THE PHYSIOLOGY OF CELL-DIVISION 721 
cytoplasm during rest, may therefore be regarded as an essen- 
tially homogeneous phase bounded externally and internally by 
a semi-permeable surface. 
What will be the electrical conditions in such a system? As 
already explained, each surface is to be regarded as permeable to 
H-ions, hence as corresponding to an ion-liberating surface, like 
that of a metallic plate immersed in an ionizing solvent like water. 
The conditions will hence be essentially as follows: Imagine a 
hollow zine sphere immersed in a solution of a zine salt and con- 
taining in its interior a second solution of zine salt (fig. 1). The 
Fig. 1. Representing in section a hollow zinc sphere immersed in zinc sulphate 
solution and containing the same solution in its interior. The orientation of the 
double layers is shown. The metal is uniformly negative, the adjoining solution 
positive. The analogy to the conditions in the resting cell is obvious,—7. e., 
there are two concentric electrically polarized surfaces separated by a homo- 
geneous conducting medium. 
two surfaces correspond to the two semi-permeable surfaces in 
the cell; at each surface zinc ions will tend to pass into the solu- 
tion with a pressure depending on the solution-tension of the zinc 
and on the concentration of zine ions in the adjoining solution. 
There will thus be a potential difference at each surface calculable 
Jed Mae 2 
from the formula: H = oF ln = ; the only possible condition of 
; , 
equilibrium however will be that these two potential differences 
should be equal, since if one surface of the zinc be at a higher 
potential than the other, electricity will pass through the freely 
conducting metal to equalize the potentials.“* The potential- 
44 The case is obviously different from that of a concentration-cell in which two 
metallic plates are immersed in unequally concentrated solutions of a salt of the 
metal, and the two solutions freely communicate. In the above system the two 
surfaces are in metallic connection but the solutions are separated by an impermeable 
partition. If the partition were rendered permeable to ions, e.g., by boring a 
hole through the sphere, thus placing the two solutions in communication, a typi- 
