778 THE POPULAR SCIENCE MONTHLY. 



it also becomes mute, unless special educational measures are em- 

 ployed ; and in adults destruction of the auditory center inter- 

 feres sadly with talking, while destruction of the motor speech 

 center does not seem to interfere at all with the understanding of 

 speech. 



When reading is first undertaken, the auditory and motor 

 speech centers with their association fibers are already well de- 

 veloped. The visual center, V, now begins to work with them. 

 When impulses from the eyes reach this center, the sensation of 

 sight occurs. The appearance of each letter calls up the memory 

 of its sound through the association fibers, V A, and a number of 

 these elementary sounds uttered in quick succession are recog- 

 nized by the learner as a word. Its meaning is awakened by the 

 auditory center, and at first it is necessary to read aloud in order 

 to make the association impulses from this center sufficiently 

 exact and vigorous. Later, the memories of the sound and of its 

 utterance suffice without its actual reproduction, but in most per- 

 sons these memories remain an essential part of the reading pro- 

 cess throughout life. As this is read, the reader is doubtless con- 

 scious of the sound and of the incipient utterance of each word. 



In learning to write, the motions of the hand become auto- 

 matically associated with the memory of the corresponding utter- 

 ance. It might be supposed that in writing the appearance of 

 each word is recalled and copied ; but this is not the case, al- 

 though the visual memory may be an aid to correct spelling. 

 Words may be written with no recollection of their appearance. 



The correctness of the foregoing statements is proved by the 

 effects of disease of the language centers, as shown by observation 

 of speech defects during life, followed by post-mortem examina- 

 tion of the brain. 



Destruction of the visual centers of both sides causes blindness ; 

 but when these centers themselves are unharmed, disease may be 

 so situated as to cut off their communication with other centers. 

 In this case the patient sees, but does not recognize what he sees, 

 and is said to be mind-blind. If the affection is so slight that he 

 can still recognize ordinary objects, but not written or printed 

 words, which are more difficult, he is only word-blind. To a per- 

 son afflicted with word-blindness the print of his own language is 

 like that of a foreign one. George Eliot, with her usual sure 

 touch in medical matters, gives an interesting illustration of this 

 affection in the case of Tito's foster-father, Baldasarre ; yet Ro- 

 mola was finished in 1863, when very few physicians were aware 

 of the existence of such cases. Reading in such a case is, of 

 course, impossible ; but writing is not prevented, although the 

 patient can not read what he has just written. Speaking and the 

 understanding of speech are not interfered with at all. 



