iv ELECTROMOTIVE ACTION IX MUSCLE 395 



upper muscles of the forearm also, as described in Fig. 125, i.e. 

 once more, in the direction of the arrows, first an atterminal (this 

 time ascending), and then an abterminal (descending), phase of 

 the action current. 



The " nervous equator," i.e. that section of the muscle " in 

 which would fall the common centre of gravity of all the nerve- 

 endings, if these last have a certain uniform equilibrium," 

 lies, in the human forearm, pretty close to the elbow. Tl/c 

 ap$>roximatc equality of both phases is remarkable, from which 

 it may be concluded " that a decrement of the excitatory wave does 

 not exist in the intact muscle wit// normal circulation," and this at 

 once explains why the action current fails to appear with any 

 certainty on tetanising without the rheotome. Hence the ascend- 

 ing current observed by du Bois-Beymond in voluntary innerva- 

 tion of the arm and leg is no current of action from the muscle. 

 That it is a " secretion current " caused by the activity of the 

 skin-glands in the sense of Bequerel's original presumption, 

 follows directly from the experiments of Hermann and Luch- 

 singer, to be discussed below. The results obtained by du Bois- 

 Keymond on leading off simultaneously from a perspiring and a 

 dry hand, upon which the former shows a descending current, 

 cannot be recognised as a valid objection, since they depend not 

 so much upon the secretion present as upon the sccretort/ pro<r** 

 caused by excitation of the nerve. Like Bernstein's experiments 

 on the negative variation, or current of action, in frog's muscle, 

 the experiments of Hermann on the human forearm give the 

 requisite opportunity for determining the velocity of excitation 

 in normal human muscle. Its most probable value is 10-13 

 m. per sec. 



Matthias (30) has recently published a graphic record of the 

 action current in the human forearm, obtained by Hermann's 

 " rheotachygraphic " method. 



Smooth muscles, owing to the much slower period of all excita- 

 tion phenomena, are in many respects more suited to the investiga- 

 tion of the action current than striated muscles, which have hitherto 

 been almost exclusively investigated. It is evident that where 

 the wave of contraction is as prolonged as, e.g., in the rabbit's 

 ureter, the phasic action current will be directly demonstrable in 

 a sensitive galvanometer without applying to the repeating 

 method. In the last resort, however, the number of objects 



