504 



COMPARATIVE ELECTRO-PHYSIOLOGY 



A vegetable nerve was adjusted for balance, with the 

 ends projecting some distance beyond the electrodes. In 

 order to show that the effect of injury is due to stimulus as 

 such, and not to any particular form of it, I now made a 

 thermal instead of mechanical section, by applying salt 

 solution heated to about 60 C. in the region A, at a distance 

 of I cm. to the right of E (fig. 310). The effect of this 

 stimulation was to induce a moderate excitation of the right 

 arm of the balance, relatively to the left. If this moderate 

 stimulation were to induce 

 any increase of excitability 

 and conductivity, that fact 

 would be demonstrated by 



FIG. 310. Experimental Arrange- 

 ment for Studying After-effect of 

 Stimulus on Conductivity and 

 Excitability 



The stimulator adjusted to obtain 

 balance between E and E'. Stimulus 

 of moderate or strong intensity is 

 applied to a point on the right of E. 

 Upsetting of the balance in an 

 upward direction shows an en- 

 hancement, and in a downward 

 direction, depression, of con- 

 ductivity and excitability. 



FIG. 311. Photographic Record 

 Showing Effect of Moderate 

 Stimulation in Enhancing 

 Conductivity and Excita- 

 bility 



otted line at beginning shows 

 the resting-current, as a per- 

 sistent effect of stimulation. 

 The upsetting of the balance 

 upwards constitutes a positive 

 variation of the resting- 

 current, and indicates en- 

 hanced conductivity and 

 excitability. 



the upsetting of the balance, the resultant response being 

 upwards. That this is what actually occurs will be seen 

 from the records in fig. 311. It will be noticed that in 

 consequence of stimulation to the right of E, that point 

 became, more or less permanently, galvanometrically negative. 

 This is represented by the dotted line upwards at the 

 beginning of the record. It must be remembered that before 

 the application of the thermal section, the right and left hand 

 excitations, proceeding from the electro-thermically stimu- 



