VARIOUS THEORIES OF THE ORGANISM 27 



reactions, it is evident that the association between the reaction- 

 complex and the substratum must continue as long as the reaction- 

 complex continues. It is probable that if we could duplicate the 

 reaction-complex in the laboratory it would be impossible to 

 designate any particular point in the process as the point where 

 life begins. Life is not any particular reaction nor any particular 

 substance, but a great system of processes and substances. Struc- 

 ture and function are then indissociable. And yet in the broad 

 sense function produces structure and structure modifies function. 

 At first glance it may appear that this relation is quite unique, that 

 nothing like it exists in the inorganic world. As a matter of fact, 

 however, the same relation exists everywhere in dynamic systems 

 in nature. 



Various authors have from time to time compared the organism 

 with one or another inorganic system. Roux ('05), for example, 

 has carried out in some detail the comparison between the organism 

 and the flame. Although this analogy contains much that is valu- 

 able, especially on the chemical side, it is imperfect morphologically 

 because the morphology of the flame is much less stable and per- 

 sistent than that of the organism. Some years ago (Child, '11) I 

 found the analogy between the organism and a flowing stream 

 useful for purposes of illustration. While as regards metabohsm 

 the river is much more widely different from the organism than 

 the flame, yet as regards the relation between structure and func- 

 tion there are certain resemblances between the two which are of 

 value for the present purpose. Such analogies serve merely to 

 call attention to certain points. The flow of water — the current 

 of the stream — is the dynamic process and is comparable in a 

 general way to the current of chemical energy flowing through the 

 organism. On the other hand, the banks and bed of the stream 

 represent the morphological features. Wherever such a system 

 exists, certain characteristic developmental changes occur which, 

 though much less definite and fixed in locahzation and character 

 than in the organism, are nevertheless of such a nature that we 

 can predict and control them. 



Neither water alone nor the banks and bed alone constitute 

 the system which we call a river; and in nature the banks and bed 



