NEGATIVE VARIATION OF THE MUSCLE-CURRENT. 203 



plier has assumed a fixed deflection, the extent of which 

 depends on the strength of the muscle-current, the key 

 at S is opened. Inductive currents pass through the 

 nerve, and the muscle contracts. At the same instant 

 the deflection of the multiplier is observed to decrease. 

 If the irritation of the nerve is interrupted, the deflec- 

 tion of the multiplier again increases; and when the 

 irritation is again commenced, it again decreases, and 

 this process continues as long as the muscle continues 

 to afford powerfu. contractions. 



Fig. 55. The muscle-current during contractiox. 



This experiment, therefore, shows that the current 

 of the gastrocnemius is weakened during contraction. 

 This may be most strikingly shown by a variation of 

 the experiment just described. After the muscle has 

 been placed in position and a deflection of the multi- 

 plier has been caused, the muscle- current may be com- 

 pensated, as described in Chapter X. § 4. Two currents, 

 equal but in opposite directions — the current of the 

 muscle and that of the compensator — now, therefore, 

 pass through the muscle and cancel each other. As 

 long as these two currents are equal, no deflection can 

 occur in the multiplier. When the nerve is then irri- 



