36 INDIVIDUALITY IN ORGANISMS 



so are the basis of the geometrical space relations and 

 the sequences in time which arise during the develop- 

 ment of the individual. They may then be called 

 axial gradients. The region of highest rate in such a 

 gradient is the apical, the region of lowest rate the basal 

 region of the axis which represents the general direction 

 and course of the gradient. 



Other factors besides actual rate of metabolic reac- 

 tions are doubtless concerned in the formation and 

 establishment of these gradients in protoplasm, but 

 these are associated either with the rate of reaction or 

 its change, or with the character of the protoplasm in 

 which the reaction occurs and have to do rather with 

 particular cases than with the gradient in general. The 

 intensity of reaction, for example, is probably such a 

 factor. A sudden or very rapid increase in rate on 

 excitation is probably more effective in producing trans- 

 mitted changes than a gradual increase, and it is also 

 probable that in protoplasm with a high reaction- 

 intensity excitations are transmitted to greater distances 

 than where the reaction-intensity is low. Excitation 

 and transmission are undoubtedly also correlated with 

 the physiological stability and physico-chemical con- 

 stitution of the protoplasm. Such factors as these 

 may play a part in determining length, slope, or other 

 characteristics of the gradient, but the primary factor 

 in its production appears to be rate of reaction. 



In a metabolic gradient a relation of dominance 

 and subordination exists between the level of highest 

 and the levels of lower metabolic rate. A brief con- 

 sideration will show that this relation is a simple and 

 necessary result of the differences in rate of reaction. 



