CONCLUSIONS AND SUGGESTIONS 171 



levels of the gradient are not specifically different, but 

 differ in quantity. If the transportation of chemical 

 substances is the only means of correlation between 

 the different levels of the gradient, it is impossible to 

 understand either how the gradient can persist or how 

 a relation of dominance and subordination can arise 

 between levels of higher and those of lower metabolic 

 rate. Specific chemical correlation between parts is 

 possible only when specifically different parts are present, 

 and the definite space relations which we find associated 

 with physiological dominance do not usually appear in 

 such correlation. In short, I believe it is impossible 

 to conceive of the process of organic individuation with 

 the definite, constant, and orderly character which it 

 actually possesses as having its origin in transportative 

 or chemical correlation alone. 



If, however, the metabolic gradient arises and is 

 maintained by the transmission of excitation from the 

 region of highest metabolic rate, this region becomes 

 dominant simply because its metabolic rate is so high 

 that it determines and maintains the gradient in rate, 

 and the differences in rate at different levels bring about 

 sooner or later differences in constitution and character 

 of the protoplasmic substratum. In regions of high 

 rate only certain relatively stable substances remain as 

 constituents of the substratum, and others are broken 

 down and eliminated. In regions of lower rate, on the 

 other hand, other substances accumulate as parts of 

 the substratum because under these conditions they are 

 less readily or less rapidly broken down than where the 

 rate is higher, and it is also probable that the character 

 of synthesis differs with the rate of metabolism. In 



