There are, first, the _cosmic_ causes of crime; that is to say, all the influences of the external inorganic world, the influence of temperature on crime, the increase of crimes of violence in hot weather, the periodicity of other kinds of crime, the influence of climate, the influence of diet. Then there is the _biological_ factor. Under this head we include the consideration of all the personal peculiarities of the individual, anatomical, physiological, psychological. These peculiarities may be atavistic, atypic, or morbid. Lastly, there is the _social_ factor in crime. Criminal sociology deals with the production of crime by social influences, and by economic perturbations. Infanticide is nearly always related to the social factor; and the study of the various social influences which promote or hinder infanticide is extremely instructive. The relations between crimes against the person and the price of alcohol, and between crimes against property and the price of wheat, also belong to this department of the study of crime. Society prepares crimes, as Quetelet said; the criminal is the instrument that executes them. “The social environment,” Lacassagne has well said, “is the cultivation medium of criminality; the criminal is the microbe, an element which only becomes important when it finds the medium which causes it to ferment: _every society has the criminals that it deserves_.” It is impossible to over-estimate the importance of the social factor in crime. To some extent it even embraces the others, and can be made to regulate and neutralise them. But we cannot deal wisely with the social factor of crime, nor estimate the vast importance of social influences in the production or prevention of crime, unless we know something of the biology of crime, of the criminal’s anatomical, physiological, and psychological nature. This book is concerned with the study of the criminal man. CHAPTER II. THE STUDY OF THE CRIMINAL. When Homer described Thersites as ugly and deformed, with harsh or scanty hair, and a pointed head, like a pot that had collapsed to a peak in the baking-- ἄισχιστος δὲ ἀνὴρ ὑπὸ Ἴλιον ἦλθεν. φολκὸς ἔην, χωλὸς δ’ ἕτερον πόδα. τὼ δέ οἱ ὤμω κυρτώ, ἐπὶ στῆθος συνοχωκότε. αὐτὰρ ὕπερθεν φοζὸς ἔην κεφαλὴν, ψεδνὴ δ’ ἐπενήνοθε λάχνη