FATIGUE OF VOLUNTARY MUSCULAR CONTRACTION 529 



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 

 consumed by the contraction. This increase in time falls very slightly on 

 the latent period, is more pronounced in the contraction phase, but is very 

 marked in the relaxation phase, figure 355. 



FIG. 355. Contractions of the Gastrocnemius Muscle to Show Fatigue. The numbers 

 printed on the figure indicate the contraction in the series which is recorded. (Lee.) 



9. Fatigue of Voluntary Muscular Contraction. The human vol- 

 untary muscles are used to demonstrate this experiment. Use a Mosso's 

 ergograph, or any one of its numerous modifications. If the original form is 

 used, then the muscle should be loaded with about 3 kilos, and contractions 

 once a second recorded until the muscle can no longer lift the load. The load 

 may have to be adjusted to the individual, but should be chosen so that ex- 

 haustion will be obtained with about fifty contractions. This experiment 

 does not demonstrate complete exhaustion, but merely fatigue down to a 

 certain level. If an apparatus is previously arranged for direct stimulation 

 of the muscles by electric currents it will be found that the contractions of 

 the muscles still occur after the voluntary power is lost, showing that at least 

 a part of the phenomenon, possibly the chief part, is located in the nervous 

 tissue rather than in the muscle substance. 



10. The Effect of Temperature on Muscle Contractions. Pre- 

 pare a muscle nerve and mount it in Porter's latest form of temperature ap- 

 paratus. Adjust the levers for vertical records on the smoked paper of the 

 kymograph. Begin with a temperature of the tap water and gradually lower 

 the temperature of the preparation by adding small amounts of crushed ice 

 at first, later ice and some salt crystals, to the external chamber. Take care 

 to lower the external temperature very slowly and gradually say about one 



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