644 



SCIENCE 



[N. S. Vol. iXLII. No. 1088 



that it shall be impermeable to both the ions 

 into which this salt is electrolytically dissociated. 

 If impermeable to one only of these ions, the other, 

 diffusible, ion can not pass out beyond the point 

 at which the osmotic pressure due to its kinetic 

 energy balances the electrostatic attraction of the 

 oppositely charged ion, which is imprisoned. 

 There is a Helmholtz double layer formed at the 

 membrane, the outside having a charge of the 

 sign of the diffusible ions, the inside that of the 

 other ions. Now, suppose that we lead off from 

 two places on the surface of a cell having a mem- 

 brane with such properties to some instrument 

 capable o'f detecting differences of electrical po- 

 tential. It will be clear that we shall obtain no 

 indication of the presence of the electrical charge, 

 because the two points are equipotential, and we 

 can not get at the interior of the cell without de- 

 stroying its structure. But if excitation means 

 increased permeability, the double layer will dis- 

 appear at an excited spot, owing to indiscriminate 

 mixing of both kinds of ions, and we are then 

 practically leading off from the interior of the 

 cell, that is, from the internal component of the 

 double layer, while the unexcited spot is still led 

 off from the outer component. The two contacts 

 are no longer equipotential. Since we iind experi- 

 mentally that a point at rest is electrically posi- 

 tive to an excited one, the outer component must 

 be positive, or the membrane is permeable to cer- 

 tain cations, impermeable to the corresponding 

 anions. Any action on the cell such as would 

 make the membrane permeable, injury, certain 

 chemical agents, and so on, would have the same 

 effect as the state of excitation. If we may as- 

 Bume the possibility of degrees of permeability, 

 the state of inhibition might be produced by de- 

 crease of permeability of the membrane of a cell, 

 which was previously in a state of excitation owing 

 to some influence inherent in the cell itself or 

 coming from the outside. This manner of ac- 

 counting for the electromotive changes in cells is 

 practically the same as that given by Bernstein. 



The suggestion of Ostwald was questioned by 

 physical chemists, e. g., Walden, Tammann 

 and Nernst. Recent experiments carried on 

 in the writer's laboratory have shown that the 

 attempt to explain the E.M.F. in tissues by 

 the idea of a selective ion permeability and its 

 changes (which the writer had originally also 

 adopted) is neither tenable nor necessary. 

 Space permits to point out only a few of the 

 reasons for this statement. 



1. Loeb and Beutner found that if we lead 

 off from two places on the surface of an intact ) 

 plant leaf (e. g., rubber plant) or fruit (e. g., 

 apple) with two solutions of the same electro- 

 lyte but of different concentration, the lower 

 concentration is always positive to the higher; 

 and the E.M.F. depends upon the ratio of the 

 two concentrations as expressed by Nernst's 

 well-known formula. In the most ideal objects 

 for this purpose the E.M.F. corresponds quan- 

 titatively to Nernst's formula. In all cases a 

 spot of tissue (no matter whether plant or 

 animal) in contact with distilled water is posi- 

 tive if compared with a spot in contact with a 

 physiological salt solution or a Einger solu- 

 tion.2 



According to the theory of Bernstein, which 

 Bayliss adopts, a spot of muscle or leaf in con- 

 tact with distilled water should be negative to 

 a spot in contact with a physiological salt solu- 

 tion, since we know that distilled water causes 

 an increase in permeability. This increase in 

 permeability is shown not only by the facts of 

 cytolysis, but also by direct observations on the 

 eggs of Fundulus in the writer's floating ex- 

 periments. Thus one of the most general phe- 

 nomena in electrophysiology contradicts the 

 theory of selective ion permeability. 



The experiments of Beutner and of Loeb 

 and Beutner have shown that the E.M.F. which 

 appear at the surface of living tissues can be 

 imitated if we bring a watery salt solution in 

 contact with a substance immiscible in water, 

 such as lecithin or oleic acid (which for experi- 

 mental purposes was dissolved in guaiacol).^ 

 According to Beutner's theory* traces of the 

 salts are soluble in the water immiscible phase 

 and one ion combines here with an anion or 

 cation (or both combine in the case of an 

 amphoteric electrolyte). The common ion of 

 the salt in the water and of the water immis- 



2 Loeb, J., and Beutner, R.^ Biocliem. Ztsdhr., 

 1912, XLL, p. 1. 



3 Loeb and Beutner, Biochem. Ztsdhr., 1913, 

 LL, p. 288; 1914, LIX., p. 195. 



4 Beutner, Ztschr. f. physik. Chem., 1914, 

 LXXXVII., p. 385; Jour. Am. Chem. Soc, 1914, 

 XXXVI., pp. 2,040 and 2,045. 



