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The *Shennong Bencao Jing* (Divine Farmer's Materia Medica) states: Medicines possess four qi (vital energies): cold, hot, warm, and cool. This refers to both their nature (xing) and qi. There are also four odors: fragrant, foul, fishy, and musky. For example, Chenxiang (Aquilaria Wood), Tanxiang (Sandalwood), Bingpian (Borneol), and Shexiang (Musk) have a fragrant odor; Awai (Ferula Assa-foetida) and Dasuan (Garlic) have a foul odor; fish and clams have a fishy odor; chickens, ducks, and foxes have a musky odor. This combines the four odors with the four natures in its description. The *Benjing* mentions only the four natures of cold, hot, warm, and cool, but does not mention the four odors, which may be an omission. The five flavors are sour, salty, sweet, bitter, and pungent.

Generally, heaven and earth establish positions, and only the Five Elements (Wood, Fire, Earth, Metal, Water) generate all living things. That which generates is qi; that which completes is flavor. For instance, cold qi tends to harden, so salty flavor can be used to soften hardness; hot qi tends to soften, so bitter flavor can be used to firm up softness; wind qi tends to disperse, so sour flavor can be used to astringe; musky qi tends to gather/astringe, so pungent flavor can be used to disperse; Earth represents central qi, harmonizing all things, so sweet flavor can be used to moderate urgency. These four qi and five flavors are the guidelines of medicine. Practitioners must understand them in detail to fulfill the trust of saving lives.

The *Huangdi Neijing* (Yellow Emperor's Inner Canon) states: In treating disease, one must clearly understand the transformations of the Six Qi (Wind, Cold, Summer Heat, Dampness, Dryness, Fire) and their respective treatments, as well as the origins of the five flavors and five colors, and what is suitable for the five Zang organs. Only then can one discuss the meridians related to excess and deficiency leading to disease. Carefully observe the appropriateness of the qi, do not miss the pathogenesis of the disease, and how will the primary treatment work? It is said: Preparing materials according to the annual climate ensures no primary efficacy is missed. (This refers to harvesting herbs according to the year.) What are materials prepared according to the year? They are the concentrated essence of heaven and earth. What about those corresponding to the ruling qi? They correspond to the ruling qi of the year, but vary in abundance or deficiency. (Deficiency results in weak potency; abundance results in pure potency.) What about non-year-specific materials? They are scattered. (Without concentrated essence, the qi scatters; scattered materials lack purity.) Thus, although the substance may be similar, their grades differ. Flavors and qi vary in intensity; properties and actions vary in stillness or agitation; indications for treatment and preservation vary in quantity; and the depth of therapeutic transformation varies.

Medicines possess natures of cold, hot, warm, and cool, and categories such as sour, bitter, pungent, salty, sweet, and bland, each having specific functions that must be understood. The qi and flavor of medicines need not be identical; for example, items with the same qi may all have a salty flavor and cold nature. Generally, items with the same qi must contain various flavors, and items with the same flavor must contain various qi. Their mutual qi and flavor vary in density, and their properties and actions are unequal. Formulators must clearly understand their applications.

All medicinal insects and plants have specific places of origin. Roots, leaves, flowers, and fruits must be harvested at specific times. If the place is incorrect, the nature and flavor will differ slightly; if the time is incorrect, the qi and juice will be incomplete. Furthermore, there are differences between new and old materials, and between refined and coarse qualities. One must select and use them properly to achieve efficacy.