THE ELEMENTS OF NERVE PHYSIOLOGY 47 



cannot doubt that there are actual material changes 

 in the tissue, though it is not likely that the most 

 refined microscopic technic will ever make them recog- 

 nizable. 



It will now be apparent that while conductivity is the 

 most conspicuous property of all nervous systems, it has 

 associated with it, though in a varying degree, the capacity 

 to be modified by use. The power to conduct impulses 

 along fixed pathways with fixed reactions ensuing is highly 

 characteristic of those forms of life which we regard as 

 lower and simpler. The second power is obviously pro- 

 portional to the rank which we involuntarily assign to 

 animals. So far as they possess it, they have the chance 

 to profit by individual experience. This would seem to be 

 the same thing as intelligence objectively viewed. Com- 

 plexity of action does not necessarily imply such an 

 endowment. We marvel at the community life of bees, 

 and we are inclined to endorse Darwin's assertion that 

 the brain of the ant is the most wonderful particle of 

 matter in the universe, but upon reflection we are led to 

 give cats and dogs credit for immeasurably superior 

 organization. 



An old ant is probably little better than a young one 

 in meeting the exigencies of its environment. Maturity 

 in the insect is a matter of size and strength rather than 

 any acquirement of profitable responses to stimulation. 

 But maturity in the dog means an acquirement of just 

 such responses and it also means that dogs have indi- 

 viduality. The inherited nervous mechanism in the one 

 case is all but rigid; in the other it is plastic in a high de- 

 gree. We cannot deny to the ant some trace of this 

 capacity for modification through experience; the ability 

 to return to the nest seems to demonstrate it, but we do 

 not expect to find it impressive. It will be noted that the 

 plastic property is met with in those nervous systems 

 which in the beginning of the animal's life are most 

 inadequately fitted to meet the demands made upon them. 

 We might conceive of a nervous system, as well prepared 



