68 THE POPULAR SCIENCE MONTHLY. 



It was believed for a long time that the cerebral hemispheres were 

 insensible and inexcitable to direct stimulation. The Germans Fritsch 

 and Hitzig discovered, however, that parts of the cerebrum would 

 respond to a very gentle current of electricity. This beginning has 

 been carefully followed up by Ferrier, Munk, Goltz, and many others, 

 until we now have, amid much disagreement and uncertainty, some 

 results that are interesting, to say the least. 



All experiments on the cerebrum are of two kinds (stimulation of 

 the surface and destruction of the surface), and are necessarily made 

 on the lower animals. Dupuy offered an objection to experiment by 

 electrical stimulation, which, if well founded, would destroy the entire 

 value of the undertaking. He claimed that the effects produced by 

 electricity at the surface of the hemispheres were due wholly to con- 

 duction of the current through the mass to the corpora striata below 

 and so to the muscles. Dupuy proved that conduction did take place 

 through the cell-mass of the hemispheres. He placed the leg of a frog 

 in contact with the rear of a brain, and by application of electricity 

 to the front of this brain produced strong movements in the limb. 

 Ferrier's answers to Dupuy are a sufficient refutation of the objec- 

 tion. 



If the effects observed under electrical stimulation are due to con- 

 duction, we could not have (as is the case) strikingly different results 

 from application of the electrodes to very closely adjacent areas. 

 Further, when the striata themselves are stimulated, there is always a 

 general contraction of muscles on the entire opposite side of the body. 

 There is no limitation of the movements to special groups of muscles, 

 as always happens when particular centers on the brain-surface are 

 stimulated. Again, there are many portions of the brain which give 

 no response to electrical stimulus. How can this be so if such move- 

 ments as are produced result from conduction, especially since many 

 of these silent regions of the brain are no more remote from the striata 

 than the responsive ones ? 



Experiment and pathology, despite all the contradictions, seem to 

 point to the existence of a motor zone on the surface of the hemi- 

 spheres. This means that certain parts of the brain are directly con- 

 cerned with the movements of particular muscles and groups of mus- 

 cles ; also, that these parts can not be shown to be connected with 

 sensations. The natural, primary occasions of their activity may be 

 the states of consciousness which we call volitions ; they are not, so 

 far as evidence goes, the states of consciousness we call sensations. 



It is of interest to observe that these motor regions are situated in 

 the anterior portions of the hemispheres, and occupy here a relatively 

 small space. They lie above the Sylvian fissure, and are mostly on the 

 fourth frontal and ascending parietal convolutions. 



The experiments have been performed on a great variety of ani- 

 mals, and repeated a large number of times. The monkey is, of course, 





