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Non-toxic.

Ma Xian (Horse Bit, a type of iron) treats difficult labor and infantile convulsions. During childbirth, the mother may hold this object in her hand; alternatively, it can be boiled to make a decoction, one cup of which is taken orally (Recorded by famous physicians). [Origin] (According to *Tu Jing*): Ma Xian refers to the iron bit used in horse bridles, available everywhere. Old iron ingots can be used by medical practitioners as needles. ○ Careful analysis: Iron is hard and heavy in texture, and its nature is sedative and downward-draining; thus, it has the efficacy of treating convulsions. Horses traverse vast lands, moving in accordance with the earth and possessing robust vitality. To gallop, one must rely on the bridle for guidance; therefore, using Ma Xian to induce labor also derives from the meaning of "robustness and compliance." [Color] Black. [Taste] Slightly salty. [Nature] Neutral. [Qi and Taste] The taste is stronger than the qi; belongs to Yin within Yang. [Odor] Fishy. [Indications] Difficult labor in women, infantile convulsions. [Preparation] Boil to extract juice. [Efficacy] (According to *Bie Lu*):

Non-toxic. Grows in saline-alkali soil.

Taiyin Xuanjing (Dark Essence of Great Yin) treats the expulsion of wind-cold pathogenic factors, damp-bi syndrome, tonification of essence and qi, treatment of chronic cold syndromes in women, leukorrhea, accumulation of cold qi in the heart and abdomen, relief of headaches, and release of the muscle layer (Recorded by famous physicians). [Origin] (According to *Tu Jing*): Produced in Jiexian Jiexi Pool, and also found in the salt storage warehouses of Tongzhou Prefecture. Those with a blue-white color resembling turtle shell patterns are considered superior, likely because they are formed according to Yin numbers, possessing six-pointed crystalline structures, hence named Taiyin Xuanjing. Closer to the ground, there are large sheets of red or blue-white ore, which are of secondary quality. Shen Cunzhong stated that dark saline lands produce Yinjingshi (Yin Essence Stone), which is a type of salt essence from Jiexi Pool. It is non-toxic, tastes more salty and bitter, appears blue-black, measures three to two inches in length, resembles the mouth of an iron plowshare, and is harvested in March and April. It also treats the expulsion of wind-cold. Also known as Nijing (Mud Essence), it is likely a category of Xuanjing. It was not seen in ancient prescriptions but is frequently used in modern times for tonic medicines and the treatment of Shanghan (Cold Damage). [Timing] (Growth) No specific time. (Harvesting) No specific time. [Usage] Turtle-shell patterned ones are preferred. [Texture] Similar to Jingquanshi (Well Spring Stone). [Color] Blue-white. [Taste] Slightly salty. [Nature] Warm and soft. [Qi and Taste] Taste is strong, Qi is weak; belongs to Yin within Yang. [Odor] Rotten/Old. [Indications] Tonifies essence and qi, eliminates accumulations. [Preparation] Grind into fine powder. [Compound Treatment]: Mix Xiao Shi (Niter), Liu Huang (Sulfur), each 2 liang, and Sha (Sand) 1 liang. Grind finely, place in a porcelain bottle, seal tightly, and heat around the bottle with half a jin of fire for about half a day. When the medicine turns blue-purple, stop heating. After cooling, remove. Mix evenly with snow water collected in the twelfth lunar month until moist. Place in a porcelain jar and dry in the shade under the north side of the house. Then bury in the ground for twenty-seven days, take out, grind finely, and mix with wheat paste to form pills the size of chicken heads. First, take a hot bath, then dissolve one pill in Ai Tang (Mugwort Decoction) and ingest. Cover with clothing to induce sweating. This is named Zhengyang Dan (True Yang Pill). Used for Shanghan on the third day, presenting with headache, high fever, and stiffness/weakness of the four limbs.