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original food and natural food must be his best food. Nevertheless, I shall now pursue a line of argument independent of all which has preceded.

1. I must first propound to the reader what purposes food fulfils. The human body in every instant undergoes change: it perpetually moves, perpetually decays, and perpetually has to be rebuilt. The action of the atmosphere on the blood is the ultimate cause: air received into the lungs meets the dark blood of the veins—dark because charged with carbon (the element of coal). The air attracts the carbon out of the blood, and leaves it scarlet. The carbon, united to the oxygen of the air, makes carbonic acid, a suffocating gas which is breathed out. A portion of oxygen remains in the blood, which is now driven by the heart into the arteries, and reaches all parts of the system. In its passage it diffuses animal heat, replaces deficiencies, and takes up all the decayed matter, which again it carries back to the lungs, unless it finds some other exit. Thus, muscles, tendons, nerves, bones, nails, hair, all the solids and all the fluids of the body, perpetually decaying, are perpetually renewed by the blood, which has been called liquid flesh.

The blood is thus gradually exhausted, and requires supply; and its supply must be had from food. The food must compensate the tissues for their destruction by vital actions, and by the oxygen of the air under which they rust. Such is the first end to be served by food. A second is to supply animal heat. For the former service the food must contain the chemical element entitled nitrogen, or azote, which abounds in albumen (or white of egg); hence Dr. Prout calls this sort of aliment the albuininous. Albumen and