682 SECRETION AND ABSORPTION B Y THE SKIN. 



skin itself is a seat of electro-motive force, which he located in the 

 glands. The current is in the direction from the free to the deep sur- 

 face, the former being electrically negative to the latter. A current so 

 oriented may be termed " ingoing," and is the normal direction of the 

 " current of rest " of all secreting membranes, so far investigated. 



The discovery was corroborated by Rosen thai, 1 and extended to the 

 case of the stomach and gut mucosse in the frog and rabbit, while 

 Hermann 2 found a similar current in the skins of many fish, and, 

 more recently, in the tree frog, proteus, and axolotl. 3 Such currents as 

 a rule exhibit spontaneous variations in intensity, especially in the case 

 of the skin of the frog. 



Valentin, 4 and later Roeber, 5 furthermore found that in the case of 

 the frog's skin excitation of the cutaneous nerves causes a variation in 

 the electro-motive force of the resting skin, and the latter observer 

 that this phenomenon could be produced by reflex excitation, and 

 was not abolished by curare. 



The direction of the " current of action " evoked by excitation of 

 nerves was not found to be constant by Roeber, a fact corroborated by 

 all subsequent investigators. Thus Engelmann 6 observed a double 

 excitatory variation of the "current of rest," namely, an outgoing 

 followed by an ingoing current (negative followed by positive 

 variation), while Hermann 7 noted an ingoing " current of action," 

 often preceded by an outgoing current of short duration, and Bayliss 

 and Bradford 8 state that it is " scarcely possible to speak of a normal 

 excitatory variation." 



Hermann and Luchsinger 9 found that the cat's foot also gave an 

 ingoing " current of rest," but that the current developed on excitation 

 of the sciatic was constantly ingoing, and prevented from development 

 by the exhibition of atropine. 



Luchsinger 10 demonstrated the existence of exactly similar currents 

 in the snout of the pig, goat, cat, and dog on excitation of the cervical 

 sympathetic or infra-orbital nerve, and Hermann and Luchsinger n in the 

 tongue glands of the frog, though in the latter case excitation of the 

 hypoglossal or glossopharyngeal nerve gave a triphasic " current of 

 action," an outgoing being interpolated in a long lasting ingoing 

 phase. Tarchanoff 15J has further indicated that parts of the skin of 

 man rich in sweat-glands (e.g. palm of hand), are negatively electrical 

 to parts poor in sweat-glands (e.g. skin over deltoid), and that the 

 ingoing " current of action " of such glands can be excited reflexly by 

 very slight stimuli, such as sound or even the expectation thereof, 

 odours, or mental effort. 



The well-known Willkilrversuch of du Bois Reymond, in which, 

 when the index-fingers of the two hands are immersed in vessels of 

 liquid in circuit with a galvanometer, a voluntary effort of the 



1 Arch. f. Physiol., Leipzig, 1865, S. 301. 



2 Arch.f. d. ges. Physiol., Bonn, 1882, Bel. xxvii. S. 280. 



3 Ibid., 1894, Bd. Iviii. S. 242. 



4 Ztschr.f. rat. Med., 1861, Bd. xv. S. 208. 



5 Arch. f. Physiol., Leipzig, 1869, S. 633. 



6 Arch. f. d. ges. Physiol., Bonn, 1872, Bd. vi. S. 97. 



7 Ibid., 1878, Bd. xvii. S. 291 ; and 1882, Bd. xxii. S. 280. 



8 Journ. Physiol., Cambridge and London, 1886, vol. vii. p. 223. 



9 Arch.f. d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 310. 



10 Ibid., 1880,' Bd. xxii. S. 152. u Ibid., 1878, Bd. xviii. S. 460. 



12 Ibid., 1890, Bd. xlvi. S. 46. 



