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Qingdai (Indigo Naturalis) is the dried form of Dian Lan (Indigofera tinctoria). The *Bencao* (Compendium of Materia Medica) states that those produced in Persia are authentic, which is actually an error. It tastes bitter, is cold in nature, and is non-toxic. It can kill parasites and eliminate heat, resolve erythema and swelling as well as carbuncles and toxic sores, and concurrently treat metal weapon injuries (Jinchuang), but has no other efficacy. Other books highly praise it, but these claims are not credible. Only for Hou Bi (sore throat with obstruction), if caused by excess fire, can it be treated both internally and externally, yet various *Bencao* texts fail to mention this. Generally, this substance serves only as an assistant or guide drug (Zuo Shi). It may be used in large doses only for killing parasites: using a single ingredient up to 1 liang (approx. 30-50g depending on historical context), ground into powder, mixed with Shen Qu (Medicated Leaven) 3 qian (approx. 9-15g) and Shijunzi (Quisqualis Fructus) 3 qian, formed into pills, and taken within one day, all parasites will die. ([Commentary] Qingdai parasite-killing formula is miraculous; tested repeatedly with verified results.) For other diseases, it need not be used in large doses. Since Qingdai is cold in nature, it damages Stomach Qi; long-term use prevents digestion of food.

Someone asked: "Qingdai is a minor substance, yet you also use it cautiously; is this not excessive?" Alas! A mistake in even one herb can kill a person, let alone elucidating the *Bencao*; how can one speak lightly? Therefore, although the substance is extremely minute, I dare not neglect it.

Someone asked: "Although Qingdai is extremely minute, Zhang Zhongjing used it to treat Shaoyang disease (Shanghan) with macules (Fabang); why did you not mention this?" I replied: "The 'erythema and swelling' I mentioned earlier is another name for macules; it does not mean the whole body swells up as erythema and swelling. Qingdai is extremely minute but can transform macules because it excels at cooling Lung Metal Qi. The Lung governs skin and hair; macules appearing on the skin are precisely due to Fire in the Lung. However, macules are not solely due to Lung Fire; they must accompany Stomach Fire. Qingdai can also clear Stomach Fire. Thus, Zhang Zhongjing used it for two purposes: retreating Lung and Stomach Fire, thereby easily resolving skin macules."

Tianma (Gastrodiae Rhizoma) tastes pungent and bitter, is neutral in nature, and is non-toxic. It enters the Lung, Spleen, Liver, Gallbladder, and Heart meridians. It can stop dizziness and vertigo, treat wind and remove dampness, cure tendon and bone spasms and paralysis, unblock blood vessels, open orifices, but its other claimed efficacies are not entirely credible. This is a drug that causes harm without benefit and should perhaps be deleted. However, when external pathogens are extremely vigorous and obstructed between the collaterals and blood vessels, what else but Tianma can serve as a guiding drug to direct substances that tonify Qi and Blood or attack pathogens directly into the diseased area? Therefore, it must be recorded in detail. As long as its functions are understood, misuse will be avoided. In short, Tianma is best at expelling external pathogens and driving out internally closed phlegm, but persons with dual deficiency of Qi and Blood must absolutely not use it lightly. ([Commentary] Tianma is universally...)

Someone asked: "People generally treasure Tianma, why do you alone warn against using it lightly?" I replied: "I warn against light use because Tianma can only be used to subdue pathogens. Those without pathogens who use it will inevitably suffer harm. Therefore, I state its merits and point out its faults, fearing that people will misuse it and damage their bodies."