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 Biedermaim 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 will be the direction of the " action current " elicited by 



1 Biedermaim, ibid., 1893, Bd. liv. S. 209. 



2 Hermann, loc. cit. ; Reid, Phil. Trans., London, 1893, Bd. clxxxiv. p. 335. 



3 Reid, Jo urn. Physiol., Cambridge and London, 1894, vol. xvi. p. 359. 



4 Arch.f. d. ges. PhysioL, Bonn, 1894, Bd. Iviii. S. 242. 



5 Ibid., 1880, Bd. xxii. S. 30. 6 Bohlen, ibid., 1894, Bd. Mi. S. 97. 



