THE NERVOUS SYSTEM 105 



a certain meaning, when combined in a definite way, 

 which always conveys the same idea to one's mind. Edu- 

 cation, therefore, would be, in this sense, simply the 

 formation of certain habits; and as the frequent repeti- 

 tion of the same act leaves each time a firmer impress on 

 the mind, the habit may finally become automatic and be 

 performed without definite consciousness. As the 

 thoughts of at least a large majority of mankind are al- 

 ways dependent on sensations received from without, it 

 is apparent that without the association areas the high- 

 est intellectual functions, which are entirely dependent 

 on such associations, can not be performed; and it fol- 

 lows that disturbance in any of the areas, or in the con- 

 ducting paths which lead between them, may give rise 

 to an interruption of function, or at least such a dis- 

 turbed condition, that connected thought becomes im- 

 possible. Temporarily such an interruption occurs in 

 the delirium of illness and permanently in various types 

 of insanity. Neither is it surprising that parts of an 

 area alone may be affected. Thus a symptom of "word 

 blindness" may, and does occur in which there is a com- 

 plete failure to recognize printed or written words 

 though speech is not affected. 



The association areas referred to must not be con- 

 founded with those fibers the corpus callosum which 

 run between the two halves of the cerebrum and associ- 

 ate, or coordinate, the action of similar centers, for ex- 

 ample, make the centers for the two upper extremities 

 act in concert, as in swimming. 



The most widely scattered, and one of the most im- 

 portant, association areas is that called the "language 

 area." In order that the fullest use may be made of a 

 language, it must be spoken, heard, written and read. 

 This necessitates not only the highly specialized nerves 



