iv ELECTROMOTIVE ACTION IN MUSCLE 393 



brought forward, which relate partly to the direction of the 

 current observed, partly to the possibility of referring it to 

 changes of temperature in the muscle, or electromotive action 

 in the skin, however originated. As regards the first point, the 

 contradiction was emphasised between the descending effect in 

 muscular contraction of the frog's leg, and the ascending current 

 in the arm (or foot) of the human subject. Du Bois-Reymond 

 indeed found that a P.D. did exist in the skinless leg of the 

 rabbit in the sense of a descending " rest current," with a corre- 

 sponding ascending negative variation. With regard to Hermann's 

 theory as applied to the currents of groups of muscles, i.e. whole 

 extremities, neither the above objection, nor du Bois' proof of the 

 corresponding variation in the leg of the rabbit, need detain us. 

 On the other hand, in the commission appointed by the Paris 

 Academy to inquire into du Bois-Reymond's experiments on man, 

 the elder Bequerel did raise an objection against his inter- 

 pretation, which we must examine more closely, since in spite of 

 du Bois Reymond's objection it has subsequently been thoroughly 

 substantiated. 



According to Bequerel, voluntary tetanus of the arm produces 

 increased secretion from the skin of the finger, in consequence of 

 which the electromotive properties of the skin itself may undergo 

 alteration. And when du Bois-Reymond himself, at Bequerel's 

 request, dipped the forefingers of both hands into the leading-in 

 vessels, after voluntarily contracting and relaxing one arm, there 

 was in fact " a weak effect in the same direction as if the 

 arm belonging to the immersed finger had been contracted " ; but 

 this was referred to the prolonged after-effect (supra) of the 

 supposed negative variation. Du Bois considered the follow- 

 ing experiment to be conclusive in favour of his interpretation. 

 The hand and lower part of the arm were confined in a gutta- 

 percha bag, bound to the arm below the elbow, to produce 

 local perspiration. The same parts were further bound with a 

 woollen cloth. After some time the perspiring arm was com- 

 pared with the normal limb by the usual galvanometric method, 

 on which it appeared that the former was not, as might have 

 been expected from Bequerel's theory, negative, but, on the 

 contrary, positive to the latter. That, notwithstanding, there 

 was in du Bois-Reymond's voluntary experiment nothing more 

 than the effect of a secretion current, was first ascertained at a 



