WORK AND FATIGUE 



57 



rigid clamp, while the other is attached to the spring, which 



is stretched by the contraction when the muscle is stimulated. 



The length of the line written by the lever AB records 



what the muscle is capable 



of doing at the time ; and 



if the records of successive 



contractions are made on 



the smoked surface of a 



slowly revolving drum, as 



in the figure, we have at 



once a record of the course 



of fatigue. 



Such fatigue tracings may 

 also be taken from a muscle 

 within the body, and hence 

 with its circulation intact. 

 Thus the work of the biceps 

 muscle in bending the arm 

 at the elbow (Fig. 23) may 

 be recorded by instruments 

 essentially similar to that 

 used with the excised muscle. 

 In Fig. 34 we have repro- 

 duced a tracing of this kind. 



It is quite evident that a 

 continuous line joining the 

 highest points reached by 

 the several contractions will 

 represent graphically the 

 course of fatigue, and in 

 Fig. 35 the line a represents 

 this so-called " curve of 

 fatigue " in the experiment 

 whose results are given in 

 Fig. 34. It falls off at first 



FIG. 34. Record of the successive con- 

 tractions of the flexor muscles of the 

 elbow joint 



Showing the gradual decrease in working 

 power to a fatigue level. The muscle con- 

 tracted once every three seconds against 

 the resistance of a strong spring, which 

 was stretched each time as far as the 

 strength of the muscle permitted 



