4 8 4 



COMPARATIVE ELECTRO-PHYSIOLOGY 



conductivity-variation induced by two different agents which 

 are applied simultaneously, one on the arm C and the other 

 on C'. 



It is possible again to compare the variation of con- 

 ductivity with that of responsivity, by applying one agent at 

 a responding region, say E, and the other on the opposite arm 

 of the balance at C f . The mode of investigation of receptivity 

 changes will be described presently. 



In fig. 291 we have the complete apparatus. The animal 

 or vegetal nerve, N N, rests on non-polarisable electrodes of 



E, 



FIG. 291. Complete Apparatus of Conductivity Balance 

 The nerve N supported on electrodes E 2 , E 3 . The two other electrodes 

 E, E 4 are not used in this experiment, but are employed for experiments 

 on electrotonus ; T, thermal stimulator, the relative lengths of the 

 arms of the balance being adjusted by the slide s. 



a U -shape. For the present experiments, two electrodes, E 2 

 and E 3 , are sufficient, their mutual distance being capable of 

 any variation by movement along a sliding-bar. The same 

 apparatus might be used for experiments on electrotonus, in 

 which two additional electrodes would be required. The 

 position of the electrothermic stimulator T is capable of very 

 careful adjustment for purposes of balance, by means of the 

 sliding-rod S. A glass cover, not shown in the figure, fits into 

 the groove which is represented by a double dotted line sur- 

 rounding the apparatus, and thus enables the chamber con- 

 taining the nerve to be kept in a properly humid condition. 



