142 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



and speech elaboration. It would be aside from the 

 purpose of this discussion to describe the effects of 

 disease in different regions of the cerebrum. A vast 

 accumulation of careful observations has enriched 

 cerebral pathology, and from it there has sprung up a 

 science and an art of cerebral localization which has 

 been of the utmost service to medicine. But many 

 of the local defects of the brain are of interest chiefly 

 for their effect on functions other than mental, such 

 as motion, hearing, and vision. All I desire to point 

 out here is that each hemisphere of the brain is 

 related mainly to the opposite side of the body, and 

 that each hemisphere may be roughly divided into a 

 posterior area, carrying on in part the functions of 

 perceptive discrimination, and an anterior area (in 

 front of the fissure of Rolando), subserving the final 

 elaboration of executive activity or motion. A 

 variety of circumscribed defects in different parts of 

 the cerebral cortex lead to special disorders of func- 

 tion, as when a loss in the occipital cortex of one hemi- 

 sphere causes half blindness in each eye, or when 

 the defects in hearing centers in the temporal region 

 cause an inability to understand spoken words and 

 even the loss of ability to arrange words discrim- 

 inately in spontaneous thought and speech. Fre- 

 quently, also, there are defects of combination or 

 elaboration in which the correlation of the auditory, 

 visual, and labile components of speech or thought is 

 involved. Such an involvement interferes pro- 

 foundly with the general powers of the individual to 



