514 PHYSIOLOGY 



they were before the lesion. The amount of impairment of intelligence 

 will vary in different cases according to the extent of the lesion. 

 Thus softening generally affecting the occipital lobe may, with 

 hemianopia, cause ' word-blindness,' or alexia, a loss of power 

 Amentia Dementia 



(3) 



(4) 



(5) 



FIG. 233. Types of lesions giving rise to deficient intellectual power. 

 In amentia, the deficiency is due to failure of development; in 

 dementia, to atrophy of the cells (especially small pyramidal) 

 previously present in the cortex. (MoTT.) 



of appreciating the meaning of pronounced or written words. In 

 most individuals, and certainly in the uneducated, this power may 

 be cut out altogether without interfering considerably with the 

 mental powers. On the other hand, from babyhood upwards we 

 have learnt the meaning of words and their grouping by auditory 

 impressions. If the whole of the auditory associations be destroyed 

 by an extensive lesion in the first and second -temporal convolutions 



