32 PSYCHOLOGY. 



electrodes to a point close by ou tlie surface changes tlie 

 movement in ways qnite inexplicable by changed physical 

 conduction of the current; c) if the cortical ' centre' for a 

 certain movement be cut under with a sliarj) knife but left 

 in situ, although the electric conductivity is physically 

 unaltered by the o2:)eration, the ^physiological conductivity 

 is gone and currents of the same strength no longer pro- 

 duce the movements which they did ; d) the time-interval 

 between the application of the electric stimulus to the cor- 

 tex and the resultant movement is what it would be if the 

 cortex acted physiologically and not merely physically iu 

 transmitting the irritation. It is namely a well-known fact 

 that when a nerve-current has to pass through the spinal 

 cord to excite a muscle by reflex action, the time is longer 

 than if it passes directly down the motor nerve : the cells- 

 of the cord take a certain time to discharge. Similarly, 

 when a stimulus is applied directly to the cortex the muscle- 

 contracts two or three hundredths of a second later than it 

 does when the place on the cortex is cut away and the elec- 

 trodes are applied to the white fibres below.* 



(2) Cortical Ablations. When the cortical spot w^hich ia 

 found to produce a movement of the fore-leg, in a dog, 

 is excised (see spot 5 in Fig. 5), the leg in question becomes 

 peculiarly afi'ected. At first it seems paralyzed. Soon, how- 

 ever, it is used with the other legs, but badly. The animal 

 does not bear his weight on it, allows it to rest on its dorsal 

 surface, stands with it crossing the other leg, does not remove 

 it if it hangs over the edge of a table, can no longer 'give the 

 paw' at word of command if able to do so before the opera- 

 tion, does not use it for scratching the gi-ound, or holding a 

 bone as formerly, lets it slip out when lunning on a smooth 



* For a thorough discussion of the various objections, see Ferrier's 

 'Functions of the Brain,' 2d ed., pp. 227-334. and Fran^ois-Franck's 

 • Lecons sur les Fonctions Motrices du Cerveau ' (1887), Legon 31. The most 

 minutely accurate experiments on irritation of cortical points are those 

 of Pauetli, iu Ptiliger's Archiv, vol 37. p. 528. — Recently the skull has been 

 fearlessly opened by surgeons, and operations upon the human brain per- 

 formed, sometimes with the happiest results. In some of these operations 

 the cortex has been electrically excited for the purpose of more exactly 

 localizing the spot, and the movements first observed in dogs and monkeys 

 have then been verified in men. 



