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In the *Su Wen: Treatise on Malaria* (Sùwèn · Nuè Lùn), the Yellow Emperor asked: All malaria diseases are caused by wind pathogen, and their accumulation and发作 have fixed times. Why is this? Qibo replied: When malaria first begins to manifest, it initially presents with hair standing on end, followed by stretching and yawning. Then the attack commences, characterized by shivering with chattering teeth (hán gǔ hé), pain in the waist and spine. When the cold subsides, both internal and external heat arise, causing severe headache as if splitting, thirst, and a desire for cold beverages. The Yellow Emperor asked: What qi causes this? Qibo said: This is due to the upper and lower jiao of yin and yang qi contending with each other, alternating between deficiency and excess, and shifting positions. When yang qi merges into yin, yin becomes full while yang becomes deficient. Deficiency of Yangming channel qi leads to shivering with chattering teeth; deficiency of Juyang (Taiyang) channel qi leads to pain in the waist, back, head, and neck. When all three yang channels (Taiyang, Yangming, Shaoyang) are deficient, yin qi prevails. When yin qi prevails, bones become cold and painful. Cold originates internally, hence both interior and exterior feel cold. When yang is excessive, there is external heat; when yin fluid is deficient, there is internal heat. With both internal and external heat, panting and thirst occur, leading to the desire for cold drinks. These conditions result from summer injury by summer-heat pathogen. The intense heat lingers inside the skin but outside the stomach and intestines, which is where Ying Qi (nutritive qi flowing within vessels) resides. This makes sweat pores loose and Couli (skin texture and pores) open. Consequently, autumn qi invades; sweating combined with exposure to wind, or bathing allowing water qi to settle within the skin, causes the pathogen to reside alongside Wei Qi (defensive qi flowing outside vessels). Wei Qi travels through the Yang aspect during the day and the Yin aspect at night. This pathogen moves outward with Wei Qi emerging into Yang, and inwardly presses with Wei Qi entering Yin. The mutual friction between interior and exterior results in daily attacks.

"Starting with hair standing on end, stretching, and yawning" refers to the state of malaria onset, where hairs erect, the body extends, and one yawns. The human body has exterior Yang and interior Yin, upper Yang and lower Yin. When blood and qi circulate freely and yin and yang communicate smoothly, health and peace are maintained. The malaria pathogen, arising from summer-heat, hot water qi, and wind-cold pathogens, lodges in the area between the skin and the stomach/intestines, the dwelling place of Ying Qi. Thus, the pathogen mixes with blood and qi, causing mutual rejection between yin and yang, contention between upper and lower, alternation of deficiency and excess, and shifting of yin and yang. Cold reaches its extreme, and heat reaches its extreme. Water and fire are manifestations of yin and yang; cold and heat are the natures of water and fire. Disharmony of yin and yang in the body signifies conflict between water and fire, resulting in cold and heat manifestations. The pathogen residing with Wei Qi means that as Wei Qi exits Yang during the day and enters Yin at night, completing one cycle daily, the pathogen is forced inward and outward accordingly, causing daily disease episodes. If the pathogen penetrates deeply, attacks may occur every one or two days due to deeper lodging.

The Yellow Emperor asked: What causes attacks occurring every other day? Qibo replied: Because the pathogen lodges deeply, pressing inwardly on the Yin aspect. Yang qi alone flares up, while Yin pathogen adheres internally. Yin and Yang contend but cannot exit easily, hence the every-other-day pattern.

When the pathogen is in the Wei aspect, it manifests according to the entry and exit of Wei Qi. If it lodges deeply in the Yin aspect, attempting to contend with Yang, Yang moves swiftly while Yin pathogen moves slowly, preventing immediate exit, thus causing every-other-day attacks. Generally, Yang moves fast like the sun, and Yin moves slow like the moon, following natural laws.

The Yellow Emperor asked: What causes attacks to occur later or earlier each day? Qibo replied: When the pathogen lodges in Fengfu (DU16) and descends along the Du Meridian, Wei Qi gathers at Fengfu once daily. The next day, Wei Qi descends one vertebral segment. Thus, attacks occur progressively later because the pathogen initially lodged in the back. Whenever Wei Qi reaches Fengfu, Couli open; when Couli open, pathogen enters; when pathogen enters, disease manifests. Hence, daily attacks occur slightly later. From Fengfu, descending one segment daily, after twenty-five days it reaches the coccyx. On the twenty-sixth day, it enters the spine and injects into the Fulu Zhi Mai (hidden Du vessel). Ascending for nine days, it emerges in Quepen (ST12). As the pathogen rises daily, attacks occur progressively earlier.

Pathogens lodging in the body have no fixed location. Previously stated: pathogen in skin/intestine area with Wei Qi causes daily attacks; pathogen in Yin aspect causes every-other-day attacks, without time variation. This section discusses pathogen initially lodging in the spine. Since Wei Qi must gather at Fengfu daily, when Wei Qi arrives, Couli open, allowing spinal pathogen to enter Fengfu vacuously. Meeting Wei Qi triggers disease. However, Wei Qi's gathering at Fengfu is timed due to its regular course. If pathogen enters Fengfu (a Du Meridian point) and descends one segment daily along the spine, meeting Wei Qi becomes delayed, so attacks occur later. By day 25, pathogen reaches coccyx; day 26, it enters the spine's hidden vessel, ascending. Nine days later, it emerges in Quepen. Rising daily, it meets Wei Qi earlier, so attacks occur earlier. This differs from previous cases where pathogen resided with Wei Qi. Thus, malaria pathogen lies dormant in blood and qi, manifesting only upon stimulation by Wei Yang. Deep lodging in Yin causing delayed attacks indicates difficult-to-treat cases. Inferring from this, the Classic states "Winter injury by cold leads to Spring Warm diseases." Winter is extreme Yin season; cold is extreme Yin pathogen. Yin adding to Yin hides the pathogen unnoticed. In Spring, Yang Qi ascends, stimulating body Qi to activate the pathogen, causing Warm disease. Cold transforms into Warm following Heaven and Earth Qi changes. Wu Keyou failed to understand this, denying the Classic, showing foolish self-opinion. Did he not consider that malaria pathogen is also imperceptible when dormant? Yin-Yang changes are subtle and infinite. Without grasping ultimate principles, how can one judge arbitrarily!

Every-other-day attacks occur because pathogen presses inwardly on the five Zang organs and connects horizontally to Mu Yuan (Membrane Source). The path is long, qi is deep, movement is slow, unable to travel with Wei Qi simultaneously or exit together, hence every-other-day manifestation.

This reiterates the logic of every-other-day attacks. Yang moves, Yin rests, a natural trait. Pathogen in Yang aspect moves easily and manifests; pathogen in Yin aspect lies dormant and imperceptible. It requires Yang Qi stimulation and simultaneous exit with Wei Qi to manifest. Due to long distance and slow speed, it cannot exit daily with Wei Qi, hence every-other-day onset. Attacks every two days indicate even deeper lodging. Pathogen must emerge externally and dissipate with Yang Qi to decline. Thus, deeply lodged Yin pathogen is lingering and hard to cure.

The Yellow Emperor asked: You said Wei Qi reaching Fengfu opens Couli, allowing pathogen entry and disease onset. Now Wei Qi descends one segment daily; when it activates, it is not necessarily at Fengfu. Why do some cases still manifest daily? Qibo replied: This is because the pathogen lodged in the head/neck and descended along the spine. Thus, deficiency/excess varies, and pathogen invasion sites differ, so it does not always align with Fengfu. If pathogen strikes head/neck, disease manifests when Qi reaches head/neck; if back, when Qi reaches back; if waist/spine, when Qi reaches waist/spine; if limbs, when Qi reaches limbs. Disease manifests where Wei Qi meets the pathogen. Therefore, Wind has no fixed "Fu" (abode). Wherever Wei Qi activates, it opens Couli; wherever pathogen combines with Wei Qi, that becomes its abode.

The Yellow Emperor questioned why daily attacks occur if Wei Qi descends segments and might not meet pathogen at Fengfu. Qibo explained that individuals vary in deficiency/excess, so pathogen enters vacuities differently, not always at Fengfu. Earlier, late/early attacks were due to spinal pathogen meeting Wei Qi at Fengfu. If pathogen lodges in head/neck, back, waist, or limbs without fixed location, disease manifests only when circulating Wei Qi encounters it. Thus, Wind has no fixed abode; wherever Wei Qi opens Couli and pathogen enters/meets Wei Qi, that is the abode, not necessarily Fengfu. This shows Ying and Wei Qi circulation follows constant rules. Pathogen invasion has no fixed site and spreads everywhere, causing diverse variations. The Classic elucidates these principles thoroughly.

The Yellow Emperor asked: Wind and Malaria are similar and same category, yet Wind persists constantly while Malaria has remissions. Why? Qibo replied: Wind pathogen stays in its local area, hence persistent; Malaria Qi follows meridians, sinking and pressing inwardly, hence manifesting only when Wei Qi responds.

This clarifies why different diseases arise from external pathogens. Feeling Wind pathogen causes fever and headache; pathogen stays locally, requiring medication to induce sweating for resolution. Once cured, it does not recur because pathogen is expelled. Malaria recurs after remission because pathogen flows with meridians, mixing with blood and qi, sinking inwardly, remaining imperceptible. It manifests only upon Wei Yang stimulation. As Wei Qi circulates interior/exterior, separating from pathogen, pathogen remains dormant and disease remits.