Page:Popular Science Monthly Volume 14.djvu/506

490 of the left, and never with disease of the right side of the brain. To the brief explanation of this curious fact we shall presently return; but we may in conclusion remark certain facts now known respecting the localization of other functions. Professor Ferrier, of King's College, London, employing electricity as the only agent and means of stimulation to which the non-sensitive brain will respond, has succeeded in mapping out in the brains of higher animals the centers which govern many of the common movements of life, and which from reasonable analogy may be presumed to be represented in the human brain as well. As these acts are the practical outcome of ideas, the parts of the brain concerned in the production of definite ideas may thus be regarded as being in one sense mapped out and recognized; although it is hardly necessary to remark that the regions of Dr. Ferrier in no wise correspond to those of the old phrenology, while in many cases, indeed, they are utterly opposed to it. Thus the sense of touch is found to be localized in the inner surface of the hemispheres of the brain, and this fact alone tells against the phrenologist, to whom the mere brain-surface is the brain itself.

Thus the work of localizing movements and important centers of the senses has so far proceeded with success. There yet remains for observation the curious case of aphasia or speechlessness, and its location in a "speech-center" or "speech-organ" in the front of the left hemisphere of the brain. It is a noteworthy fact in brain-physiology, that when an animal has been rendered blind by the destruction of the sight-center of one side, blindness disappears and sight gradually returns, since the remaining and normal sight-center of the opposite side assumes the functions of its neighbor. Complete blindness only ensues when both sight-centers are diseased. The same remark holds good of the movements of the mouth and tongue in speech, these being "bilateral," so that the center of these latter movements on one side may be destroyed without causing paralysis of the tongue, provided the center of the other side is uninjured. Movements of the hands and feet are, on the contrary, one-sided. Destruction of one center governing these latter movements insures complete cessation of the movements on the opposite side of the body. Now, in aphasia or speechlessness, we merely perceive the results of the destruction of the single speech center—the left—which man normally possesses. Just as we use the right hand in preference to the left in prehension and in writing, and as the movements of this hand are regulated by the left side of the brain, so our faculty of articulation is also unilateral and single-handed, so to speak. The memory of sounds and words forms the basis of our speech—"the memory of words is only the memory of certain articulations"—and those parts of the brain which regulate articulation are also the memory-centers for speech or the result of articulation. Thus, when the speech-center is disorganized, not merely the power of articulation disappears, but also the memory of words. But while the left side is