CHAP. IL] THE BRAIN. 1037 



it i.s 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 a 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 ex- 

 periment 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 movements resulting from the 

 stimulation of a particular area are not confined to the appropriate 

 muscles, but spread to the corresponding 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 anaesthesia 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 tne 

 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 contractions 

 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 appre- 

 ciably shortened. The appropriate contractions 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 speak, be traced through the central 

 white matter of the hemisphere down to the internal capsule. 

 We may conclude from these results, that when the current is 

 applied to the surface of the cortex, certain parts of certain struc- 



