The use of certain minerals thought to promote health by correcting deficiencies at the cellular level. Tissue salts therapy, or the Schuessler biochemic system of medicine, was developed in the 1890s by a German doctor, scientist, and homeopath who identified 12 principal mineral salts he believed essential to health. In the Schuessler system, biochemic tissue salts are considered to be minerals in energy form, essential in cell formation and normally derived from organically grown plant foods eaten raw. Because of chemical additives and poor soil treatment, Schuessler believed the mineral and vitamin content of plant foods had diminished to levels inadequate for proper cell development. Symptoms of tissue salt deficiencies include signs of premature facial aging that are read by trained facial analysis therapists, who work out individual mineral replacement regimens for people, depending on their symptoms. The therapy is not clinically proven.