This condition refers to mental disorders arising usually during the period of puberty or adolescence, therefore, between the ages of fourteen and twenty-five for the most part, although apparently similar cases may arise in later years. The term dementia refers to mental deterioration and enfeeblement, while “praecox” signifies adolescence, though some writers infer that the term praecox may be used to indicate the early or precocious development of the mental enfeeblement. Certain it is that in most cases deterioration, with its resulting symptoms of mental enfeeblement giving rise to the term dementia, usually occurs in time, though by no means always early. It is a chronic progressive disease which may terminate in a complete loss of mentality; in other cases it may become arrested in any stage and remain so permanently; in still others it may recover, though this is rare. By reason of the variability of the symptoms, three groups are generally recognized, first suggested by Kraepelin. Each is differentiated by more or less characteristic symptoms and referred to under the head of the Hebephrenic, Catatonic and Paranoid types, although all have certain symptoms in common and there are mixed types. =Etiology.=—According to the authorities some form of hereditary factor can be found in some fifty per cent or more of all cases; this is supposed to create a predisposition, a natural weakness of the nervous system, which renders it unable to bear the ordinary storm and stress of life, so that the mechanism becomes according to the French expression, “wrecked upon the rock of puberty or adolescence;” in other words, a premature giving way of the nervous system, being inherently unable to stand the strain of life. Another suggestion is that it represents the outcome of abnormal types or reactions of the individual to the environment, with a failure of proper adjustment to surroundings and the formation consequently of mental problems which to the patient are incapable of solution. This may be called the psychological theory. The most commonly accepted idea, however, is the physical causation. According to this the disease results from auto-intoxication, the intoxicant arising from the disturbances of the glands with internal secretions, more particularly the sexual glands. This endocrine theory is supposed to be supported by the fact of the appearance of this disease most commonly at the time of puberty and shortly thereafter. The osteopathic conception fits in very well with this latter view, inasmuch as the spinal lesions are quite capable of explaining not only a disturbance of innervation to the glands with the resultant interference in their normal secretion, but also could produce disorder of the circulation and nutrition to the brain.