352 ELECTRO-PHYSIOLOGY 



The seat of electromotive action must accordingly be referred to 

 the margin between dying and living substance (" demarcation 

 surface "). Hermann therefore designates the " current of rest " 

 iii the muscle, the "demarcation current." Hering (14) has 

 recently expounded Hermann's principle of interpretation on very 

 general considerations. The proposition that uninjured resting 

 muscle or nerve has no current implies to him " that such a 

 tissue does not develop a current that can be led off externally, so 

 long as its metabolism, i.e. the internal chemical action in all its 

 parts, is equal. Every disturbance of equilibrium sets up currents 

 that can be led off." Hering also emphasises the fact already 

 brought forward by Hermann, that alteration of chemical action 

 in any part of the living continuum may appear not merely " in 

 that the part concerned becomes negative to the unaltered parts, 

 but also that it may become positive to the same." If then the 

 part that differs chemically from the remaining substance is 

 termed (relatively) altered, we must distinguish between " a 

 (relatively) positive and a (relatively) negative alteration" to which 

 must be added that " the alteration is characterised not by altered 

 chemical composition, but by altered chemical action, which may 

 of course give rise to altered composition." As has been shown 

 in another section (e.g. fatigue in muscle), Hering distinguishes 

 in every living substance between the ascending alteration, the 

 descending alteration, and the state of equilibrium. 



" Both ' up ' and ' down ' changes may occur with very 

 different rapidity, according as the strength of assimilation 

 exceeds that of dissimilation, or vice versa, to a greater or 

 less extent. If all parts of a living continuum are equi- 

 potential, or if they alter with the same rapidity in an ascend- 

 ing or descending direction, no current that can be led off will 

 be produced. Each variation in rapidity, or direction of 

 alteration, will, however, produce a current that can be led off. 

 Accordingly, we may conceive every variation in rapidity of 

 the positive or negative alteration, as arranged in a series, 

 so that the quickest ascending change formed the upper, so 

 to say, positive the quickest descending change, the lower, so 

 to say, negative end of the series. If two portions of a living 

 continuum which give different chemical reactions are connected 

 by an external conductor, they will cceteris paribus yield a stronger 

 current in proportion with the distance between the two leading- 



