THE PHYSIOLOGY OF CELL-DIVISION 729 
centers negative.” The chromosomes in the nuclear area, being 
negatively charged bodies, are influenced by the electrostatic 
forces existing in the field and spread out laterally in a symmet- 
rical position between the adjoining negative areas. The lines of 
force, indicated by the radiations, converge in each hemisphere 
toward the intermediate regions of greatest negativity; the latter 
evidently correspond to the more or less definitely circumscribed 
astral centers.*! | 
During this period ions must be regarded as slowly diffusing 
along the gradients in such a manner as to equalize the potentials. 
Just as the region midway between the two most positive areas 
(superficies and nuclear region) retains its original negativity 
longest, so the region midway between the two most negative 
areas (the astral centers) retains its original positivity longest. 
That is, the gradient of decreasing negativity or increasing posi- 
tivity is from the astral centers toward the periphery and toward 
the original nuclear area. Wéathin the nuclear area a region sym- 
metrically situated with reference to the two astral centers will 
thus, so long as the potentials remain unequalized, be the region 
of highest potential or greatest positivity. The position of this 
region will coincide with a plane equidistant from and perpendicu- 
lar to the astral centers, and to this plane negative particles will 
tend to be drawn; hence the gathering of the chromosomes in this 
‘equatorial plate’ position. 
‘3¥or the sake of definiteness I express myself here as if the negative and posi- 
tive areas were sharply circumscribed; this of course cannot be the case where 
ions are free to diffuse; it is with more or less steep gradients that we are dealing. 
The astral centers, under the above conditions, represent merely the regions of 
greatest negativity; the plane midway between the two, the region of the greatest 
positivity; the potential changes continuously and probably quite uniformly— 
judging from the usual disposition of the fibrils—between these two regions. ‘The 
conditions are essentially like those in the solution between the plates of a battery 
with closed external circuit, though the gradient in the cell is much steeper. 
‘4 The degree of development of the radiations will depend on the steepness of 
the gradient, on the time during which it persists, and on the density of the cur- 
rent-lines. This is probably why the spindle-fibers are the most constant, definite, 
and persistent of all; it also suggests the reason why radiations do not normally 
extend from the nuclear region to the equator of the cell. Possibly the neighbor- 
hood of the other oppositely oriented fields also interferes with the formation of 
such radiations. 
