ACTION, in Physiology, is applied to the functions of the body, whether vital, animal, or natural.—The vital functions, or actions, are those which are absolutely necessary to life, and without which there is no life; as the action of the heart, lungs, and arteries.—The natural functions are those which are instrumental in repairing the several losses which the body sustains; for life is destructive of itself, its very offices occasioning a perpetual waste. The manducation of food, the deglutition and digestion thereof, also the separation and distribution of the chyle and excrementitious parts, &c. are under the head of natural functions, as by these our aliment is converted into our nature. They are necessary to the continuance of our bodies.—The animal functions are those which, though not absolutely essential to life, are distinctive of animal existence, such as sensation, and voluntary motion.