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Qian Yi, a pediatrician, courtesy name Zhongyang, is recorded in the *History of Song* as a renowned figure of his generation. He exclusively used Baixiang Wan (Hundred-Auspicious Pill) to treat severe cases of smallpox presenting with black depression, believing it could turn disaster into fortune, hence the name "Baixiang." Later generations abandoned its use due to ignorance of drug properties! Daji (Euphorbiae Pekinensis Radix), with its ability to drain water, has a bitter and cold taste and purple-red color; it can purge fire-toxin from water. When soaked in water, its color turns green-cyan, which is likely following the principle of the child (Water) draining the mother. The origin of smallpox toxin lies in the Kidney. If at the onset there is lower back pain, abdominal pain, chills, and teeth grinding, this indicates excessive heat-toxin that cannot be vented outward. This condition is critical within moments. Without using drugs like Daji, Dahuang (Rhei Radix et Rhizoma), or Mangxiao (Natrii Sulfas) to employ the method of removing firewood from under the cauldron (treating the root cause), one would be helpless awaiting death. Therefore, I elucidate this point. (By draining the internal accumulation, the toxin can be vented to the exterior.)

Zhang Kaizhi stated: The first three days of smallpox eruption correspond to Spring's generation; the next three days of swelling correspond to Summer's growth; the subsequent three days of pus formation correspond to Autumn's maturation; and the final three days of scabbing correspond to Winter's storage. If maturation fails during Autumn and Winter, it is often because the disease was brewed in Spring. Thus, although heat-toxin is abundant, if it can grow and vent outward without internal stagnation, it will invariably mature by Autumn and Winter. Even if righteous Qi is deficient and collapsing, bold use of warming and tonifying methods is permissible. However, if pathogenic toxin lingers and interior/exterior clarity is lost, where pathogens gather, righteousness must be deficient. To tonify righteous Qi hinders the clearing of heat-toxin; to clear heat-toxin hinders the recovery of deficiency. Therefore, those with abundant heat-toxin unable to vent die within three to five days; those who vent but have unclear interior Qi ultimately develop adverse complications. Skilled practitioners of smallpox treatment should prevent issues at the initial stage.

Although there are many methods to reduce the severity of smallpox, none match the profound principles and immediate efficacy of Xuantu Wan (Black Rabbit Pill). Smallpox is an innate toxin. Heaven generates Water (One), Earth generates Fire (Two); Water and Fire harmonize, Yin and Yang interact, forming the fire-toxin within Water. Xuan (Black) represents the color of Heaven and Water; Shen (参) means to participate; participating in the transformation and nurturing of Heaven and Earth. Tusizi (Cuscutae Semen), also known as Nuluo, is called Yunu (Jade Maiden) in the *Erya*. The rabbit embodies the soul of the Moon, a purely Yin entity, hence the title Jade Maiden. *Baopuzi* states: The root of newly sprouted Cuscuta resembles a rabbit's paw; its juice mixed with elixirs instantly transforms into miraculous substances. Generally, objects require the qi of cool water and earth to sprout. Cuscuta, possessing pure Yin nature, elongates its threads when warmed by fire, demonstrating the subtle application of Yin and Yang in physical laws. The *Neijing* states: The Kidney is Supreme Yin; Supreme Yin stores abundant Water. The Lung is Taiyin. Shaoyin is the Winter pulse. Thus, the root of the disease is in the Kidney, the branch in the Lung, both involving fluid accumulation. This reflects the connection between Lung and Kidney Heavenly Waters. (The Lung belongs to Heaven.) Xuanshen (Scrophulariae Radix) possesses the nature and color of Heaven and Water, capable of clearing and venting smallpox from within the Water. Tusizi has the subtle application of Yin and Yang, capable of venting Yang-toxin from within Supreme Yin. Therefore, administering this pill to infants within 100 days, or up to three years of age, results in fewer cases for those with strong toxins, and no eruption for those with weak toxins. (Even with abundant heat-toxin, there is no risk of adverse complications.) Mr. Lu Ziyong of my hometown had no children until age fifty. He obtained a unique formula for conceiving offspring, resulting in two sons who both suffered severely from smallpox. Presumably, the conception formula contained too many hot-natured herbs! Subsequent children were raised with Xuantu Wan. By age sixty-five, he had six sons and six daughters, all grown, none harmed by smallpox. Are the effects of Xuantu Wan shallow? (The Lu family kept this as a secret prescription.)