THE DUAL FORCE OF THE DIVIDING CELL 



By MARCUS M. HARTOG, MA.., F.L.S., F.R.A.S., 



Professor of Natural History, Queen's College, Cork 



In giving such an explanation of the present state of our know- 

 ledge of the forces involved in karyokinesis as will be intelligible 

 to the readers of Science Progress, I shall suppose these to 

 belong, on the one hand, to those interested in biology with a 

 superficial acquaintance with physics, and on the other to the 

 physicists with but a scant knowledge of biology. The task is 

 no easy one : when approaching the problem from the biological 

 side, I found that to deal with it I had to steep myself in 

 Faraday's conception of lines of force till I could, so to speak, 

 handle them freely; while I found my physical friends and 

 counsellors most unwilling to tackle the explanation of pro- 

 cesses whose sequence had mainly to be inferred from the 

 co-ordination of innumerable fixed microscopic sections. To do 

 my best will still, I fear, leave the following pages somewhat 

 hard reading for both categories of readers. 



Hermann Fol in 1873 gave the first account of the " mitotic " 

 figure of the dividing cell, so named some years later by 

 Flemming, because at this stage the plastic cytoplasm exhibits 

 a definite threadlike structure. He wrote : " On either side of 

 these remains of the nucleus are seen aggregates of plasma, 

 closely associated granules which form two starlike figures. 

 The rays of these stars are formed of the granules, serried into 

 straight files. Several of these files stretch in bows from the 

 one star or attraction-centre to the other. The whole picture 

 is extremely clear, and has a vivid resemblance to the way 

 in which iron-dust strewn between the two poles of a magnet 

 arranges itself. ... I rank myself entirely on the side of 

 Sachs's theory of cell-division ('Furchung') by centres, not at 

 all, I may say, on theoretical grounds, but because 1 have seen 

 these centres." 



Fol's observations have been followed and confirmed and 



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