184 RESPONSE IN THE LIVING AND NON-LIVING 



the variation depending on the intensity of the stimulus 

 (figs. 4, 7, 54). 



Relation between stimulus and response. In all 

 three classes we have found that the intensity of re- 

 sponse increases with increasing stimulus. At very high 

 intensities of stimulus, however, there is a tendency 

 of the response to reach a limit (figs. 30, 32, 84). 

 The law that is known as Weber-Fechner's shows a 

 similar characteristic in the relation between stimulus 

 and sensation. And if sensation be a measure of phy- 

 siological effect we can understand this correspondence 



FIG. 112. UNIFORM KESPONSES IN (A) NERVE, (P) PLANT, AND (M) METAL 



The normal response in nerve is represented ' down.' In this and following figures, 

 (A) is the record of responses in animal, (P) in plant, and (M) in metal. 



of the physiological and sensation curves. We now 

 see further that the physiological effects themselves are 

 ultimately reducible to simple physical phenomena. 



Effects of superposition. In all three types, ineffec- 

 tive stimuli become effective by superposition. 



Again, rapidly succeeding stimuli produce a maxi- 

 mum effect, kept balanced by a force of restitution, and 

 continuation of stimulus produces no further effect, in 

 the three cases alike (figs. 17, 18, 86). 



Uniform responses. In the responses of animal, 

 vegetable, and metal alike we meet with a type where 

 the responses are uniform (fig. 112). 



