52 



BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



is no doubt to be accounted for in largest part by 

 the fact that what we are wont to call muscular fatigue 

 is in reality quite largely central or nervous fatigue. When 

 a subject under experiment continues to exert force through 

 the arm, say, until his muscles become perfectly inert, they 

 may then be stimulated with electricity to act with initial vigor,, 

 indicating that they are still in workable condition; and after 

 a period of stimulation in this way, the will of the subject 

 remaining quiescent, he can again voluntarily energize the arm,, 

 as is shown in the following figures. 



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lUfifl 



UdlMiUillMiL _ 



i 





Fig. 5. — Showing ergographic tracings (1) in voluntary effort, (2) in electrical 

 stimulation of nerve, (3) in electrical stimulation of muscle. (Scripture 1 

 after Mosso.) The relative heights of the tracings represent the relative 

 amounts of energy expended in the several forms of stimulation. It can 

 be seen that in voluntary effort the subject gradually loses power of exer- 

 tion and is soon unable to exert any force whatever ; but if at this point a 

 nerve leading to the muscle which has been acting (in this instance the 

 middle finger was exercised) be excited by electricity, the tracings show that 

 the muscle is as vigorous as ever. The fatigue in the voluntary effort 

 must then have been central or mental. Again, if when action ceases from 

 nerve excitation the muscle be directly stimulated there is once more a re- 

 turn of power, indicating that the muscle itself fatigues much more slowly 

 than the nerve mechanisms concerned in voluntary effort. 



Fig. 6 shows the rhythm in the fatigue of voluntary effort (Scripture 2 ). At F 

 is shown a period when the subject could exert no force whatever, although 

 he earnestly endeavored to. Soon after this space of paralysis, however,, 

 there is a return of ability again for a brief time. These tracings were ob- 

 tained upon the dynamometer by means of the hand grip. 



iThe New Psychology, p. 231. 

 2 Ibid., p. 229. 



