THE FUNCTIONS OF THE CEREBRUM. 273 



bell, becomes stored away in nerve cells lying in or close to that 

 center, and when the bell is moved sound memories are likewise 

 stored in the auditory center. At first these remain as -isolated 

 memory impressions and the animal is unable to associate the 

 sight with the sound of the bell But later, with repetition, the 

 visual and the auditory centers become linked together, through 

 nerve cells and fibers which occupy the associational areas, so 

 that the invocation of one memory is followed by association 

 with others. It is evident that the intricacy of this interlace- 

 ment of different centers will, in large part, determine the in- 

 tellectual development of the animal, and the possibility of his 

 learning to judge of all the consequences that must follow every 

 impression which he receives or every act which he performs. 

 In man these associational areas are very poorly developed at the 

 time of birth, so that the human infant can perform but a few 

 acts for itself. Everything has to be learned, and the learning 

 process goes hand in hand with development of the associational 

 areas, which proceeds through many years. On the other hand, 

 most of the lower animals are born with the associational areas 

 already laid down and capable of very little further increase, 

 so that, although much more able, than the human infant, of 

 fending for itself at birth, the lower animal does not afterwards, 

 develop mentally to the same extent. 



The practical application of these facts concerning the func- 

 tions of different areas of the cerebrum is in the study of mental 

 diseases. To serve as an example we may take aphasia. This 

 means inability to interpret sights or sounds or to express the 

 thoughts in language. In the former variety called sensory 

 aphasia the patient can see or hear perfectly well, but fails 

 to recognize that he has seen or heard the object before. He 

 fails to recognize a printed word (word blindness) or to in- 

 terpret it when spoken (word deafness). The lesion responsible 

 for this condition is located in the associational areas and not 

 in the centers themselves. In the other variety, called motor 

 aphasia, the patient understands the meaning of sounds or 

 sights, of spoken or written words, but is unable to express his 

 thoughts or impressions in language. The lesion in this case in- 



