PHYSIOLOGICAL BASIS OF PATTERN 25 



dients, not because it is assumed that they are purely 

 or primarily metabolic in character, but because our 

 knowledge of protoplasm in general indicates that 

 metabolism, and more specifically oxidation, is a funda- 

 mental factor in life and the chief source of the energy 

 of living organisms and because the data of observation 

 and experiment indicate that differences in the rate of 

 metabolism and particularly of oxidation are character- 

 istic features of these gradients. Protoplasm is a 

 system in which the chemical reactions of metabolism 

 are so intimately associated with other factors, e.g., 

 colloid dispersion, active mass of enzymes, permeability 

 of limiting surfaces, electrolyte, and water content, 

 etc., that to attempt to distinguish one particular factor 

 rather than another as primary is at present impossible. 

 The axial gradients are not simply oxidative or meta- 

 bolic gradients but gradients in the general physiological 

 state of the particular protoplasm concerned, and in 

 this physiological state oxidation and associated with it 

 other metabolic reactions are important factors. The 

 term " metabolic gradient" as used in this connection 

 means only that the metabolic factor is a characteristic 

 feature of the gradients. The term "physiological 

 gradient," which avoids all specific implications, might 

 be substituted for it. 



In the development and differentiation of the axiate 

 pattern the apical region or head of the organism arises 

 from the region of greatest activity or highest metabolic 

 or oxidative rate, the "high end" of the major or polar 

 gradient, and other organs at different levels of the 

 gradient. The simplest forms of radial symmetry in 

 axiate organisms in which there is no differentiation 



