v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 465 



cells. The glands thus appear merely more or less deeply pitted 

 in the continuity of the layer of cells, from the inner surface of 

 which it is possible to lead off, since, as was said above, the 

 secretory layer covering the tongue is nearly everywhere in direct 

 connection with the fluid contents of the glandular membrane. 

 If the tongue is excised at the root, and stretched upon any 

 indifferent conducting surface, such as a block of salt clay, we 

 shall obviously have to test the electromotive action of the 

 epithelium of the whole upper surface (which clothes not only 

 the glands but also the papillae lying between them), even if 

 the inferior surface of the tongue were not invested with a simi- 

 larly constructed, even layer of cells, the single elements of which 

 are generally placed symmetrically with those of the upper 

 surface. Between the two lies a thick layer of connective 

 tissue and striated muscle, which, under normal circumstances, 

 must be regarded as non-electromotive. 



In every case, therefore, it is possible to lead off from the 

 basal part of the individual cell-elements of the upper and lower 

 surface of the tongue. On the assumption of a perfectly equal 

 electromotive action of the epithelium of both surfaces (a hypo- 

 thesis which must, however, be excluded on account of the very 

 different mass -relations of the cell layers in question), there 

 would, of course, be no effect on leading off from two symme- 

 trically opposed points of the upper and lower surface. The web 

 of the frog's hind-leg, e.g., on leading off from both sides, gives 

 only weak and irregular electrical effects on account of its 

 symmetrical structure. The tongue, on the contrary, under the 

 same conditions, yields almost invariably a strong current directed 

 in the leading -off circuit from under to upper surface, i.e. an 

 " entering " current in Hermann's sense, which often sends the 

 scale far out of the field of vision. Since, as will be gathered 

 from the following, the lingual currents undergo very considerable 

 alteration from the most insignificant mechanical impacts, it is 

 essential to proceed with great caution, avoiding the slightest 

 pull or contact. The following was, in our experiments, the 

 most convenient method of leading off' from the excised tongue, 

 through which blood is no longer circulating. The frog was 

 weakly curarised, until it just lost power of movement ; the 

 external skin was then carefully removed along the whole region 

 of the lower jaw, to exclude any possible complication from its 



2 H 



