I. In pursuance of the intention, signified in my “Notes on the Mental Deficiency Act” in the Journal for July, 1916, to consider, as practically as may be, the subject of mental defect as a factor in the production of crime, I find it desirable to make some introductory remarks concerning the recently increasing literature of what is known as “Criminology.” This term may be properly applied to investigations undertaken with a view to giving such an account of criminal conduct and criminal men as may assist in the formation of practical measures towards the prevention of the one and the appropriate treatment of the other. Most of the more modern discussions on crime and criminals have either directly or indirectly been occasioned by the efforts of persons concerned in some way with prison administration, or otherwise specially conversant with convicted criminals, who strive to discover just principles on which to base their practice. But the growing bulk of doctrine and debate on the causation of crime, the genesis and treatment of the criminal, the meaning of “responsibility,” and even the State's “right” to “punish” offenders at all, consists to a great extent of definitely formulated theories largely based on preconceived assumptions regardless of fact, and often mutually contradictory. This occasions much difficulty to those who aim at any clear understanding of the subject; and the difficulty is increased by the frequently indefinite and equivocal use of the words “crime,” “criminal,” and “punishment,” which denote the very subjects of discussion. Thus the handling of the whole matter becomes widely diffused, leaving no firm ground on which to rest any useful conclusion. Sundry kinds of topics, sociological, ethical, psychological, and biological, become involved in the dispute, and the student may even be landed and left in the midst of such perennial controversies as those about the “freedom of the will,” and the nature, and even existence, of the relation between mind and matter.