L.] 



VELOCITY OF NERVE-IMPULSE. 



251 



With slight modifications the two processes are identical, only in 

 using the spring-myograph it is necessary to use such a coiled spring 

 as will canse the glass plate to move with sufficient rapidity to give 

 an interval long enough for the estimation of the latent period. It 

 may be done also on a revolving drum provided the drum moves 

 with sufficient rapidity. 



(a.) Use the spring-myograph and arrange the experiment 

 according to the scheme (fig. 176), i.e., an induction coil for single 

 shocks with the trigger-key of the myograph (i, 2) in the pidmary 

 circuit; in the secondary circuit (which should be sliort-circuited, 

 not represented in the diagram) place a Pohl's commutator icithout 

 cross-bars (C). Two pairs of wires from the commutator pass to 

 two pairs of electrodes («, h), arranged on a bar in the moist 

 chamber, Measui'e the distance between the electrodes. 



FlQ. 176. 



-Scheme for Estimating the Velocity of Nerve-Energy. 



{h,) Make a nerve-muscle preparation with a long nerve (N), 

 clamp the femur (/), attach the tendon {m) to a writing-lever, and 

 lay the nerve over the electrodes, the distance between them being 

 known. It is well to cool the nerve by iced normal saline, as the 

 velocity of the impulse is thereby much diminished. 



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

 the lever to mark on the glass, close the trigger-key in the primary 

 circuit, and unshort-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, the glass plate shoots 

 across. The tooth (3) breaks the primary circuit, and a curve is 

 inscribed on the plate. 



{(i.) Short-circuit again, replace the glass ])late, close the trigger- 

 key, reverse the commutator. This time the stimulus will pasa 



