HEBEPHRENIA (insanity of pubescence and adolescence) occurs within the ages of fourteen and twenty-three or thereabouts. Like insanity in general among persons in early life, it most commonly indicates an hereditary predisposition to mental or nervous diseases or an early-developed brain defect or injury, possibly an exalted emotional state or an increased nervous sensitiveness produced by masturbation. It is a mild form of primary dementia, modified by the mental changes going on during adolescence. Indeed, it is simply an exaggeration and prolongation of the curious psychological development of that period, too well known to need description, which goes on in the most insidious way possible through months or years of what seems silliness, absurd fancies, foolish sentimentality, egotism, impaired common sense, and diminished judgment and self-control, to a slowly-advancing dementia, which even then is not always recognized as disease. The result is an arrest of brain development on various planes of intellect, and a preservation of the youth's tastes and sense and intelligence, as modified by the morbid propensities characterizing an unhealthy development of the change from boyhood or girlhood and {172} youth to adult life, with the adult's strength—a curious combination of intellectual brightness, it may be, with lack of mind. For this characteristic condition Westphal uses the expressive term Permanenz der Flegeljahre (permanence of the usually transitory state, which then commonly results in permanent arrest of brain development on the plane of the mind at a definite age of adolescence); and yet there may be more than that—mental deterioration, which in years may lead to pronounced dementia. Cases of primary dementia occurring within the years of puberty and adolescence are often classed as hebephrenia and conversely, so that one term, primary dementia, is thought sufficient by many writers on insanity.