Page:Popular Science Monthly Volume 18.djvu/624

606 that binds together the different parts of the cerebro-spinal system and which makes it probable that a simple local trouble will produce general functional perturbation. The brain is like a complex machine, in which, if a screw loosens, or a nut gives way, or a rod bends or breaks, at once all goes wrong. It is not that the screw, nut, or rod in question is the immediate cause of the movements of the machine, but that the failure of these accessories may, for the moment, produce accidents as grave as would be caused by disturbance in much more important parts. Again, cerebral lesions tend to spread and become general. And yet, we have to accept the lesions caused by disease, for we can not produce them at will.

With these reservations, the clinical method is still of the first importance. By means of it we verify in man the hypotheses of experiment, and assure ourselves of the existence of the intellectual and sensitive regions of the brain. Neither medicine nor physiology opposes the use of the clinical method in cerebral localization. But only circumscribed lesions that have little or no tendency to become general, or to act at a distance by compressing the brain, or otherwise, can come to the aid of our theory. When there is a lesion of the cortical region of the brain which fulfills these conditions, the resulting symptoms may be of two orders—either stimulative or paralytic of the true function. These are the two opposed symptoms that we produce experimentally by electrization and ablation of the substance of the convolutions. It goes without saying that the symptoms vary with the locality of the lesion: the intellectual region gives delirium; the motor region, spasms; the sensitive region, subjective sensations. The symptoms of functional paralysis are also diversely represented by mental feebleness, motor paralysis, and anæsthesia limited to one sense. A lesion frequently presents both orders of symptoms, which succeed each other, or alternate, according to its nature. This fact is as important as the division of the symptoms into two great classes. We will now consider the facts in the same order as before.

The middle region of the superior face of the brain appears to be the motor region. In fact, limited lesions of this region bring on marked troubles in the motor innervation of the body, such as monoplegia, or limited paralysis, or equally limited spasms. Putting aside those cases where the lesions cause general trouble, and regarding those where the symptoms are limited, we come at a constant relation between certain lesions and certain troubles. In ocular monoplegia, the eye can not be controlled by the will. Brachial and crural monoplegia are more frequent; sometimes a single member, arm or leg, sometimes both; but successively, because of the extension of the lesion to both centers, which are near together. In this case the lesion advances slowly and invasively; at the autopsy we can often appreciate the differences of age of the extreme points of the diseased spot. Not far from the brachial and crural centers is the center that