LABORATORY MANUAL OF PHYSIOLOGY. 



circuit with the primary. Place signal magnet (b) in circuit with 

 the tuning fork giving 100 interruptions per second. Introduce a 

 short-circuiting key in each circuit. Place the nerve of the muscle 

 preparation on the electrodes from the secondary coil of the in- 

 ductorium. 



The three levers, the one attached to the muscle, that of signal 

 magnet (a), which is in circuit with the current stimulating the 

 nerve, and that of signal magnet (b), which is in circuit with the 

 tuning fork, will then begin their tracings directly under each 

 other, so that exact time comparisons may be made. 



Close the short-circuiting keys in both circuits. Start the drum 

 to spinning rapidly. When the drum has reached the height of its 

 speed, open both keys. Close the tuning fork key immediately. 

 Stop the drum. There will be three tracings to interpret. The 

 signal magnet (a) marks the exact instant that the nerve was 

 stimulated. The muscle lever marks the period of contrac- 

 tion of the muscle. The tuning-fork lever marks the time re- 

 lations. 



Does the muscle twitch begin exactly at the moment of stimula- 

 tion ? If not, how much time elapses between the application of 

 the stimulus and the onset of contraction ? 



What is the form of the single-twitch curve ? How does the pe- 

 riod of contraction compare with that of relaxation ? 



VIII. THE VELOCITY OF THE NERVE IMPULSE. 



With the same arrangement of apparatus as in the previous ex- 

 periment, ascertain the period of latent stimulation when the stim- 

 ulating electrodes are on the nerve near the muscle; when the elec- 

 trodes are on the nerve some distance from the muscle. Measure 

 the length of nerve between the two points of stimulation. Esti- 

 mate the difference in time of latent stimulation. This difference 

 will be equivalent to the time that it takes the nerve impulse to 

 travel over the length of nerve measured. From this the velocity 

 per second can be easily determined. 



