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Wang Haicang stated: Yin poison (Yin Du) originally arises from deficiency-cold of the Kidney Qi, following sexual activity or consumption of raw and cold foods, after which wind pathogen is contracted. Internally, yin-cold is latent; externally, cold damage (Shang Han) is suffered. Or, external cold is felt first, leading to internal yin-cold accumulation. When both interior and exterior are yin-cold, Yang Qi cannot maintain its guard, thus Yin poison erupts. Symptoms include heavy body, eye pain, physical fatigue with severe heat sensation, cold reversal in the four limbs, continuous cold sweat on the forehead and back of hands, frequent thirst and irritability, mental confusion as if losing something. Within two or three days, one might be able to walk without feeling particularly heavy. Pulse diagnosis reveals six pulses that are deep (Chen), fine (Xi), and rapid (Ji); the Chi position is short and small, while the Cun Kou position may be absent. If cooling medicines are taken, thirst becomes worse and irritability intensifies. For those with these symptoms, immediate administration of medicines to restore Yang and retreat Yin will bring peace; only tonifying deficiency and harmonizing Qi is needed. Formulas such as Zheng Yuan San (Correct Origin Powder) are suitable. Yin syndromes should not induce sweating. However, if Qi is upright, pulse is large, and fever has not subsided, inducing sweating with medicine is permissible. Similarly, if Cun Kou pulse is small and Chi pulse is slightly large, the situation is the same. Accumulated yin-cold affects the lower part, causing微弱 Yang Qi to diminish in the upper part. Thus, symptoms manifest as heavy body, cold reversal in four limbs, worsening abdominal pain, throat discomfort, fullness and hardness below the heart, irritability, thirst, continuous deficient sweating, occasional delirium, cyanotic nails, and dark blue-black complexion. The six pulses are deep and fine, with more than seven breaths per pulse beat. For those with these symptoms, moxibustion should be rapidly applied to the Qihai (CV6) and Guanyuan (CV4) acupoints, 300-200 moxa cones, until the hands and feet become warm. Simultaneously, medicines such as Jin Ye Dan (Golden Liquid Pill) and Lai Fu Dan (Returning Return Pill) should be taken according to the syndrome.

Commentary: This discussion on Yang Qi failing to maintain its guard, or accumulated yin-cold affecting the lower part causing微弱 Yang Qi to diminish in the upper part, leading to Yin poison, offers significant insight compared to the *Huo Ren Shu*’s description of Yin poison as excessive Yin Qi and sudden collapse of Yang Qi. However, merely discussing "failing to maintain" and "diminishing" is less clear than Zhao’s explanation of the *Huo Ren Shu*: "Extreme excess of Yin Qi and extreme deficiency of Yang Qi constitute Yin poison; extreme excess of Yang Qi and extreme deficiency of Yin Qi constitute Yang poison." This interpretation avoids the notion of absolute exhaustion, making the principle clearer. Pulse patterns of Yin excess repelling Yang are attached to the Hot Syndromes chapter. See Hot Syndromes chapter for details.

Respectfully noted: In popular tradition, Cold Phlegm, Hong Kong Foot (Gout/Feet Qi), Food Stagnation, and Labor Fatigue are considered similar to Cold Damage. However, comparing their manifestations, are there really only these four syndromes? Therefore, various syndromes are collected and discussed.

The book *Ci Nan Zhi* states: The Foot-Taiyang channel is the Great Yang, the Old Yang, and the head of all Yang channels, so it undergoes transmission frequently. Transmission from Taiyang to Yangming is called Minor Evil, representing Water transmitting to Earth, also known as following the channel within limits. Transmission from Taiyang to Shaoyang is called crossing the channel. Transmission from Taiyang to Taiyin is called transmission due to mistaken purgation. Transmission from Taiyang to Shaoyin is called Interior-Exterior transmission; when Taiyang becomes severe and transmits to Shaoyin, Water overcomes Fire and Fire overcomes Water, representing changes between the North and South regions. Within moments, the harm to humans is far greater than in Taiyang disease alone. If not distinguished early, it will certainly become an incurable disease, let alone cases of indiscriminate prescription. Transmission from Taiyang to Jueyin is called Head-to-Tail transmission. Jueyin ascends along the Du Mai and connects with Taiyang, also named following the channel within limits. The disasters and changes are extremely serious and numerous.

Commentary: This can be said to reveal the secret method of Zhang Zhongjing. Zhao also stated: Transmission through the Six Channels in Cold Damage involves deficiency or excess, cold or heat, all caused by pathogenic factors. There are Yang pathogens transmitted in sequence, Yin pathogens entering the primary channel directly, and pathogens sinking inward after purgation; all must be distinguished. However, Cheng Wuji cited Hua Tuo saying: Cold Damage on day 1 is in the skin, day 2 in the flesh, day 3 in the muscles, day 4 in the chest, day 5 in the abdomen, day 6 enters the stomach and transmits to the interior. This aligns roughly with Cheng’s discussion that unresolved cases after seven days constitute a second cycle, and unresolved cases after fourteen days constitute passing the cycle. These are generalizations. Therefore, there are no fixed treatment examples; only Six Channel transmission is precise. Thus, Taiyang transmission is most common because initial pathogenic invasion takes advantage of deficiency to transmit. Transmission scenarios include staying in the primary channel for three to five days, or not transmitting for ten-plus days; some transmit past one channel and do not continue; many result from mistaken medication. Generally, pathogens in Yang channels are easy to treat, but once entering Yin divisions, they become critical, as Yang is weak, Yin is strong, Righteous Qi is deficient, and Pathogenic Qi is substantial. Moreover, cases of mistaken purgation causing sinking, sweating causing deficiency, or transmission to other channels lead to damaged syndromes where collapse and peril await immediately. Scholars must be cautious.