APHASIA, a-fa'zIa-a or -z1-a. (Gk. 'Atpacrla, speechlessness, from ci,a, priv. OcipaL, phanai, to speak). A term used to denote certain derange ments of speech which are the results of certain disease or injury of the mechanism of speech. This mechanism is complicated, but it funda mentally consists of two parts, the receptive part and the emissive. When there is inter ference with the former, sensory aphasia is the result, while motor aphasia is the conse quence of trouble with the latter. The chief types of sensory aphasia are word-deafness and word-blindness, while the chief motor aphasias are motor vocal aphasia and motor writing aphasia, or agraphia. The mechanism of speech has been built up gradually in the course of evolution, and consists of a number of centres in the brain. The motor speech-area is in the third frontal convolu tion (Broca's convolution), and injury to this part of the brain or of the nerve tracts leading from it to control the motions of the tongue and lips produces motor vocal aphasia. With this affection the person may know what he wishes to say. hut is unable to say it; he may be able to talk, but not say the word he wishes. All grada tions of this affection, from slight to severe forms, exist, and it is one of the commonest forms of aphasia. The auditory centre, or centre for audi tory memories, or that portion of the brain which intellectually hears and understands spoken speech, is in the first temporal convolution. Any defect of this centre, or of the fibres which go from it to the motor speech centre, produces what is known as word-deafness. In this form the person may hear perfectly well, may read and speak, but does not understand spoken language. It is as though he
were listening to a foreign language. The sounds of the words convey no meaning to him. There are varying degrees in this affection as well, from slight attacks in which only certain words lose their significance, to complete loss of the under standing of spoken language. The third centre is that of the optical mechanism by which the printed or written word is understood. This cen tre is located in the occipital lobes, and disease or injury of its cells or of the fibres which lead from it to the motor speech centre produces word blindness. In this form of aphasia the person, although capable of seeing, does not comprehend what he sees. Words might as well he written in Chinese characters; he would understand them as well. He is capable of talking and of repeat ing aloud what is said to him, or of writing what may be said or what he reads. In this latter case he would be copying only. In a fourth type of aphasia, agraphia. which is not considered a true aphasia by many, the person is unable to write what he desires to write. He is capable of going through the motions of writing. but not understandingly. Aphasia is a symptom of many brain troubles. The most important cause is some type of hemorrhage into the brain sub stance, involving these areas. Tumors, injuries of the brain, exhaustion, and some of the insam ties may ne accompanied by aphasia. The treat ment is that of the underlying disease. Consult: Gould and Pyle, ryclopmdia of Medicine and Surgery (Philadelphia, 1900).