6 S 2 SE CRE TION AND ABSORPTION B i T 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 Rosenthal, 1 and extended to the 
case of the stomach and gut mucosae 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 Eoeber, 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 Eoeber, a fact corroborated by 
all subsecpnent 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 " noted an ingoing " current of action," 
often preceded by an outgoing current of short duration, and Bayliss 
and Bradford s 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," hut 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 u 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 12 has further indicated that parts of the skin of 
man rich in sweat-glands {e.g. palm of hand), are negatively electrical 
td parts poor in sweat-glands {e.g. skin over deltoid), and that the 
ingoing " current of action " of such glands can be excited renexly by 
very slight stimuli, such as sound or even the expectation thereof, 
odours, or mental effort. 
The well-known Willkiirversuch of du Bois Pieymond, 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./. Physiol., Leipzig, 1865, S. 301. 
2 Arch. r. </. ges. Physiol., Bonn, 18S2, Bd. xxvii. S. 280. 
3 Ibid., 1894, Bd. lviii. 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. 8. 280. 
8 Joum. Physiol., Cambridge and London, 1886, vol. vii. p. 223. 
; ' Arch. f. d. ges. Physiol., Bonn, lS7s. Bd. xvii. S. 310. 
J0 /^Y/.,'lSS0, Bd. xxii. S. 152. » Ibid., 1S7S, Bd. xviii. S. 460. 
12 Ibid., 1890, Bd. xlvi. S. 46. 
