THE ELECTROMOTIVE PHENOMENA 323 



tory fibres from which are supplied to the gland, 

 causes the surface to become still more negative, 

 i. e. the secretion current is increased (positive 

 variation). Stimulation of the sympathetic, which 

 also sends fibres to the gland, causes the secretion 

 current to lessen (negative variation). 



ELECTROTONIC CURRENTS 



It has already been shown that the irritability 

 and conductivity of the nerve are altered by the 



Fig. 55. 



galvanic current. So also are the electromotive 

 properties. 



Place one pair of non-polarizable electrodes 

 near the middle of a long piece of extirpated 

 nerve, and one other pair at each end, on the 

 cross-section and longitudinal surface as in Fig. 

 55. Connect the middle pair through a key 

 with two dry cells. Connect each of the other 

 pairs through a short-circuiting key with a 



