464 ELECTRO-PHYSIOLOGY CHAP. 



(cf. F. E. Schultze, 78). And since we know that neither morpho- 

 logically, nor with regard to physiological function, is there any 

 fundamental difference between uni- and multicellular mucous 

 glands, it is natural to regard the rest current of the fish's skin as 

 referable to the goblet cells which function as unicellular glands. 

 Hermann actually does this when, in terms of the alteration 

 theory, he reckons each partial mucin metamorphosis of single 

 cells, as well as the elements of the secretory glands, as a source 

 of regular electromotive action, a force " which, entering by the 

 free epithelium, is directed in the gland from lumen to matrix." 

 Such currents are, in fact, demonstrable wherever mucin - 

 forming cells, or glands, are present (skin of fish and naked am- 

 phibia, tongue, mucous membrane of throat, stomach, and cloaca). 

 And that electromotive action may further, in Hermann's sense, 

 be predicated of other non-glandular epithelial cells seems to be 

 established by the recent researches of E. Waymouth Reid (88). 



Seeing that, with the exception of the plant currents to be 

 considered later, the experimental data of " cell currents " are 

 founded almost solely upon electromotive action in uni- and 

 multicellular mucous glands, the details of these observations 

 must be examined a little more closely. The most appropriate 

 object for experiment is perhaps the tongue of the frog, with its 

 wealth of goblet cells and mucous glands, in which, moreover, it 

 is easy to expose the secretory nerves. As regards the opinion 

 expressed by Engelmann (supra} of the origin of skin currents, 

 it is notable that the lingual glands containing characteristic 

 mucous cells lie free of muscle in the connective tissue immediately 

 under the surface, the papillae of which are covered with a single- 

 layered epithelium consisting of goblet and ciliated cells. The 

 mucous, viscous content of the glandular membrane is everywhere, 

 as appears from transverse sections, in direct connection with the 

 mucous layer covering the surface of the tongue, as we should 

 expect from the wide mouth of the glands. The epithelium of 

 the under surface of the tongue, turned to the floor of the mouth, 

 is also rich in goblet cells. 



Various methods may be employed to investigate the " current 

 of rest " in the tongue, as will presently be described. Speaking 

 generally, we may picture the surface of the tongue as a freely 

 and irregularly folded surface, covered in its whole extent with a 

 single layer of secretory cells, intermixed sparsely with ciliated 



