CENTRAL NERVOUS SYSTEM. 683 



Earlier Observations. It was demonstrated by Fritsch and Hitzig in 

 1870 ] that if a constant current was applied to the surface of the dog's brain, 

 it was possible by interrupting it to obtain movements of the limbs and face 

 when the electrodes were placed on certain parts of the cerebral cortex, and 

 the reaction varied according to the place of stimulation, a constant rela- 

 tion subsisting between the two. From this time on, active investigations 

 of the relations thus suggested have been pursued, both by stimulating small 

 areas in the cortex of various animals, including the monkey and man, and 

 by the removal of various parts of the cerebral hemispheres and cortex, 

 together with the study of the effects of pathological lesions in man. The 

 results following removal of parts are complicated by the transitory effects 

 of the lesion, and can best be treated by themselves later on. The results 

 following the stimulation of the cortex are the simplest, and will next be 

 described. 



Stimulation of Cortex. The common method of experiment is to apply 

 the faradic current by means of fine but blunt electrodes, the ends of which 

 are but two or three millimeters apart, to the exposed surface of the cerebral 

 hemispheres, the pia being undisturbed. Rabbits, dogs, and monkeys have 

 been the animals most commonly studied. 



If the current be slight, its application for one or more seconds causes a 

 response in the shape of movements of muscles, which are thrown into co- 

 ordinated contraction. The contraction continues for some time after the 

 stimulus has been removed. When the stimulus is very strong, instead of a 

 limited and co-ordinated response, there may be a widespread contraction of 

 many muscles, resembling an epileptic convulsion. This, however, occurs 

 more commonly in the lower than in the higher mammals. On the other 

 hand, the irritability of the cortex is easily reduced, so that it becomes irre- 

 sponsive, and often immediately after the first exposure of the brain there is a 

 time during which a response cannot be obtained. 



Turning to the areas of the cortex which are occupied by the extension of 



FIG. 182. Lateral view of a human hemisphere. The cortical visual area on this aspect is shaded ( V). 



the pathways from the special sense-organs, it is found that the visual area 

 alone exhibits any elaboration when examined by the method of stimulation. 



1 Archivfur Anatomic und Physiologie, 1870. 



