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The way sages preserve the lives of the people is by taking the Five Grains (Wugu) as the nourishing staple, the Five Fruits (Wuguo) as assisting foods, the Five Livestock (Wuchu) as beneficial supplements, and the Five Vegetables (Wucai) as filling additions, while toxic drugs (Du Yao) are used to attack pathogenic factors. Therefore, even mild substances like Gancao (Licorice Root) and Renshen (Ginseng), if misused, can cause harm; they all belong to the category of toxic drugs. Those ancients who enjoyed taking tonic foods inevitably developed strange diseases, just as those fond of warfare inevitably encounter strange calamities. Thus, the establishment of armies is to eliminate violence, arising only when no other choice remains; the establishment of medicines is to attack diseases, also used only when necessary. The principle behind them is the same. Therefore, the harm caused by disease, whether minor consuming essence or major damaging life, is like a hidden enemy state. To use the specific properties of herbs to attack the excesses of Zang-Fu organs, one must know both oneself and the enemy, employ various methods to control it, thereby avoiding the risk of premature death decreed by Heaven. Hence, for pathogens transmitting through meridians, seizing the area before they arrive cuts off their key routes; for violent acute diseases, urgently protecting uninfected areas defends one's borders; for illnesses complicated by retained food, eliminating the food first burns the enemy's supplies; for old diseases relapsing with new ones, preventing their combination cuts off the enemy's internal support. Differentiating meridians and avoiding indiscriminate medication is called the "Guide Army." Prescribing formulas contrary to cold or heat patterns is called the "Intercepting Strategy" (Xingjian). Treating one disease in stages allows winning against many with few, preventing mutual rescue between front and rear, causing the enemy's momentum to naturally decline. Treating multiple diseases together concentrates force on the core, causing dispersion without command, leading to total collapse. When the disease is advancing, do not treat too aggressively; preserving Yuan Qi (Primal Qi) exhausts the enemy's strength. When the disease is receding, pursue its course relentlessly, adding potent agents to strike at its stronghold. For deficiency-type pathogens, attack should not be excessive; using harsh drugs for tonification when mild ones suffice is like exhausting the people's strength during a nation's decline. For excess-type injuries, attack must not be delayed; using harsh drugs balanced with common ones is like a wealthy nation displaying its might. However, selecting materials must be appropriate, instruments must be good, deadlines must not be missed, and deployment must have method—these points are too numerous to list. Sun Tzu's thirteen chapters cover all the methods of treating disease.