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Hu Tong Lei (Poplar Tamarisk Gum Resin)

Salty and bitter in flavor, greatly cold in nature, non-toxic. It primarily treats severe toxic heat, and fullness and oppression with vexation in the heart and abdomen; when mixed with water and taken orally, it induces vomiting. It also treats cattle and horses suffering from acute jaundice with black sweat; grinding two to three liang of the drug in water and administering it orally leads to immediate recovery. Furthermore, it serves as a soldering agent for gold and silver. It is produced in the flat marshes and valleys west of Suzhou. Its shape resembles Huang Fan (Yellow Alum) but is solid and firm. Some pieces contain rotten wood, said to be formed when the sap of the Hu Tong tree seeps into alkaline (pronounced 'jian') and saline soils. The tree is tall and robust, with bark and leaves resembling those of white poplar, blue paulownia, or mulberry. Hence it is called Hu Tong Mu (Hu Poplar), which is suitable for making utensils. It is also known as Hu Tong Lv (Hu Poplar Law). "Lv" and "Lei" are phonetic corruptions of each other. The *Records of the Western Regions* states: Hu Tong resembles mulberry but has curved branches.

Chen Yuxi and others respectfully note according to the Shu Ben Tu Jing: It is found west of Liangzhou. When newly sprouting, it resembles willow; when mature, it is intermediate between mulberry and paulownia. The sap flows underground, mixing with earth and stones, taking the shape of Jiang Shi (Ginger Stone), with an extremely salty and bitter taste, dissolving upon contact with water, similar to alum minerals. It is harvested in winter. Ri Hua Zi states: It treats wind-induced toothache. There are two types: Mu Lv (Wood Law) is not suitable for medicinal use; Shi Lv (Stone Law) resembles small stone flakes, with those of yellow earth color being superior. It is suitable for dental medicinal use and can clear fire toxins and facial toxins.

The *Tu Jing* states: Hu Tong Lei is produced in the flat marshes and valleys west of Suzhou; currently, merchants from Xifan also trade it. It is passed down that the tree is very tall and robust, with bark resembling white poplar or blue paulownia. The drug initially resembles willow, gradually growing to resemble mulberry or paulownia. Its sap seeps into the ground, adhering to large stones, and is harvested in winter. It resembles Huang Fan or Jiang Shi, with an extremely salty and bitter taste, dissolving in water like Xiao Shi (Niter). In ancient prescriptions, it was rarely used; now it is the most important substance for treating oral and dental conditions. Another name is Hu Tong Lv. "Lv" and "Lei" have similar pronunciations. However, there is a type of Mu Lv that is extremely similar but unsuitable for use.

Maritime Medicines: Respectfully noting the *Ling Biao Ji*: It originates from Persia. It is the resin of the Hu Tong tree, named Hu Tong Lei. There is also Shi Lei (Stone Tear), collected from rocks. It treats wind-related gan disease causing toothache, and bone cavity wind consumption, capable of softening all substances. Excessive intake causes vomiting. Writing it as "Lv" is incorrect.

Tong Dian: The Lou State of the Western Barbarians produces much Cheng Liu (Tamarisk), Hu Tong, and Bai Cao (White Grass). Bai Cao is favored by cattle and horses. Hu Tong also resembles trees eaten by insects with sap flowing out, commonly known as Hu Tong Lei, which can be used to solder gold and silver; colloquially, "Lei" is erroneously called "Lv".