v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 483 



of the magnitude of excitation effect upon the strength of the 

 current of rest, as expressed both in the degree of deflection with 

 a given intensity of excitation, and in the fact that it takes less 

 strength of coil to produce a given deflection in proportion as the 

 E.M.F. of the current of rest is lower. AY hen the last is at a 

 considerable height we have often, after compensating with 

 the coil at 160 (1 Dan. in the primary circuit) observed a 

 negative variation which drove the scale far off the field of vision. 

 At the same time the changes of form and position in the tongue 

 in consequence of direct muscular excitation were so insignificant 

 as to exclude the possibility that the effects described can be 

 caused by, or along with, them. Still it cannot be denied that 

 these accessory effects, which are inevitable with strong currents, 

 do produce a most undesirable complication, and we have there- 

 fore endeavoured to determine by special control experiments to 

 what degree the excitation effects observed on the galvanometer 

 are actually affected by them. It is not difficult to abolish the 

 electromotive activity of the lingual mucosa, either locally at the 

 lead-off, or on the entire surface, without affecting the deeper 

 muscles, and with these the mobility of the tongue. If the 

 appearance of the negative variation has been ascertained at any 

 given position of the coil, and a grain of salt is then applied to 

 the tip of the lingual electrode, there will follow immediately 

 (partly in consequence of chemical excitation) a very rapid and 

 marked diminution of force in the entering rest current. The 

 excitation previously employed will now lie ineffective, although 

 the lingual muscles contract after as before stimulation. The 

 same result is obtained on cautiously treating the mucosa with 

 NH 3 in gas or solution. So that, while there can be no 

 doubt that we have to include the mechanical excitation due 

 to movements of the tongue contracting under the leading-off 

 electrodes, it may, on the other hand, be accepted that the 

 main result in this case is due to the electrical excitation of the 

 mucosa. As a proof of this we may instance the behaviour of 

 small fragments of the mucous coat, which are easily separated 

 with scissors from the subjacent muscle-layer. As was said 

 above, these, when examined on clay, as a rule exhibit before 

 long a vigorous current, which on tetanising yields a strong 

 negative variation without any material change of form in the 

 fragment. 



