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[Physical Characteristics]
The Wei (Micro) pulse is extremely fine and extremely soft; it seems to exist but not really, as if about to cease yet not completely cut off.
The term "Wei" implies proximity to nothingness. Zhang Zhongjing said: "Like the fat floating on the surface of soup." This describes its softness and lack of strength. "Like silk threads." This describes its fineness and difficulty in being seen. The ancients' eight characters "seems to exist but not really, as if about to cease yet not completely cut off" truly capture the spirit of the Wei pulse.

[Main Pathologies]
The Wei pulse is vague and indistinct, indicating a great decline of Qi and Blood.
If the Wei pulse appears at the Left Cun position, it indicates Heart deficiency with anxiety and fright.
If the Wei pulse appears at the Left Guan position, it indicates cold contraction and Qi insufficiency.
If the Wei pulse is obtained at the Left Chi position, it indicates exhaustion of marrow and withering of essence.
If the Wei pulse appears at the Right Cun position, it indicates middle jiao cold and shortness of breath.
If the Wei pulse appears at the Right Guan position, it indicates stomach cold and abdominal distension.
If the Wei pulse is obtained at the Right Chi position, it indicates Yang decline and extreme cold.

According to those who calculate units: ten "Wei" equal one "Hu", ten "Hu" equal one "Si" (thread), ten "Si" equal one "Hao" (hair), and ten "Hao" equal one "Li". From this deduction, since one "Li" is very small, dividing it into ten thousand parts only then can it be named "Wei", thus showing how minute and hard to see the Wei pulse is. The common people, failing to examine the meaning of the Wei pulse, often mention "Wei" and "Xi" (Fine) together whenever they see a fine pulse. How imprecise their speech is! When lightly pressed, it feels as if non-existent, hence it is called Yang Qi decline; when heavily pressed, it feels as if about to cease, hence it is called Yin Qi exhaustion. The Xi (Fine) pulse is slightly larger, obvious and easy to see, unlike the Wei pulse which is vague and hard to see. Although the conditions they indicate are somewhat similar, their forms must not fail to be distinguished. Li Shizhen said: "The Wei pulse primarily governs diseases of long-term deficiency and weak blood. Yang Wei leads to aversion to cold, Yin Wei leads to fever." Without potent tonification, it is difficult to restore health. As for the pseudo-pulse manual saying: "Swirling敗血 (stagnant blood) indicates Small Intestine deficiency." How can this be placed under the Wei pulse? If there are no other accompanying signs, even if the pulse is weak but the rhythm is not chaotic, there is still a chance of survival in one out of a hundred cases. If obtained in an acute disease, life might still be saved, implying that the pathogenic factor has not penetrated deeply. If obtained in a chronic disease, it is mostly incurable because the healthy Qi is about to extinguish, and ordinary herbal medicines cannot support it.

In Taiyang disease patterns, only Shaoyin presents with the Wei pulse; other meridians do not. The Taiyang Bladder is the interior-exterior pair of the Shaoyin Kidney. Once the Wei pulse and aversion to cold appear, Zhang Zhongjing would treat from the Shaoyin perspective early on, using Fuzi (Prepared Aconite Root) and Ganjiang (Dried Ginger). This is because the Wei pulse with aversion to cold is precisely due to the decline of Yang Qi. The Book of Songs says: "The moon is dim, the sun is dim; the people below are indeed sorrowful." Even in celestial phenomena, Yang cannot be dim; how much less can human Yang be weak! Since the Kidney already has Yin excess and Yang deficiency, cold arises internally. If external cold also breaks through directly, the person will perish shortly. Thus, Zhang Zhongjing considered it an acute critical condition and used acrid-hot herbs to rescue the last ray of True Yang from the depths. Sudden attack by cold involves Yang deficiency and Yin excess, which is most critical.
The *Suwen · Tiaojing Lun* states: "Yin excess generates internal cold." Due to Jue Qi (rebellious Qi) moving upward, cold accumulates in the chest and does not dissipate, causing warm Qi to depart and leaving only cold. Where cold stays, blood coagulates; where blood coagulates, pulses become obstructed. Its pulse is large and forceful yet choppy, hence termed "Zhong Han" (Cold Strike). Having stated that Yin excess generates internal cold, why also say "therefore Cold Strike"? Does this not mean internal cold arises first, followed by external cold entering? Having stated that blood vessels are obstructed, why also say the pulse is large and choppy? Is it not because external cold strikes, causing the pulse to be large, and blood vessels close, causing the pulse to be choppy? There is deep doubt here; please clarify. First, the Wei Yang protecting the exterior of the body is most solid. Taiyang protects the back, Yangming protects the front, and Shaoyang protects the sides. Now, if it bypasses the Three Yang and directly strikes Shaoyin, could it truly fall from the sky? It is likely that Jue Qi moves upward and accumulates in the chest, causing Stomach cold; Stomach cold allows cold food and inhaled cold air to enter the Stomach. The Kidney is the gate of the Stomach; external cold breaks through the gate directly into the Shaoyin Kidney, hence called "Zhong Han". This is what the classic implied but did not state explicitly. Second, the pulse being large and choppy, although called Cold Strike, is not necessarily an acute sudden disease. Acute Cold Strike would definitely present with a weak pulse. Perhaps the classic generally discusses the pulses of Shanghan (Cold Damage) and Zhonghan (Cold Strike), hence saying large and choppy. Zhang Zhongjing treats Shanghan as a heat disease and Zhonghan as a cold disease, discussing them separately. The pulse of Shanghan is mostly Da (Large), Fu (Floating), Shu (Rapid), Dong (Surging), Hua (Slippery) as Yang pulses, and Chen (Deep), Se (Choppy), Ruo (Weak), Xian (Wiry), Wei (Micro) as Yin pulses. If a Yang disease shows a Yin pulse, it indicates death; how much more so if a Yin disease or acute disease reversely shows a Yang pulse like Large? If only large and choppy, involving two Yang and one Yin, what urgency is there? This is also what the classic implied and was hard to discern.