498 MUSCLE-NERVE PHYSIOLOGY 



8. 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 

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



FIG. 354. Contractions of the Gastrocnemius Muscle to Show Fatigue. The numbers printed 

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



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

 marked in the relaxation phase, figure 354. 



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 



