MUSCLE-NERVE PHYSIOLOGY 



attached to the recording drum. Adjust the apparatus and lever and revolve 

 the drum at a rapid rate, allowing the automatic key to be opened while the 

 drum is turning at a rapid speed. Or take a record on the pendulum myo- 

 graph, which is especially constructed for this experiment, figure 352. The 

 muscle contraction now is recorded as a wave which shows some consider- 

 able duration in time. Repeat the experiment, introducing a 100 double 

 vibration tuning fork to record the speed of the drum, and taking care to 

 mark the exact point on the record where the automatic key is opened. In 

 this record the muscle contraction shows three different periods or phases. 

 The first, a period of no activity, called the latent period, taking about o.oi 



FIG. 351. Arrangement of Apparatus in the Induction Coil, as Shown for Single 



Inductions. 



of a second; the second, the period of rapid shortening known as the con- 

 traction phase, taking about 0.04 of a second on the average; and the third, 

 a period of rapid relaxation or return to the normal, which takes about o . 05 

 of a second, see figure 353. 



The time and character of the simple muscle contraction will be influ- 

 enced by: i, load or tension; 2, the exact temperature; 3, by the amount of 

 work it has previously done, or fatigue; 4, by the time since it was isolated 

 from the circulation. Perform a series of experiments varying these effects, 

 and record the results by the following outline: 



6. The Relation of the Contraction to the Strength of the Stimu- 

 lus. Minimal and Maximal Stimuli. Prepare a muscle nerve of the 

 frog and mount in the moist chamber and arrange for stimulating the muscle 



