INORGANIC RESPONSE 



119 



many days (fig. 71). While discussing the subject of 



fatigue in plants, I have adduced considerations which 



showed that the residual 



effect of strain was one 



of the main (muses for 



the production of fatigue. 



This conclusion receives 



independent support from 



the records obtained with 



metals. 



In this connection the 

 important fact is that the 



Various typical fatigue FIG. 71. FATIGUE SHOWN BY TIN 



WlKE WHICH HAD BEEN CONTINU- 

 OUSLY STIMULATED FOR SEVERAL 

 DAYS 



effects exhibited in living 

 substances are exactly re- 

 produced in metals, where there can be question neither 

 of fatigue-product producing fatigue effects, nor of those 

 constructive processes by which they might be removed. 

 We have seen, both in muscles and in plants, that if 

 sufficient time for complete recovery be allowed between 

 each pair of stimuli, the heights of successive responses 

 are the same, and there is no apparent fatigue (see 

 page 39). But the height of response diminishes as 

 the excitation interval is shortened. We find the same 

 thing in metals. Below is given a record taken with 

 tin (fig. 72). Throughout the experiment the amplitude 

 of vibration was maintained constant, but in (a) the 

 interval between consecutive stimuli was 1', while in (b) 

 this was reduced to 30". A diminution of height 

 immediately occurs. On restoring the original rhythm 

 as in (c), the responses revert to their first large value. 



