儿医钱乙，字仲阳，载在宋史，一代之名流也。专用百祥丸，治痘之黑陷甚者，谓能转祸为福，故有
百祥之名。后人置之不用者，不知物性故耳！夫大戟性能泄水，味苦寒而色紫赤，能泻水中之火毒，浸于
水中，其色青翠，盖从子以泄母也。夫痘毒发原在肾，如初起腰疼肚痛，寒战切牙，乃热毒太盛，不能
透发，此危在俄顷，非大戟、大黄、芒硝之类，为釜底抽薪之法，则束手待毙矣。故表而出之。
（疏杀其衷，则透发于外矣。）
张开之曰∶痘之初发三日，主春生；起胀三日，主夏长；贯脓三日，主秋成；结痂三日，主冬藏。若
秋冬之不能收成者，多缘病酿于春，故热毒虽盛，而能生长透发，内无留蓄，至秋冬无有不收成者，即正
气虚脱，不妨大用温补。如使邪毒留滞，外内不清，邪之所凑，其正必虚，欲补其正气，则碍于热毒，欲
清其热毒，又妨于正虚，是以热毒盛而不能透发者，死于三五之期，虽透发而里气不清者，终成 稗。善
治痘者，当预防其初焉。
夫稀痘之方法虽多，未有如玄菟丸之理甚精微，验若桴鼓。盖痘乃先天之毒，天一生水，地二生火，
水火相济，阴阳互交，乃水中之火毒也。玄乃水天之色，参者参也，参天地之化育者也。菟丝子一名女萝，
《尔雅》名为玉女。盖兔乃月魄，纯阴之物，故有玉女之称。《抱朴子》云∶菟丝初生之根，其形如兔
握，割其血以和丹药，立能变化神异之品也。夫凡物得清凉水土之气，而后能发芽。菟丝秉纯阴之性，故
得火暖而丝长，此物理阴阳之妙用也。《内经》云∶肾者，至阴也；至阴者，盛水也。肺者，太阴也。少
阴者，冬脉也。故其本在肾，其末在肺，皆积水也。是肺肾天水之相通也。（肺属天。）玄参具水天之性色，能于
水中以清发其天花。菟丝有阴阳之妙用，能于至阴之中而透其阳毒。是以婴儿在百日内，与此丸服之，或
服至三岁，则毒盛者稀，而毒微者不出矣。（即热毒盛者，亦无险逆之虞。）同邑卢子由先生，五十无子，得一种子奇
方，即生二男，皆为痘坏。盖种子方中，不无多热药耳！后复生子，皆以玄菟丸服之，至六十有五，连举
六男六女，俱已长成，皆不为痘疹所坏。玄菟之功效，岂浅浅哉！（卢氏以此为秘方。）
儿科医生钱乙，字仲阳，记载于《宋史》，是一代名流。他专门使用百祥丸，治疗痘疮黑陷严重的情况，认为能够转危为安，所以有“百祥”这个名字。后人将其搁置不用的原因，是不了解药物性质的缘故！大戟的性能能泄水，味道苦寒且颜色紫赤，能泻除水中的火毒，浸泡在水中，其颜色变为青翠，这大概是顺应子（水）来泄母（土/火之源）的道理。痘毒的发源在于肾，如果初起时出现腰痛、腹痛、寒战咬牙，这是热毒太盛，不能透发出来，这种情况危急就在顷刻之间，如果不是用大戟、大黄、芒硝这类药物采取釜底抽薪的方法，那就束手待毙了。所以我将其阐明出来。（疏泄其内部的郁结，就能使痘毒透发于体外。）
张开之说：痘疮初发的三天，对应春季的生发；起胀的三天，对应夏季的生长；贯脓的三天，对应秋季的成熟；结痂的三天，对应冬季的收藏。如果在秋冬季节不能收成（指痘疮不能顺利结痂脱落），大多是因为病根酿成于春季，所以虽然热毒旺盛，但能够生长透发，体内没有留滞蓄积，到了秋冬季节没有不能收成的。即使是正气虚脱，不妨大胆使用温补法。如果邪毒留滞，内外不清，邪气聚集的地方，正气必然虚弱，想要补益正气，就会碍于热毒；想要清除热毒，又会妨碍正气的恢复。因此，热毒旺盛而不能透发的，会在三五天内死亡；虽然透发但里气不清的，最终也会变成坏证。善于治疗痘疮的人，应当在初期就进行预防。
稀痘的方法虽然很多，但没有像玄菟丸那样道理精微，效果灵验如响应鼓声。痘疮是先天之毒，天一生水，地二生火，水火相济，阴阳互交，这是水中之火毒。玄是水天的颜色，参是参赞的意思，参赞天地化育的功能。菟丝子又名女萝，《尔雅》中称为玉女。兔子是月魄，属于纯阴之物，所以有玉女的称呼。《抱朴子》说：菟丝子刚生出的根，形状像兔爪，割取其汁液调和丹药，立刻能变化成神奇异异的物品。大凡物体得到清凉水土之气，然后才能发芽。菟丝子秉承纯阴的性质，所以得到火温暖后丝才伸长，这是物理中阴阳的妙用。《内经》说：肾，是至阴；至阴，是盛水的地方。肺，是太阴。少阴，是冬脉。所以病的根本在肾，末梢在肺，都是积水所致。这是肺肾天水相通的表现。（肺属天。）玄参具备水天的性质和颜色，能在水中清发天花（痘疮）。菟丝子有阴阳的妙用，能在至阴之中透发阳毒。因此在婴儿百日内，服用此丸，或者服到三岁，那么毒盛的就会稀少，毒微的就不会出痘了。（即使热毒旺盛，也没有险逆的忧虑。）同乡卢子由先生，五十岁没有儿子，得到一个奇特的种子方，生了两个男孩，都因痘疮而败坏。大概是因为种子方中不免多用热药吧！后来再生孩子，都用玄菟丸喂养，直到六十五岁，接连生了六个男孩六个女孩，都已长成，都没有被痘疹所害。玄菟丸的功效，难道浅薄吗！（卢氏将此作为秘方。）
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.)