1. _Rules relative to the general or indirect causes of onanism._--The genital sense, and, consequently, the venereal desires, may be felt too vividly and too early, in consequence of different circumstances, which may be divided into two groups. Some belong to the human body, and consist in certain innate acquired arrangements of the organization, in consequence of which the venereal sense presents more or less susceptibility. Others consist in different influences, as education, food, climate, kind of life, &c.; which may act on the sensibility in general, and particularly on that of the genital system. We will begin with the rules connected with the former. _Of the innate or acquired causes of venereal excitement, and of the rules of preservation connected with them._--Some individuals seem, as it were, marked by their organization, to become victims of venereal excesses. In them, the genital sense is excited, and exercises great power, long before the usual period of its manifestation. In others, on the contrary, this sense is not excited until late: in fact, it is so slight, that even this excitement may be doubted. In the present state of the science, these differences can by no means be accounted for. In many cases, however the great development of certain organs, the increase of their vitality or their diseased state exercise considerable influence on the strength and precocity of the venereal sense. Gall, and the phrenologists of his school, place amativeness in the cerebellum. They consider this organ as the legislator of the sexual parts, the seat of physical love; and assert that the differences in the mass and vitality of this portion of the brain, correspond exactly to the differences of the intensity of the genital desires. We will proceed to mention the different facts on which these physiologists formed their opinion. Comparative anatomy furnishes them with no argument worthy of mention: in fine, facts contradictory to Gall’s opinion may be derived from numerous classes of animals who have been deprived of their cerebellum, and yet have exercised the act of reproduction. This opinion applies only to man, and the mammalia resembling him. The relation between the development of the cerebellum and that of the genital organs, has furnished a more plausible reason: it has been adduced as an argument, that, in the encephalon, the fibres of the cerebellum are the last to appear distinctly; and this organ is not perfect, till from the age of eighteen to twenty-six years. A remark of Sœmmering, also, has been adduced, to show that the cerebellum, at the period of puberty, is to the cerebrum as one to five, while in infancy it is only as one to seven. We have already seen that the genital sense is more powerful in males than in females. But it is said positively, that the cerebellum is commonly smaller in females than in males.