Psychical Nerve Force 163 



or the individual becomes mentally blind; that 

 is, he can still see, as appears from his fol- 

 lowing objects moved in front of his eyes 

 and avoiding obstacles placed in his path, 

 but he no longer recognises what he sees. 

 The dog no longer crouches when threatened 

 with a whip or attempts to avoid a stone thrown 

 at him ; the man stares at the most familiar 

 objects as if they were wholly unknown to him, 

 and recognises them only when he touches 

 them. Again, the auditory sensory cortical 

 centres are located in well-defined areas of the 

 cerebral hemispheres (Fig. 17). The func- 

 tions performed by a part of their living sub- 

 stance is to retain the impression made on them 

 by word sounds spoken by another person ; this 

 part is recognised as constituting our auditory 

 word centres. When these charged centres are 

 re-excited, part of their energy is released, and 

 extends to the motor centres which order the 

 action of muscles controlling the vocal ap- 

 paratus. If, however, these auditory word 

 centres are destroyed by disease, the latent 

 word sounds established upon them perish and 

 cannot be replaced, and a person affected in 



