v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 463 



epithelial and glandular layer. Since du Bois-Beymond found 

 the skin current particularly strong in the toad, where the 

 skin glands are vigorously developed, while the glandless skin 

 of fishes (eel, tench, pike, perch) appeared entirely devoid of 

 current, the presumption was " that the electromotive activity 

 of the skin is in relation with the special dermic secretions 

 peculiar to the naked amphibians." This view subsequently 

 obtained substantial support from the observations of Eosenthal 

 (75) and Bober (76). The former found not merely that the 

 skin glands of the frog and other naked amphibians are the 

 seat of electromotive forces, directed invariably from mouth 

 to fundus, but that the same holds good of the mucous glands 

 of the stomach, so that these electromotive forces " may with 

 great probability be regarded as an essential property of 

 glandular substance, just as we are accustomed to reckon 

 electromotive forces among the essential vital manifestations of 

 nerve and muscle." 



This view is opposed to a later theory brought forward by 

 Engelmann (72, p. 97), according to which the "gland currents" 

 in question are of " myogenic " origin, initiated by the layer of 

 contractile fibre-cells which surround each glandular body exter- 

 nally. Engelmann tried to make good this interpretation, which 

 of course stands and falls with the pre-existeuce theory, from a 

 long series of excellent observations, to which we shall frequently 

 have occasion to return in the sequel. Yet it is incontestable 

 that even from the standpoint of the pre-existence theory, the 

 reaction of the skin current of the frog tells against rather than 

 for Engelmann's hypothesis. 



Hermann, again, proposes " that it is not, or not pre-eminently, 

 the glands, but the epithelial layer which is (during rest) the seat 

 of electromotive skin action." The reasons which originally 

 compelled du Bois-Eeymond to regard the glands as the essential 

 cause of the skin currents in naked amphibia, i.e. absence of the 

 same in the " non -glandular " skin of fishes, were believed by 

 Hermann to be put out of court by the demonstration of a regular, 

 ingoing skin current in a great number of the fishes examined 

 (75). To this it might certainly be objected that the skin of the 

 fish is not really glandless, but contains innumerable unicellular 

 mucous glands (" goblet cells "), which in many cases may be 

 regarded as one large, superficially flattened, mucous gland 



