VELOCITY OF NERVE ENERGY. 205 



Two pairs of wires from the commutator pass to two pairs 

 of electrodes (a, b), movable on a bar within the moist 

 chamber. Measure the distance between the electrodes. 



(b.) Make a nerve-muscle preparation with the nerve as 

 long as possible (N), clamp the femur (/), attach the tendon 

 (ra) to a writing-lever, and lay the nerve over the electrodes^ 

 the distance between them being known. 



(c.) Arrange the glass plate covered with smoked paper r 

 adjust the lever to mark on the glass, close the trigger-key 

 in the primary circuit, and un-short-circuit the secondary. 

 Turn the bridge of the commutator so that the stimulus will 

 be sent through the electrodes next the muscle (a). Press 

 the thumb-plate, and shoot the glass plate. The tooth (3) 

 breaks the primary circuit, and a curve is inscribed on the 

 plate. 



(d.) Short-circuit again, replace the glass plate, close the 

 trigger-key, reverse the commutator. This time the stimulus 

 will pass through the electrodes away from the muscle (b). 

 Un-short-circuit the secondary circuit, and shoot the glass 

 plate. Again another curve will be inscribed, this time a 

 little later than the first one. 



(e.) Replace the glass plate, close the trigger-key, short- 

 circuit the secondary circuit, and shoot the plate. This 

 makes the abscissa. 



(/.) Replace the glass plate, close the trigger-key, and 

 bring the tooth of the glass plate (3) just to touch the 

 trigger-key ; raise the writing-lever to make a vertical 

 mark. This indicates the moment when the stimulus was 

 thrown into both points of the nerve. 



(g.) Remove the moist chamber, push up the glass plate, 

 close the trigger-key, and arrange a tuning-fork vibrating 

 250 D.Y. per second to write under the abscissa. Shoot 

 the plate again and the time-curve will be obtained. Fix 

 the tracing, draw ordinates from the beginning of the 

 curves obtained by the stimulation of a and b respectively, 

 measure the time between them from the time-curve (this 

 gives the time the impulse took to travel from b to a), and 

 calculate the velocity from the data obtained. 



