THE CONDUCTIVITY BALANCE 



485 



In all these experiments by balance, it is to be borne in 

 mind that adjustment is always made for perfect balance 

 at the beginning of the record, and represented by a short, 

 more or less horizontal, line. 



In order to show the typical effects of induced variations 

 of excitability, in upsetting the balance, I shall first give 

 records of experiments carried out on the nerve of frog. 

 Dilute sodium carbonate is known to be an agent which 

 enhances excitability. A long-continued application, or the 



application of a stronger dose, 

 may, however, bring about a 

 depression. When a dilute 

 solution of Na 2 CO 3 was ap- 



FIG. 292. Effect of Na 2 CO 3 Solution 

 on Responsive Excitability of Frog's 

 Nerve 



In this and following records the hori- 

 zontal line at the beginning indicates 

 exact balance. The upsetting of the 

 balance in the up-direction repre- 

 sents either the enhanced respon- 

 sivity of the right-hand responding 

 point E, or the increased con- 

 ductivity of the right-hand arm c. 

 Down -curves represent correspond- 

 ing absolute or relative depressions. 

 Na,CO 3 applied to E is seen to exalt 

 the responsivity of that point. 



FIG. 293. Effect of CuSO 4 on Frog's 

 Nerve 



The down record shows depression of 

 excitability. 



plied at the responsive point E on the right side, the up- 

 setting of the balance upwards immediately indicated the 

 greater excitability induced by the reagent. The long- 

 continued action of this reagent, however, showed that the 

 enhanced excitability was undergoing a gradual decline 

 (fig. 292). 



In order to exhibit the characteristic upset caused by 

 a depressing agent, I employed on another specimen a 

 toxic solution of copper sulphate, applying it at E on the 

 right. The previous state of equilibrium is s seen by the 

 horizontal line at the beginning of the record, and the 



