CEREB RAL COR TEX SENS A TION. 26 1 



meaning of a bone, or the use to which it may be put ; he may 

 hear the crack of a whip, but he no longer shows signs of 

 fear, for he does not remember its sting ; his former purpose- 

 ful behavior has entirely disappeared ; in short, he has lost 

 memory and judgment." WALLER. 



In an earlier chapter we learned that the cortex (gray mat- 

 ter of the outside of the brain) is the central organ of intelli- 

 gent sensation and motion. The functions of Volition, of 

 Consciousness, of Intelligence, seem to reside in, or rather to 

 depend upon the activities of, the cells of the gray matter of 

 the convolutions of the cerebrum. This we have learned from 

 experiments on the lower animals, and from accidents and dis- 

 ease in the case of man. All sensation seems to be in the 

 gray matter of the convolutions of the cerebrum, and yet it is 

 itself insensible ; it may be cut and cause no sensation. But 

 when the nerve impulses from the various parts of the body 

 reach the gray matter of the cerebrum, they rouse the cells 

 here to an activity that gives us what we call sensation. It is 

 never a sensation until it reaches this part, and -is properly 

 interpreted. 



While each hemisphere mainly controls the muscles of the 

 opposite half of the body, it also, in part, has control of its 

 own side. Paralysis of one side (hemiplegia) is due to injury 

 of the opposite cerebral hemisphere. 



Much has been learned of late years as to the location of 

 special functions in the brain. Many of the motor centers 

 have been determined in the following manner : In some of the 

 lower animals the brain has been exposed, and on stimulat- 

 ing certain portions with an electric current, the movements 

 that followed were noted. In apes, "particular movements 

 of the arm, forearm, hand, and thumb can be produced by 

 excitation of particular spots, almost as regularly as definite 

 notes can be sounded on a piano by touching particular keys." 



