The vital functions, or actions, are those which are absolutely necessary to life, as the actions of the heart, lungs, and arteries. On the action and reaction of the solids and fluids upon each other, depend the vital functions. The pulse and respiration are the external signs of life. Vital diseases are all those which hinder the influx of the venal blood into the cavities of the heart, and the expulsion of the arterial blood from them.
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 occasion a perpetual waste. The manducation, the deglutition, and digestion of food, the separation and distribution of the chyle, and excrementitious parts, etc. comprise 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 we perform at will, as muscular motion, and all the voluntary actions of the body; they are those which constitute the sense of touch, taste, smell, sight, hearing, perception, reasoning, imagination, memory, judgment, and other affections of the mind. Without these a man may live, but not so comfortably as with them.
The sexual actions are those of the organs of generation of either sex.
Private actions are such as regard particular parts.
Public actions are those which are performed for the sake of the whole body; such is the action of the stomach in digesting the aliment, etc. These are called functions.
But each part hath an action peculiar to itself. Thus the offices performed by the muscles, vessels, glands, and viscera, are called their respective act ion. See Professor Whytt's Treatise on Vital Motions.