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Medical texts often state that blood and sweat are different in name but similar in nature. Zhu Danxi followed this view, thus proposing the theory that "inside it is blood, outside it is sweat." This seems to imply that blood is sweat, and sweat is blood. However, one should know that the origins of blood and sweat cannot be simply discussed as being of the same category. The *Classic of Internal Medicine* (*Neijing*) states: "The Heart governs blood, and blood is generated by the Heart." It also says: "The Kidney governs five fluids; when they enter the Heart, they become sweat." Furthermore, it states: "Sweat is the fluid of the Heart." Here, it says sweat is the fluid of the Heart, not that sweat is the blood of the Heart. Blood is generated by the Heart, governed by the Spleen, and stored in the Liver. Its fundamental principle originates from the essence-qi of food and drink, received in the Middle Jiao (Middle Burner), transformed into juice, harmonized among the Five Zang Organs, and distributed throughout the Six Fu Organs to nourish the body. As for sweat, it is the body's Jin-Ye (body fluids). When the Cou-Li (pores and skin texture) are loose and the skin/hair follicles fail to protect the exterior, pathogenic factors such as Wind, Summerheat, Dampness, and Heat invade, causing evaporation and emergence, resulting in profuse sweating. Thus, sweat is transformed by the Yang Qi of the body; hence it is said, "When Yang acts upon Yin, it is called sweat." It should be stated that "inside it is Qi, outside it is sweat." This can be explained in terms of Qi, but not analogized with Blood. How can sweat outside be confused with blood inside? In the human body, there are nasal mucus, tears, saliva, phlegm/fluid, feces, and urine; all belong to the transformation of the same water source and emerge from the Nine Orifices. Therefore, what comes out of the nose is called mucus (Ti), what comes out of the eyes is called tears (Lei), what comes out of the mouth is called spit (Tuo) or saliva (Xian), what comes out of the two lower orifices is called feces and urine, and what is excreted through the skin/hair follicles is called sweat. If sweat can be compared to blood, then mucus, tears, spit, saliva, feces, and urine could also be referred to as blood!

Regarding the meaning of Tian Gui (Heavenly Water/Menstrual Essence), various schools interpret it as Jing-Blood (Essence and Blood), which fails to detail the purport of the *Neijing*. Examining the classic text: "At age fourteen, a girl's Tian Gui arrives, and her menstruation occurs at regular times; at age sixteen, a boy's Tian Gui arrives, and his Jing-Essence overflows and is discharged." Thus, Tian Gui appears first, and then Jing-Blood follows; it is clear that Tian Gui is not synonymous with Jing-Blood. Tian Gui is the True Water born from Heavenly One, which in the human body is called Yuan Yin (Primal Yin) or Yuan Qi (Primal Qi). Before birth, this Qi is contained within the parents and is called Xian Tian Yuan Qi (Pre-natal Primal Qi); after birth, this Qi transforms within oneself and is called Hou Tian Yuan Qi (Post-natal Primal Qi). Initially, when Qi is born, True Yin is very slight; only when it becomes abundant does Jing-Blood flourish. However, True Yin must be sufficient before Jing-Blood can be transformed; thus, True Yin precedes Jing-Blood, and Jing-Blood follows True Yin. Otherwise, when Tian Gui ceases at age forty-nine for women and sixty-four for men, why do the Jing-Blood throughout the body continue to circulate within Ying and Wei (Nutritive and Defensive levels) without becoming depleted? From this, we know that Tian Gui is not Jing-Blood. Those who claim that Jing-Blood is Tian Gui propagate erroneous theories starting from Wang Bing and Chen Liangfu.