ELECTROPHYSIOLOGY 353 



when measured immediately after injury, is higher than that 

 measured later. The latter is a normal membrane or concentra- 

 tion potential or both. The difference between the total poten- 

 tial first measured and the final potential is that due to injury. 



The increased acidity of injured regions is a possible cause of 

 injury potentials. Increase in hydrogen-ion concentration 

 indicates electric activity. Furthermore, freshly exposed sur- 

 faces of tissues oxidize readily. The oxidation itself, as well as 

 the greater acidity of the tissue, indicates that injured tissues 

 are the seat of electric forces. 



Other Potentials. — Potentials exist wherever there is an 

 interface separating-ions of different distribution. We can, 

 therefore, increase considerably the list of potentials — if not 

 of actual ones, then merely so-called ones — which are useful 

 as names to designate specific instances. Such are surface 

 potentials, at the interface air-hquid (a fairly well recognized 

 potential) ; and, if we select the particular ion responsible, then, 

 hydrogen-ion potentials, between acid-conductor-base (a kind 

 of concentration potential). There are also electrokinetic 

 potentials due to selective adsorption and ionization (of proteins) ; 

 but, as they do not involve a flow of current and cannot therefore 

 be measured directly, they will not be considered here. 



It will be noticed that in this discussion of potentials no 

 extensive use has been made of mathematical formulation. 

 This is unnecessary for the operational definition and classifica- 

 tion of phenomena. 



The role of all types of potentials in life is not fully under- 

 stood other than that they release energy. As life is the sum 

 total of all energy manifestations that occur in protoplasm, 

 electric potentials are a part of that whole which we call life. 



Potential Differences between Cell Parts. — Potential differences 

 between body parts — for example between injured and unin- 

 jured tissues— are capable of experimental proof. In the case of 

 the individual hving cell, there is no satisfactory way of measuring 

 potential differences; but evidence that they exist, though 

 indirect, is nevertheless to be had. There is, first, the fact that 

 any system containing a selectively permeable membrane 

 bathed in electrolytes is certain to have potential differences, 

 due to an unequal distribution of ions. Such potentials must 

 exist within living cells and between one cell and another. The 



