It will be utterly impossible in the short time allotted to me, to enter at any length upon the various causes of idiocy, a study of which is, however, fraught with many a useful lesson. Suffice it to say that as the cause is always antecedent to any personal history of the child, idiocy is never dependent on the idiot himself, who has never become so through any vices of his own; he being in many instances the feeble expression of parental defects, and sometimes of parental vices, and is therefore more an object for commiseration than certain lunatics, who, in many instances, have become so through faults of their own. As to the social aspect of idiocy, it recognises no distinction of rank; it may occur in the homes of the affluent, or in the hovels of the most indigent. It is found in all civilised countries, but it is not an evil necessarily inherent in society, and is the result of the violation of natural laws, in some way or other, and at some time or other, and the effect may not show itself for two or three generations. A very large class of persons ignore the conditions upon which health and reason can co-exist; they pervert the natural appetites of the body, and the natural emotions of the mind, and thus bring down the awful consequences of their own ignorance upon the heads of their unoffending children. Idiocy may be a congenital infirmity, or may be developed in early infancy. In the first category, the cause must necessarily be traced to intra-uterine life, and must be sought for in the history of the parents; in the second class, the cause may sometimes depend upon parental defects, and sometimes is due to a cerebral affection occurring soon after birth, but even in this class of cases, hereditary predisposition must be considered as a powerful factor in the genesis of the disease. In fact, the development of idiocy, whether congenital or otherwise, is in most instances to be attributed to an hereditary morbid vice, and it is one of the most common and striking forms of the degeneration of the human species. Hereditary tendencies have much to do with the development of physical defects and bodily ailments, and this result is especially apparent in diseases of the nervous system; and there can be no doubt that heredity is a potent factor in the production of idiocy. Dr. Ireland says, "idiocy is, of all mental derangements, the most frequently propagated by descent;" and the statistics of Ludwig Dahl, of Christiana, showed that fifty per cent. of idiots had insane relations, those of Dr. Fletcher Beach showed a history of hereditary predisposition in 76 per cent., whilst those of Moreau, of Tours, give a proportion as high as 90 per cent.