Cell, by R.J. Dubos. Cambridge, 



Mass. 

 Scholander, P. F., Claff, C. L. and Sveinsson, S. L. (1952). Respiratory studies 



of single cells III. Oxygen consumption during cell division. Biol. Bull. Woods 



Hole 102, 185-199. 

 Swann, M. M. (1953). The mechanism of cell division. A study with carbon 



monoxide on the sea-urchin egg. Quart. J. micr. Sci. 94, 369-379. 

 Swann, M. M. (1954). The mechanism of cell division. Experiments with ether on 



the sea-urchin egg. Exp. Cell Res. (in press). 

 Wilson, E. B. (1925). The cell in development and heredity. 3rd ed., Macmillan, New York. 

 Zeuthen, E. (1950). Respiration during cell division in the egg of the sea-urchin 



Psammechinus miliaris. Biol. Bull. Woods Hole 98, 1 44-151. 

 Zeuthen, E. (1953). Growth as related to the cell cycle in single-cell cultures of 



Tetrahymena piriformis. J. Emhryol. exp. Morphogen. 1, 239 — 249. 



Discussion 



Chairman: H: V. Brondsted 



M. Westergaard. Has it been possible to fix the eggs and see how inhibition affects the 

 differentiation of the chromosomes during mitosis ? It seems a pity that the physio- 

 logical approach to the study of mitosis has a tendency to become detached from 

 microscopic information about the chromosome cycle. 



M. M. Swann. The sea-urchin egg is not a very satisfactory material for chromosome 

 studies, and I have only made a few observations. Clearly, more ought to be done 

 along these lines. 



E. ^euthen. I have found that the 32 P uptake during mitosis varies cyclically (Zeuthen, 

 1 95 1, Publ. Staz. zool. jYapoli 23, Supplement, 47-69). This might perhaps be evidence 

 of the building up of a store of some phosphorus compound. 



M. M. Swann. Agreed. 



C. D. Darlington. Indications that DNA is an important component of Professor 

 Swann's 'reservoir' are of several kinds. Cells when x-rayed may be forced into mito- 

 sis too soon and produce half-size chromosomes presumably with a half charge of 

 DNA. Their prophases may also be reversed so that when they return to mitosis they 

 have a double set of chromosomes, certainly with double DNA (Darlington and 

 La Cour, 1945, J. Genet. 46, 180-267.) In the differentiation of the bone-marrow, red 

 precursors with a high mitotic rate are marked by a strong DNA charge on the chro- 

 mosomes, high spiralization and a compact and effective spindle. White precursors 

 with a low mitotic rate have a low DNA charge, low spiralization and a hollow and 

 less effective spindle. This DNA-plus-protein contrast is exaggerated with pernicious 

 anaemia, where it leads to the formation of ineffective red cells lacking a balanced 

 chromosome complement (La Cour, 1944, Proc. Roy. Soc. Edin. 62, 73-85). In pollen 

 grains there is normally a differentiation, determined by a cytoplasmic gradient, 



195 



