Celery is a very good source of fiber, and a good source of potassium and calcium. Look for bunches with a good tight formation, leaves should be fresh and unwilted. Stems should be firm and crisp when snapped. Brown or cracked bunches should be avoided. The whole plant is gently stimulant, nourishing, and restorative; it can be liquefied, with the juice taken for joint and urinary tract inflammations, such as rheumatoid arthritis, cystitis, or urethritis, for weak conditions, and for nervous exhaustion. More specific uses: The seeds are mainly used as a diuretic, these help clear toxins from the system, so are especially good for gout, where uric acid crystals collect in the joints, and arthritis. Source: http://en.wikipedia.org/wiki/Celery Stock is the strained liquid that is the result of cooking vegetables, meat, or fish and other seasoning ingredients in water.