PHYSIOLOGICAL BASIS OF PATTERN 39 



metabolism or oxidation, nor is it to be regarded as 

 taking the place of any other method of investigating 

 physiological condition or rate of metabolism or oxida- 

 tion. Its chief value is as a supplement to other 

 methods. In the first place it enables us to demon- 

 strate the existence of certain characteristic, non- 

 specific regional differences in physiological condition in 

 organisms, which because of their unicellular character, 

 or their small size, or because of the complications intro- 

 duced by separating different body regions, are not 

 available material for other more direct and more exact 

 methods. Even in these forms, however, the action of 

 external chemical agents is in general from the surface 

 inward, consequently the information given by the sus- 

 ceptibility method concerns, first of all, the superficial 

 regions of the cell or body, but it is possible in many 

 cases to learn something concerning differential suscepti- 

 bility of internal parts and organs. 



Second, by the modification and control of develop- 

 ment through differential susceptibility, the method 

 enables us to show that the differences in condition 

 indicated by differences in susceptibility are fundamental 

 factors in organismic pattern. The conclusions con- 

 cerning the relation between susceptibility and rate of 

 metabolism or oxidation mean no more than that rate 

 of metabolism or oxidation is a factor in the conditions 

 which determine susceptibility, and it is not claimed 

 that this conclusion is universally valid. Undoubtedly, 

 in the more highly differentiated organisms and in more 

 advanced stages of development the qualitative differ- 

 ences in different organs may determine differences in 

 susceptibility which are more or less specific as regards 



