HYGIENE OF THE NERVOUS SYSTEM 323 



giving any particular thought to them, and perhaps with- 

 out knowing that we do make the necessary movements 

 in the same succession, time after time. In such a case 

 the first muscular contraction (as, for instance, the first 

 voluntary motion after we have decided to retire to rest) 

 is the setting in motion of a chain of events, each of which 

 follows without thought from the sensation of the pre- 

 ceding muscular contraction. To change the order of the 

 movements costs a definite effort, as when we decide for 

 some reason to put on or off the left shoe first, when we 

 have formed a habit of putting on or off the right one 

 first. 



469. Character. --It is the habits acquired which deter- 

 mine character. What a man has made himself by the 

 time he is twenty-five or thirty years of age, through the 

 pathways formed in the plastic substance of his brain, 

 such he is almost sure to remain to the end of life. In 

 many cases habits are by that time so strong that they 

 cannot be changed. The brain seems to have become har- 

 dened, " set," so that new channels for nervous impulses 

 can no longer be made. Even earlier in life many habits 

 of daily practice have usually become unchangeably 

 formed. The methods of speech, especially the idioms of 

 ordinary conversation, for one's whole life, are those ac- 

 quired in childhood. A man may become learned, pol- 

 ished, and scholarly in prepared or written productions 

 while still retaining in daily familiar speech rude and 

 uncultivated expressions learned in early years. It would 

 be too much to say that even fixed habits cannot be 

 changed, but to accomplish a change requires an amount 

 of determination and persistence not common among men. 



470. To build into the material substance of the nerv- 

 ous system a tendency to do right and wise acts in the 



