THE FORE-BRAIN 



561 



merely a physical conductor of the current to the white matter of 

 the centrum ovale, but its elements are physiologically excited, 

 and through them the excitation is transmitted to the nerve-fibres 

 (Fran^ois-Eranck and Pitres). 



This last fact can be demonstrated experimentally by comparing 

 the motor reactions evoked on exciting the cortex and those 

 obtained on exciting the subjacent white matter with the same 

 current. 



After diligent research Eran^ois-Franck and Pitres (1878-79) 

 established the fact that, generally speaking, the white matter 

 is less excitable than the grey. If, after ascertaining the 

 minimal current capable of pro- 

 ducing a given movement by 

 stimulation of the cortex the grey 

 matter is excised, and the same 

 'current applied to the white 

 matter lying immediately below 

 it, the reaction is no longer 

 obtained. It is necessary to in- 

 crease the strength of the current 

 before the movement can be 

 evoked again. 



On the other hand, the excit- 

 ability of the cortex under the 

 action of certain toxic substances 

 is more easily lost than the ex- 

 citability of the white matter ; 

 this is seen after chloral narcosis. 

 While the dog lies in the chloral 

 narcosis, even the strongest 

 stimulation of the cortex fails 

 to elicit any muscular response, 

 while stimulation of the subjacent white matter is still effective, 

 even with comparatively weak currents. This fact, first observed by 

 Francois -Franck and Pitres, and confirmed by Richet, Bubnoff and 

 Heidenhain, and de Varigny, is of great theoretical importance. 

 It seems to show that the cortical substance rendered inexcitable 

 by chloral, may w r hile preserving its physical conductivity 

 oppose an insurmountable barrier to the transmission of the 

 stimulus applied to its surface. 



Another important fact brought out by Francois- Franck and 

 Pitres is the delay in the muscular reaction, which is perceptibly 

 greater when the cortex is electrically stimulated than when the 

 electrical stimulus is applied to the centrum ovale. To avoid 

 experimental errors, or reduce them to a minimum, in demonstrat- 

 ing this fact it is necessary to operate on one and the same animal 

 by simultaneously exciting a region of the cortex and an adjacent 



VOL. in 2 o 



Fio. 284. Lost time in muscular contraction 

 on exciting the cortical centre M, and the 

 underlying white matter M'. (Franc,ois- 

 Franck and Pitres.) The middle line shows 

 the time in T^TT sec. The lower line marks 

 the application of the stimulus. In A the 

 lost time=x)nr sec. ; in B=T^ sec. 



