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 

(a) (b) (c) 
Fic. 72.—Diminution or RESPONSE DUE TO SHORTENING THE PERIOD OF 
LECOVERY 
The stimulus is maintained constant. In (a) the interval between two suc- 
cessive stimuli is one minute, in (6) it is half a minute, and in (ce) it is again 
one minute. The response in (b) is feebler than in either (a) or (c). 
of response or fatigue. Again, we saw in the last 
chapter that mcrease of stram 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 
o maintained 
be complete. This interval, however, being 
constant, the recovery periods virtually undergo a 
eradual reduction, and successive recoveries become 
