We humans are 97% salty water. The salt portion, which amounts to about 250 grams in the adult, maintains fluid and nutrient balance in the body as well as transmission of nerve impulses to and from the brain and contraction of muscles, including those of the heart. (Derangements of some of these functions, such as hypertension, may respond to adjusting salt intake.) Body salt needs to be continually replenished. Thus, the craving of humans for salty foods may have a physiologic basis.
Salt has been a sought-after condiment since ancient times. The word “salary” comes from salarium, an allowance of money for salt that was given to men serving in early Roman armies. Homer called salt “divine,” and Plato described it as “a substance dear to the gods.”
Before refrigeration, salt was also an important food preservative. Salt curing was one of the four major methods of keeping meats and fish edible (the others were drying, smoking, and freezing). The enormous quantities that were needed made it a major factor in early commerce. Some of the first trade routes were created for traffic in salt.
Salt occurs in various forms in nature. Sodium chloride, or common salt, which is what we sprinkle on food, was initially extracted from sea water or surface deposits, and later mined. Mining, with various refinements, produces most of the table salt in use today. The mined salt, which contains impurities, is purified for domestic use.
In addition to its role in maintaining homeostasis, salt has another medicinal virtue, being mildly antiseptic when applied externally. A dip in the ocean will speed up the healing of a small cut on the skin, and nothing is more efficacious as a gargle for a sore throat than good old salty water.