INORGANIC RESPONSE 133 



cular deflection is slight. In the next, the curve is rapidly 

 ascending, i.e. a small variation of impressed force 

 produces a relatively large molecular effect. And 

 lastly, a limit is reached, as seen in the third part, where 

 increasing force produces very little further effect. In 

 this cause-and-effect curve, the first part is slightly 

 convex to the abscissa, the second straight and ascend- 

 ing, and the third concave. 



Increase of response with increasing stimulus. We 

 shall find in dealing with the relation between the 

 stimulus and the molecular effect i.e. the response 

 something very similar. 



On gradually increasing the intensity of stimulus, 

 which may be done, as already stated, by increasing 

 the amplitude of vibration, it will be found that, 

 beginning with feeble stimulation, this increase is at 

 first slight, then more pronounced, and lastly shows a 

 tendency to approach a limit. In all this we have a 

 perfect parallel to corresponding phenomena in animal 

 and vegetable response. We saw that the proper 

 investigation of this subject was much complicated, in 

 the case of animal and vegetable tissues, by the ap- 

 pearance of fatigue. The comparatively indefatigable 

 nature of tin causes it to offer great advantages in the 

 pursuit of this inquiry. I give below two series of 

 records made with tin. The first record, fig. 83, is for 

 increasing amplitudes from 5 to 40 by steps of 5. 

 The stimuli are imparted at intervals of one minute. 

 It will be noticed that whereas the recovery is complete 

 in one minute when the stimulus is moderate, it is not 

 quite complete when the stimulus is stronger. The 



