226 ELECTRO-PHYSIOLOGY CHAP. 



itself by a marked reaction, i.e. only the ascending current 

 normally discharges the make excitation, while the descending 

 current, which is usually more effective, either produces no 

 excitation at all (with medium currents), or excites in a much 

 less degree than the ascending current. Hermann (28) succeeded 

 in establishing this fact of " polar negative action " at the idio- 

 muscular swelling on a still firmer basis, by experiments with 

 cooled muscle. The same thing occurs where all trace of local 

 contraction has already died out ; for the latter disappears in 

 some cases by itself, more especially when the muscle is immersed 

 in 0'6 / Q salt solution. Here, as in the persistent closure 

 contraction due to the constant current, a state of depressed 

 excitability at the seat of the idio-muscular contraction must 

 have intervened, from the partial continuous excitation consequent 

 under certain conditions upon a mechanical excitation (extension), 

 which is indeed a necessary consequence of the fact that every 

 excitation is accompanied by metabolism. 



We have already mentioned repeatedly that the response of 

 a sartorius, of which one end has been killed mechanically or by 

 heating, to the electrical current, can be satisfactorily interpreted 

 on the hypothesis of a localised diminution of excitability at the 

 seat of stimulation, and we have now to examine the data for this 

 conclusion. 



Since it is a well-substantiated fact that an uninjured muscle, 

 surrounded on all sides by the sarcolemma, is excited each time 

 an electrical current passes out at any point of its surface, and 

 since, further, the nature of the conductor by which the entrance 

 or exit of the current is effected is experimentally indifferent 

 apart from the unavoidable polarisation of metal electrodes the 

 response of a muscle injured at one end seems at first sight to 

 be an exception to the general rule. Here we find that both the 

 closing and opening excitation are usually wanting, or appear 

 much weakened, when the current passes from living un- 

 injured, into dead, muscle-substance, or vice versd. It is easy 

 to demonstrate that the dead contractile substance per se reacts 

 to current like any other animal tissue (tendon, bone, etc.) that 

 behaves as an indifferent conductor ; the clay points of impolaris- 

 able electrodes can be covered with dead muscle, and current 

 led through them to the uninjured surface of a muscle, without 

 causing any hindrance or difficulty to the excitatory process. 



