Page:Popular Science Monthly Volume 18.djvu/623

Rh and topography of a certain number of centers which Ferrier has studied with great care.

Take, for example, the visual center: its stimulation caused disordered reflex actions, indicating unpleasant visual perceptions. This alone is insufficient proof; but we can control the region in question by ablation, which brings on unilateral or bilateral blindness, according as we operate on one or both of the visual centers. Stimulation of the auditive centers, in the same part of the brain, provokes movements of the ears, eyes, and head, showing astonishment or terror, just like those caused by a violent and unexpected noise. Ablation causes deafness; the animal remains indifferent to all sounds. Excite the centers of touch, and the signs indicate disagreeable or painful tactile impressions. Ablation brings on complete anæsthesia of the same parts; you may prick, cut, and bruise the animal, and he remains insensible.

Some experiments seemed to indicate the existence of centers of taste and odor, but it is difficult to trace their limits. They are intermingled like the gustative and olfactive sensations. Electricity causes movements indicating unpleasant tastes and odors, and extirpation of the parts ends these sensations. The animal will respire odors, or taste savors that in the normal state would make him fly about the laboratory, and it all passes unperceived. Still more hypothetical are the centers of the organic needs of hunger and thirst, and more yet those of sex, but Ferrier's arguments are strong in favor of their existence.

The presence of a third, or intellectual region, is proved, as far as it can be, by experiments on the lower animals. It is difficult to understand the mental action of a dog, Indian pig, or even of a monkey. Ferrier observed numerous facts tending to establish the intellectual function of the anterior region of the brain. Electricity could hardly be employed in these researches; but ablations, when performed with caution, brought on notable changes in the habits of animals. The monkeys chosen by Ferrier were remarkable for their vivacity and intelligence, prying about right and left, and observing everything. After the operation they became stupid and apathetic. But these indications are not convincing. The clinic alone can decide whether physiology sustains the doctrine of cerebral localization.

We know in what the clinical method consists. Applied most often to man, it amounts to this: to observe the symptoms of cerebral disease, and at the autopsy to connect the lesions, discovered by the naked eye or the microscope, with the symptoms, as cause and effect. It is true that in cerebral pathology there is great difficulty in separating the essential from the accidental, and distinguishing cause and effect among a plurality of causes. Besides, it frequently happens in cases of cerebral disease that at the autopsy no appreciable lesions can be found. The question is still further complicated by the solidarity