ORGANISM AND MECHANISM 121 



things happen, there is a chain of events which may be long 

 or short, intricate or simple, but which is quite clearly 

 stateable in chemico-physical, i.e., theoretically mechanical, 

 language. But it is otherwise when a living structure 

 responds to a stimulus. " There is in reality no experi- 

 mental evidence whatsoever that the process can be under- 

 stood as one of physical and chemical causation. . . . 

 When we attempt to trace a connection we are lost in an 

 indefinite maze of complex conditions, out of which the 

 response emerges" (Haldanc, 1913, p. 34). A very 

 familiar fact is that the same stimulus applied to two ap- 

 parently similar animals or to the same animal at different 

 times evokes different answers. We can indeed give reasons 

 for this, but the reasons are not mechanical reasons. 



Why is it that we cannot adequately describe the life of 

 the organism in terms of chemistry and physics ? Let us 

 take an answer from the philosophical physiologist, already 

 quoted, Dr. J. S. Haldane, in his contribution to Life 

 and Finite Individuality (1918). Because the organism 

 " forms itself and keeps itself in working order and ac- 

 tivity " (p. 14), and "the idea of a mechanism which is * 

 constantly maintaining or reproducing its own structure is 

 self-contradictory " (p. 16). " Empirical observations with 

 regard to the behaviour of living organisms point clearly 

 to the conclusion that in each detail of organic structure, 

 composition, environment, and activity there is a manifesta- 

 tion or expression of the life of the organism regarded as a 

 whole which tends to persist. It is this manifestation which 

 distinguishes biological phenomena; and, through all the 

 temporary variations of structure, activity, composition, and 

 environment, it can be traced more and more clearly with 

 every year of advance in biological investigation. We can 



