The Mechanics of Mitosis 31 



and vice versa. If, however, we assume that the centrosomes are 

 pulsating synchronously and in opposite phases, or oscillating 

 synchronously and in the same phase, we obtain the desired repul- 

 sion, and at the same time we get mitotic figures corresponding to the 

 configuration of the lines of magnetic force between opposite poles. 

 That is, we get a configuration of spindle fibers and astral rays 

 precisely like the actual ones. 



The cases of tri- and multi-polar spindles, so difficult to explain 

 on electrostatic grounds present much less difficulty here. If each 

 centrosome were oscillating along a path radial to the common 

 nuclear center and in the same phase, mutual repulsion, combined 

 with the proper configuration of the astral rays, would be obtained. 



The movements and configuration of the chromosomes are also 

 better explained on hydrodynamic grounds than by previous 

 assumptions. It is not even necessary to assume that they execute 

 any independent oscillatory or pulsating motions. Bjerknes has 

 shown that bodies suspended within the field of force of oscillating 

 or pulsating bodies are attracted or repelled depending on whether 

 they are lighter or heavier than the surrounding medium. This 

 attraction or repulsion is due to oscillations induced in the sus- 

 pended bodies by the permanently oscillating or pulsating bodies. 

 The chromosomes, if heavier than water, or the cell fluid in which 

 they are suspended, would be repelled from each centrosome and 

 would come to occupy a position midway between them in the 

 equatorial plate. Moreover, they would not move outward to the 

 boundary of the equatorial plate. Their induced oscillations, 

 though repelling them from each centrosome, would attract them 

 toward each other, and this action would tend to keep them in 

 the observed axial position. If the chromosomes should become 

 lighter than the cell liquid, the repulsion from the centrosomes 

 would change to an attraction. This immediately suggests that 

 it may be simply a change in specific gravity of the chromosomes 

 which causes them to diverge, after splitting, back toward the cen- 

 trosomes. 



It is now of interest to inquire whether this hydrodynamic action 

 at a distance could possibly be strong enough to account for the 

 actual movements of the centrosomes. It is, of course, almost 



