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MUSCLE-NERVE PHYSIOLOGY 



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

 siderable duration in time, figure 354. Introduce a 100 double vibration 

 tuning fork to record the speed of the drum, and take care to mark the exact 

 point on the record where the automatic key is opened. (Instead of the 

 automatic key one may use a hand key in connection with a signal magnet to 

 mark the point of stimulation.) 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 of a second; the second, the period of rapid 

 shortening known as the contraction 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 0.05 of a second, see figure 354. 



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

 enced by: a, load or tension; b, the exact temperature; c, by the amount of 

 work it has previously done, or fatigue ; d, 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: 



FIG. 354. Record of a Simple Contraction of the Gastrocnemius of the Frog. Time 

 in .01 of a second. St, Moment of stimulation. Record taken on a rapid drum that was 

 provided with an automatic key. 



12. The Effect of Fatigue on the Time of the Simple Contraction. 

 Prepare a muscle nerve and mount it in the moist chamber, arrange for the 

 record as directed under 5 above. Make a series of records of the simple 

 contraction when automatically stimulated, recording only every tenth or 

 twentieth contraction the intermediate contractions should be shunted and 

 are used merely to produce fatigue. After a time the contractions will not 

 only diminish in amplitude, but there will be a gradual increase in the time 



