158 



THE POPULAR SCIENCE MONTHLY. 



inent of the study of cortical localization, and indeed for the 

 removal of psychology from the realm of speculation to that of 

 scientific demonstration. 



The method of removing certain cortical areas of the brain 

 and then noting the effect is termed the extirpation method ; it 



was by this method, practiced 

 upon monkeys, that Prof. Scha- 

 fer, of London, and myself estab- 

 lished the position of the center 

 for vision in that animal. The 

 monkey's brain is so similar to 

 the human brain that with some 

 modification results may be trans- 

 ferred from one to the other. 



Fig. 8 shows the part of the 

 monkey's brain which, when re- 

 moved, produces blindness in the 

 corresponding half of each eye, 

 and Fig. 9 shows the parts which, 

 when removed, produce complete 

 and permanent blindness in both 

 eyes. Now, while the positions 

 of the areas for the other sjjecial 

 senses have not been so satisfac- 

 torily demonstrated, the exist- 

 ence of such centers can not be 

 doubted. 



With these data, and the aid 

 of Fig. 10, a fundamental step in 

 the process of mental develop- 

 ment may be investigated. 



By way of the route as indi- 

 cated in the figure, an impression 

 made upon a specially construct- 

 ed end organ, the eye, is trans- 

 mitted along the cell process con- 

 stituting the optic nerve, and so 

 onward till it reaches a cell, or 

 probably cells, in the occipital 

 lobe ; thence by means of the communicating fibers constituting 

 the white matter, and previously described, the arm center is ex- 

 cited and a motor impulse passes out to the muscles moving the 

 arm, and the hand is put into the flame ; immediately a second 

 impression is conveyed inward to the pain center and thence to 

 the arm center, from which a second impulse emanates, resulting 

 in a withdrawal of the hand. Finally, after one or more experi- 



Fn;. 4. 



