MENTAL CONSTITUTION. 325 MENTAL PROCESS. breaks up into two or more selves, or cores of interest, aljout each of wliieli f,'atlier elements con- genial to itself. Such ijorsoiialities are usually detieient in stability and in breadth and rich- ness of mental content. They exist incipiently in the normal mind. and where the transformation is gradual resiilt in healthy alterations of character and in the broadening of intelligence; in a more lively form, though still subject to the domina- tion "of one supreme self, they may give the dra- niatic creations of the novelist; but in extreme oases they result in exaggerated transpositions of thought and feeling, partaking of the nature of insanity. Apart from these more general variations, minds are characterized by dift'ercnces in the form and trend of their presentations. One per- son, for example, thinks largely in visual images; another's thought takes shape in internal eonver- satimis; while yet another is more keenly con- scious of his attitude toward things, the way he will act in their presence or the way he imagines that they feel. Again, presentations in the same field of sensation may vary in quality, ditterent minds having different characteristic modes of perception; so a landscape always appeals to the artist aesthetically, to the agriculturist or promoter by its practical possibilities. This is not due merely to ditTerence of interest, but to an actual variation in the quality of the presen- tation. The variation appears again in powers of memory and imagination, where there is al- ways in evidence a natural selection of elements due to the mind's aptitude. Herein lies the chief factor of individuality, the mind's com- plexion or characteristic style of thought and feeling, serving to throw it into relief against that background of qualities common to all con- sciousness which in mankind we term human nature. MENTALITY OF INSECTS. See section on Social Insects under Insect; also Instinct. MENTAL PATHOLOGY. The science of abnormal mental process. The intimate depen- dence of consciousness upon the functioning of the central nervous system enables us to approach the investigation of morbid mental conditions from the vantage ground of physiology. The brain, which is the substrate of mind, may, like any other organ of the body, exhibit (1) de- fects — i.e. lack of some structure — or (2) ab- riormality of function, whether it be (a) tem- porary — i.e. a disorder — or ( 6 ) permanent — i.e. a disease. 'Defectives' are, then, persons who suffer, congenitally or from early childhood, from the absence of some group or grou|)s of mental elements in consequence of some luiderlying structural gap in the nervous system; they are the lilind, the deaf, the paralytic, etc. The eases of Laura Bridgman and Helen Keller, the blind deaf-mutes, are typical. From careful reports of their educational progress, and from special psychological and neurological examination of their mental and physiological organization, val- uable data have i)een secured. Temporary dis- turbances of normal mental functioning are af- forded in the consciousness of dreams (extreme inattention), hypnosis (extreme attention), and the intoxication of various drugs. Frequent at- tempts have been made to examine mind as spe- cific phases of it are rendered ana'sthetic or hyperaesthetic in these ways. Hashish (extract of Cannabis Indica), e.g., greatly magnifies our consciousness of duration and extent, and also induces visual hallucination. Chronic mental derangement is excmi)lified by the various forms of insanity — mania, melancholia, dementia, gen- eral paresis, etc. — the extended investigation of which by oompetent alienists has thrown much light upon the nature of the more complicated mental processes. Abnormal mental types are, as one writer puts it, "psychological experiments made for us by Nature herself." Especially is this true when the infirmity is isolated, when a single group of mental processes — e.g. a sense department — is either entirely lacking or extraordinarily empha- sized. Such a state of atlairs simplifies matters for the psychologist. He is able to find out the relative value of the group concerned in the nor- mally organized mind, and, as a consequence, to proceed more successfully with the analysis of the adult human consciousness. (See Psychol- ogy.) Take, for example, cases of the anaesthesia of particular internal organs which lie beyond that experimental control which is of supreme importance in the laboratory investigation of the external sense organs. Evidence of this sort has been of weight in referring the sensation of gid- diness to the semicircular canals of the internal ear. ( See St.tic Sense. ) From observations of senile dementia Hughlings Jackson has estab- lished the law that, in the gradual loss of mem- ory with advancing age, the latest mental stviff, that acquired with most difficulty, first decays. The successive .stages of dissolution consequent upon the inroads of cerebral deterioration re- trace the steps of evolution. The various types of aphasia (q.v. ) have been of great assistance in the solution of the problem of the cortical localization of function, as well as in the more strictly psychological problems of apperception (q.v.) and language. Bibliography'. Lewis, Mental Diseases: Path- olofficul Aspects of Insanitij (London, 1889) ; Hall, Mind, iv. ( 1S70, 149); Maudsley, The Pnthologtj of Mind (London. 1879); Mereier, Hanitji and Insanity (London, 1890) ; Binet, The I'si/cholofiy of Reasonin;/, Based jipon Experi- mental Researches in Ili/pnotism (Eng. trans., Chicago. 1899) : Ribot. Les maladies de la me- moire (Paris. 1891) ; Diseases of the Will (Eng. trans., Chicago, 1894) ; Diseases of Personality (Eng. trans.!^ Chicago, 1894) ; Sully, The Hu- man Mind, i.. 19. 7-i. ii., 3'20f. (lx)ndon, 1892) ; Titchener, An Outline of Psi/eholodv (New York, 1899). MENTAL PROCESS. A phrase employed by modern psychologv- in two nearly related meanings. ( 1 ) In the first place, it is tending to replace the older static conception of 'mind' (q.v.). Stout, e.g., defines psycliology as "the positive science of mental process." in preference to speaking of it as the 'science of mind.' and .James declares that "the first fact for us as psychologists is [not that mind exists, but] that thinking of some sort goes on. ... If we could say in English 'it thinks.' as we say 'it rains" or 'it blows.' we should be stating the fact most simply." (2) But not only is mind, as a whole, a 'stream' of thought and feeling; each separate element of mind or mental formation that our analysis teases out of the total con- sciousness is itself a process. Every sensation
