Bloat is a disease that has been described in agricultural writings since at least A.D. 60. Few livestock diseases have such a long and colorful history. Even the names for bloat have changed considerably over the years. In past centuries, a bellyful of gas was attributed to a poison, to excessive gas production, or to blockage caused by the excessive consumption of dense feed. These and other explanations were the objects of experimental research in several countries from the 1940s to the 1960s. Some current practices have been used for many years. For example, placing an animal's front feet on a mound so that the front feet are higher than the back feet helped to ease bloat because the esophagus was thus elevated, and the gas was expelled more easily. Enforced moderate exercise, such as walking, was a commonly-used treatment for bloat and was often effective if used before bloat reached the acute stage. Another method involved placing a stick or rope through an animal's mouth to encourage salivation, which breaks down rumen foam. A book published in the early 18th century emphasized the need for care when cattle are first put into "clovergrass."