STIMULATION OF MUSCLE AND NERVE 159 



pass the maximal break currents through the 

 electrolyte. 



Iodine will be set free at the anode -and will 

 combine with the starch to form blue iodide of 

 starch. 



Mark the positive post on the secondary coil 

 with a plus sign. 



2. Connect the poles of the secondary coil 

 through a pole-changer with non-polarizable 

 electrodes. Make a nerve-muscle preparation. 

 Tie a ligature about the nerve about two cen- 

 timetres from the central end. Place one elec- 

 trode on each side of the ligature. The passage 

 of a nerve impulse from the central electrode 

 to the muscle will be prevented by the lig- 

 ature, although the electric current can still 

 pass between the electrodes. Turn the pole- 

 changer so that the electrode on the periph- 

 eral (muscle) side of the ligature shall be first 

 the anode and then the cathode, and test the 

 irritability to weak induction currents, begin- 

 ning with the secondary coil some distance from 

 the primary, and gradually increasing the intensity. 



Only cathodal stimulation will produce con- 

 traction. The same result can be secured by 

 separating the cathode and anode with ammonia. 

 If the nerve is painted with ammonia in the 

 intrapolar region, break currents cease to cause 



