x ELECTROMOTIVE ACTION IN NERVE 329 



portionately greater. Hence, at close of excitation, autonomous 

 dissimilation preponderates over autonomous assimilation, and 

 the living matter, owing to its gradual depreciation, returns to 

 par" (I.e. p. 39). The effect of the anode upon muscle and nerve 

 is, according to Hering, to be regarded as a similar assimilatory 

 stimulus. If, e.g., the living matter had previously been at par, 

 and, therefore, in autonomous equilibrium between D and A, it 

 rises above par at the point where the current enters. When 

 the current ceases to flow, there is a corresponding autonomous 

 down change at the point of entrance, which is the more rapid in 

 proportion as the substance has risen above par during the 

 previous "up" change. Thus, the point of entrance may become 

 the starting-point of a second excitation (" opening excitation ") 

 spreading over the fibre. At the point of exit, on the contrary, 

 there is an autonomous up change on breaking the current, 

 provided this point has not been seriously injured by the previous 

 action of the current, or, generally speaking, disturbed in its 

 assimilatory conditions. 



" Since a rapid allonomous ' down ' change occurs during the 

 passage of current, at the point of exit, this point is negative to 

 the rest of the fibre (in so far as the latter is not in transmitted 

 1 excitation ') ; while the point of entrance, in consequence of 

 localised allonomous ' up ' change, gives the opposite reaction. 

 This causes an internal current in the fibre, opposed in direction 

 to the led-in, foreign current. This internal current weakens the 

 foreign current. It has been termed a ' polarisation current.' 

 But inasmuch as it is a physiological heterodromous current, an 

 intrinsic vital manifestation, it must be rigorously distinguished 

 from those polarisation currents which are not properly physio- 

 logical, since they do not arise from the up or down changes in 

 the living substance that occur at the points where current enters 

 or leaves it; for heterodromous currents may also appear, with 

 artificial excitation, in dead tissues, or parts that are no longer 

 intrinsically excitable in the still living organ. 



" Given normal activity of living matter, an autonomous down 

 change may, as we have seen, appear at the anode, on opening 

 the foreign current this point being now negative to the rest of 

 the fibre, in so far as the latter is not undergoing progressive 

 descending alteration ; while the kathode becomes positive to the 

 rest of the fibre, in virtue of an autonomous ' up ' change. A 



