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 
