THE PHYSIOLOGY OF CELL-DIVISION 715 
that both ions then pass with equal readiness, will have a similar 
effect ;27 such an effect will follow any marked general increase in 
the ionic permeability of the membrane, since the selective per- 
meability to different ions will then tend to disappear. If we 
take a limiting case and suppose that the membrane is freely per- 
meable to one ion of the electrolyte, e.g., the cation (hydrogen- 
ion) of an acid, and completely impermeable to the anion, the 
surface adjoining the solution with the lower H-ion concentra- 
tion will be positive relatively to the other surface; if the con- 
centrations be known, the potential-difference can be calculated 
from Nernst’ ay Oe me 
rom Nernst’s equation, a ap ae 
difference between two adjoining unequally concentrated solu- 
tions of any electrolyte with ions of unequal velocity; in the pres- 
ent case, since v=o, the potential-difference will be equal to 
R fe C2 
Fr In a 
Ce ; 
In ar for the potential- 
1 
This formula is identical with that expressing the factors deter- 
mining the potential-difference between any ion-liberating surface, 
e.g., a metallic plate, and the solution, e.g., of its own salt, in con- 
tact with it.22 Such a membrane in fact acts essentially as an 
ion-liberating surface, freeing ions (H-ions) with a certain solu- 
tion-tension; it may thus play the same part as one of the 
ion-liberating surfaces (usually surfaces of metallic plates) in a 
galvanic battery. The same theory thus applies to the conditions 
under which potential-differences arise in a system containing 
27 The potential-difference in this case will fall to that existing between adjoin- 
ing solutions of the electrolyte unseparated by a membrane. 
28 In this formula Z denotes the potential-difference in volts, & the gas constant, 
T the absolute temperature, F the Faraday constant, 1.e., the number of coulombs 
of electricity carried by a gram ion (here assumed to be monovalent), wu velocity 
of cation, v of anion, In natural logarithm, cz ionic concentration of the stronger, 
c) of the weaker solution. The interposition of amembrane impermeable to anions 
of course reduces their velocity to zero. 
29 In such a case ¢ is the solution-tension with which the ions are liberated from 
the surface, c; the concentration of the ions in the solution. For a polyvalent 
Jesh WG 
metal the formula is 2 = —— In = n being the valence of the cation. 
Cj 
