322 THE NERVOUS SYSTEM 



Habit is a law or property of the material world, and 

 all our habits of life and action, mental as well as physical, 

 are now understood to have their basis in the physical 

 constitution of our bodies. The particles of matter which 

 compose inorganic bodies act and react upon one another 

 in a certain way, and ever after they act and react in that 

 same way more easily, that is, with less resistance than in 

 other ways, and by repetition of this action a habit is 

 established. In organic bodies this property is still more 

 marked. A pathway of discharge of nervous influence 

 in the brain, once formed, is afterward the channel by 

 which efferent nervous currents tend to pass outward. 

 All our activities are due to this streaming outward of 

 nervous currents excited by the constant streaming inward 

 of other nervous currents, or by stimulation originating 

 in the brain itself. A new channel once made for the out- 

 ward flow becomes the path of least resistance for the 

 next wave, which deepens the bed of the stream and de- 

 termines more surely the course of following impulses. 

 In course of time the nervous pathway becomes so deeply 

 cut that, given a certain incoming impulse, the resulting 

 nervous discharge can make its progress outward by that 

 course alone which has been prepared for it by permitting 

 previous impulses to pass that way. Then a habit has 

 become "fixed," and we all know how difficult it is to 

 change a fixed habit. 



We have already seen how the possibility of acquiring 

 habits relieves the brain of the necessity of attention to 

 many of the movements of the muscles and vastly increases 

 the number of things which one can do. Most of us estab- 

 lish in time an order of proceeding for the daily processes 

 of dressing and undressing, for example, so that we go 

 through them, day after day, in a certain routine without 



