CEREBR \l. I 01 ILIZATIO B 15 



called the indifferenl electrode and consisting of a flal pi eing 



placed on some other pari of the body, Buch as the Bkin of the back. Tliis 

 unipolar method gives much finer results than when the ordinary bipolar 

 electrodes are employed. 



Before we describe the results which have been obtained by the u 

 nf this method, a question arises which if may be well to consider 

 briefly; namely, how do we know thai the electric currenl is really stimu- 

 lating the center presenl in the gray matter of tl . and not 

 the numerous nerve fibers thai constitute the white matter <>f the brain 

 and along which, between the two electrodes, it is plain some of the 

 electric currenl musl pass? The evidence thai we are really stimulating 

 miters is as follows: I The latenl period for a response produced by 

 stimulating the centers is much longer than that which follows upon di- 

 rect stimulation of the white matter. '_' Under deep narc that 



produced by chloral or morphine, tl ffed >f stimulation of the gray 



matter is greatly delayed and altered in type; whereas stimulation <»t' the 

 white matter gives the usual response. (3 A weaker current suffices to 

 stimulate the gray matter than thai required for the exposed white 

 matter. 



Tn order to demonstrate the movements which follow stimulation 

 the cerebral <-<>)-i<>x, [\ is necessary, as will be inferred from the p 

 ceding remarks, thai the animal be nol too leeply anesthetized! Pur- 

 thermore, it is necessary to ho very careful in adjusting the strength 



of stimulati mployed, for the results vary considerably accordingly. 



Winn the stimulus is of the proper intensity, the movements are Iocj 

 in some particular group of muscles, for example, those of the thumb 

 or of the hand, whereas, if the stimulation is strong, the movements 

 spread over much larger areas. As a result of feeble or moderj mu- 



lation, it is found thai the muscles which move are those of the oppos 

 side uf the body, and thai the localization is finer the higher the position 

 of the animal in the scale of development. The movements are perfectly 

 coordinate and purposeful in character, and reciprocal innervation is 

 evident. 



There is. however, a marked difference in the reactions obtained by 

 stimulation of the motor cortex and those obtained by eliciting spinal 

 reflexes. For example, the movements produced bj Btimulatii 

 cortex are much m idily modified by slight variations in 1 1 



dition of the animal, the blood supply, the degn 



are those elicited by stimulation of r iptor neuroi s. A can idy 



of this difference h.-is been made in recenl ; Bro 



rington." They observed the behavior of h 



acl ing on the elbow w hen thi 'tivc corl mil- 



