钱氏论痘疮。发散利下皆不可妄。又曰。非微汗则表不解。非微下则里不解。言表热方炽。
痘点未见之先。或外感寒邪。约束腠理。痘因出不快。此当微汗之。令阴阳和。营卫通。俾痘易
出。而毒易解。若原无闭塞不快而妄汗之。则成表虚痒塌斑烂之患也。如痘出时。烦热谵语。喘
胀便秘。此毒蓄于肠胃之间。当微下之。但脏腑疏通。陈 涤去。气血和平。而毒易升发。若原
无里实壅热而妄下之。则元气下陷。致变灰白虚脱之证矣。张涵高曰。余治血热毒壅便结之证。
每用凉膈散下之。百不失一。
或问时气之盛衰。而痘出之轻重者。何也。盖痘之出。必假天行时气而发。天时疫气。有盛
而有衰。人之生禀。有强而有弱。疫气盛行。虽轻亦能变重。禀弱者当之。必致于危。厉气已衰。
虽重亦能变轻。禀强者当之。益见其轻。故贫贱家儿。多历辛苦风寒。更无浓味伤脾。即有重证。
亦能抵当。富贵家儿。暖衣浓味。少见风日。脾胃脆弱。不经劳苦。凡遇小疾。亦为大病。譬之
阴地草木。岂能御冰霜烈日乎。临证之际。可不辨人之强弱贵贱。参时气之盛衰。而为施治哉。
痘有死而复生者。非气血相离也。乃毒火弥炽。气血壅遏不行。故肢体俱冷而气绝。本不终
绝。虽绝必通。毒火有时而少解。则正气渐复而苏。尝见痘儿气绝。转卧于地。良久复生者。得
土气以化毒热。而正气复矣。然虽气绝而死。其心胸必温暖。若胸冷气绝复生者。未之有也。
钱乙论述痘疮的治疗，指出发散解表和通下攻里都不可随意妄用。他又说：如果不通过微微发汗，表邪就不能解除；如果不通过微微通便，里邪就不能解除。这是因为当体表热势正盛、痘疹尚未显现之前，如果患者外感寒邪，导致腠理闭塞，痘点因此难以顺利透出，此时应当采用微汗法，使阴阳调和，营卫之气通畅，从而使痘疹容易发出，毒邪容易化解。如果原本没有表闭不畅的情况而妄用发汗法，就会导致表虚、瘙痒塌陷、斑烂等祸患。
如果在痘疹发出时，出现烦躁发热、胡言乱语、气喘腹胀、大便秘结等症状，这是毒邪蓄积在肠胃之间，应当采用微下法（轻微通便）。只要脏腑气机疏通，陈旧的积滞涤除干净，气血恢复平和，毒邪就容易随痘疹升发透达。如果原本没有里实热结的情况而妄用攻下法，就会导致元气下陷，进而演变为痘色灰白、虚脱的危重证候。张涵高说：我治疗血热毒盛、大便干结的证候，每用凉膈散进行攻下，百次治疗无一失手。
有人问：时令疫气的盛衰，与痘疹病情的轻重有什么关系呢？大概痘疹的发出，必须借助天行时气（流行性气候因素）才能发动。天时疫气有旺盛和衰减之分，人的先天禀赋有强壮和虚弱之别。如果疫气盛行，即使病情轻浅也能转变为重症；如果禀赋虚弱的人遭遇此疫气，必定会导致危险。如果厉气已经衰减，即使病情深重也能转变为轻症；如果禀赋强壮的人遭遇此情况，病情会显得更加轻微。所以贫贱人家的孩子，多经历辛苦风寒，且没有厚味饮食损伤脾胃，即使患有重症，也能抵挡得住。富贵人家的孩子，穿着暖和，饮食肥甘厚味，少见风吹日晒，脾胃脆弱，不经劳苦，凡是遇到小病，也会变成大病。这就像生长在阴地的草木，怎么能抵御冰霜烈日呢？所以在临证诊疗时，难道可以不辨别病人的强弱贵贱，参考时气的盛衰，从而制定治疗方案吗？
痘疮有死而复生的情况，这并不是因为气血分离，而是毒火过于炽盛，导致气血壅遏不通，所以四肢冰冷甚至看似气绝。但这并非真正的终结，虽然看似气绝，但生机必然通达。当毒火暂时稍减时，正气逐渐恢复就会苏醒。我曾见过出痘的孩子气绝倒地，过很久又复活的情况，这是因为得到了土气（接触地面）来化解毒热，从而使正气恢复。然而，即使是气绝而死，其心胸部位必然是温暖的。如果是胸中寒冷、气绝后又复活的，从未有过这种情况。
Qian Yi discussed the treatment of smallpox, stating that both diaphoresis (inducing sweating to release the exterior) and purgation (draining downward to clear the interior) should not be used recklessly. He further stated: "If there is no slight sweating, the exterior pathogen cannot be resolved; if there is no slight purgation, the interior pathogen cannot be resolved." This refers to the situation where the exterior heat is intense before the smallpox spots appear. If the patient has contracted cold pathogenic factors externally, constricting the cou li (skin pores and interstices), the smallpox will fail to emerge quickly. In this case, one should employ slight diaphoresis to harmonize Ying and Wei (nutritive and defensive qi), allowing the smallpox to emerge easily and the toxin to resolve. However, if there was no exterior obstruction or difficulty in emergence, and one recklessly induces sweating, it will lead to complications such as deficiency of the exterior, itching, collapse of lesions, and ulceration.
When the smallpox is emerging, if symptoms such as irritability, fever, delirium, wheezing, abdominal distension, and constipation occur, this indicates that the toxin is accumulated between the zang-fu organs, specifically the intestines and stomach. One should employ slight purgation. As long as the zang-fu organs are unobstructed, old stagnation is cleared away, and qi and blood return to harmony, the toxin can easily rise and manifest through the eruption. Conversely, if there is no interior excess or heat accumulation, and one recklessly uses purgation, it will cause the Yuan Qi (original qi) to sink, leading to critical conditions characterized by grayish-white lesions and deficiency collapse. Zhang Hangao stated: "In treating conditions of blood heat, toxin congestion, and constipation, I always use Liang Ge San (Cool the Diaphragm Powder) for purgation, with a success rate of nearly 100%."
Someone asked: "What is the relationship between the prevalence of seasonal epidemic qi and the severity of smallpox?" Generally, the emergence of smallpox relies on Tian Xing Shi Qi (seasonal epidemic climate factors) to develop. Seasonal epidemic qi varies in its intensity (prosperous vs. declining), and human congenital endowment varies in strength (strong vs. weak). When epidemic qi is prevalent, even mild cases can become severe; if a person with weak endowment encounters this, it will inevitably lead to danger. When malignant qi declines, even severe cases can become mild; if a person with strong endowment encounters this, the condition appears even lighter. Therefore, children from poor families, who endure hardships and exposure to wind and cold, and do not consume rich foods that damage the spleen, can withstand even severe conditions. In contrast, children from wealthy families, who wear warm clothes, consume rich diets, lack exposure to wind and sunlight, have fragile spleens and stomachs, and are unused to labor, may turn minor illnesses into major diseases. This is like plants growing in shady places; how can they withstand frost and scorching sun? Thus, in clinical practice, must one not distinguish the strength and social status of the patient, and consider the prevalence of seasonal qi, to determine the treatment strategy?
There are cases of smallpox patients dying and then reviving. This is not due to the separation of qi and blood, but rather because the toxin-fire is excessively intense, causing qi and blood to stagnate and cease flowing, resulting in cold limbs and apparent cessation of breath. However, this is not true death; although breath seems absent, life force remains connected. When the toxin-fire temporarily subsides slightly, the righteous qi gradually recovers, leading to revival. I have seen children with smallpox who appeared dead, lying on the ground, only to revive after a long while. This is attributed to receiving the energy of the earth (contact with the ground) to transform toxin-heat, thereby restoring righteous qi. However, even in cases of apparent death due to qi cessation, the chest and heart region must remain warm. There has never been a case of revival where the chest was cold upon apparent death.