According to the fact that spleen belongs to yin, it shows that spleen belongs to yin, that is, the part that reaches yin. There are two reasons: first, from the text, according to (Song Benyu) "reach, reach also", that is, the meaning of arrival; Secondly, from the medical point of view, it is recorded in Neijing that long summer is the most yin. For example, in Su Wen Bi Lun, "when yin meets this, it is tendon bi", and according to the five internal organs, the spleen should be long in summer, and long summer is the season when seasonal qi changes from yang in spring and summer to yin in autumn and winter, that is, when yang reaches yin, so the spleen is also called yin, which means reaching yin. If the theory of yin and yang is used to explain the human body, there is no alternate transformation of vulva in the operation of various qi in the human body, and yin depends on exhaustion. From the beginning of its birth, it can bear yang and open yin, so it can make qi pivot vertically. This pivoting function is only available in Neijing, including the pivoting of five zang-organs qi and the pivoting of ying-Wei qi.