APHANITE

aphanite, a name given (from the gr. [greek: aphanes], invisible) to certain dark-coloured igneous rocks which are so fine-grained that their component minerals are not detected by the unaided eye. they consist essentially of plagioclase felspar, with hornblende or augite, and may contain also biotite, quartz and a limited amount of orthoclase. although a few authorities still recognize the aphanites as a distinct class, most systematic petrologists, at the present time, have discarded it, and regard these rocks as merely structural facies of other species. those which contain hornblende are uniform, fine-grained diorites, vogesites, &c., while when pyroxene predominates they are ascribed to the dolerites, quartz-dolerites, &c. hence, any rock which is compact, crystalline and fine grained, is frequently said to be _aphanitic_, without implying exactly to which of the principal rock groups it really belongs. aphasia[1] (from gr. [greek: a], privative, and [greek: phasis], speech), a term which means literally inability to speak, and is used to denote various defects in the comprehension and expression of both spoken and written language which result from lesions of the 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 category are included (a) inability to speak (motor vocal aphasia, or _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 special region of the cortex of the brain. these regions, which are termed the speech centres, are, in right-handed people, situated in the left cerebral hemisphere; this is the reason why aphasia is so commonly associated with paralysis of the right side of the body. a study of the acquisition of the faculty of speech throws light upon the education of the speech centres, and 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 birth the 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 play a most important part in the process of learning to speak. the child born deaf grows up 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." 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 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 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 vision which are situated one in either occipital lobe. destruction of the visual speech centre produces visual aphasia or alexia. word blindness, sometimes used as the equivalent of visual aphasia, is, like word deafness, a misleading term. the individual is not blind, he 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 writing, a consequence of _amnesia verbalis_, results. on the other 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 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 "oh! dear!" and the like are retained. the utterance of unintelligible sounds is still possible, however, and there is neither defective voice production (_aphonia_) nor paralysis of the mechanism of 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 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 fibres which pass from it towards the internal capsule, agraphia is not 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 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 close between the graphic centre and that for the fine 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 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 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 place of words (_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 commissures which connect these with the motor centres. _object blindness_ (syn. mind-blindness) refers to an inability to recognize an object or its uses by the aid of sight alone. the probable explanation would seem to be that the 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 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 touch alone although the qualities which, under normal circumstances, suffice for its detection can be accurately described. _amusia_, or loss of the musical faculty, may occur in association with or 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 middle cerebral artery. when this artery is blocked close to its origin by an _embolus_ or _thrombus_, total aphasia results. it may be, however, that only one of the smaller branches of the artery is obstructed, and, according to the region of the brain to which this 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 tumour, abscess, haemorrhage or meningitis may be so situated as to damage or destroy the individual speech centres or their connecting commissures. the amount of recovery to be expected in any given case depends upon the nature, situation and extent of the lesion, and upon the 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 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. bibliography.--broca, _bulletin de la societe anatomique_ (1861); wernicke, _der aphasische symptomen-complex_ (breslau, 1874); kussmaul, _ziemssen's cyclopaedia_, vol. xiv. p. 759; wyllie, _the disorders of speech_ (1895); elder, _aphasia and the cerebral speech mechanism_ (1897); collins, _the faculty of speech_ (1897); bastian, _aphasia and other speech defects_ (1898); byrom bramwell, "will-making and aphasia," _british medical journal_ (1897); "the morison lectures on aphasia," _the lancet_ (1906). see also the works of charcot, hughlings jackson, dejerine, lichtheim, pitres, grasset, ross, broadbent, mills, bateman, mirallie, exner, marie and others. (j. b. t.) footnote: [1] in 1906 pierre marie of paris expressed views (_la semaine medicale_, may 23 and october 17, and elsewhere) upon the question of aphasia which have given rise to much animated controversy, since they are in many respects at complete variance with the classical conception which has been represented in the present article. marie holds that broca's convolution plays no special role in the function of speech. he admits that a lesion in the region of the lenticular nucleus is followed by inability to speak, but this defect is, in his opinion, to be regarded as an anarthria. he further admits the production of sensory aphasia--the aphasia of wernicke, as he prefers to call it after its discoverer--by lesions which destroy the angular and supramarginal gyri, and the upper two temporo-sphenoidal convolutions, but he regards the essential 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 combination of sensory aphasia and anarthria. these conclusions have been vigorously attacked, more especially by dejerine of paris (_la presse medicale_, july 1906 and elsewhere). aphelion (from gr. [greek: apo], from, and [greek: helios], sun), in astronomy, that point of the orbit of a planet at which it is most distant from the sun. apogee, apocentre, aposaturnium, &c. are terms applied to those points of the orbit of a body moving around a centre of force--as the earth, saturn, &c.--at which it is farthest from the central body. aphemia (from gr. [greek: a], without, and [greek: pheme], speech), in pathology, the loss of the power of speech (see aphasia). aphides (pl. of aphis), minute insects, also known as "plant-lice," "blight," and "green-fly," belonging to the homopterous division of the order hemiptera, with long antennae and legs, two-jointed, two-clawed tarsi, and usually a pair of abdominal tubes through which a waxy secretion is exuded. these tubes were formerly supposed to secrete the sweet substance known as "honey-dew" so much sought after by ants; but this is now known to come from the alimentary canal. both winged and wingless forms of both sexes occur, and the wings when present are normal in number, that is to say two pairs. apart from their importance from the economic standpoint, aphides are chiefly remarkable for the phenomena connected with the propagation of the species. the following brief summary of what takes place in the plant-louse of the rose (_aphis rosae_), may be regarded as typical of the family, though exceptions occur in other species: eggs produced in the autumn by fertilized females remain on the plant through the winter and hatching in the spring give rise to female individuals which may be winged or wingless. from these females are born parthenogenetically, that is to say without the intervention of males, and by a process that has been compared to internal budding, large numbers of young resembling their parents in every particular except size, which themselves reproduce their kind in the same way. this process continues throughout the summer, generation after generation being produced until the number of descendants from a single individual of the spring-hatched brood may amount to very many thousands. in the autumn winged males appear, union between the sexes takes place and the females lay the fertilized eggs which are destined to carry the species through the cold months of winter. if, however, the food-plant is grown in a conservatory where protection against cold is afforded, the aphides may go on reproducing agamogenetically without cessation for many years together. not the least interesting features connected with this strange life-history are the facts that the young may be born by the oviparous or viviparous methods and either gamogenetically or agamogenetically, and may develop into winged forms or remain wingless, and that the males only appear in any number at the close of the season. although the factors which determine these phenomena are not clearly understood, it is believed that the appearance of the males is connected with the increasing cold of autumn and the growing scarcity of food, and that the birth of winged females is similarly associated with decrease in the quantity or vitiation of the quality of the nourishment imbibed. sometimes the winged females migrate from the plant they were born on to start fresh colonies on others often of quite a different kind. thus the apple blight (_aphis mali_) after producing many generations of apterous females on its typical food-plant gives rise to winged forms which fly away and settle upon grass or corn-stalks. closely related to the typical aphides is _phylloxera vastatrix_, the insect which causes enormous loss by attacking the leaves and roots of vines. its life-history is somewhat similar to that of _aphis rosae_ summarized above. in the autumn a single fertile egg is laid by apterous females in a crevice of the bark of the vine where it is protected during the winter. from this egg in the spring emerges an apterous female who makes a gall in the new leaf and lays therein a large number of eggs. some of the apterous young that are hatched from these form fresh galls and continue to multiply in the leaves, others descend to the root of the plant, becoming what are known as root-forms. these, like the parent form of spring, reproduce parthenogenetically, giving rise to generation after generation of egg-laying individuals. in the course of the summer, from some of these eggs are hatched females which acquire wings and lay eggs from which wingless males and females are born. from the union of the sexes comes the fertile egg from which the parent form of spring is hatched. see generally g.b. buckton, _british aphides_ (ray soc. 1876-1883); also economic entomology. (r. i. p.) aphorism (from the gr. [greek: aphorizein], to define), literally a distinction or a definition, a term used to describe a principle expressed tersely in a few telling words or any general truth conveyed in a short and pithy sentence, in such a way that when once heard it is unlikely to pass from the memory. the name was first used in the _aphorisms_ of hippocrates, a long series of propositions concerning the symptoms and diagnosis of disease and the art of healing and medicine. the term came to be applied later to other sententious statements of physical science, and later still to statements of all kinds of principles. care must be taken not to confound _aphorisms_ with _axioms_. aphorisms came into being as the result of experience, whereas axioms are self-evident truths, requiring no proof, and appertain to pure reason. aphorisms have been especially used in dealing with subjects to which no methodical or scientific treatment was applied till late, such as art, agriculture, medicine, jurisprudence and politics. the _aphorisms_ of hippocrates form far the most celebrated as well as the earliest collection of the kind, and it may be interesting to quote a few examples. "old men support abstinence well: people of a ripe age less well: young folk badly, and children less well than all the rest, particularly those of them who are very lively." "those who are very fat by nature are more exposed to die suddenly than those who are thin." "those who eject foaming blood, eject it from the lung." "when two illnesses arrive at the same time, the stronger silences the weaker." the first aphorism, perhaps the best known of all, which serves as a kind of introduction to the book, runs as follows:--"life is short, art is long, opportunity fugitive, experimenting dangerous, reasoning difficult: it is necessary not only to do oneself what is right, but also to be seconded by the patient, by those who attend him, by external circumstances." another famous collection of aphorisms is that of the school of salerno in latin verse, in which joannes de meditano, one of the most celebrated doctors of the school of medicine of salerno, has summed up the precepts of this school. the book was dedicated to a king of england. it is a disputed point as to which king, some authorities dating the publication as at 1066, others assigning a later date. the dedication gives the following excellent advice:-- "anglorum regi scribit schola tota salernae. si vis incolumem, si vis te reddere sanum, curas tolle graves: irasci crede profanum: parce mero: coenato parum; non sit tibi vanum surgere post epulas: somnum fuge meridianum: ne mictum retine, nec comprime fortiter anum: haec bene si serves, tu longo tempore vives." another collection of aphorisms, also medical and also in latin, is that of the dutchman hermann boerhaave, published at leiden in the year 1709; it gives a terse summary of the medical knowledge prevailing at the time, and is of great interest to the student of the history of medicine. aphraates (a greek form of the persian name aphrahat or pharhadh), a syriac writer belonging to the middle of the 4th century a.d., who composed a series of twenty-three expositions or homilies on points of christian doctrine and practice. the first ten were written in 337, the following twelve in 344, and the last in 345.[1] the author was early known as _hakkima pharsaya_ ("the persian sage"), was a subject of sapor