FATIGUE OF MUSCLE AND NERVE 47 



which has died and passed into rigor whether natural or the effect 

 of heat (see p. 43) is also acid. 



Fatigue in voluntary contraction. This is investigated by the 

 ergograph (Fig. 41), the muscles of the fingers being fatigued by 

 causing them to repeatedly raise a heavy weight or repeatedly deflect 

 a strong spring. The extent of the contractions is recorded upon a 

 very slowly revolving drum, and a fatigue curve or ergogram which 

 always shows individual peculiarities is thereby produced in the same 

 manner as with the frog muscle-nerve preparation. 



In Mosso's ergograph and Porter's modification the records are 

 made upon a horizontal drum ; in Waller's modification (dynamo- 

 graph), in which a strong spring is used in place of a weight, the 

 drum is vertical. 



In the case of voluntary contractions the result is complicated 

 by the fact that fatigue of nerve-cells in the central nervous system 

 occurs before fatigue of the muscle itself or of the nerve endings in 

 the muscle. This fact can be shown by direct faradic stimulation of 

 the median nerve (or of the finger muscles) after the fatigue curve is 

 complete. It is found that the muscle can still be made to contract 

 by such peripherally applied stimuli. 



