On the Scientific Study of Human Nature, 469 



ency of thought to move in its long-accustomed cerebral 

 tracks. 



Now, when we experience a feeling, or think a thought, 

 or determine an act — that is, in every case of excitement 

 and discharge — there is a partial decomposition of the 

 nervous structure in action. In every such act there is loss 

 of energy, or partial exhaustion, the cells and fibres fall 

 below par, and the equilibrium is restored by the nutrition 

 of the weakened part. Brain repair thus takes place in ac- 

 cordance with the modes of mental action^ and, as in the black- 

 smith's arm muscular nutrition is commensurate with its 

 exercise, and augments power, so in every special kind of 

 mental exercise, cerebral nutrition co-operates to raise the 

 standard of nervous power. As waste accompanies exer- 

 cise, and repair follows waste, the nutrition of the organ 

 is determined by the modes of mental activity — given asso- 

 ciations and ideas become patterns, as it were, in con- 

 formity to which the brain is moulded. In this way the 

 organic processes re-enforce mental acquisition, and as- 

 similation tends to perpetuate states of feeling and modes 

 of thought and action. Throughout infancy, childhood, 

 and youth, when nutrition is in excess, the brain is thus 

 adapted to its circumstances, and grows to the order of im- 

 pressions and ideas which it receives. 



We have seen that the office of volition is to determine 

 the course of thought and direct bodily actions to specific 

 ends. This capability is the noblest element of our nature, 

 but is greatly variable in different individuals by habit and 

 constitution, and is inexorably limited in all. The will is 

 not an absolute despot, with unbounded authority to do 

 what it lists, but rather a constitutional President, exercis- 

 ing vast power, it may be, but strictly subject to the laws 

 of the organic state. Its regnant prerogative, as we have 

 seen, is that of controlling the attention, by which it is 

 enabled to wield the entire energy of the organism to the 



