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 1s at 
first shght, 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 
to 40° by steps of 5°. 
° 
increasing amplitudes from 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 
