POTENTIALS AT PHASE BOUNDARIES 209 



The benzene, diminishing the dielectric constant of the oil phase 

 decreases the dissociation of the dissolved acid and thus renders the 

 oil phase more negative. ^^ The correlation of the chemical con- 

 stitution of an oil with its position in the electromotive series still 

 needs further investigation. 



59. Physiological applications of the theory of boundary potentials 



It appears appropriate at this juncture to examine the relation 

 of the above observations to the electromotive forces found in living 

 tissues. In fact, these currents produced without metals, observed 

 by the physiologists several decades ago, served as a stimulus for 

 the above described studies which were undertaken to elucidate 

 biological processes. The fundamental physiological observations 

 date back to DuBois-Rej^mond^- which stated briefly were as fol- 

 lows: Whenever a living tissue (muscle, nerve, leaf or fruit) was 

 injured (cut, crushed, etc.) at any place, and an injured and an 

 uninjured place were connected by means of unpolarizable electrodes 

 an electric current of 0.02-0.1 volts was produced, the injured spot 

 being negative with respect to the uninjured spot. Also whenever 

 the uninjured surfaces of any two related organs (tendon and muscle, 

 root and leaf or stem) were connected in the same manner, a cur- 

 rent was obtained (the tendon being negative towards the muscle, 

 the root negative towards the leaf). These observations provoked 

 the hope of explaining the nature of vital processes on the basis of 

 electric phenomena. Physical science of that day had not yet 

 reached an adequate interpretation of those observations; for it 

 was then still impossible to reproduce so great potential differences 

 without the use of metals. A "molecular theory" attempted by 

 DuBois-Rejinond was of a purely descriptive character. Soon 

 afterwards L. Hermann^^ discovered that injured parts of the same 

 tissue showed no potential differences towards each other, and hence 



" This finding will be recalled later in the section dealing with Coehn'a 

 Rule. 



^'' E. Du Bois-Reymond, Untersuchungen iiber tierische Elektrizitat. 

 Berlin 1848, 1849, 1860, C. Reimer; Gesammelte Abhandlungen zur Muskel und 

 Nervenphysik. Leipzig 1875; see also Helmholtz, AUgemeine Monatsschr. f. 

 Literatur u. Kunst. Kiel, April 1852. 



" L. Hermann, Weitere Untersuchungen zur Physiologic der Muskeln und 

 Nerven. Berlin 1867. 



