120 



RESPONSE IN THE LIVING AND NON-LIVING 



Thus we see that when the wire has not completely 

 recovered, its responses, owing to residual strain, under- 

 go diminution. Height of response is thus decreased 

 by incomplete recovery. If then sufficient time be not 

 allowed for perfect recovery, we can understand how, 

 under certain circumstances, the residual strain would 

 progressively increase with repetition of stimulus, and 

 thus there would be a progressive diminution of height 



y 



VVVV\i VV-vl 



(a) (b) (c) 



FIG. 72. DIMINUTION OF KESPONSE DUE TO SHORTENING THE PERIOD OF 



RECOVERY 



The stimulus is maintained constant. In (a) the interval between two suc- 

 cessive stimuli is one minute, in (5) it is half a minute, and in (c) it is again 

 one minute. The response in (6) is feebler than in either (a) or (c). 



of response or fatigue. Again, we saw in the last 

 chapter that increase of strain necessitates a longer 

 period of recovery. Thus the longer a wire is stimu- 

 lated, the more and more overstrained it becomes, and 

 it therefore requires a gradual prolongation of the in- 

 terval between the successive stimuli, if recovery is to 

 be complete. This interval, however, being maintained 

 constant, the recovery periods virtually undergo a 

 gradual reduction, and successive recoveries become 



