IDIOCY, that condition in which there is permanent mental deficiency which has re sulted from a disease or deficiency of develop ment of the brain either before or at the time of birth or at an early period of life. It is thus academically distinguished from a psycho sis, which is a condition of mental disturbance occurring in the developed brain. Idiocy is a term of very wide applicability owing to the fact that very many grades of arrested develop ment occur. In a general sense it is applied chiefly to the worst of these forms, while the term imbecility is used to denote the milder forms. The distinction between idiocy and im becility is thus a somewhat arbitrary one, for the two conditions shade into each other by almost imperceptible degrees. An idiot is un able to attend to himself; an imbecile may.
The causes which result in idiocy and imbecility are often very obscure. A large proportion of cases are congenital; that is, they arise from causes acting in utero. The child is born with a brain already hopelessly impaired. Heredity is thus a very evident cause; defects in the ancestral stock and vices in the parents and near progenitors are doubt less very active. Alcoholism, syphilis and other chronic poisoning, chiefly lead, are certainly among these causes; as well as consanguinity and various diseases in the parents. Injuries to the mother while pregnant may be responsi ble. The subject of ante-natal disease is still a very obscure one, but evidence is not lacking to show that the lmtus may suffer from dis ease; and in the critical stage of development of the brain before birth this organ may stiffer irreparable damage. The same may be said of the infant and very young child. Injury and disease may act most disastrously upon the un developed brain. Thus blows upon and injuries to the head may cause idiocy; also injuries at the time of birth, due to difficulties in the labor, may act. The various infectious diseases of childhood are responsible for some cases; thus scarlet fever, measles, whooping cough and cerebrospinal fever have been noted as causes of permanerrt arrest of development. No doubt in many cases it is difficult or even impossible to detect the active cause.
The following are the most universally recognized varieties of idiocy: In this form the brain and its enveloping skull-case remain abnormally small. In extreme grades the deformity is
very striking. These are among the lowest and worst forms of idiocy, and in some cases there is scarcely a spark of intelligence. The patient cannot be said to do more than vegetate. The original cause probably acts in these cases at a very early period in the ante-natal life, and determines an almost complete arrest of brain development.
Hydrocephalus.— In this form the natural cavities or ventricles of the brain become enor mously distended and the skull is correspond ingly enlarged. The mental impairment varies within wide limits. In some cases the idiocy is almost if not quite as great as in micro cephalus, but in other cases a fair degree of intelligence is preserved. There may be also various forms of paralysis, speech defect, epi leptoid seizures and impairment of the special senses. Hydrocephalus probably depends upon closure of one or other of the outlets of the cerebrospinal fluid between the ventricles of the brain.
Occlusion or stoppage of one of the main arteries of the brain at an early period of development, not necessarily ante-natal, may cause such an arrest of develop ment of a portion of the brain-mass that a cavity results, and this is called porencephalus. Such a stoppage of an artery may be caused presumably by injury or by one of the in fectious diseases. The symptoms are usually arrest of development of the mental faculties in various degrees, speech defects, paralysis, such as hemiplegia, athetoid movements and epilepsy.
Mongolian Idiocy.— In some cases the patient bears a real or fancied resemblance to certain racial types, as' the Negroid, Mongo lian, etc. The latter of these is the best marked, and is now included (after Langdon Down) in most descriptions. The patient's head is de ficient in the posterior. region; he is of short statue, has oblique and widely separated eyes and a flattened nose. The attempt is made by some writers to construct special Mental fea tures for the Mongolian idiot, but with not very great success. He is simply an idiot, with varying degrees of mental power, and his resemblance to a Calmuck is only accidental.