Chap, xvii.] THE PENDULUM MYOGRAPHION: 183 



from the secondary coil n go to the sides of the com- 

 mutator c, which has no cross; wires pass from c to 

 a and b, points in the course of the nerve n of the 

 muscle m caught in the forceps F. The muscle is 

 attached to the lever I, whose point touches the glass 

 plate. According to the position of the commutator 

 the nerve may be stimulated at a or b. Let it be 

 arranged to stimulate at a ; set the pendulum as shown 

 in Fig. 89, release it, and get the curve of its contrac- 

 tion. Bring the pendulum back to its original posi- 

 tion ; see that the lever which has been knocked away 

 from contact is restored, taking care to give no shock 

 in doing so. Then reverse the commutator so as to 

 stimulate at b, release the pendulum, and get a second 

 curve. The second curve will be a little in front of 

 the first. The difference between the two, which 

 should spring from the same base line, is evidently due 

 to the delay caused by the time taken by the nervous 

 stimulus to pass from b to a. To measure this time a 

 chronograph must be brought up against the plate, 

 and, on allowing the pendulum to swing again, a 

 tracing of time in lOOths or 200ths sec. is obtained. 

 The difference of time, then, between the first and 

 second curve, is the time taken by the nerve current 

 to pass from b to a, and if this distance be carefully 

 measured the rapidity of the nerve current is obtained. 

 If now the pendulum be brought with the hand just 

 to the place where it breaks the contact of the lever 

 with the binding screws, and the lever of the myograph 

 be caused to make a vertical line there, without any 

 movement of the glass plate being allowed, a mark will 

 be obtained indicating the moment of interruption of 

 the primary current, i.e. the moment of stimulation of 

 the muscle. It will be found that this mark does not 

 coincide with the commencement of the muscle curve, 

 which occurs a little later ; and the difference in time 

 between the two gives the period of latent stimulation, 



