742 CORTICAL MOTOR REGION. [BOOK m. 



area,' as we may call it, of the right hemisphere is stimulated, it 

 is the left fore limb which is moved ; and so with the other areas ; 

 it is only in exceptional cases, as in certain movements of the 

 eyes, that the effect is bilateral ; a movement confined to the 

 same side as that stimulated is never witnessed. 



The results are most clear when the current employed as a 

 stimulus is not stronger than is just sufficient to produce the 

 appropriate movement (roughly speaking an interrupted current 

 just perceptible to the tongue of the operator is in ordinary 

 cases a useful one), and when the cortex is in good nutritive 

 condition. In any experiment the results obtained by the 

 earlier stimulations, soon after the cortex has been exposed, are 

 the best ; after repeated stimulations the surface is apt to become 

 hyperaemic, and it is then frequently observed that the move- 

 ments resulting from the stimulation of a particular area are not 

 confined to the appropriate muscles, but spread to the corre- 

 sponding muscles of the opposite side, then to muscles connected 

 with other cortical areas, and at last to the muscles of the body 

 generally ; at the same time the movements lose their distinctive 

 purposeful character and the animal is thrown into convulsions 

 of an epileptiform kind. It not unfrequently happens that an 

 experiment has to be stopped in consequence of the onset of 

 these epileptiform convulsions. The response of movement to 

 stimulation may be observed while the animal is under the 

 moderate influence of an anaesthetic, but a too profound anaes- 

 thesia lessens or annuls the effects. 



In order to carry out a closer analysis of the phenomena it is 

 desirable to watch or record the contraction of a particular group 

 of muscles, or perhaps better still a particular muscle, e. gr. the 

 area for extension of the hind limb may be studied by help of the 

 extensor digitorum communis of the limb. When this is done 

 the following important facts may be observed. The area of 

 cortex having been found which gives the best movements, and 

 the stimulus being no stronger than is necessary, isolation of the 

 area from its lateral surroundings by a circular incision carried to 

 some little depth will not prevent the development of contrac- 

 tions in the muscle ; but these do cease, even without the 

 circular incision, if by a horizontal section the grey cortex is 

 separated from the subjacent white matter. After removal of 

 the cortex, stimulation of the white matter underlying the area 

 produces the appropriate contraction ; not only however is a 

 stronger stimulus necessary, but also the latent period, that is 

 the time intervening between the beginning of the application 

 of the stimulating current and the beginning of the muscular 

 contraction is appreciably shortened. The appropriate contrac- 

 tions not only appear when the white matter immediately below 

 the cortex is stimulated, but by making successive horizontal 

 sections and stimulating each in turn, the effect may, so to 



