28 SENESCENCE AND REJUVENESCENCE 



and the current have been associated from the beginning. Here 

 also structure and function are connected as in the organism: the 

 configuration of the channel modifies the intensity and course of 

 the current and the current in turn modifies the morphology of 

 the channel by deposition at one point, giving rise to structures 

 such as bars, islands, flats, and by erosion at another. And besides 

 this, the river possesses a considerable capacity for self -regulation. 

 Where the channel is narrower the rate of flow is higher, and vice 

 versa. A dam raises the level until equilibration results and the 

 flow continues. It is of course true that only in the lower reaches 

 does the river resemble the organism in the accumulation of 

 structural material: over most of its course it is primarily an 

 erosive agency. It does, however, exhibit what we may call a 

 physical metabolism on which its morphogenesis depends. The 

 current carries certain materials and the character of these differs 

 with the current. When the energy of the current is no longer 

 able to carry them they are deposited and take part in the building 

 up of structure. Certain materials are more readily carried by 

 the stream than others, and these may be eliminated from the river 

 and take no part in its morphogenesis. 



But the most important point for present purposes is that in 

 the river, as in the organism, structure and function are indis- 

 sociable and react upon each other. From the moment the current 

 begins to flow it is a constructing agent, i.e., it determines form 

 along its channel, and from the same moment the structure already 

 existing affects the flow of the current. It is evident then that the 

 relation between structure and function in the living organism is 

 not fundamentally different from that in the flowing stream. 

 Structure and function are indissociable and mutually determining 

 as long as the river exists and the organism lives. In a very inter- 

 esting series of papers Warburg 1 has recently demonstrated the 

 close interrelation between function and structure for the oxidation 

 processes and the fundamental structure of the cell, the occur- 

 rence of the oxidations being very directly dependent upon the 

 existence of the cell structure. 



1 Warburg, 'i2a, 'i2&, '13, '140, 'i4&. 



