54 RESPONSE IN THE LIVING AND NON-LIVING 



2. The next figure shows-how little variation is pro- 

 duced with low value of stimulus, but with increasing 

 stimulus the response undergoes a rapid increase, 

 after which it tends to approach a limit (fig. 33, a). 



3. ,\s an extreme instance of the case just cited, 

 I have often come across a curious phenomenon. 

 During the gradual increase of the stimulus from a low 

 value there would be apparently no response. But 



Ib) 



A 



12 16 22 32 4-5 



A 



10 20 30 C 



4-0 



FIG. 33. RESPONSES TO INCREASING STIMULI PRODUCED BY INCREASING 

 ANGLE OF VIBRATION 



.(a) Record with a specimen of fresh radish. Stimuli applied at intervals of two 

 minutes. The record is taken for one minute. ' 



(6) Record for stale radish. There is a reversed response for the feeble stimu- 

 lus of 5 vibration. 



when a critical value was reached a maximum response 

 would suddenly occur, and would not be exceeded when 

 the stimulus was further increased. Here we have 

 a parallel to what is known in animal physiology as the 

 ' all or none ' principle. With the cardiac muscle, for 

 example, there is a certain minimal intensity which 

 is effective in producing response, but further increase 

 of stimulus produces no increase in response. 



4. From an inspection of the records of responses 



