The blood, the fountain whence the spirits flow, The generous stream that waters every part, And motion, vigor, and warm life conveys To every particle that moves or lives; 15 This vital fluid, thro’ unnumber’d tubes Pour’d by the heart, and to the heart again Refunded; scourg’d for ever round and round, Enrag’d with heat and toil, at last forgets Its balmy nature; virulent and thin 20 It grows; and now, but that a thousand gates Are open to its flight, it would destroy The parts it cherish’d and repair’d before. Besides, the flexible and tender tubes Melt in the mildest, most nectareous tide 25 That ripening nature rolls; as in the stream Its crumbling banks; but what the vital force Of plastic fluids hourly batters down, That very force, those plastic particles Rebuild: So mutable the state of man. 30 For this the watchful appetite was giv’n, Daily with fresh materials to repair This unavoidable expence of life, This necessary waste of flesh and blood. Hence the concoctive powers, with various art, 35 Subdue the cruder aliments to chyle; The chyle to blood; the foamy purple tide To liquors, which thro’ finer arteries To different parts their winding course pursue; To try new changes, and new forms put on, 40 Or for the public, or some private use. Nothing so foreign but th’ athletic hind Can labour into blood. The hungry meal Alone he fears, or aliments too thin, By violent powers too easily subdu’d, 45 Too soon expell’d. His daily labour thaws, To friendly chyle, the most rebellious mass That salt can harden, or the smoke of years; Nor does his gorge the rancid bacon rue, Nor that which Cestria sends, tenacious paste 50 Of solid milk. But ye of softer clay Infirm and delicate! and ye who waste With pale and bloated sloth the tedious day! Avoid the stubborn aliment, avoid The full repast; and let sagacious age 55 Grow wiser, lesson’d by the dropping teeth.