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APHANITE

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Originally appearing in Volume V02, Page 164 of the 1911 Encyclopedia Britannica.
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APHANITE , a name given (from the Gr. a¢avils, invisible) to certain dark-coloured igneous rocks which are so See also:

fine-grained that their component minerals arc not detected by the unaidedeye. They consist essentially of See also:plagioclase See also:felspar, with See also:hornblende or See also:augite, and may contain also See also:biotite, See also:quartz and a limited amount of See also:orthoclase. Although a few authorities still recognize the aphanites as a distinct class, most systematic petrologists, at the See also:present See also:time, have discarded it, and regard these rocks as merely structural facies of other See also:species. Those which contain hornblende are See also:uniform, fine-grained diorites, vogesites, &c., while when See also:pyroxene predominates they are ascribed to the dolerites, quartz-dolerites, &c. Hence, any See also:rock which is compact, crystalline and fine grained, is frequently said to be aphanitic, without implying exactly to which of the See also:principal rock See also:groups it really belongs. APHASIA' (from Gr. a, privative, and Oats, speech), a See also:term which means literally inability to speak, and is used to denote various defects in the comprehension and expression of both spoken and written See also:language which result from lesions of the See also:brain. Aphasic disorders may be classed in two groups:—first, receptive or sensory aphasia, which comprises (a) inability to understand spoken language (auditory aphasia), and (b) inability to read (visual aphasia, or alexia); second, emissive or motor aphasia, under which See also:category are included (a) inability to speak (motor vocal aphasia, or See also:aphemia), and (b) inability to write (motor graphic aphasia, or agraphia). It has been shown that each of these defects is produced by destruction of a See also:special region of the cortex of the brain. These regions, which are termed the speech centres, are, in right-handed See also:people, situated in the See also:left cerebral hemisphere; this is the See also:reason why aphasia is so commonly associated with See also:paralysis of the right See also:side of the See also:body. A study of the acquisition of the See also:faculty of speech throws See also:light upon the See also:education of the speech centres, and See also:helps to elucidate their physiological interaction and the phenomena of aphasia. The auditory speech centre is the first to show signs of functional activity, for within a few months of See also:birth the See also:child begins to understand spoken language. Some months later the motor vocal speech centre begins to functionate.

The memories of the auditory word images which are stored up in the auditory speech centre See also:

play a most important See also:part in the See also:process of learning to speak. The child See also:born See also:deaf grows up See also:mute. The visual speech centre comes into activity when the child is taught to read. Again, when he learns to write and thus begins to educate his graphic centre, he is constantly calling upon his visual speech centre for the visual images of the words he wishes to produce. From these remarks it will be seen that there is a very intimate association between the auditory speech centre and the motor vocal speech centre, also between the visual speech centre and the graphic centre. Auditory Aphasia.—The auditory speech centre is situated in the posterior part of the first and second temporo-sphenoidal convolutions on the left side of the brain. Destruction of this centre causes " auditory aphasia." See also:Hearing is unimpaired but spoken language is quite unintelligible. The subject of auditory aphasia may be compared to an individual who is listening to a See also:foreign language of which he does not understand a word. Word deafness, a term often used as synonymous with auditory aphasia, is misleading and' should be abandoned. Auditory aphasia commonly interferes with vocal expression, for the ' In 1906 See also:Pierre See also:Marie of See also:Paris expressed views (La Semaine medicale, May 23 and See also:October 17, and elsewhere) upon the question of aphasia which have given rise to much animated controversy, since they are in many respects at See also:complete variance with the classical conception which has been represented in the present See also:article. Marie holds that See also:Broca's convolution plays no special role in the See also:function of speech. He admits that a See also:lesion in the region of the lenticular See also:nucleus is followed by inability to speak, but this defect is, in his See also:opinion, to be regarded as an anarthria.

He further admits the See also:

production of sensory aphasia—the aphasia of Wernicke, as he prefers to See also:call it after its discoverer—by lesions which destroy the angular and supramarginal gyri, and the upper two temporosphenoidal convolutions, but he regards the essential See also:foundation of sensory aphasia as a diminution of intelligence. There are, in his opinion, no sensory images of language. Motor aphasia is, he believes; nothing more than a See also:combination of sensory aphasia and anarthria These conclusions have been vigorously attacked, more especially by Dejerine of Paris (La Presse medicale, See also:July 1906. and elsewhere). See also:majority of people when they speak do so by recalling the auditory memories of words stored up in the auditory speech centre. Amnesia verbalis is employed to designate failure to call up in the memory the images of words which are needed for purposes of vocal expression or silent thought. Visual Aphasia or Alexia.: The visual speech centre, which is located in the left angular gyrus, is connected with the two centres for See also:vision which are situated one in either occipital See also:lobe. Destruction of the visual speech centre produces visual aphasia or alexia. Word See also:blindness, sometimes used as the See also:equivalent of visual aphasia, is, like word deafness, a misleading term. The individual is not See also:blind, he See also:sees the words and letters perfectly, but they appear to him as unintelligible cyphers. When the visual speech centre is destroyed, the memories of the visual images of words are obliterated and interference with See also:writing, a consequence of amnesia verbalis, results. On the other See also:hand, when the lesion is situated deeply in the occipital. lobe, and does not implicate the cortex, but merely cuts off the connexions of the angular gyrus with both visual centres, agraphia is not produced, for the visual word centre and its connexion with the graphic centre are still intact (pure, or sub-cortical word blindness). Motor Vocal Aphasia or Aphemia.—The centre for motor vocal speech is situated in the posterior part of the third left frontal convolution and extends on to the See also:foot of the left ascending frontal convolution (Broca's convolution).

Complete destruction of this region produces loss of speech, although it often happens that a few words, such as yes " and " no," and, it may be, emotional exclamations such as " Ohl dear!" and the like are retained. The utterance of unintelligible sounds is still possible, however, and there is neither defective See also:

voice production (aphonia) nor paralysis of the mechanism of See also:articulation. The individual can recall the auditory and visual images of the words which he wishes to use, but his memory for the complicated, co-ordinated movements which he acquired in the process of learning to speak, and which are necessary for vocal; expression, has been blotted out. In the See also:great majority of cases of motor vocal aphasia there is associated agraphia, a circumstance which is perhaps to be accounted for by the proximity of the graphic centre. When the lesion is situated below the cortex of Broca's convolution but destroys the See also:fibres which pass from it towards the See also:internal See also:capsule, agraphia is hot produced (sub-cortical or pure motor vocal aphasia). Destruction of the auditory speech centre is, as we have seen, commonly accompanied by more or less interference with vocal speech, a consequence of amnesia verbalis. Agraphia.—Discussion still rages as to the presence of a special writing centre. Those who favour the See also:separate existence of a graphic centre locate it in the second left frontal convolution. It may be that the want of unanimity as to the graphic centre is to be explained by an anatomical relationship so See also:close between the graphic centre and that for the fine See also:movement of the hand that a lesion in this situation which produces agraphia must at the same time cause a paralysis of the hand. Destruction of the visual speech centre by obliterating the visual memories of words (amnesia verbalis) produces agraphia. Further, several instances are on See also:record in which agraphia has followed destruction of the commissure between the visual speech centre and the graphic centre. As already mentioned, agraphia is very often associated with motor vocal aphasia.

A number of aphasic defects are met with in addition to those already mentioned. Thus paraphasia is a See also:

condition in which the patient makes use of words other than those he intends. He may mix up his words so that his conversation is quite unintelligible. In the most pronounced forms he gabbles away, employing unrecognizable sounds in See also:place of words (See also:jargon and gibberish aphasia). Paragraphia is a similar defect which occurs in writing. Both paraphasia and paragraphia may be produced by partial lesions of the sensory speech centres or of the cornmissures which connect these with the motor centres. See also:Object blindness (syn. mind-blindness) refers to an inability to recognize an object or its uses by the aid of sight alone. The probable See also:APHIDES explanation would seem to be that the See also:ordinary centre for vision has ,been isolated from the other sensory centres with which it is connected. Not uncommonly there is associated visual aphasia. Optic aphasia was introduced to designate a somewhat similar See also:state in which, although the uses of an object are recognized, the patient cannot name it at sight, yet, if it is of such a nature that it appeals directly to one of. the other senses, he may at once be able to name it. Tactile aphasia is a rare defect in which there exists an inability to recognize an object by See also:touch alone although the qualities which, under normal circumstances, suffice for its detection can be accurately described. Amnsia, or loss of the musical faculty, may occur in association with or See also:independent of aphasia.

There is reason for believing that special receptive and emissive centres = exist for the musical sense exactly !analogous to those for speech. The speech centres are all supplied by the left See also:

middle cerebral artery. When this artery is blocked close to its origin by an embolus or thrombus, See also:total aphasia results. It may be, however, thart only one of the smaller branches of the artery is obstructed, and, according to the region of the brain to which this See also:branch: is distributed, one or more of the speech centres may be destroyed. Occlusion of the left posterior cerebral artery causes extensive softening of the occipital lobe and produces pure word blindness. Further, a See also:tumour, See also:abscess, See also:haemorrhage or See also:meningitis may be so situated as to damage oridestroy the individual speech centres or their connecting commissures. The amount of recovery to be expected in any given See also:case depends upon the nature, situation and-extent of the, lesion, and upon the See also:age of the patient. Even after Complete destruction of the speech centres, perfect recovery may take place, for the centres in the right hemisphere of the brain are capable of education. This is only possible in See also:young individuals. In the great majority of instances the nature of the lesion is such as to render futile all treatment directed towards its removal. In suitable cases, however, the education of the right side of the brain may be very greatly assisted by an intelligent application of scientific methods. BisiaoGRAPrIY.—Broca, Bulletin de la Societe anatomique (1861) ; Wernicke, Der Aphasische Symptomen-complex (See also:Breslau, 1874) ; Kussmaul, Ziemssen's, Cyclopaedia, vol. xiv. p.

759; Wyllie, The Disorders of Speech (1895); See also:

Elder, Aphasia and the Cerebral Speech Mechanism (1897) ; See also:Collins, The Faculty of Speech (1897) ; See also:Bastian, Aphasia and other Speech Defects (1898) ; See also:Byrom See also:Bramwell, " Will-making and Aphasia," See also:British Medical See also:Journal (1897) " The See also:Morison Lectures on Aphasia," The See also:Lancet (1906). See also the See also:works of See also:Charcot, Hughlings See also:Jackson, Dejerine, Lichtheim, Pitres; Grasset, See also:Ross, Broadbent, See also:Mills; See also:Bateman, Mirallie, Exner, Marie and others. (J. B.

End of Article: APHANITE

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