ELECTRO-MOTIVE PHENOMENA IN SKIN GLANDS. 683 
muscles of one forearm (e.g. grasping a rod) gives a current passing up 
the contracting arm, is probably to be explained by the concomitant 
excitation of the sweat-glands on the side of action. 
Not only in the case of membranes containing complex glands is an 
ingoing " current of rest " observed, but also in secreting membranes 
supplied with unicellular glands (goblet cells), as the pharynx and 
cloaca of the frog, 1 or the skin of the fish; 2 and furthermore, in certain 
membranes, quite free of secretory structures, and covered only by 
stratified epithelium, such as the skin of the pigeon and the mucosa of 
the crop of the same bird in winter. 3 
The attempts to explain the causation of the above currents, it must 
be confessed, have not been very satisfactory. 
As regards the constantly observed ingoing " current of rest," it is 
obviously of the first importance to determine whether it is of purely 
epidermic origin, of purely glandular origin, or whether it receives a 
component from both sources. The experiments with the non-glandular 
skin of the bird above-mentioned show that simple stratified epithelium 
can give rise to such a current, and Hermann 4 has further proved that 
shaving the epidermis of the cat's foot lowers the electro-motive force of the 
" current of rest." Furthermore, Bach and Oehler 5 found that pencilling 
the skin of the frog with solution of corrosive sublimate abolished the 
" current of rest," though the excitatory change from the glands beneath 
could still be obtained by exciting the nerves of the skin. 
On the other hand, it can hardly be denied that in such cases as 
the gastric mucosa of the frog, where the epithelium is practically all 
converted into unicellular glands (goblet cells), the marked ingoing 
" current of rest " is of glandular origin, 6 and this must also be the case 
in such a membrane as the cloacal mucosa of the frog. 
It is simplest, in the present state of knowledge, to admit that both 
stratified epithelium and gland protoplasm can give rise to currents. 
Hermann and Biedermann consider such currents due to alteration 
of metabolic activity in the continuity of protoplasm. Protoplasm 
becoming " altered " to mucus in a goblet cell is negative electrically to 
the unaltered material at the base of the cell, and the same in the 
process of keratinisation in the continuity of epithelium. Since altered 
parts are negative electrically to unaltered or less altered, the result will 
be an ingoing current, whether we choose the glands or the epidermis, 
or both, as the source of the electro-motive force of the " current of rest." 
If we turn to the case of the " action current," it is only in the case 
of the mammalian glands that any clear explanation on the above 
hypothesis is feasible. In these glands, as already mentioned, the 
" current of action " is purely ingoing, and it is only necessary to assume 
that in action the " difference " between the base and the free border of 
the cells becomes more marked than at rest, with a concomitant develop- 
ment of electro-motive force with ingoing current. 
In the skins and other secreting membranes of amphibians and fish, 
we are met with the difficulty that it is not possible to predict with 
certainty what w T ill be the direction of the " action current " elicited 1 >y 
1 Biedermann, ibid., 1893, Bd. liv. S. 209. 
2 Hermann, loc. cit. ; Reid, Phil. Trans., London, 1893, Bd. clxxxiv. p. 335. 
3 Reid, Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 359. 
4 Arch. f. d. ges. Physiol., Bonn, 1894, Bd. lviii. S. 242. 
5 Ibid., 1880, Bd. xxii. S. 30. 6 Bohlen, ibid., 1894, Bd. lvii. S. 97. 
