《黄帝内经·灵枢·阴阳清浊》
黄帝说：阴清而阳浊，浊气之中有清气，清气之中有浊气，清气和浊气的这些情况应该怎样区别呢？
黄帝曰：夫阴清而阳浊，浊者有清，清者有浊，清浊别之奈何？
The Yellow Emperor said: Yin is clear and yang is impure. Impure Qi contains clear Qi, and clear Qi contains impure Qi. How should we differentiate these Qi?