Library

Essence (Jing), marrow, blood, milk, sweat, fluid (when exiting the body it is called sweat, when retained inside it is called fluid), Jin (fluids from the mouth), nasal mucus (accumulated in the brain, exiting from the nose), tears, and urine are all forms of water, and they all belong to the Kidney. The reason why blood alone is red is that blood is transformed by the Heart Fire; the colors of the aforementioned fluids are all white, which are transformations of Lung Qi.

The Kidney belongs to Yin, and the Lung belongs to Yang; when Yang interacts with Yin, fluids are transformed. The Kidney belongs to Water, and the Heart belongs to Fire; when Water interacts with Fire, blood is formed, because blood is created by the Heart Fire. Therefore, the *Classic* states that "the Heart generates blood," also says "blood belongs to the Heart," and further states that "the Heart governs the blood vessels of the body." Red is the color of Heart Fire. If Heart Fire is insufficient, the blood color will be pale. If Heart Qi is deficient and cold, blood will coagulate and turn purple-black; purple-black is the manifestation of the Kidney's color, indicating a lack of fire. There are also cases where excessive fire causes blood stasis resulting in a purple-black color; in general, this demonstrates the close relationship between blood and the Heart. (Zhang Jieshi said: Wherever there is blood in the body, touching it causes pain; pain perception belongs to the Heart's domain, and red is the color of fire, hence it is said that the Heart generates blood. He also said: In areas of numbness in the body, there is no blood color, meaning blood does not reach there, and thus the Heart cannot govern it, so one feels no pain or itch. He also stated: Zhao claimed that blood follows Xiang Huo (Ministerial Fire) in its circulation, hence its red color, which is incorrect. Xiang Huo resides in Kan Water and cannot reveal itself; Yang is obscured by Yin, so its color is black. As for Heart Fire, Yang is mature, and Yin is closed by Yang, so the interior is dark and the exterior is bright, making its color red. If blood followed Xiang Huo, it would necessarily be black, not red.)

Sweat, fluid, Jin, tears, and urine are all clear and pure, generated by Yang. Essence, marrow, blood, milk, and nasal mucus are all thick and turbid, formed by Yin. Yang nature is rapid, and its generation is easy, so when Qi arrives, it generates immediately. (For example, when sorrow moves Qi, tears flow like a spring; when internal heat steams, sweat pours like rain, as can be seen.) Yin nature is slow, and its formation is difficult, so it must accumulate before becoming abundant. Subdividing them, essence, marrow, and nasal mucus form one category, while blood and milk form another. The formation of milk is easier than that of blood, hence it is said that blood is difficult to form but easy to deplete.

Marrow is stored and not excreted; nasal mucus is essentially brain marrow, and its excretion occurs due to brain heat disease. Only essence is stored yet can be excreted; its excretion occurs due to the harmonious and smooth interaction of Yin and Yang, thereby enabling reproductive functions. Blood is also stored and not excreted, which is significantly different from essence being stored yet excretable. Thus, essence is dynamic while blood is static; essence is Yang while blood is Yin. (Menstruation in women is an overflow, not an excretion.) Essence is scarce and blood is abundant, marking a distinction of nobility and baseness. Essence represents life/youth while blood represents death/old age, marking a distinction of youth and old age. (Essence is white, transformed by Lung Qi, belonging to Clear Yang. Clear Yang is Shao Huo (Lesser Fire); less fire means vitality. Blood is red, formed by Heart Fire, belonging to Turbid Yang. Turbid Yang is Zhuang Huo (Blazing Fire); blazing fire means aging.) Water congeals into ice, which melts upon seeing the sun; blood congeals into clots, which do not dissolve even after boiling. Water moves with Qi and can exit the body externally; blood moves with Qi but circulates only internally. The distinctions of clear/turbid and Yin/Yang in their qualities can be observed here. The old view that blood is governed by the Heart aligns with the meaning of "the Heart generates blood." But why is it said that blood is transformed by the Spleen, received/stored by the Liver, distributed by the Lungs, and excreted by the Kidneys? The answer is: The *Classic* states that when food and drink enter the Stomach, the Middle Jiao receives the Qi, extracts the juices, transforms them, and turns them red to become blood. This implies that the clear Qi of food and drink in the Stomach relies on the Spleen's transportation and transformation to generate blood, hence it is said to be transformed by the Spleen. However, a fetus in the womb has not yet ingested food or drink, yet already possesses blood; this shows that blood is primordial water, merely relying on postnatal nourishment for growth, not entirely dependent on the postnatal. (Another saying regarding the Spleen controlling blood refers to the idea that blood circulates following Spleen Qi.) Furthermore, the *Classic* states that when a person lies down, blood returns to the Liver. This likely means that wakefulness belongs to Yang, sleep belongs to Yin; Yang governs the exterior and tends upward, while Yin governs the interior and tends downward. During wakefulness, blood moves with Yang, circulating outward and upward; during sleep, blood settles with Yin, moving inward and downward. All five Zang organs are internal, but the Liver and Kidney reside in the lower jiao and are the organs where blood returns. Mentioning the Liver implies the Kidney as well. Why? The Liver is dynamic, the Kidney is static; since the dynamic aspect pertains to the Zang, the static aspect can be inferred, hence it is said that the Zang receives [blood] from the Liver. (Another interpretation: Blood is not stored [by itself], but is regulated by the Liver's free flow, so attributing storage responsibility to the Liver is also valid.) The statement about distribution by the Lungs refers to the principle that blood follows Qi in its movement. The statement about excretion by the Kidneys conflates essence and blood; observing how ancients often referred to "father's essence and mother's blood" makes this clear. One must understand that this is essence, not blood, and should not be mixed together. Blood in the meridians circulates, while blood in the Zang-Fu organs remains in its proper place. The above clarifies the principles of blood; detailed pathological manifestations, pulse diagnoses, and treatments are described below.

Blood follows Qi in its movement. If Qi is cold, movement is sluggish, causing blood to stagnate. If Qi is hot, movement accelerates, causing blood to boil. (Generally, blood belongs to Yin and requires Yang to move, so it coagulates when encountering cold. Qi belongs to Fire, manifesting as either Shao Huo or Zhuang Huo, so it burns when encountering heat.) Sluggishness in the skin results in painful Bi syndrome; coagulation in the collaterals results in abscesses and masses; stasis accumulation in the intestines and stomach leads to decay and corruption; deficiency-cold failing to contain leads to prolapse and hemorrhage; boiling in the upper jiao leads to vomiting and epistaxis; flowing into the lower jiao leads to hematochezia; obstruction in the meridians leads to carbuncles and toxins; floating on the skin leads to rashes. Moreover, excessive dampness steaming leads to leprosy-like conditions; dry blood transforming leads to consumption and parasites. The causes of disease are numerous, but fundamentally fall into two categories: cold and heat. Generally, blood stasis is relatively easy to treat, whereas blood dryness is difficult to cure. Cases without tidal fever are mild, while those with tidal fever are severe.