Page:Popular Science Monthly Volume 18.djvu/625

Rh presides over the muscles of the face. As before, this center may be affected alone or simultaneously with the other. It depends upon the nature of the lesion whether the invasion is sudden, or slow and progressive, ending in feebleness rather than in paralysis. The proximity of the brachial and facial centers explains their apparent solidarity in the normal state, as shown by the grimaces that often accompany vigorous use of the arms. It seems as if the second center were stimulated by the activity of the first. We close our enumeration of the centers which the clinic has proved to exist by reference to the center of articulate language, discovered long ago by Broca, which attends to the coördination of phonetic movements.

We have seen that lesions of the motor region of the brain may be manifested by spasms as well as by paralysis. These monospasms have been long known, but it was Hughlings Jackson who first attributed them to lesions of the motor region of the brain. Prior to this they had been described by Bravais, but he did not seek for their origin or signification. They are localized convulsions, or partial epilepsy, and Hughlings Jackson thinks they are due to nervous tension. Any new excitement added to those already stored up will produce discharge or spasm. Like monoplegia, they may be limited to an arm or leg, or even the face; but these phenomena are seldom noticed, and we have few observations upon them. When the spasm involves several parts of the body, it always begins at the same point and follows the same order. Dr. Maragliano has made a very interesting study of partial epilepsy, and explained its causes and signification. Both monospasms and monoplegia indicate the same localization of power.

The sensitive region is found, by experiment, behind the motor centers. While limited lesions of this region often manifest themselves externally as circumscribed anæsthesia, it sometimes happens that they remain latent when they are seated on only one hemisphere. There is no sign of pathological perturbation, and in this case we seem forced to admit functional substitution, or the possibility of the regular action of two sensitive, homologous regions, notwithstanding the absence of one of the two corresponding cerebral hemispheres. What does this signify? Must we abandon the doctrine of localization as regards the sensitive centers? A single center suffice for the two parts of the body? This anomaly is probably due to insufficient observation. Disease of the cerebral centers may give no further symptom than enfeebled sensibility, which might pass unperceived. Lesions of the motor region often result not in total paralysis but in slight paralysis—a feebleness and not an abolition of the functions. But there are cases where lesions of the sensitive region are accompanied by less equivocal symptoms, and it is from these that we affirm localization.

Symptoms may be of two orders, according to the nature and the phase of the disease: symptoms of excitation, which produce