《黄帝内经·素问·金匮真言论》
北方黑色，与肾相通，肾开窍于前后二阴，经气内藏于肾，在五味为咸，与水同类，在五畜为猪，在五谷为豆，与四时中的冬季相应，在天体为辰星，他的疾病多发生在溪和骨，在五音为羽，其成数为六。此外，其嗅味为腐。
北方黑色，入通于肾，开窍于二阴，藏精于肾，故病在谿。其味咸，其类水，其畜彘，其谷豆，其应四时，上为辰星。是以知病之在骨也。其音羽，其数六，其臭腐。
The black of the north corresponds to the kidneys, which open at the front and back two vaginas, and their inner Qi is stored in the kidneys. Among the five tastes, it is salty and of the same type as water; among the five animals, it is the pig; among the five grains, it is the bean; among the four seasons, it corresponds to winter; in the celestial bodies, it is the Jade Star; its diseases mostly occur in the buttocks and bones; and among the five musical notes, it is the Yu note, and its counting number is six. In addition, its smell is rotten.