MUSCULAR ACTIVITY 



95 



the extent of the shortening of the muscle. Suppose, next, the 

 smoked surface to be moved to such position that the writing 

 point of the lever touches it at i, and, the muscle being left at rest 

 the surface to be moved evenly from left to right; the horizontal 

 line io would then be traced, its length depending on the distance 

 through which S moved during the time the lever was marking on 

 it: and it is clear that if S move uniformly, and we know its rate 

 of movement, we can very readily calculate from the length of io 

 how long S was moving while that line was being traced: for ex- 

 ample, if we know the rate of movement to be ten centimeters per 



FIG. 47. Diagram to illustrate the method of obtaining a graphic record of a 

 muscular contraction. 



second, and on measurement find io to be one centimeter long, the 

 time during which the surface was moving must have been VQ- of a 

 second; and each tenth of io correspond to iVo" of a second. 



If we set the recording surface in motion and while the lever 

 point is tracing a horizontal line cause the muscle to contract, the 

 point will be raised as long as the muscle is contracted, and the 

 line drawn by it will be due to a combination of two simultaneous 

 movements a horizontal, due to the motion of S, a nearly verti- 

 cal, due to the shortening of the muscle; the resulting line is a 

 curve known as the curve of a simple muscular contraction. Let the 

 surface S be placed so that the writing point is at q and then be set 

 in uniform motion from left to right at the same rate as before 



