方书多言血与汗异名而同类。丹溪因之，遂有在内为血，在外为汗之论。似乎血即是汗，汗即是血
矣。岂知血与汗之由来，有不可以同类并言者。经云∶心主血，血生于心。又云∶肾主五液，入心为
汗。又云∶汗者，心之液。此言汗为心之液，而非曰心之血。血生于心，统于脾，藏于肝，而其原则自水谷之
精气，受于中焦，变化取汁，和调于五脏，洒陈于六腑，以奉生身者也。若夫汗则为人身之津液，因腠理
疏，皮毛不能外卫，风、暑、湿、热之邪干之，则蒸然发出，津津而为汗。是汗乃身之阳气所化，故曰阳加于
阴，谓之汗。当云在内为气，在外为汗。此可以气言，而不可以血类也。庸有在外之汗，而可以在内之血混言
之乎？人之一身，有涕、泪、涎、唾、便、溺，皆属一水之化，而发于九窍之中。故鼻之所出曰涕，目之所
出曰泪，口之所出曰唾、曰涎，二阴之所出曰便、溺，而皮毛之所泄则曰汗。汗可以血类之，则涕、泪、唾、
涎、便、溺，亦可以血言之矣！
天癸之义，诸家俱以精血为解，是不详《内经》之旨也。玩本经云∶女子二七天癸至，月事以时下；男子
二八天癸至，精气溢泻。则是天癸在先，而后精血继之，天癸非即精血之谓明矣。天癸者，天一所生之真
水，在人身是谓元阴，即曰元气。人之未生，此气蕴于父母，谓之先天元气；人之既生，此气化于吾身，
谓之后天元气。但气之初生，真阴甚微，及其既盛，精血乃旺。然必真阴足而后精血化，是真阴在精血之
先，精血在真阴之后。不然女子四十九，男子六十四，而天癸俱绝，其周身之精血，何以仍营运于荣卫
之中，而未尝见其涸竭也？则知天癸非精血明矣。其以精血即为天癸者，王太仆、陈良甫以下之谬论也。
医书中多认为血与汗名称不同但本质相同。朱丹溪沿袭此说，于是有了“在内为血，在外为汗”的论点。这似乎暗示血就是汗，汗就是血。哪里知道血与汗的来源，有不能简单归为同类而谈论的道理。《内经》说：心主司血液，血液由心生。又说：肾主管五种体液，进入心脏则化为汗。还说：汗是心的体液。这里说汗是心的体液，而不是说汗是心的血液。血液由心生，由脾统摄，由肝贮藏，而其根本原理源自水谷的精微之气，受纳于中焦，经过变化提取汁液，调和于五脏，散布于六腑，以供养生命身体。至于汗，则是人身上的津液，因为腠理（皮肤纹理及毛孔）疏松，皮毛不能在外护卫，风、暑、湿、热等邪气侵犯它，便蒸腾而出，津津渗出成为汗。所以汗是由身体的阳气所化生，因此说“阳加于阴，谓之汗”。应当说是“在内为气，在外为汗”。这可以用气来解释，而不能用血来类比。哪里有在外的汗，却能在内的血混为一谈的呢？人的全身，有鼻涕、眼泪、涎液、唾液、大便、小便，都属于同一水源的变化，而从九窍中排出。所以鼻子排出的叫涕，眼睛排出的叫泪，口排出的叫唾、叫涎，前后二阴排出的叫便、溺，而皮毛排泄出来的叫汗。如果汗可以比作血，那么涕、泪、唾、涎、便、溺，也可以称作血了！
关于天癸的含义，各家都解释为精血，这是没有详察《内经》的宗旨。细读本经说：女子十四岁天癸至，月经按时来潮；男子十六岁天癸至，精气满溢外泄。那么天癸在先出现，然后精血才随之产生，天癸并非就是精血，这已经很明白了。天癸，是由天一之水所生的真水，在人体中称为元阴，也就是元气。人未出生时，这股气蕴藏于父母体内，称为先天元气；人出生后，这股气化生于自身，称为后天元气。只是气初生时，真阴非常微弱，等到它旺盛后，精血才兴旺。然而必须真阴充足之后精血才能化生，是真阴在精血之前，精血在真阴之后。不然的话，女子四十九岁、男子六十四岁时，天癸都枯竭了，那周身之精血，为何仍然在营卫之中运行，而没有见到枯竭呢？由此可知天癸不是精血，这很明白了。那些认为精血就是天癸的人，是从王冰、陈良甫以来的谬论。
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.