v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 507 



glands, and so makes a lead-off possible. In the tongue, at all 

 events, this is certainly the case. It was said above that the 

 other reasons, in particular the experiments of Bach and Oehler 

 on the corroded skin, which Hermann brings forward against the 

 participation of the glands in the skin " rest current," are by no 

 means conclusive. At any rate, it cannot be denied that the 

 surface epithelium does contribute to the rest current the 

 more so, since recent experiments have demonstrated electro- 

 motive effects in skin that is perfectly free of glands (88). If, 

 in view of Hermann's theory of the cause of the entering skin 

 and mucosa currents, it was desired to predict the effect most 

 likely to ensue with direct or indirect excitation, the positive 

 variation, i.e. augmentation of the rest current, would inevitably 

 be selected, and explained by the processes of alteration in the 

 glandular epithelium strengthened or perhaps initiated by excita- 

 tion. But from the above it appears that the exact contrary is 

 the case the negative variation is more and more the exclusive 

 consequence of excitation, in proportion with the E.M.F. of the 

 entering rest current. 



And that the latter itself cannot lie explained by the above 

 simple hypothesis is quite evident from the reactions described 

 with energetic cooling. It should here be noted more especially 

 that in this respect the complicated, richly glandular objects 

 (tongue) coincide with the most simply constructed (throat and 

 cloacal mucosa), so that there can be no question of referring the 

 opposite electrical effects before and after cooling, to any anatomi- 

 cal difference in the elements. Hence no other conclusion is 

 possible but that the same epithelial cell, almost to the same degree, 

 is able to give electromotive response now in the one direction and 

 now in the other. In this, as in many other respects, the cell 

 current in question differs fundamentally from the electrical 

 manifestations of nerve and muscle. In these the strongest 

 cooling at most produces diminution, never, however, reversal of 

 the demarcation current. This is a good instance of how little 

 the galvanometer is able to indicate the quality of the chemical 

 process which in both cases underlies the homodromous differ- 

 ences of potential. As Hering aptly remarks, it can only express 

 " alterations and differences of chemical action in the different 

 parts of a living continuum, together with the magnitude and 

 time relations of such action." 



