Page:Popular Science Monthly Volume 18.djvu/622

604 the center under experiment. Here electricity provokes movements of the leg on the opposite side, owing to the cross-action of the hemispheres. 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 combination of movements, like those required for swimming or prehension; the fingers may lock together with force, as if to retain an object, or extend themselves with a lively movement, as if to scatter something. It is probable that, if our instruments were more perfect, 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, coördinates the elementary and individual movements required to produce the desired 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 constant needs of experiment, Ferrier operated upon dogs, jackals, Indian pigs, rats, pigeons, frogs, fishes, anything that was going. These experiments 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 inferior 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 undeniable that there is a region in the brain where stimulation produces movements varying with the zone or center excited.

Behind this region we find the sensitive centers which receive impressions made upon the sensory nerves, and form perceptions from them. As the terminations 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 outward world the origin of sensations, of which 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