210 HYDROGEN ION CONCENTRATION 



he ascribed the observed current to the destructive (death) proc- 

 esses at the place of injury, a theory which subsequently was ex- 

 panded into the so-called "alteration theory." When, later, dif- 

 fusion potentials became better known, it was attempted to utilize 

 them for the explanation of these phenomena. ^^ But diffusion 

 potentials of corresponding order of magnitude can arise only as an 

 exception in the diffusion of free mineral acids toward neutral solu- 

 tions, and besides, they demand conditions never met with in the 

 living organism. Even when the presence of such acids as lactic 

 acid is taken into account, the maximal diffusion potentials could 

 amount to no more than a few millivolts, whereas currents of injury 

 usually amount to several centivolts. Wilhelm Ostwald^^ gave a 

 material stimulus to the reinvestigation of this problem. In the 

 course of an investigation of the electrical properties of precipitation 

 membranes he expressed the conjecture that the currents observed 

 in muscles and nerves, and even in the electric fishes, have their 

 origin in the properties of similar membranes. He ascribed to these 

 membranes the peculiarity of being permeable either only to anions 

 or only to cations. The diffusion of an electrolyte through such a 

 membrane would therefore result in a separation of the ions and 

 hence in a potential difference. This explanation has the great 

 distinction of being the first to introduce the phase boundary as 

 the place of origin of an electromotive force. And yet the concep- 

 tion of ionic permeability did not prove to be capable of adequate 

 and quantitative investigation. To be sure, the physiologists 

 attempted to extend this theory by trying to find the ions to which 

 living membranes are impermeable. Bernstein^*^ ascribed this 

 property to the K-ions. Hober" could not confirm this. He 

 thought to have shown that the permeability of the cell membrane 

 to the different ions varied with the effect of different ions upon 

 the membrane. He assumed that the colloidal state of the mem- 

 brane changed under the influence of the various ions, and that 

 along with it the permeability varied. This assumption appeared 

 all the more plausible, as the ionic series, so frequently encountered 



i« Oker-Blom, Pfliigers Arch. f. d. ges. Physiol. 84, 191 (1901). 

 '» Wi. Ostwald, Zeitschr. f. physikal. Chem. 6, 71 (1890). 

 '« Bernstein, Pflligers Arch. f. d. ges. Physiol. 92, 521 (1902). 

 ^' Hober, Physikalische Chemie der Zelle und Gewebe. Leipzig 1911, p. 

 487. 



