KARYOKINESIS 93 



and as far as we know diffusion alone, is able to produce a 

 spindle between homologous poles. 



A glance at the photograph is enough to show that the 

 spindle is formed between poles of the same sign. The lines 

 of diffusion radiate from one centre and converge towards 

 the other centre in curves, giving the double convergence 

 characteristic of a spindle. The central drop merely supplies 

 the necessary material, and should have a concentration but 

 slightly less than that of the plasma, so as not to set up its 

 own lines of diffusion. The photograph shows clearly that the 

 rays of the spindle traverse the equator without any break. 

 It has been objected that these lines form not so much a 

 spindle as two hemi-spindles, but it is clear that these two 

 hemi-spindles are continuous and form a single sheaf of rays 

 uniting the two poles of concentration. This is a phenomenon 

 entirely unknown in the magnetic or electric fields, where two 

 poles of the same sign, one on either side of a pole of the 

 contrary sign, give two separate spindles. In a magnetic field 

 it is impossible to make the lines emanating from one pole 

 converge, except to a pole of opposite sign. Hence if we 

 admit the homopolarity of the centrosomes, we must also 

 admit that diffusion is the vera causa of karyokinesis, since, as 

 I showed at the Grenoble Congress in 1904, diffusion and 

 diffusion alone is capable of producing a spindle between two 

 poles of the same sign. 



Nuclear Division. — In order to reproduce artificially the 

 phenomena attending the division of the nucleus, we may 

 proceed as follows. We cover a perfectly horizontal glass 

 plate with a semi-saturated solution of potassium nitrate 

 to represent the cytoplasm of the cell. The nucleus in 

 the centre is reproduced by a drop of the same solution 

 coloured by a trace of Indian ink, the solid particles of 

 which will represent the chromatin granules of the nucleus. 

 The addition of the Indian ink will have slightly lowered 

 the concentration of the central drop, and this is in 

 accordance with nature, since the osmotic pressure of the 

 nucleus is somewhat less than that of the plasma. We 

 next place on either side of the drop which represents the 



