94 THE MECHANISM OF LIFE 



nucleus a coloured drop of solution more concentrated 

 than the cytoplasm solution. The particles of Indian ink 

 in the central drop arrange themselves in a long coloured 

 ribbon, apparently rolled up in a coil, the edges of the 

 ribbon having a beaded appearance. After a short time 

 the ribbon loses its beaded appearance and becomes smooth, 

 with a double outline, as is shown in .V, Fig. 32. This coil 

 or skein of ribbon subsequently divides, forming a nuclear 

 spindle, while the chromatin substance collects together in 

 the equatorial plane as in B, Fig. 32. 



A more advanced stage of the nuclear division is shown 

 at C, Fig. 32, where the chromatin bands of artificial chromo- 

 somes are grouped in two conical sheafs converging towards the 

 two centrosomes. For some considerable time these conical 

 bundles remain united by fine filaments, the last vestiges of 

 the nuclear spindle. The final stage is that of two artificial 

 cells in juxtaposition, whose nuclei are formed by the original 

 centrosomes augmented by the chromatin bands or chromo- 

 somes (Fig. 32, D). 



The resemblance of these successive phenomena to those 

 of natural karvokinesis is of the closest. The experiment 

 shows that diffusion is quite sufficient to produce organic 

 karyokinesis, and that the only physical force required is that 

 of osmotic pressure. If in the cytoplasm of a cell there are 

 two points of molecular concentration greater than that of 

 the general mass, the nucleus must necessarily divide with all 

 the phenomena which accompany karvokinesis. In nature 

 these two centres of positive concentration are introduced into 

 the protoplasm of the cell by fecundation — that is. by the 

 entrance of the centrosomes of the sperm cell. In certain 

 abnormal cases the concentration may be produced in the cell 

 itself by the formation of two centres of catabolism or 

 molecular disintegration, since, as we have seen, molecular 

 disintegration raises the osmotic pressure. This phenomenon, 

 namely the production of karyokinesis from centres of cata- 

 bolisin, may account for the abnormal karyokinesis of cancer 

 cells and the like. The subject is one which would well repay 

 further investigation. 



