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Taste and nature: Acrid, neutral, non-toxic. Indications: Treats malignant sores caused by wind-heat, ulcers (yang-ju), scabs, and the pathogenic qi of scabies residing in the skin.
(Iron filings are the iron chips falling from the anvil while a blacksmith is hammering. Additionally, when cast iron forms patterns resembling orchids or moths that fall to the ground, it is commonly called "iron moth," now used in fireworks.)
Iron is named Black Metal, originates from the northwest, and belongs to Water among the Five Metals. Endowed with Metal Qi, it treats Wind disorders. Endowed with Water Qi, it treats Heat disorders. Malignant sores and ulcers are Heat conditions. The qi of scabs and scabies in the skin is a Wind condition. By using iron refined by fire into black metal, one clears the heat-toxin of sores; thus, it treats malignant sores and ulcers. By using iron chips shed from the skin, one kills parasites in the skin; thus, it treats the qi of scabs and scabies in the skin. *Suwen: Bingneng Lun* mentions Shengtie Luo Yin (Decoction of Raw Iron Filings), stating its ability to direct rebellious Qi downward. Nowadays, people apply rust powder to treat ding swellings, scalds and burns, centipede bites, Xi'er sores, double tongue, and foot swelling, which aligns with the principle of treating wind-heat malignant sores.

Taste and nature: Bitter, sour, salty, cold, non-toxic. Indications: Treats various poisons, Gu toxicity, Zhu diseases, evil ghosts, and miasma; kills toxins from Gouwen (Gelsemium elegans), Zhen feathers, and snake venom; dispels evil pathogens, prevents confusion and nightmares; long-term use makes the body light and agile.
(Rhino horn comes from Dian Nan, Jiaozhi, and Southern Fan regions. There are three types: Mountain Rhino, Water Rhino, and Si Rhino. Mountain and Si rhinos live in forests and are easily obtained; Water rhinos enter water and are rarest. They resemble black water buffaloes, have pig-like heads, large bellies, elephant-like feet with three hooves, spiky tongues, and feed on thorns. Each pore on their skin produces three hairs. They have two horns on the forehead; some have a single central horn, named Single-horn Rhino. Some have two short forehead horns and one long nasal horn. Some have a white vein running straight to the tip, capable of connecting with Heaven's Qi, remaining dry even under night dew, named Tongtian Rhino (Sky-Piercing Rhino), which is highly effective medicinally. Others include Cold-Repelling Rhino (warm in winter), Heat-Repelling Rhino (clears summer heat), Water-Parting Rhino (parting water three chi deep when held), Dust-Repelling Rhino (dust does not cling when worn as hairpin or belt), and Anger-Dispelling Rhino (wearing it dispels anger). These are all rare treasures. Rhinoceros horn powder, wrapped in thin paper and kept warm against the chest, steams dry and crushes easily into powder. Thus, *Guitian Lu* states: Emerald dust is brittle, gold's breath can pulverize it, and so can rhino horn powder.)
Rhinoceros horn is black and resembles a pig, belonging to Water animals. It perches near trees, has three toes, and three hairs per pore, endowing it with Wood Qi. It lives in Southern Yue, endowing it with Fire Qi. The horn inherits the generative cycle of Water, Wood, and Fire, hence its bitter, sour, salty, and cold nature. As a spiritual beast with a Yang-gang structure in its horn, it treats hundred poisons, Gu toxicity, Zhu diseases, evil ghosts, and miasma, similar to Wen Qiao lighting a rhino horn to see strange entities underwater. Since rhinos eat thorns and do not avoid toxic herbs, they kill Gouwen herb toxin. Gouwen is a toxic herb causing intestinal rupture if ingested. It also kills Zhen bird and snake venoms, meaning it eliminates not only herb toxins but also animal venoms. Endowed with the essence of Water and Fire, it dispels evil, preventing confusion and nightmares. Long-term use harmonizes Water and Fire, resulting in a light body.