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Regardless of whether the smallpox lesions are sparse or dense, as long as the pathogenic toxins are fully expelled without remaining latent, their eruption occurs gradually and thoroughly, and their crusting and healing occur cleanly within the expected timeframe, how could there be residual toxins? If the lesions do not erupt completely, fail to develop thoroughly, or heal unevenly, the patient will naturally have residual heat. Symptoms may include thirst accompanied by abdominal pain, vomiting, and diarrhea; red and scanty urine with dysuria; constipation; mental confusion and lethargy; fatigue in the four limbs; reduced appetite; and restlessness in sitting and lying down. These are all signs that residual toxins have not been cleared. When eruptions are clean, they appear in three or four waves, varying in size. Even at the stage of pustule formation and crusting, new lesions may emerge in previously empty sites, indicating complete eruption. If only an initial layer appears with no subsequent filling of gaps, it indicates latent toxins remain. Regarding thorough development, one must observe the hands and feet, as Qi and Blood are less likely to reach these distal areas. If the lesions are full and plump with sufficient pus fluid, it can be considered thoroughly developed. If lesions remain flat and fail to suppurate, although toxins have emerged, they have not reached the extremities, implying lingering latent pathogens. Regarding even healing, from the face downward, if the scabs are clean without ulceration, it is considered even. If healing occurs too early or fails to form scabs, it implies internal sinking of toxins. In such cases, residual toxins exist. One must examine the meridians and locations involved, as well as patterns of cold/heat and deficiency/excess, employing tonification or purgation, release or dispersion, aiming for balance. If treatment fails and the condition persists, it constitutes a deteriorated syndrome (Huai Zheng), and aggressive attack therapies should not be used recklessly.

1. Fever persisting after eruption may stem from either deficiency or excess syndromes. If the patient can eat, feels irritable and thirsty, has red urine, and constipation, it is an excess syndrome. It is appropriate to treat with Sishun Qingliang Yin (Four-Obedience Cooling Decoction) or Sanhuang Wan (Three-Yellow Pill). If residual toxins remain post-smallpox presenting with various heat symptoms, Dalianqiao Yin (Large Forsythia Decoction) is optimal. If stool is not constipated, urine is not red, the patient trembles while sitting or lying, and food intake is minimal, it is a deficiency syndrome. It is appropriate to treat with Tianyuan Tang (Origin-Regulating Decoction) or Wufu Yin (Five-Fortune Decoction) added with Shaoyao (Paeonia Root).

The *Xin Jian* states: Residual heat after smallpox is deficient heat. Deficient heat often manifests in the afternoon, with a red face and lips, or delirious speech. It must never be treated as excess heat. Instead, use Tianyuan Tang or Baoyuan Tang (Protect-the-Origin Decoction) added with Huanglian (Coptis Rhizome). For severe heat, Dalianqiao Yin is suitable. If purgatives are used recklessly, damaging Stomach Qi, other complications may arise, leading to an incurable deteriorated syndrome.

Xu Shi stated: For persistent residual heat after smallpox, treatment should be based on severity. High fever requires promoting urination; mild heat requires resolving toxins. Promoting urination guides Heart Fire outward, allowing residual heat to dissipate even without cooling herbs. Mild heat requires toxin resolution because unresolved mild heat may progress to high fever. For promoting urination, Daochi San (Guide Out the Red Powder) is suitable; for resolving toxins, Xijiao Dihuang Tang (Rhinoceros Horn and Rehmannia Decoction) is suitable. If there is only superficial fever without other symptoms, Chaihu Maidong San (Bupleurum and Ophiopogon Powder) alone is appropriate.