Hormesis is the term for generally favorable biological responses to low exposures to toxins and other stressors. It comes from Greek hórmēsis "rapid motion, eagerness", itself from ancient Greek hormáein "to set in motion, impel, urge on". A pollutant or toxin showing hormesis thus has the opposite effect in small doses as in large doses. A related concept is Mithridatism, which refers to the willful exposure to toxins in an attempt to develop immunity against them. Hormetics is the term proposed for the study and science of hormesis.