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Sweet and neutral, non-toxic.

[Invention] Yuanjia (Trionyx sinensis Shell), after being roasted and soaked in yellow wine, treats scrofula (tuberculous lymphadenitis of the neck), kills parasites, expels wind, and treats malignant sores, hemorrhoids, and stubborn scabies. Its efficacy is similar to that of Biejia (Turtle Shell). However, Biejia enters the Liver meridian, whereas Yuanjia enters the Spleen meridian; therefore, their primary indications differ slightly.

Salty and cold, with slight toxicity. Crabs not exposed to frost are toxic. Excessive consumption causes abdominal pain and diarrhea; fresh ginger, Perilla leaves, fermented soybean juice, and reed rhizome juice can all detoxify it.
Crabs have a propensity to enter snake holes; if they absorb snake venom, they grow rapidly. Thus, crabs weighing over one *jin* (approx. 500g) can be fatal if ingested by mistake. Furthermore, crabs with eyes facing each other, spotted legs, and red eyes possess high toxicity and must not be eaten.
The *Shennong Bencao Jing* (Divine Farmer's Materia Medica) states that it treats evil qi and heat-induced knotting pain in the chest, facial swelling, and deviation of the mouth and eye. It can degrade lacquer, and burning it attracts mice.
[Invention] The crab has a hard outer shell and soft inner meat; its raw state is green and cooked state is red, clearly embodying the image of Yin enveloping Yang. Its nature is specifically dedicated to breaking blood stasis, thus it can reconnect severed tendons and bones. The *Shennong Bencao Jing* records its treatment of chest evil qi, heat-knotting pain, facial deviation, and swelling, all of which are caused by blood stasis. Its ability to degrade lacquer implies that modern use of raw crushed crab for treating lacquer dermatitis or applying it to burns aims at dispersing blood stasis. The *Ri Hua Zhencao* records its use for tendon and bone fractures, applied raw as a poultice. Chen Cangqi stated that it can reconnect severed tendons; removing the shell, taking the yellow part, crushing it, lightly stir-frying it, and inserting it into the wound allows the tendon to knit together. This shows its function is not only to disperse but also to harmonize blood. Generally, red-colored substances are hot in nature, except for crabs and persimmons, which are cold. Therefore, these two should not be consumed together, as this causes diarrhea and induces *zheng jia* (abdominal masses). Pregnant women should avoid eating it because its nature is to move against the current and sideways. Crab claws are specific medicines for inducing labor to expel a dead fetus and placenta. The *Shenzao Decoction* from the *Qianjin Fang* (Essential Prescriptions Worth a Thousand Gold) treats intrauterine fetal death and twin pregnancies where one dies and the other lives. Administration of this formula expels the deceased fetus while keeping the living one safe; it is a miraculous prescription. However, the crab used must be one that moves vigorously on one side while remaining still on the other. The prescription uses one *sheng* of crab claws, one *chi* of Licorice Root (*Gancao*), and ten *dou* of flowing water from the east. Boil using reed fire until reduced to two *sheng*, strain, add two *liang* of genuine Donkey-hide Gelatin (*Ejiao*), melt it, and take in one dose or divided into two doses. If the patient is too weak to swallow, instilling it orally will revive them. This utilizes the crab's blood-dispersing property and the characteristic that crab claws detach upon touch. However, naturally detached claws with feet attached must be used. The *Danfang* (Prescription Manual) treats jaundice due to blood accumulation, chest and hypochondriac knotted pain without edema: calcined crab shell powder mixed with brown sugar, taken with unadulterated rice wine (three *qian*). Effect is seen within a few doses. If edema is present, it is a Qi disorder, and the blood-dispersing action of crab is unnecessary. For women with mastitis presenting as hard swelling, one dose of crab shell ash can dissipate the swelling. Additionally, burning crab mixed with cinnabar produces smoke that repels bedbugs, killing them upon exposure, demonstrating its insecticidal power. There are many similar species of crab. Aside from less common ones like *Qiumu* (Mud Crab) and *Yongjian* (Swimming Crab), *Pengqi* (Small Mud Crab) and *Peng* are abundant in spring. *Pengqi* claws are smooth, non-toxic, and can be pickled in vinegar for consumption. *Peng* claws have toxic hairs; accidental ingestion causes vomiting and diarrhea. Another type lives in sand holes and hides when people approach; this is called *Shagou* (Sand Dog). Although Li Shizhen stated it should not be eaten, it is now used in seafood delicacies, which cannot be compared to *Pengqi*.