186 C. M. CHILD 
organism is not then to be compared with a machine constructed 
of certain definite parts, which have been put together in some 
way, and which, after completed construction, begin to function. 
It is much more nearly comparable to a river, which molds its 
banks and bottom, forming here a bar, there an islaad, here a 
bay, there a point of land, but still flowing on, though its course, 
its speed, its depth, the character of the substances which it: 
carries in suspension and in solution allare altered by the structural 
conditions which it has built up by its own past activity. In 
such a system a wide range of equilibration exists and we see both 
the adjustment of function to form and of form to function. The 
relation between structure and function in the organism is similar 
in character to the relation between the river as an energetic proc- 
ess and its banks and channel. From the moment that the river 
began to flow it began to produce structural configurations in its 
environment, the products of its activity accumulated in certain 
places and modified its flow, but just so long as the flow continues 
the process of equilibration goes on.? 
If we consider merely a certain region of the river with the water 
containing certain substances in suspension and in solution enter- 
ing at one end, depositing some of these substances and taking up 
others as conditions determine in the course of its passage, and 
finally passing out at the other end bearing certain substances 
more or less different from those which it brought in, the analogy 
becomes even more complete. In fact this region of the river, 
together with its bed, shows a real, though chiefly a mechanical 
rather than a chemical metabolism. 
I believe that this comparison between a river with its channel 
and the organism is far more thanafanciful analogy. Theindivid- 
dualorganismismerely a section from that current of energy which 
constitutes the essence of life, and in the individual we see the 
mutual correlation and interaction between the current and the 
conditions under whichit findsitself, between the energetic process 
2 Rignano (’07) has referred briefly to this analogy between the river and the 
organism, using the case of a river equilibrating itself in connection with the piers 
of a bridge to illustrate the process of equilibration in organisms. See also 
Delage, L’ Heredité, ete., 1903. 
