Thus aversion is always the instinctive, or conscious cognition of a noxious influence. Pleasure, its opposite, is not merely, as has been sometimes maintained, the absence of discomfort--_i.e._, a negative state--but something positive. Every part of the organism has definite needs which assert themselves as a conscious or unconscious tendency, as an inclination or appetite; the satisfaction of these needs is felt as a pleasure which can rise to a feeling of bliss. The first need of each organ is to manifest itself in activity. Its simple activity is a source of pleasure to it, so long as it does not go beyond its powers. The activity of the cerebral centres consists in receiving impressions, and in transforming them into representations and movements. This activity produces in them feelings of pleasure; they have in consequence a strong desire to receive impressions so as to be put into activity by them, and experience feelings of pleasure. This, broadly sketched, is the natural history of the feelings of pleasure and pain. The reader who has mastered it will experience no difficulty in comprehending the nature of aberration. Unconscious life is subject to the same biological laws as conscious life. The vehicle of the unconscious is the same nervous tissue--although, it may be, another portion of the system--in which consciousness is also elaborated. The unconscious is just as little infallible as consciousness. It can be more highly developed or retarded in its development; it can be more or less stupid or intelligent. If the unconscious is incompletely developed, it distinguishes badly and judges falsely, it deceives itself in the knowledge of what is prejudicial or favourable to it, and instinct becomes unreliable or obtuse. Then we get the phenomenon of indifference to what is ugly, loathsome, immoral. We know that among the degenerate divers arrested developments and malformations appear. Particular organs or entire systems of organs are arrested at a degree of development which corresponds to infancy, or even to the fœtal life. If the highest cerebral centres of the degenerate stop in their development at a very low stage, they become imbeciles or idiots. If the arrest of development strikes the nervous centres of unconscious life, the degenerate lose the instincts which, in normal beings, find expression in nausea and disgust at certain noxious influences; I might say, their unconscious life suffers from imbecility or idiocy.