BIOELECTRIC PHENOMENA 313 



potentials of the poly]:)hasic living system, protoplasm, 

 which in its nature is subject (especially if highly "irrit- 

 able") to rapid variations of chemical or metabolic 

 activity. Such variations imply corresponding altera- 

 tions (breakdown, construction, etc.) of those j)roto- 

 plasmic structures, including the interfacial films, whose 

 formation and maintenance depend on this metabolic 

 activity. Apparently during the normal stimuhition of 

 any irritable cell, e.g., a muscle cell, the electromotor 

 properties of the cell surface change in such a manner 

 that the surface adopts temporarily properties like those 

 of an injured or altered surface; i.e., one which has lost 

 its semi-permeabiUty. This effect, the result of a 

 metabolic change of some kind, in which oxidations 

 probably play a chief part, is a reversible one; conse- 

 quently a reversible electromotor variation accompanies 

 it. It is as if the injury-current were temporary, and 

 lasted for only a brief period, whose duration depends on 

 the rate at which a complete surface layer with the 

 original properties can be re-formed. It has already 

 been pointed out that certain forms of injury-current, 

 those caused by KCl solution, are reversible if the injury 

 is not too extensive.' On such a hypothesis we may 

 understand why the whole reversible bioelectric variation 

 occupies a definite time, characteristic for each irritable 

 tissue; this time is determined by the tissue's own 

 specific rate of metaboUc construction and destruction. 

 The special reaction-velocities characteristic of the 



» It is well known that with excessive stimulation of any kind the 

 return of the normal positixity is delayed or incomplete (Hermann and 

 others). All transitions from complete reversibility to irreversibility 

 can be obtained. (Cf. Ebbecke, "Mcmbraniindcrung u. Xcrvcncr- 

 regung," Arch. ges. Physiol., CXCV [1922], 555; cf. pp. 581 fl.) 



