THEORIES OF INDIVIDUALITY 37 



In the first place, the apical region (a, Fig. i) is the chief 

 factor in determining the rate of reaction at other levels, 

 for in the varying conditions of a natural environment 

 it responds more rapidly or with a higher rate of reaction 

 than other levels of the gradient to external exciting 

 conditions, and it is also more sensitive and may react to 

 conditions which produce no reaction at lower levels 

 of the gradient. With every such increase of metabolic 

 rate in response to external exciting factors a gradually 

 decreasing wave of change spreads from this region of 

 highest rate, as in the original excitation which gave 

 rise to the gradient, though the intensity, velocity, and 

 limit of effectiveness of the transmitted change may be 

 much greater than in the original transmission. 



This change transmitted from the apical region a 

 plays the chief part in determining the metabolic con- 

 dition at other levels, because a is the region of highest 

 metabolic rate and the changes transmitted from it are 

 more intense than those from other levels and because the 

 establishment of the protoplasmic gradient makes con- 

 duction in this direction more effective than in any other. 

 Consequently the region a dominates or controls other 

 regions within a certain distance and to a greater or 

 less degree by influencing, through the changes trans- 

 mitted from it, their metabolic rate. Dominance or 

 control of one part over another in the organism is 

 fundamentally, I believe, a matter of difference in 

 metaboHc rate, the region of higher rate being dominant. 



If, after such a gradient is established, some other 

 region, such as h, Fig. 2, undergoes excitation at the 

 same time as a and by an external factor of the same 

 intensity as that acting at a, the response will be 



