42 INDIVIDUALITY IN ORGANISMS 



but, once established, it may persist through many 

 generations. 



The question at once arises whether a quantitative 

 gradient, such as has been described, constitutes an 

 adequate basis for the physiological specialization and 

 structural differentiation which arise in relation to the 

 axes of the individual and in the higher organisms 

 become very complex. Organs showing very definite 

 qualitative differences in chemical constitution and 

 metabolism and great differences in functional activity 

 develop in the organism. Qualitative specific differ- 

 ences of some sort are commonly believed to be necessary 

 as a starting-point for such complexity, hence the usual 

 theoretical assumption of some sort of underlying 

 organization as the basis of organic individuality. 

 Some of the facts bearing upon this question will be 

 considered in later chapters; here attention may be 

 called to three points: first, it is a familiar fact of 

 chemistry that purely quantitative differences may bring 

 about the formation of qualitatively different products 

 from the same reacting substances, and in a complex 

 physico-chemical system, such as living protoplasm, the 

 possibilities for the origin of qualitative from quantita- 

 tive differences is very much greater than in the simple 

 chemical reaction in the test tube; secondly, it is by no 

 means clear what is quantitative and what is qualitative 

 in organic structure and form, or in metabolism, for 

 many structural difterences which are ordinarily con- 

 sidered as qualitative prove on analysis to depend on 

 quantitative differences in certain constituents of the 

 complex; and, thirdly, morphological differences usually 

 regarded as qualitative can unquestionably be produced 



