THE NERVOUS SYSTEM 51 



function of coordinating body processes. Through 

 evolution the nervous system has acquired certain 

 specific qualities, which are, for nerve fibers, that of 

 facilitating the conduction of impulses ; for nerve cells, 

 that of holding energy which may be released by nerve 

 impulses for adaptive ends; and for certain, as yet 

 unknown, portions of nerve tissue, that of being 

 permanently modified by each adequate stimulus, so 

 that the reactions to successive stimuli of the same 

 kind vary in intensity. 



The reactions of a given animal or species are gov- 

 erned by the nervous mechanisms it has evolved, 

 by the forces to which its nervous system has been 

 attuned. In other words, the complex organism differs 

 from the simple only in the number of its reacting 

 units and their attunement. It would seem, there- 

 fore, that the manifold reactions of man differ only in 

 number and complexity, but not in principle, from the 

 simple adaptive reactions of Venus' fly-trap in catching 

 and digesting its insect food. 



The Typical Adaptive Reaction 



Venus' fly-trap, which is found in the damp, infertile 

 regions of North Carolina, possesses .one of the most 

 remarkable adaptive mechanisms in nature. Dar- 

 win has given a graphic description of this plant in 

 his volume on " Insectivorous Plants." Its body is 

 composed of two plump leaf lobes, set nearly at right 

 angles to each other, like the pages of a book held 

 partly open, each lobe being fringed on the outer edge 

 by a single row of sharp thorn spikes, which interlock 

 like the gates of a prison behind the unfortunate insect 



