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Shiyan (Lithornithidae Fossil):
The nature is cool, and it is non-toxic. Its flavor and meridian tropism are not recorded in various medical texts. It primarily treats urinary difficulty caused by the five types of strangury (a syndrome characterized by frequent, urgent, and painful urination), as well as intestinal wind and hemorrhoids (hemorrhoidal bleeding or swelling/pain caused by wind pathogen invading the intestines). For difficult labor in women, holding one piece in each hand yields immediate results. When used, it should be ground into a fine powder and processed by water levigation (a purification method utilizing the difference in suspension properties of coarse and fine particles in water).

Commentary: *Bencao Tujing* records that Shiyan originates from Lingling Commandery, and today it can also be found on the beaches of Qiyang County. Its shape resembles a clam but is smaller; it is actually stone. Observing its therapeutic effects, they are all functions of descending and unblocking. Dietary therapy books praise its tonifying benefits, which seems inaccurate.

Cishi (Magnetite):
The flavors are pungent and salty; the nature is cold, and it is non-toxic. It enters the Kidney Meridian. It primarily treats generalized rheumatic bi-syndrome (pain, numbness, and heaviness in limbs and joints caused by obstruction of meridians by wind-cold-damp pathogens), pain in the limbs and joints, blurred vision, deafness, tonifies deficiency and injury, eliminates irritability and swelling/toxins, and facilitates fertility. Magnetite that can attract heavy iron is considered superior. When used, it is heated red-hot in fire, quenched in vinegar seven times, and ground to an extremely fine consistency before use. Chaihu (Bupleuri Radix) serves as a guiding herb. It is contraindicated with Mudanpi (Moutan Cortex), Jiecao, and Huangshizhi.

Commentary: Why does Cishi enter the Kidney Meridian? Because its nature allows it to attract iron, by analogy, it is believed to guide the Qi of Lung Metal into Kidney Water, promoting the mutual generation of mother and child (Metal generates Water). When Water receives the clarifying energy of Metal, it becomes clear, and the Ministerial Fire (physiological fire residing in Liver and Kidney) retreats without attack. Hence, it treats the aforementioned conditions. However, long-term or excessive consumption will inevitably lead to serious harm; do not favor its efficacy while ignoring its dangers.

Leigong states: When using Cishi, do not mistakenly use Xuanzhongshi or Zhongmashi. These two stones resemble Cishi closely but cannot attract iron. Zhongmashi has a red center and rough skin; it is Iron Mountain Stone. Ingestion causes malignant sores that are incurable. A piece of Cishi that attracts one jin (approx. 500g) of iron from all four sides is named "Yannian Sha" (Longevity Sand); one that attracts eight liang (approx. 375g) is called "Xucail Shi"; one that attracts around five liang (approx. 250g) is true Cishi. For processing one jin of Cishi, use one yi (an ancient weight unit) of Wuhua Pi and one yi of Duyu. Suspend them together with fifteen liang of Cishi. Finely chop the herbs, crush them on a stone into twenty to thirty pieces, place half of the Cishi into a magnetic bottle, put the herbs underneath, and decoct in running water from the east for three days and nights. Remove, wipe dry, wrap in cloth, and hammer again on a large stone until fine. Place in a mortar, grind until extremely fine like dust, process by water levigation, and grind again into powder for use.