INORGANIC RESPONSE 



121 



more and more incomplete. These considerations may 

 be found to afford an insight into the progressive diminu- 

 tion of response in fatigued substances . ^ 



Fatigue under continuous stimulation. Fatigue is 

 perhaps best shown under continuous stimulation. For 

 example, in muscles, when fresh and not fatigued, the 

 top of the tetanic curve is horizontal, or may even be 

 ascending, but with long-continued stimulation the 

 curve declines. The rapidity 

 of this decline depends on the 

 nature of the muscle and its 

 previous condition. 



In metals I have found 

 exactly parallel instances. In 

 tin, so little liable to fatigue, 

 the top of the curve is hori- 

 zontal or ascending ; or it may 

 exhibit a slight decline. But 

 the record with platinum shows the rapid decline due 

 to fatigue (fig. 73). 



Taking any of these instances, say that in which 

 fatigue is most prominent, it is found that short period 

 of rest restores the original intensity of response. This 

 affords additional proof of the fact that fatigue is due to 

 overstrain, and that this strain, with its sign of attendant 

 fatigue, disappears with time. 



Staircase effect. We shall now discuss an effect 

 which appears to be the direct opposite of fatigue. 

 This is the curious phenomenon known to physiologists 

 as ' the staircase ' effect, in which successive uniform 

 stimuli produce a series of increasing responses. This 



FIG. 73 



The top of response-curve un- 

 der continuous stimulation in 

 tin is horizontal or ascending 

 as in figure. (&) In platinum 

 there is rapid decline owing to 

 fatigue. 



