318 THE OUTGO OF ENERGY 



until the threshold value is reached and the 

 muscle contracts. 



At the threshold value of muscular contrac- 

 tion, the current of action in the nerve will not 

 yet be demonstrable. The coils must be still 

 nearer together before the action current be- 

 comes visible. 



This experiment has a certain suggestive 

 value. It would not, however, be safe to con- 

 clude from it that the action current is not 

 an essential part in the passage from the resting 

 to the active stage. The failure to recognize the 

 action current probably lies in the method. 



Current of Action in Optic Nerve. Place two 

 non-polarizable electrodes in the moist chamber, 

 and connect them through a short-circuiting key 

 with the capillary electrometer. Kemove the 

 eye of the frog, together with a portion of the 

 optic nerve, and lay the preparation on the elec- 

 trodes in the moist chamber, letting the edge of 

 the cornea touch one electrode and the optic 

 nerve the other. Cover the electrodes and the 

 preparation with a black pasteboard box or 

 other opaque screen to shut off the light. Note 

 the position of the meniscus in the field of 

 the microscope. Open the short-circuiting key. 

 A demarcation current from the injured optic 

 nerve to the cornea will be indicated. Be- 



