CONCLUSIONS AND SUGGESTIONS 187 



The lack of specificity in the action of a great variety 

 of experimental conditions upon development and 

 morphology has often been noted. For example, the 

 aberrations or abnormalities in development, or more 

 properly the partial inhibitions of development pro- 

 duced by low temperature, various narcotics and poisons, 

 and many other conditions are essentially the same. 

 The reason for the lack of specificity undoubtedly lies 

 in the fact that the action of these various substances 

 and conditions is primarily quantitative, yet a greater 

 or less degree of differentiation, various differences in 

 form and arrangement, and even the presence or absence 

 of specific organs may be determined by their action. 



The results of the quantitative changes in living 

 .protoplasm in a particular case must of course depend 

 upon its specific constitution. The kind of specializa- 

 tion or differentiation which arises at a particular level 

 of a metabolic gradient must depend upon this constitu- 

 tion, and the developmental and morphological resem- 

 blances between different forms must of course depend 

 in general upon similarities of constitution. The 

 development of the region of highest metabolic rate 

 in the major gradient as a growing tip in plants and as 

 a central nervous system or brain in animals must result 

 from differences in constitution and dynamic processes 

 in the plant and animal protoplasm, but growing tips 

 in general and central nervous systems in general have 

 certain common characteristics. 



We must, I believe, conclude that the conception of 

 the metabolic gradient, a gradient primarily quantitative, 

 originating in and primarily determined by the dominant 

 region, as the basis of physiological and morphological 



