352 



LIFE MOVEMENT'S IN PLAJffS 



successive dott« represent the corresponding increments of 

 excitation. The gradient at any point of the curve — incre- 

 ment of excitation divided by increment of stimulus — gives 

 the susceptibility for excitation at that point. The follow- 

 ing table will show how the susceptibility for excitation 

 undergoes variation through the entire range of stimulus. 

 The average susceptibility for each point has been calculated 

 from the data furnished by the curve. 



TABLE XXX. — SHOWING THE VARIATION OF SUSCEPTIBILITY FOR 

 EXCITATION AT DIFFERENT POINTS OF THE TBOPIC CURVE. 



The induced excitation is seen to be increased very 

 gradually from the zero point of susceptibility, known as 

 the latent period at which no excitation takes place. In 

 the second part of the excitation curve, the rate of increase 

 is very rapid; the maximum rate is nearly reached at 

 point 11 of the curve and remains fairly constant for a 

 time. This is the median range where equal increment of 

 stimulus induces equal increment of excitation. The sus- 

 ceptibility for excitation then falls rapidly, and increase of 

 stimulus induces no further increase of tropic curvature. 



