560 PHYSIOLOGY CHAP. 



and Fritsch. They afford a general experimental proof of the 

 functional specialisation of different regions of the cerehral cortex, 

 while telling us nothing definite about the function of the excitable 

 as compared with the non-excitable areas. 



The objections raised against the value of the results obtained 

 by electrical stimulation of the cortex do not all stand criticism 

 and analysis. Carville and Duret, Onirnus, Dupuy, and others 

 showed experimentally that the electrical currents applied to the 

 cortex spread, more or less in proportion to their intensity, both 

 superficially and deeply beyond the area between the electrodes. 

 They concluded that the motor reactions aroused by electrical 

 excitation of the cortex are not sufficient proof either of its 

 excitability or of functional localisation, since they may be 

 interpreted as the effect of spread of current toward the basal 

 ganglia, pons, and bulb, where there are nerve elements that are 

 readily excitable. 



But it must be remembered that : 



(a) The motor reactions confined to given groups of muscles 

 can also be obtained with mechanical stimulation, which does not 

 spread, but remains strictly localised to the regions directly 

 involved (Luciani). 



(//) The effects of electrical excitation are quite definite. The 

 slightest shift in the position of the electrodes produces quite a 

 different reaction ; so soon as they are applied to the anterior 

 frontal or occipital regions all reaction ceases, even when the 

 strength of the stimulus is greatly increased (Hitzig, Ferrier). 



(c) The convolutions of the island of Keil, though they lie 

 immediately above the corpus striatum, are absolutely inexcitable, 

 while the central or Rolandic convolutions, which are more remote 

 from the basal ganglia, yield with the same current very definite 

 reactions varying at different points of the gyri (Ferrier, Griinbaum, 

 and Sherrington). 



(d) If the cortex of the postcruciate portion of the sigmoid 

 gyrus of the dog, which contains centres from which the muscles 

 of the limbs on the opposite side can be excited, lie cut with a 

 sharp knife, leaving the incised strip in position, the usual reactions 

 are no longer obtained on electrical stimulation, although electrical 

 conductivity has not been altered by the incision (Luciani and 

 Tamburini). 



(e) If after destruction of the excitable centres for the dog's 

 limbs the subjacent white matter is excited, the usual reactions 

 are obtained ; but if at the end of a few days the brain is again 

 exposed, and the current applied to the bottom of the wound, no 

 reaction will lie obtained, although the physical conditions of 

 electrical diffusion are unchanged (Albertoni and Michieli). 



(/) The cortical grey matter which yields motor reactions on 

 application of an electrical current is truly excitable ; it is not 



