THE CENTRAL NERVOUS SYSTEM ?$S 



as has been asserted, of the white fibres of the corona radiata. It is 

 undoubtedly possible to excite these fibres by electrodes directly 

 applied to the motor cortex, but in the latter case the current has 

 to be made stronger than is sufficient to excite the grey matter 

 alone. Further evidence is afforded by the following facts : (a) The 

 * period of delay,' that is, the period which elapses between stimula- 

 tion and contraction, is greater by nearly 50 per cent, when the 

 cortex is stimulated than when the white fibres are directly excited. 

 (fr) Morphia greatly increases the period of delay for stimulation of 

 the cortex, and at the same time renders the resulting contractions 

 more prolonged than normal, while the results of direct stimulation 

 of the white fibres are much less, if at all, affected, (c) Mechanical 

 stimulation of the motor areas also causes appropriate movements. 

 (</) Stimulation of the grey matter, when separated from the sub- 

 jacent white matter by the knife but left in position, is without 

 effect unless the strength of stimulus be increased, although twigs of 

 the current ought, of course, to pass into the corona radiata as easily 

 as before. 



Evidence that the phenomena are not due to accidental excitation 

 of the corona radiata is a fortiori evidence that they are not caused, 

 by escape of current to the basal ganglia, for the distance of the 

 basal ganglia from the larger part of the motor cortex is much 

 greater than the thickness of the grey matter ; and, indeed, that portion 

 of the grey matter at the bottom of the Sylvian fissure which lies 

 nearest to the basal ganglia does not respond to stimulation by motor 

 effects. 



When we have deducted from the cortex of the hemi- 

 sphere the whole Rolandic region and the sensory centres, 

 there still remains a large territory unaccounted for. Con- 

 siderable portions of the occipital, parietal and temporal 

 lobes, nearly the whole of the island of Reil and the greater 

 part of the frontal lobe anterior to the ascending frontal 

 convolution are ' silent areas,' and respond to stimulation 

 by neither motor nor sensory sign. By a process of exclu- 

 sion it has been supposed that they are the seat of intel- 

 lectual operations. This function has been more particularly 

 assigned to the frontal lobes, but we have little real know- 

 ledge to guide us to a decision. Extensive destruction and 

 loss of substance of the pre-frontal region may occur without 

 any marked symptoms, except some restriction of mental 

 power or loss of moral restraint. Thus in the famous 

 ' American crowbar case,' an iron bar completely transfixed 

 the left frontal lobe of a man engaged in blasting. Although 

 stunned for the moment, he was able in an hour to climb a 



