Hides are the pelts of the larger animals—cattle, horses, buffalo, elephants, and so on; Skins come from smaller animals—calves, sheep, goats, pigs, deer, beaver, etc.—and from birds, fish, and reptiles; Leather is any hide or skin _after it has been tanned_. As the legislature of colonial Virginia put it in 1691 (in an act that will shortly engage our attention again): And for the avoyding of all ambiguities and doubts, which may and doe grow and arise upon the difinition and interpretation of this word leather, _Be it enacted and declared_, that hydes and skinns of oxe, steer, bull, cow, calfe, deer, goats and sheep being tann’d shall be, and ever hath been reputed and taken leather. The key word is “tanned.” Like any organic matter, skins and hides will soon begin to decay unless they receive some kind of preservative treatment. They may be simply scraped and sundried—or salted or smoked or soaked in brine or in slaked lime. From some of these processes may come extremely tough and durable products—rawhide, parchment, and vellum are limed—but they are not leather because they have not been _tanned_. [Illustration: _Taneur_ _This illustration from Diderot’s great eighteenth-century French encyclopedia shows the essential operations in a tannery: A) washing hides in a stream; B) scraping hair or flesh from a hide on the “beam”; C) soaking hides in a series of lime pits; D) bedding hides in a tanning vat with a layer of shredded bark between each hide; E) stirring lighter hides in a hot water tanning solution._] Tanning brings about within the fibrous structure of a pelt certain chemical and physical rearrangements that are still imperfectly understood. Their effect, however, is to render the pelt permanently imputrescible, pliable when dry, and capable of sustaining repeated wetting without hurt. The agents responsible for the transformation, known as “tannins,” are found in almost all plants, in certain minerals, and in various readily oxidizing oils. _TANNING AND CURRYING_ The ancient Sumerians, Babylonians, Assyrians, Egyptians, central Asians, and Chinese all knew tanned leather and used it. But who first discovered how to tan it, when that happened, and where, must remain forever unanswered, since the invention of tanning came before the invention of written records. Primitive leatherworkers probably stumbled on different processes at different times and places, and quite possibly a number of widely separated workers discovered the same processes independently.