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The diagnosis of smallpox relies entirely on observing its *xing* (form) and *se* (color). By *xing* (form), we mean the shape of the pustules. Normal forms include: at the initial stage, being pointed or round, firm and dense; during the eruption phase, rising, flourishing, and growing; when forming pus, being full and plump; and during the crusting phase, being gathered and solid, with a luster like water droplets. Flatness or depression are variations of form. Therefore, if upon emergence, the lesions appear faintly like mosquito bites, hollow like shed silkworm skins, thin as bran flakes, dense like needle heads, or resembling heat rash (*Fei Zhen*, miliary rash) or cold-induced millet-like bumps, they will certainly fail to erupt and lead to death. If they adhere in clumps, are indistinct, have flaccid and floating flesh, are soft, tender, and thin, or if the skin ulcerates, they will certainly fail to crust over and lead to death.

By *se* (color), we mean the hue of the pustules. Brightness is preferred over dullness; moisture is preferred over dryness; a mature, waxy appearance is preferred over delicate tenderness. Red should not be overly brilliant, for brilliance implies a tendency to rupture; white should not be grayish, for grayness makes crusting difficult. The progression from red to white, from white to yellow, and from yellow to black represents the normal sequential transformation of colors throughout the disease course. Purple hues upon emergence or grayish-white tones during eruption indicate abnormal color changes. Furthermore, the *Ke* (nest/base), *Gen* (root), *Jiao* (foot), and *Di* (ground) are four aspects that are difficult to describe exhaustively but fundamentally revolve around "form" and "color." This is an unchanging essential method.

What is the *Ke* (nest)? It refers to the center which is translucent and raised. What is the *Gen* (root)? It refers to the outer ring which is red. Observing whether this ring is red allows one to discern the emptiness or fullness in the center and the depth of the *Du* (toxin). Whether the *Ke* rises indicates the depth of the root and the sufficiency or deficiency of *Qi* (vital energy) and *Xue* (blood). The term *Jiao Di* (foot ground) also depends on the roundness and integrity of the root/nest and the density of the pustules. Areas with red halos are called *Jiao* (foot); when individual pustules have clear boundaries without scattering or mixing, it is termed "clear foot." Empty spaces between pustules are called *Di* (ground); when pustules do not connect, it is termed "clear ground." In summary, the root should be active, the nest should rise, the foot should be firm, and the ground should be broad. If these four conditions are met, even severe smallpox need not cause concern.

Roundness is the form of *Qi*. When *Qi* is abundant, the nests are round and the surrounding area is clean. The halo is the form of *Xue*. When *Qi* is abundant, the nests are bright and the redness is lively. Thus, *Qi* deficiency leads to depressed tops, and *Qi* dispersion leads to collapsed nests. However, in cases of extreme *Qi* deficiency where there is no collapse, it is due to *Huo* (fire/toxic heat) carrying them up; thus, although they appear round, they are actually empty shells like blisters. *Qi* deficiency results in pale halos, and *Xue* exhaustion results withered halos. Yet, in cases of extreme *Xue* deficiency where the exterior remains red, it is due to *Huo* floating upward; thus, although a round halo is seen, it is actually withered and lacks moisture. *Xing* and *Se* are the manifestations of *Qi* and *Xue*, while *Qi* and *Xue* are the roots of *Xing* and *Se*. A maxim states: "Having both base and top is ultimately noble; having top but no base is inadvisable." Observing this, while the top is crucial, the base (*Pan*, synonymous with root/foot) is even more important. The base signifies the foundation, and the top signifies sufficiency. Ultimately, the entire course of smallpox depends on *Qi* and *Xue*; the base requires *Qi* and *Xue* to support it, and sufficiency requires *Qi* and *Xue* to circulate. Comparing form and color, it is better to have a flat form with lively red color than a pointed/round form with dull color. This is expressed as: "Better to have color without distinct form, than form without color." Sufficiency derives from *Qi*, which can become vigorous quickly. The base relates to *Xue* (blooming) and is constrained by *Qi*. Since *Qi* and *Xue* work together, and tonifying *Xue* rarely yields rapid effects, the base (related to blood) is emphasized further.