LOCALIZATION OF THE CEREBRAL FUNCTIONS. 645 



whether a comparatively restricted portion of the cortex suffices 

 for the performance of all the functions of the hemispheres, are 

 questions surrounded with difficulty, and which, up to the pre- 

 sent, cannot be answered with any degree of certainty. The 

 experimental evidence hitherto brought forward on the subject 

 seems, in many points, to be contradictory, a fact which may be 

 explained partly by the difficulties with which such experiments 

 are beset, and partly by different observers being anxious to 

 uphold with too great fervor either the localization or non-local- 

 ization theory in their entirety. 



The leading experimental experiences which have been 

 recorded are the following : 



1. Extensive tracts of the cortex of the hemispheres may be 

 removed, by accident or experiment, without interfering with 

 the cerebral functions in any marked or tangible way. Both 

 men and animals have lived for years, after the loss of a con- 

 siderable quantity of brain substance, without showing impair- 

 ment of either mental or bodily faculties. 



2. Lesion of a certain part of the frontal lobe of the left hemi- 

 sphere of man (posterior part of the third frontal convolution) has 

 been so frequently followed by the loss of the faculty of speech 

 aphasia that pathologistsnow call that spot the centre of speech. 



3. Destruction of the convolutions around and in the neigh- 

 borhood of the fissure of Rolando gives rise to temporary loss of 

 power in the limbs of the other side, voluntary motion being 

 abolished when an extensive area is destroyed. This loss of 

 power is more obvious in animals with complex brains (man and 

 monkey) than in those less highly organized (dog, cat, rabbit), 

 which rapidly recover. 



4. Destruction of the surface of the posterior lobes interferes 

 with the reception of visual impressions, and if an area including 

 the angular gyri and all the posterior lobes be destroyed, the 

 animal remains blind. 



5. Extensive areas of the brain surface may be stimulated 

 mechanically, chemically, or electrically, without the least 

 response being shown by the animal, to indicate either sensory 

 or motor excitations. 



