It is in this way, through a change in the nervous system itself, that habit becomes literally a second nature; and in this way habits most opposite to the natural or rudimentary state are introduced into our human organization, and ‘nature is dominated by or absorbed in habit.’ The power of habit is seen even in the action of organs withdrawn from the will, as in the powers of adaptation to all kinds of food, to various kinds of atmosphere and climate. It is, however, in that portion of our nature directly connected with and governed by the brain that the remarkable transforming power of habit is seen, and in the sexual system this enormous power is most signally displayed. Habits may become so much a part of our nature that they are exercised unconsciously, the impression which first excited the brain being no longer noticed, though still exerting its modifying influence. But when the attention is constantly aroused, the brain acts with sustained and increasing energy; the senses are thus strengthened or perfected, and new and higher powers are developed in the individual, which through inheritance may be transmitted to a succeeding generation. It is in this way that the practice of continence or of incontinence gradually forms a distinctive characteristic of social and national life. This distinctive faculty possessed by the nervous system of modifying its own sensations, and even acquiring new aptitudes, is the physiological basis of human progress. ‘It is the foundation of education, of the power of law, of the influence of custom, and the necessary condition of hygienic improvement.’ Habits, when formed in accordance with physiological law, do not tend to indifference. By the constant repetition of impressions a new relation is gradually established between the organs or faculties affected and the cause which produces the effect. As the keenness of first sensations producing transitory pleasure diminishes, habit strengthens the important relation which grows up between faculties and the objects which modify them. It is the superior power of the new relation thus established by habit between the individual and the objects that have modified his nature, that have even caused the Swiss mountaineer to die of home-sickness, or the bereaved partner in a lifelong union to follow the beloved object to the grave.