It needs but to name appetite and satiety to suggest multitudinous facts showing that pleasures are relative not only to the organic structures but also to their states. The food which yields keen gratification when there is great hunger ceases to be grateful when hunger is satisfied, and if then forced on the eater is rejected with aversion. So, too, a particular kind of food, seeming when first tasted so delicious that daily repetition would be a source of endless enjoyment, becomes, in a few days, not only unenjoyable but repugnant. Brilliant colors which, falling on unaccustomed eyes give delight, pall on the sense if long looked at, and there is relief in getting away from the impressions they yield. Sounds sweet in themselves and sweet in their combinations which yield to unfatigued ears intense pleasure, become, at the end of a long concert, not only wearisome but, if there is no escape from them, causes of irritation. The like holds down even to such simple sensations as those of heat and cold. The fire so delightful on a winter's day is, in hot weather, oppressive; and pleasure is then taken in the cold water from which, in winter, there would be shrinking. Indeed, experiences lasting over but a few moments suffice to show how relative to the states of the structures are pleasurable sensations of these kinds; for it is observable that on dipping the cold hand into hot water, the agreeable feeling gradually diminishes as the hand warms. These few instances will carry home the truth, manifest enough to all who observe, that the receipt of each agreeable sensation depends primarily on the existence of a structure which is called into play; and, secondarily, on the condition of that structure, as fitting it or unfitting it for activity. § 66. The truth that emotional pleasures are made possible, partly by the existence of correlative structures and partly by the states of those structures, is equally undeniable.