Periods of moral decadence in the life of a people are always contemporaneous with times of effeminacy, sensuality, and luxury. These conditions can only be conceived as occurring with increased demands upon the nervous system, which must meet these requirements. As a result of increase of nervousness, there is increase of sensuality, and, since this leads to excesses among the masses, it undermines the foundation of society,—the morality and purity of family life. When this is destroyed by excesses, unfaithfulness, and luxury, then the destruction of the state is inevitably compassed in material, moral, and political ruin. Warning examples of this character are presented by Rome, Greece, and France under Louis XIV and XV.[10] In such times of political and moral destruction monstrous perversions of the sexual life were frequent, which, however, may in part be referred to psycho-pathological or, at least, neuro-pathological conditions existing in the people. It is shown by the history of Babylon, Nineveh, Rome, and also by the “mysteries” of life in modern Capitals, that large cities are the breeding-places of nervousness and degenerate sensuality. The fact which may be learned from reading Ploss’s work is remarkable, viz., that perversion of the sexual instinct (save among the Aleutians, and in the form of masturbation among the females of the East and the Nama Hottentots) does not occur in uncivilized or half-civilized races.[11] The study of the sexual life in the individual must begin at its development at puberty, and follow it through its different phases to the extinction of sexual feelings. In his “Physiology of Love,” Mantegazza describes the longings and impulses of awakening sexual life, of which presentiments, indefinite feelings, and impulses have existed long before the epoch of puberty. This epoch is, physiologically, the most important. In the abundant increase of feelings and ideas which it engenders is manifested the significance of the sexual factor in mental life.