vi.] THE FROG'S TONGUE 111 



The frog's skin gives with two electrodes applied to its 

 external surface a similar positive effect ; but in this instance 

 we found, by analysing its polar factors, that the after-effect is 

 homodrome with the exciting current by reason of an excess 

 of post-kathodic outgoing homodrome over post-anodic out- 

 going antidrome blaze. The complete formulae in the two cases 

 run as follows : 



/ Eocc 



Fruit skin\ , / 

 T f \ Resp. (tot<a.L) 

 or Leaf . r 



I Resp. t 'pcLrU&i) ( 



( E.3CC. 



Frog skln\ Resp 

 ( ffesp. 



| 68. Tongue surfaces. The frog's tongue, examined in 

 the usual way by the electrodes applied to the upper and 

 lower surfaces, presents an analogous case to that of a leaf; 

 its response, when stimulated, is the resultant of two effects 

 at the two opposite poles. The tongue, as it lies on the floor 

 of the mouth, gives an ascending resultant, which, if we might 

 be sure that the effects were outgoing at the two surfaces, 

 indicates that the upper surface of the tongue acts more power- 

 fully than the lower surface. The current of rest is descending, 

 and if we may admit as proved that the upper is the more effec- 

 tive surface, this descending resultant indicates an ingoing 

 current of rest. 



But the detailed study of the frog's tongue belongs to the 

 intricate and theoretically important subject of mucous currents, 

 which has been treated of at a considerable length by Bieder- 

 mann. I hope to discuss the whole question of mucous currents 

 in a more complete manner than is possible to-day. Any one 

 who is curious in the matter should refer to Biedermann's papers 

 or to the full account in his Electro-pJiysiology. You will find 

 there that he attributes great importance to the positive and 

 negative responses of the tongue in connection with the theory 

 of assimilatory and dissimilatory phenomena. You may very 



