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The qi and blood of the vigorous are abundant; their muscles are smooth, their qi pathways are unobstructed, and the movement of Ying Qi (Nutrient Qi) and Wei Qi (Defensive Qi) follows its normal course. Therefore, they are alert during the day and sleep soundly at night. The qi and blood of the elderly decline; their muscles become withered, their qi pathways become obstructed, the qi of the Five Zang Organs clashes with one another, their Ying Qi becomes deficient and scanty, and Wei Qi invades inward. Therefore, they lack vitality during the day and suffer from insomnia at night. (From the chapter "Ying Sheng Hui" of *Ling Shu*.)

Humans correspond to Heaven and Earth and participate in the cycles of the Sun and Moon. Thus, even in daily life, the opening and closing of Cou Li (interstices/skin pores) have their regular timing. When the moon is full, the seawater swells toward the west, human blood and essence become abundant, muscles are filled, skin is dense, hair is firm, Cou Li are closed, and dust adheres. At this time, even if one encounters Wind Pathogens (evil winds), the invasion is shallow and not deep. When the moon wanes, the seawater swells toward the east, human blood and qi become deficient, Wei Qi departs, leaving only the physical form; muscles diminish, skin becomes lax, Cou Li open, hair falls out, the texture becomes thin (" " is identical to "Jiao"), and dust falls off. At this time, encountering evil winds leads to deep invasion and sudden, violent illness. Therefore, those who encounter the "Three Deficiencies" die suddenly and rapidly; those who encounter the "Three Excesses" are not harmed by pathogens. Encountering the decline of the year (where the natal element is controlled by the annual element), meeting the emptiness of the moon (waning moon), and losing the harmony of the season (inhospitable cold or heat) constitute the "Three Deficiencies"; encountering the prosperity of the year, meeting the fullness of the moon, and obtaining the harmony of the season constitute the "Three Excesses". (Above from *Ling Shu*.)

When the weather is warm and the sun is bright, human blood becomes fluid and Wei Qi floats on the surface; thus, blood is easily dispersed, and qi moves freely. When the weather is cold and the sun is obscured, human blood coagulates and stagnates, and Wei Qi sinks inward. When the moon begins to grow, blood and qi begin to refine, and Wei Qi begins to circulate. When the moon is full, blood and qi are substantial, and muscles are firm. When the moon is empty (waning/new), muscles diminish, meridians are deficient, Wei Qi departs, and only the form remains. Therefore, when the weather is cold, do not use acupuncture; when the weather is warm, there is no need for hesitation (no taboos in treatment). When the moon is growing, do not use draining methods; when the moon is full, do not use tonifying methods; when the moon is empty, do not treat. This is called regulating according to the appropriate time.

Yang Qi governs the exterior throughout the day. At dawn, Human Qi arises; at noon, Yang Qi is most prosperous; at sunset, Yang Qi is already deficient, and the Qi Gates (pores) close. Therefore, in the evening, one should conserve and repel pathogens, not disturb the sinews and bones, and avoid exposure to fog and dew. Reversing these three periods causes the physical form to become exhausted and weakened. (Above from *Su Wen*. "Bo" means pressing or diminishing.)

Qi is Yang and corresponds to the Sun; Blood is Yin and corresponds to the Moon. Therefore, summer heat causes Qi to disperse, cold causes Qi to contract, midday makes Qi strong, and dusk makes Qi decline. The reason why diseases contracted at midday heal at midnight, and diseases contracted at midnight heal at midday, is due to the mutual substitution of Yin and Yang. When the moon grows, human blood gradually increases; when the moon dies (wanes), human blood gradually decreases. In all cases where disease resides in the Blood aspect or involves various hemorrhagic syndromes, there are instances where abundant blood leaves no room for pathogens, causing the disease to recede, and instances where diminished blood deprives pathogens of attachment, also causing the disease to recede. As for the recovery of spirit, it must occur during the phase of the waxing moon. Therefore, Zhang Zhongjing stated regarding Malaria (Nue Ji): If it starts on the first day of the lunar month, it should heal on the fifteenth. If it does not improve, it should resolve by the end of the month. Malaria is a disease where Wei Pathogens enter the Ying level; thus, the dates of Hui (last day of lunar month) and Shuo (first day of lunar month) determine the period of remission or exacerbation. I once suffered from hematochezia due to summer heat. I contracted the illness during the full moon. After the bleeding stopped, my spirit remained confused, but on the first day of the following month (Shuo), I suddenly felt clear-headed. Is it false that secular beliefs hold that the prognosis of chronic illnesses can be determined by the fluctuations in condition on the days of Shuo and Wang (full moon)?

Meridian blood and qi seem unrelated to Xing Zhen (observation of physical signs). *Ling Shu* states: In diseases of Ying Qi, blood flows up and down. Li Dongyuan said: The manifestation of blood flowing up and down is the face appearing alternately fat and thin. When blood rises with Qi, the face appears swollen like being fat; when blood descends with Qi, the face appears emaciated like being thin. People with insufficient Yuan Qi often exhibit this sign. It is also said: When Ying Qi is abundant and overflowing, the disease is in the blood vessels. This is because pathogens agitate the blood vessels, causing luster to float to the surface of the face. Observing this, how can it truly be said to be unrelated to Xing Zhen?