THE PHYSIOLOGY OF CELL-DIVISION 125 
the region adjoining the membranes where it will be highest. 
This condition can of course be only temporary since ions are 
free to diffuse through the cytoplasm. It is supposed, on the 
present theory, that it persists for a sufficient length of time to 
produce well marked effects.** 
We are now in a position to apply the above principles in inter- 
pretation of the radiations and spindle-figure of dividing-cells. 
I shall consider only the most general and constant phenomena of 
mitosis, neglecting individual variations, and shall offer a physico- 
chemical-analysis of the conditions at a time when the mitotic figure 
is fully formed (metaphase). The radiations at this time centre 
toward two definite areas one on either side of the nucleus. Of 
those which immediately adjoin the nuclear region, two sets are 
ordinarily distinguishable, (1) the spindle-fibers which show a 
definite curved course, with concavity toward the cell-axis, 
similar to the lines of force between opposite electric or magnetic 
poles, and (2) the mantle-fibers which have a more external posi- 
tion, show a straighter course, and tend to diverge. The remain- 
ing radiations spread out from each astral centre in all directions 
toward the periphery of that half of the cell. If we regard the 
fibers as indicating with a fair degree of accuracy the direction 
of the electrical lines of force, we see here distinct evidence of the 
existence in each half of the cell of two oppositely oriented electri- 
eal fields. For reasons that will be apparent shortly, the periph- 
eral regions of the cytoplasm are to be regarded as positive rela- 
“9 T may cite here two quite independent investigations indicating that the rate 
of ionic movement in protoplasm may be much less than in ordinary solution. 
Girard has found that the diffusion-rate of electrolytes through membranes which 
are the seat of an electrical polarization is much slower than through the same 
membranes in the unpolarized condition. If this be a general rule, it would 
apply to the case of ions moving along potential-gradients in the cell. Cf. Girard: 
Archives de physiologie normale et pathologique, 1910, vol. 12, p. 471. Again, 
Keith Lucas concludes, from the differences in the excitation rate of various excit- 
able tissues, that the ions concerned in the polarization resulting from electrical 
stimulation must move at vastly different rates in the different cases. The facts 
indicate that the ionic movement is 4000 times as rapid in a highly excitable tissue 
like the ‘substance @’ of the frog’s sartorius, as in the ventricular muscle of the 
same animal. If such a range of ionic velocities exists in different tissues, it is 
clear that in some the movement must be extremely slow. Possibly this condition 
is distinctive for dividing cells, which show an even slower rate of response than 
ventricular muscle. Cf. Journal of Physiology, 1910, vol. 40, p. 224. 
