v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 489 



dominance of the opposite current (negative variation) a gradual, 

 and, for the most part, irregular augmentation of the original 

 ingoing current, which obviously corresponds with the positive 

 after-effect of a short excitation, and may sometimes attain 

 important dimensions. But the mucosa current, even after long- 

 protracted excitation, will always continue to be directed inwards. 

 The mucosa of the throat and cloaca are of course capable 

 of direct electrical or mechanical excitation also, and the effects 

 are essentially the same as in the tongue, although these tissues 

 are as a rule less sensitive. While, as we have seen above, the 

 slightest contact with the lingual mucosa produces a negative 

 variation of the normal entering current, which rapidly declines 

 again as soon as the excitation is over, this is by no means 

 usual in the throat or cloacal mucosa. In these a comparatively 

 strong pressure, or pull, is required to produce any considerable 

 depression of the " rest current," which subsequently proceeds 

 as in the tongue. Much better results, and the only ones that 

 are adapted to exact investigation, are yielded by local tetanising 

 with the induction current. As regards the method employed, 

 we may refer throughout to what has already been cited. In 

 a preparation of the throat mucosa with very strong entering 

 currents, excitation with gradual approximation of the coil 

 produces even with weak currents (coil at 180) a distinct 

 monophasic negative variation of the compensated rest current, 

 which increases rapidly as the coil is pushed up, although even 

 in the most favourable cases it does not go so far that as is 

 usual in the tongue under similar conditions the scale flies 

 off the field. A slight tremor at the beginning of the deflection 

 sometimes betrays the existence of a heterodromous force, which, 

 as we shall see, leads under other conditions to a positive varia- 

 tion. If the excitation is interrupted before the scale has come 

 wholly to rest, the return swing of the magnet begins rapidly 

 at first, and then travels more slowly to its zero, sometimes even 

 beyond, in the sense of a reinforcement of the original current 

 (positive after-effect). The manifestation of excitation is quite 

 altered when the E.M.F. of the entering current of rest is 

 lower. As in the tongue, only perhaps still more markedly, 

 the strength of the negative variation depends upon the initial 

 intensity of the normal, electromotive action of the mucosa. 

 If this sinks below a certain limit, there appears regularly in 



