Note 5 — BOOK II. DIET.

In the human body, as well as in those of other animals, the larger blood-vessels are composed of smaller ones; which, by the violent motion and pressure of the fluids in the large vessels, lose their cavities by degrees, and degenerate into impervious chords or fibres. In proportion as these small vessels become solid, the larger must of course grow less extensile, more rigid, and make a stronger resistance to the action of the heart, and force of the blood. From this gradual condensation of the smaller vessels, and consequent rigidity of the larger ones, the progress of the human body from infancy to old age is accounted for.