IMPORTANCE OF EXERCISING THE BRAIN. 593 



Movements which are commonly executed together tend 

 to become so associated that it is difficult to perform one 

 .alone; many persons, e.g., cannot close one eye and keep 

 the other open. From frequent use, the paths of con- 

 duction between the co-ordinating centres for both groups 

 of muscles have become so easy that a volitional impulse 

 reaching one centre spreads to the other and excites both. 

 This association of movements, dependent on the modifica- 

 tion of brain structure by use, finds an interesting parallel 

 in the psychological phenomenon known as the association 

 of ideas; and all education is largely based on the fact that 

 the more often brain regions have acted together the more 

 readily, until finally almost indissolubly, do they so act. If 

 we always train up the child to associate feelings of disgust 

 with vvrong actions and of approbation with right, when he 

 is old he will find it very hard to do otherwise: such an 

 organic nexus will have been established that the activity 

 of the one set of centres will lead to an excitation of that 

 which habit has always associated with it. The nerve-centres 

 are throughout eminently plastic; every thought leaves its 

 trace for good or ill; and the moral truism that the more 

 often we yield to temptation the more often an evil solici- 

 tation, sensory or otherwise, has resulted in a wrong act 

 the harder it is to resist it, has its parallel (and we can 

 hardly doubt its physical antecedent) in the marking out of 

 .a path of easier conduction from perceptive to volitional 

 centres in the brain. The knowledge that every weak 

 yielding degrades our brain structure and leaves its trail in 

 that organ through which man is the " paragon of animals," 

 while every resistance makes less close the bond between 

 the thought and the act for all future time, ought surely to 

 "give us pause:" on the other hand, every right action 

 helps to establish a "path of least resistance," and makes 

 its subsequent performance easier. 



The brain, like the muscles, is improved and strengthened 

 by exercise and injured by overwork or idleness; and just 

 .as a man may specially develop one set of muscles and 

 neglect the rest until they degenerate, so he may do with 

 Jiis brain; developing one set of intellectual faculties and 



