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Chemical Senses

Taste The universally accepted taste qualities per­ ceived by humans are sweet, salty, sour, and bitter (although a few other terms like metal­ lic, alkaline, and umami have been suggested as potential taste qualities by some authors). A comparison across mammals suggests that taste information falls into these four catego­ ries across species. The source of the salty taste is the cation of a salt. The anions of salts con­ tribute other tastes (bitter, sweet, or both, to humans) depending on their structures. The cations also contribute other tastes depending on their size. The smaller cations lithium (Li) and sodium (Na) produce relatively pure salti­ ness, but larger cations like potassium (K) taste bitter as well as salty. Some species (e.g., rats) have neurons that are sodium specialists (Frank, 1985), which may aid in the detection of sodium. Schulkin (1991) has suggested that the salty taste serves a critical function in a variety of mineral deficiencies. In the wild, animals encounter salt licks, which contain sodium but also other minerals. If deficiencies in any of these minerals were to trigger an appetite for saltiness, then as the animal sat­ isfied its desire for saltiness at the salt lick, it would incidentally ingest the other minerals as well.