Idiocy is a condition of mental deficiency existing from birth, the individual being bom with a deformed or undeveloped brain, just as persons may be bom with deficient development of the limbs or of any other part of the body. The mental deficiency is shown by an unusually small head, which is very much flattened in front, the average diameter of the head being about thirteen inches, or five or six inches less than usual in health. Various other physical deformities are also present, as deficient development of the teeth, protrusion of the upper jaw, giving the child an ape-like appearance. In some cases the resemblance to sheep or monkeys is very great. The degree of mental development in idiots is often much less than that of the higher animals. Their habits are exceedingly filthy, the natural instincts which characterize the lower animals being apparently absent. In some cases, however, a considerable degree of intelligence is manifested in certain directions, such as ability to calculate correctly, a fondness for and appreciation of music, etc.

Cretinism is a form of mental deficiency in which goitre and other deformities are seen. It is found chiefly in certain parts of Switzerland, particularly in the deep gorges of the Valais, where it is supposed to be due to climatic influences, although its origin is not well understood.

Imbecility is a condition of mental weakness which comes upon an individual bom with a healthy brain. It frequently follows infantile convulsions. It is very often the result of softening of the brain, or hydrocephalus. All degrees of mental deficiency are shown by imbeciles. They generally eat voraciously, are very mischievous in disposition, frequently destroying whatever they can get their hands upon. Imbeciles do not show the peculiar deformities noticeable in idiots, being bom in a normal condition.

Much attention has been given to the study of the causes of idiocy and imbecility. The best authors attribute idiocy chiefly to two causes,- intemperance and marriage of relatives. Plenty of instances have been observed in which idiotic children are the offspring of intemperate parents. Morel, who has investigated this subject very thoroughly, shows the connection between habits of vice and intemperance and idiocy as follows: "In the first generation there is alcoholism and immorality; in the second, hereditary drunkenness, maniacal outbursts, and general paralysis; in the third, sobriety, homicidal mania, melancholia, confirmed mania, homicidal tendencies; in the fourth, feeble intelligence, stupidity, early mania, idiocy, and, finally, extinction of the stock."

Statistics have also been collected to show that the marriage of nearly related persons, as of cousins, has a marked tendency to produce idiocy in the offspring. Recent investigations have shown that this tendency does not necessarily exist on account of individuals being relatives, only as each one possesses similar tendencies, which, by combination, are intensified. The danger in the marriage of relatives is that some lurking tendency of this kind will be, by intensification, brought out in the children. Fortunately, idiots and imbecile persons are usually sterile. A peculiar form of imbecility of a very low grade is produced in children by the use of narcotics, as of "Mrs. Winslows Soothing Syrup," and similar quack nostrums containing opium.

Dr. Archibald, superintendent of the State asylum for feeble-minded children, asserts that he has found, by careful investigation, that selfabuse is a cause of a very large proportion of the cases of imbecility which come under his care.