6o4 THE POPULAR SCIENCE MONTHLY. 



the center imder experiment. Here electricity provokes movements of 

 the leg on the opposite side, owing to the cross-action of the hemi- 

 spheres. It moves as if to go forward ; or the movement may be 

 limited to the foot, or even the great-toe. Sometimes the motions are 

 still more complex, and involve many muscles, as if the animal would 

 scratch its breast or press against it some object which it had taken 

 from the ground. Again, it is the arm, forearm, or hand that moves 

 in various ways, and to different ends ; sometimes there is a com- 

 bination of movements, like those required for swimming or prehen- 

 sion ; the fingers may lock together with force, as if to retain an ob- 

 ject, or extend themselves with a lively movement, as if to scatter 

 something. It is probable that, if our instruments were more per- 

 fect, we should find in each center a number of subordinate centers 

 for the execution of single movements, or the moving of a single 

 muscle. 



The general idea of the relations of the brain and spinal cord is 

 that the brain commands and the cord obeys. The brain requires such 

 or such a movement, and the cord, working unconsciously, coordinates 

 the elementary and individual movements required to produce the de- 

 sired effect. Electrizing the centers is the same as issuing an order 

 to the cord, not of directly exciting movement. 



Monkeys being difficult to obtain in our climate, to satisfy the con- 

 stant needs of experiment, Ferrier operated upon dogs, jackals, Indian 

 pigs, rats, pigeons, frogs, fishes, anything that was going. These ex- 

 periments fully confirmed the results otherwise obtained, and showed, 

 besides, that the action of the hemispheres is of less importance as we 

 descend in the animal scale, while automatism rises. 



Ablation of a limited portion of gray matter of the brain leads 

 to the same conclusions as electrization. It produces paralysis, and 

 monkeys rarely or imperfectly recover from these lesions, while infe- 

 rior animals, as the rabbit and Indian pig, recover ; thus showing that 

 the voluntary centers are more important in monkeys than in lower 

 animals. 



Such are the facts on which we base the existence of a motor region 

 in the brain. Putting aside all questions of interpretation, it is unde- 

 niable that there is a region in the brain w^here stimulation produces 

 movements varying with the zone or center excited. 



'Behind this region we find the sensitive centers which receive im- 

 pressions made upon the sensory nerves, and form perceptions from 

 them. As the terrhinations of the nerves of sensation are specialized, 

 in exciting the centers we produce , subjective sensations, like those 

 caused by cerebral maladies, in which the intellect refers to the out- 

 ward world the origin of sensations, of w^hich the cause is in the brain ; 

 and, whether voluntarily or by reflex action, the animal operated on 

 by electricity shows by evident signs the nature of the sensations he 

 experiences. By means of counter-verification we determine the exist- 



