CHAP, vi.] THE BRAIN. 629 



composed of so-called 'sensory 'centres, a term even more objection- 

 able than 'motor' centres. 



Confining ourselves for the present to the areas, stimulation of 

 which produces movements, the question naturally presents itself, 

 Do events of importance take place in the grey matter itself 

 when stimulated, or is it that either by stimulation of the fibres of 

 the white matter, or by simple escape downwards of the current 

 employed as a stimulus, the parts below, such as the corpora striata, 

 are stimulated, and that the shaping of the movements according 

 to the locality operated on is effected in these lower parts and not 

 at the surface itself? On this point considerable controversy 

 has taken place. On the one hand it seems clear that localization 

 of function, that is to say the occurrence of definite movements as 

 the result of stimulation of definite parts, may take place in the 

 regions of the brain below the cortex, since the appropriate move- 

 ments follow upon stimulation of the several cortical areas, when 

 the grey matter has been removed, or rendered functionally incapa- 

 ble by treatment with acids and the like, or separated functionally 

 from the white matter below by an incision parallel with the surface; 

 and definite movements have been even obtained by stimulation 

 of definite parts of the surface of the corpora striata. On the 

 other hand, we have adequate evidence that when movements in a 

 muscle or group of muscles are produced by stimulation of an area of 

 the surface of the cerebrum, the movements differ in character, for 

 instance in the length of the latent period, the form of the muscle 

 curves, &c. according as the stimulus is applied to the intact cortex 

 or to the underlying white matter. Further the irritability of the 

 grey matter, falling and rising with the condition of the animal, 

 is much more variable than is that of the white matter ; and while 

 under certain circumstances stimulation of the grey matter is apt 

 to give rise to general epileptiform convulsions, stimulation of the 

 white matter rarely if ever produces such an effect. Without 

 discussing the matter any more fully we may say that the preponde- 

 rating evidence seems clearly in favour of the view that when the 

 grey matter is stimulated, some events of an important kind do 

 take place in the grey matter itself; in other words, we have 

 evidence of a localization of function in the cortex, inasmuch as 

 when a given area of the cortex is stimulated the movements in a 

 definite group of muscles which result are in part at least due to 

 changes taking place in the grey matter itself of that area. 



If such is the case, if events of importance having an especial 

 connection with certain muscles result from the stimulation of 

 a given area, it is only reasonable to conclude that in actual life 

 more or less similar events, having similar relations to the muscles, 

 take place in the area from time to time. Further it seems also 

 reasonable to suppose that these events are of such a kind that the 

 area may be regarded as a 'point d'appui' by which will and 

 intelligence are brought to bear on the muscles corresponding 



