26 RESPONSE IN THE LIVING AND NON-LIVING 



another point has to be borne in mind. In all cases of 

 stimulation of living tissue it is found that the effective- 

 ness of a stimulus to arouse response depends on the 

 rapidity of the onset of the disturbance. It is thus 

 found that the stimulus of the ' break ' induction shock, 

 on a muscle for example, is more effective, by reason 

 of its greater rapidity, than the 

 ' make ' shock. So also with the 

 torsional vibrations of plants, I find 

 response depending on the quickness 

 with which the vibration is effected. 

 \ gj ve below records of successive 

 FIG. IS.-INFLUENCE stimuli, given by vibrations through 

 the same amplitude, but delivered 

 with increasing rapidity (fig. 13). 



Thus if we wish to maintain the 

 effective intensity of stimulus con- 

 stant we must meet two conditions : 

 (1) The amplitude of vibration must 

 be kept the same. This is done by 

 means of the graduated circle. (2) The vibration period 

 must be kept the same. With a little practice, this 

 requirement is easily fulfilled. 



The uniformity of stimulation which is thus attained 

 solves the great difficulty of obtaining reliable quan- 

 titative values, by whose means alone can rigorous 

 demonstration of the phenomena we are studying 

 become possible. 



STIMULUS 



The curves a, &, c, d, are 

 responses to vibra- 

 tions of the same 

 amplitude, 80. In 

 a the vibration was 

 very slow; in b it 

 was less slow ; it was 

 rapid in c, and very 

 rapid in d. 



