428 THE NERVOUS SYSTEM. 



definite muscular contraction ; and yet the application of the electrodes 

 to neighboring spots, not more than five millimetres distant from the 

 first and equally near the base of the brain, may be without effect. Fer- 

 rier * has found, in experiments on monkeys, that stimulation of the con- 

 volutions of the insula, which lie in close proximity to the corpus stri- 

 atum, produces no visible result ; while that of the more distant con- 

 volutions in the motor region on the surface of the hemisphere causes 

 an immediate and definite movement. Lastly, decisive proof is sup- 

 plied by the experiments of Braunf and Putnam.| In these experi- 

 ments points were found on the cerebral convolutions where electric 

 stimulus produced the usual definite muscular contractions. A hori- 

 zontal section was then made one or two millimetres beneath the 

 surface, leaving the flap in place but cutting off the anatomical con- 

 tinuity of brain tissue. The irritation, then reapplied to the original 

 spot, failed to excite muscular contraction ; but if the flap were turned 

 up and the electrodes applied to the cut surface beneath, a current of 



FIG. 114. 



S' 



BRAIN OF THE DOG; profile view, showing centres of motion in the convolutions. F. Frontal 

 fissure. S. Fissure of Sylvius. 1. Flexion of head on neck, in the median line. 2. Flexion of 

 head on neck, with rotation toward the side of the stimulus. 3, 4. Flexion and extension of 

 anterior limb. 5, 6. Flexion and extension of posterior limb. 7, 8, 9. Contraction of orbicularis 

 oculi and other facial muscles. 



similar or slightly increased strength produced the same movements 

 as before. Repeated trials of this kind, the flap being alternately 

 removed and readjusted, yielded the same results. It is evident, 

 therefore, that when the electrodes, applied to the surface of the unin- 

 jured brain, cause movements on the opposite side of the body, this is 

 due not to a diffusion of the electric current toward the base of the 

 brain, but to a nervous stimulus originating in the convolutions, and 

 thence transmitted by the fibres of the white substance. 



The reality of the motor centres in the cerebral convolutions is cor- 

 roborated by other important facts of two kinds. 



First. The cortical substance of the region in question has a special 



* The Localization of Cerebral Disease. London, 1879, p. 17. 

 f Centralblatt fiir die medicinischen Wissenschaften. Berlin, June 13, 1874, p. 

 455. 



J Boston Medical and Surgical Journal, July 16, 1874. 



