Appetite (Lat, appetere, to desire or seek earnestly), in physiology, the natural desire and relish for nutritious food. The desire for food returns, in man and animals, with a certain degree of regularity, at periodical intervals. This is owing to the continuous alteration and waste of the ingredients of the animal tissues and fluids by the active powers of life, and is an indication that the time has arrived for the ingestion of food to reestablish the equilibrium between nourishment and disintegration, and thus maintain the integrity of the vital powers. The healthy appetite, in persons taking a proper amount of exercise, is the best guide for determining the frequency with which food should he taken, as well as for its quantity, and the kind of food consumed. If not satisfied within a reasonable time, the appetite becomes at first imperative and distressing, and is then apt to fail altogether; so that the desire for food disappears until the next recurrence of its habitual period of return. A morbid appetite, or a craving for food in unnatural quantity or of unnatural character, is sometimes a well marked symptom of disease.