300 



THE GROWTH OF THE BRAIN. 



power, so that the work done by a single contraction 

 was almost as great as before the loss of power. 

 The following curve represents several such periods, 

 with the loss and return of power. 1 



Since the periods do not occur upon direct stimula- 

 tion of the muscle, the loss of power is probably due 

 to changes in the nervous rather than the muscular 

 system, and the loss was therefore taken as the first 

 indication of central fatigue. By an automatic arrange- 

 ment the work which was done in these experiments 



< mm. 



II 



FIG. 70. A record of the extent of the flexions of the forefinger. 

 The light lines are those for the voluntary contractions. The 

 heavy lines, those for contractions following the direct stimu- 

 lation of the flexor muscles by electricity. In the former there 

 are periods, in the latter none. The arrow shows the direction 

 in which the curve is to be read. (Lombard.) 



was readily determined. When, therefore, it is stated 

 that there is a regular variation in the capability for 

 voluntary muscular work in the course of twenty-four 

 hours, the measure used in making this determination 

 is the amount of work accomplished between the begin- 

 ning of a record and the first evidence of central fatigue, 

 as shown by the failure to obtain a voluntary contrac- 

 tion. In this way it was that Lombard determined the 

 onset of fatigue at different hours of the day. 



It appears that this capability for work was lessened 

 by general fatigue, hunger, declining atmospheric pres- 



1 Lombard, Journ. of Physiol., 1892 



