i6 INDIVIDUALITY IN ORGANISMS 



^do know that for a given organism metabolism is in 

 general a definite and characteristic system of reactions 

 subject to variation with change in conditions but never- 

 theless maintaining in the long run a certain rate and 

 character. 



In general terms, protoplasm is the foundation of 

 structure and form, and metabolism, of function, in the 

 organism. The relation between structure and function 

 has been the subject of much discussion. For some the 

 organism possesses a certain structural organization 

 which arises in some way or other quite independent of 

 function and which makes function possible, just as a 

 man-made machine possesses a certain structure which 

 makes its function possible. Such an organism must be 

 constructed before it can begin to function, and hy- 

 potheses of this character are chiefly concerned with 

 the supposed method of construction. This conception 

 of the organism ignores the fact that it is always func- 

 tioning while it is alive : life is function. In no case does 

 the organism begin to function only after its construction 

 is completed; it always functions from the beginning; 

 it constructs itself by functioning, and the character of its 

 functional activity changes as its structural develop- 

 ment progresses. Structure and function are mutually 

 related. Function produces structure and structure 

 modifies and determines the character of function. 



Here it is possible to refer only very briefly to a con- 

 ception of the relation between structure and function 

 which I have discussed more at length elsewhere.' 

 According to this view protoplasm and structure rep- 

 resent primarily those products of metabolism which 



^ Child, Senescence and Rejuvenescence, 1915, pp. 26-31. 



