The class of defectives with which I propose to deal briefly in certain of its aspects consists of those persons over school age who are capable of earning a living in favourable circumstances, but are incapable, from mental defect existing from birth or from an early age, (a) of competing on equal terms with their normal fellows, or (b) of managing themselves and their affairs with ordinary prudence—a definition which, though rather rough, may be accepted as of some value in practice. Such persons have been found by the Royal Commission on the Feeble-Minded to constitute about 40 per cent. of all aments in the United Kingdom; and it has been estimated that their numbers in England and Wales amount to between 50,000 and 60,000. In my investigation, in the City of Dublin I found 365, or 30 per cent. of all aments. Thus they deserve separate study from their numbers alone, apart from the fact that, owing to their relatively high intelligence, they at once are more dangerous socially, and repay help better, than any other class of aments.