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[Mercury]
Also known as Gong (Quicksilver).
Pungent, cold in nature, toxic. Mercury is a heavy and sticky yin toxin; it must not enter the human abdomen. Ancient methods for treating accidental ingestion of mercury involved having the patient lie on peppers, which would absorb the mercury. In modern times, if mercury is accidentally ingested causing a sensation of heaviness and sinking in the abdomen, two jin (approx. 1 kg) of lard cut into small pieces, baked until cooked, and mixed with raw honey can be ingested to facilitate its expulsion; this is another method.

*Shennong Bencao Jing* states: It treats sores with crusts, white alopecia capillitii (a scalp condition), kills lice in the skin, induces abortion, clears heat, neutralizes the toxicity of gold, silver, copper, and tin, and when melted and refined, reverts to cinnabar.

[Invention/Commentary]
Mercury is the essence of extreme yin. Its texture is heavy and its nature is fluid. When combined with salt and alum, it becomes Calomel (Qingfen); when added with sulfur, it becomes Vermilion (Yinzhu); when heated in a crucible with sulfur, it becomes Spirit Sand (Lingsha); when refined with saltpeter and soapberry, it becomes Ascending-Descending Spirit Medicine (Shengjiang Lingyao). Its properties are soaring, agile, and changeable, unlike anything else. This is like using troops in war; effectiveness lies in proper application, grasping the key points to control the pivot. *Shennong Bencao Jing* mentions it treats sores, white alopecia, skin lice, abortion, and clearing heat. Applying it to the male genitals causes atrophy and loss of qi, because the essence of extreme yin can dissipate yang qi; thus, it is detrimental to male genital qi. The *Lingsha Dan* (Spirit Sand Pill) in the *Taiping Huimin Heji Jufang* (Formulas of Benevolent Sickness Relief Bureau) specifically uses sulfur to restrain mercury, while *Yangzheng Dan* (Nourish Righteousness Pill) uses fire-subdued cinnabar to restrain lead. These deeply embody the subtle utility of communicating yin and yang, and achieving the mutual completion of water and fire; they cannot be generalized from ordinary herbal medicines. *Qianjin Fang* (Essential Prescriptions Worth a Thousand Gold) uses it for pruritus associated with vitiligo; *Waitai Miyao* (Secret Essentials of the Outer Chamber) uses it for pruritus associated with insect-related tinea; *Meishi Jiyianfang* (Collected Effective Prescriptions by Master Mei) uses it for pruritus associated with hemorrhoids; *Zhouhou Beiji Fang* (Emergency Prescriptions Ke in the Sleeve) uses it for all kinds of malignant sores.

Cangqi stated: If mercury enters the ear, it corrodes the brain and causes contraction of all joints; placing gold or silver near the ear allows it to be removed. It must absolutely not be used for head sores, lest it enter the meridians and cause laxity of sinews and bones, rendering it incurable by any medicine.

[Calomel / White Precipitate]
Also known as Nifen.
Pungent, dry in nature, toxic.

[Invention/Commentary]
When mercury is refined with salt and alum to become Calomel (Qingfen), its pure yin nature is transformed into pungency and dryness, yet the nature of yin toxicity remains, enabling it to unblock the Large Intestine. Applied externally, it treats infant malnutrition (Gan syndrome), carbuncles, scrofula, kills parasites causing sores, tinea, and scabies, and treats wind-induced pruritus. However, due to its violent and fierce yin nature, it is effective in attacking venereal chancres (syphilis-like diseases). If ingested, the toxin invades the sinews and bones and cannot be expelled. Over time, it develops into chronic condyloma or gummas, leading to disability. Nevertheless, it must still be produced by sublimating mercury, and combined with drugs from *Sanbai Dan* (Three Whites Pill) that draw out toxins. Utilizing the principle of "like attracts like," it searches and expels pathogens. For treating leprosy (Lifeng), *Zuxian Dan* (Immortal Immortality Pill) and *Tongtian Zaizao San* (Heaven-Penetrating Rebirth Powder) are used to search and cleanse toxins, expelling them through the teeth gaps. Qian Yi's *Lijing Wan* (Relieve Convulsion Pill) and *Baibingzi* (White Cake Pills) both use it to induce the expulsion of phlegm accumulation via the large intestine; it is indeed the premier agent for inducing Mingxuan reaction (a therapeutic crisis where symptoms temporarily worsen before improvement).