JUULJ 



122 RESPONSE IN THE LINING AND NON-LIVING 



is seen under particular conditions in the response of 

 certain muscles (fig. 74, a). It is also observed some- 

 times even in nerve, which otherwise, generally speaking, 

 gives uniform responses. Of this effect, 110 satisfactory 

 theory has as yet been offered. It is in direct contra- 

 diction to that theory which supposes that each 

 stimulus is followed by dissimilation or break- down of 

 the tissue, reducing its function below par. For in these 

 cases the supposed dissimilation is followed not by a 

 decrease but by an increase of functional activity. This 

 ' staircase effect ' I have shown to be occasionally 



exhibited by plants. I have 

 also found it in metals. In 

 the last chapter we have 

 seen that a wire often falls, 

 especially after resting for 



() (6) i A - , r 



a Ions: time, into a state of 



FIG. 74. ' STAIRCASE EFFECT 



(a) in muscle (after Engelmann). Comparative sluggislllieSS, 



(b) in metal. 



and that this molecular 



inertness then gradually gives place to increased 

 mobility under stimulation. As a consequence, an 

 increased response is thus obtained. I give in fig. 74, , 

 a series of responses to uniform stimuli, exhibited by 

 platinum which had been at rest for some time. This 

 effect is very clearly shown here. So we see that in 

 a substance which has previously been in a sluggish 

 condition, stimulation confers increased mobility. Ke- 

 sponse thus reaches a maximum, but continued stimu- 

 lation miay afterwards produce overstrain, and the 

 subsequent responses may then show a decline. This 

 consideration will explain certain types of responses 



