ELECTROMOTIVE ACTION IN NERVE 337 



Hermann showed, the electromotive action of the conducting 

 tissues is perhaps of the first importance. In view of the fact 

 that muscle as well as nerve can be excited by its own demar- 

 cation current, as well as by the current of action of a second 

 preparation, provided the conditions of short-circuiting are other- 

 wise favourable, it is prima facie not improbable that the internal 

 short-circuiting of the action current may be an essential factor 

 in the wave of negative excitation (or contraction) also. 



If with Hermann (Handb. d. Physiol. i. 1, p. 256, and ii. 1, 

 p. 194) we consider the galvanic action of any excited point with 

 reference to its environment, this is found (as shown by Fig. 

 221, E) to consist in the "initiation 

 of minor currents in its immediate 

 vicinity," which are short-circuited 

 within the indifferently conducting 

 sheath of the electromotive tract. 

 As in the immediate proximity of 

 an artificial cross-section, numerous point of fibre. (Hermann.) 

 lines of current find exit on both sides of the excited segment 

 at the non-excited surface, and eventually effect an excitation 

 there, while at the excited point itself there is, on account of the 

 ingoing lines of current, a tendency to alteration in the opposite 

 sense. Hermann makes express reference to the presumably 

 high intensity of these minute currents, in which the short- 

 circuiting lines are microscopic, so that the resistance is practically 

 negligible. It is evident that a progressive wave of excitation 

 may well be produced in this way. 



The Action of Nerve upon Muscle 



opens out a further question, which has as yet found no solution. 

 Notwithstanding the fact that muscle possesses the same 

 independent excitability as nerve, and as living protoplasm in 

 general, the excitation of striated and smooth muscle occurs, in 

 the majority of cases, indirectly from the nerve. The actual 

 process of transmission is thus unknown to us, seeing that muscle 

 cannot forthwith be regarded as a prolongation of the nerve, 

 surrounded with contractile substance, although this view has 

 been advanced on several sides. Here, as elsewhere, it is seen 

 how the physiological conception of a process may, according to 



VOL. II Z 



