19 CHAPTER XXXIII. 



ELECTRICAL MANIFESTATIONS IN MUSCLE 

 AND NERVE. 



Demarcation and action currents. 



Required: Astatic galvanometer (permanently set up and adjusted 

 on a stone shelf on the wall of the dark room). Non-polarisable electrodes 

 on movable supports. Shunt or resistance. Block of paraffin. Inductorium 

 and platinum electrodes on stand. Nerve muscle preparation. 



Set up as follows : Wire the non-polarisable electrodes to 

 the shunt or resistance in short circuit and thence to the 

 galvanometer. Observe the notice that if the north binding- 

 screw of the galvanometer be positive, the spot of light will 

 be deflected to the left, and vice-versa (Fig. 47). 



Support the nerve muscle on the block of paraffin and adjust 

 the nerve across the platinum electrodes and connect the latter 

 with the circuit of the S inductorium. The last should be 

 placed not less than three feet from the galvanometer. 



Light the lamp and place it so that the reflected spot of light 

 shall be as brilliant as possible with the vertical wire in focus. 



Test the electrodes to see if they yield a current. Place 

 their points in contact, and close the circuit through the 

 galvanometer. If they do, the spot of light will travel away 

 from the middle of the scale to one side or the other. Xote 

 the amount of the deflection, and if it be more than a couple 

 of cm, fresh electrodes must be prepared. If slight, note its 

 .amount and direction. 



Place one electrode in contact with the centre of the surface 

 of the muscle, and the other near the tendon. Close the 



