CHAPTER VII. 



Rate of transmission of nerve impulse. 



Make a nerve-muscle preparation in the usual way ; 

 fix it upon the myograph, and lay the nerve out 

 upon two pairs of electrodes, one placed as near the 

 muscle as possible, the other close to the vertebral 

 column. With a large frog nearly two inches will 

 intervene between the two. Place a commutator 

 without cross wires in the secondary circuit, and 

 arrange so that by moving the bridge of the com- 

 mutator the induction shocks can be switched on 

 to one or other -pair of electrodes. The drum is 

 to be included in the primary circuit, and a short- 

 circuit key in the secondary (Fig. 29). 



Two muscle curves are now taken with a fast 

 rate of cylinder and a maximal stimulus ; this is to 

 be applied to the nerve, firstly, close to the muscle, 

 and, secondly, close to the vertebral column. The 

 muscle curves are to be taken in exactly the same 

 way, and with exactly the same precautions as to 

 the use of the stop, etc., as detailed in Chapter III., 

 and the two curves are to be traced upon one ab- 

 scissa, and a time tracing written beneath this. It 

 will be found that the curves are not coincident, 

 but that one succeeds the other by a very small 

 interval, this interval representing the time occu- 

 pied by the transmission of the nerve impulse 



