_The mental constitution of the criminal_ comprises anomalies of intelligence and feeling, especially of the moral sense, and the specialities of criminal writing and slang. _The personal characteristics of the criminal_ comprise his purely biological conditions, such as race, age, sex; bio-social conditions, such as civil status, profession, domicile, social rank, instruction, education, which have hitherto been regarded as almost the exclusive concern of criminal statistics. _The physical factors_ of crime are climate, the nature of the soil, the relative length of day and night, the seasons, the average temperature, meteoric conditions, agricultural pursuits. _The social factors_ comprise the density of population; public opinion, manners and religion; family circumstances; the system of education; industrial pursuits; alcoholism; economic and political conditions; public administration, justice and police; and in general, legislative, civil and penal institutions. <p 54>We have here a host of latent causes, commingling and combining in all parts of the social organism, which generally escape the notice both of theorists and of practical men, of criminologists and of legislators. This classification of the natural factors of crime, which has indeed been accepted by almost all criminal anthropologists and sociologists, seems to me more precise and complete than any other which has been proposed. In respect of this classification of the natural factors of crime, it is necessary to make two final observations as to the practical results which may be obtained in the struggle for just laws and against the transgression of them. In the first place, owing to ``the discovery of the unexpected relation amongst the various forces of nature, which had previously been thought to be independent,'' we must lay stress on this positive deduction, that we cannot find an adequate reason either for a single crime or for the aggregate criminality of a nation if we do not take into account each and all of the different natural factors, which we may isolate in the exigencies of our studies, but which always act together in an indissoluble union. No crime, whoever commits it, and in whatever circumstances, can be explained except as the outcome of individual free-will, or as the natural effect of natural causes. Since the former of these explanations has no scientific value, it is impossible to give a scientific explanation of a crime (or indeed of any <p 55>other action of man or brute) unless it is considered as the product of a particular organic and psychical constitution, acting in a particular physical and social environment.