The concept of "purity" and "pollution" exists in every ethnic group or culture,and the emergence and existence of this concept is closely associated with geographic environment,religious belief,mode of production,lifestyle,morals and world outlook,and is supported and restricted by a whole set of cultural logics hidden deeply in the social structure.Different ethnic groups and cultures have different criteria for classification of "purity" and "pollution".One article,behavior or social phenomenon may be deemed "pure"by one ethnic group,but "polluted" by another.The human perception of "purity" is a dynamic process that changes with the development of people's perception of themselves,the improvement of economic conditions,the interactions among ethnic groups,the dissemination of cultures,and the evaluation by "others"."Purity" and "pollution"structure ethnic,hierarchical,social,and cultural boundaries as a conceptual system of values and symbols.