痘欲其疏，疏则毒少，不欲其密，密则毒甚，此古今确论也。疏密之分，各有
喜忌，如头面欲疏，元首不可犯也，颈项欲疏，管龠不可塞也，胸背欲疏，脏腑俞
募之所附也，若夫手足，不忌其密矣。谓之疏者，非但稀少也，铺排磊落，大小匀
净，亦可以言疏，谓之密者，非必盛多也，攒聚粘连，片复一片，虽只数处，亦可
以言密。疏而凶者亦有数等，如初出时才见红点三两处，其热便退，可以语其疏也，
苟大热不解，唇口燥裂，大小便秘，烦躁不宁，或身无热，但增烦渴者，此由毒甚
郁遏于中，不能遽出，日复渐出，渐加稠密，一也。又如初出一两点，顶尖焦黑，
或三四粒作一堆者，仅见数处，他无所出，喜睡不食，烦渴，大小便涩，此由毒伏
于中，加谵妄者，不待起发而死，若能起发，后必发痈毒也，二也。亦有出现实疏，
遂生玩忽之心，禁忌不守，风寒不避，饮食所伤，汤丸之试，变生不测，三也。设
有密而吉者，治之早，卫之严，里无病，而疮悉成也。
常观朝华之草，夕而零落，松柏之坚，凌冬不衰，夫以草木坚脆不同，坚者难
坏，脆者易伤，况于人质有浓薄，气有强弱邪，彼疮痘之毒，喜老而恶嫩，苍蜡、
娇红，色之老嫩也。紧实、虚浮，形之老嫩也。浓浊、清淡，浆之老嫩也。坚浓、
软薄，痂之老嫩也。老嫩之故，卫气主之，经曰∶卫气者，所以温分肉，充皮肤，
肥腠理，司开阖者也，是故卫气强，则分肉坚，皮肤浓，腠理密，而开阖得也，所
以收敛禁束，制其毒而使不得以放肆，故色苍而蜡，形紧而实，浆浓而浊，痂浓而坚，
自然易壮易靥，虽有邪风秽毒，不能害也。如卫气弱，则分肉脆，皮肤薄，腠理疏，
而开阖失也，所以不胜其毒，而毒得以恣其猖狂之性，故色娇而红，形虚而浮，浆
清而淡，痂软而薄，易破难靥，不待邪风秽气，而先败坏矣。观夫疮之老嫩，则气
不可不养也。
痘疹希望分布稀疏，稀疏则毒邪较轻；不希望分布密集，密集则毒邪深重，这是古今公认的定论。疏与密各有其宜忌，例如头面部希望稀疏，因为头部是元首所在，不可受犯；颈项部希望稀疏，因为咽喉要道不可堵塞；胸背部希望稀疏，因为脏腑的俞穴和募穴依附于此；至于手足部位，则不忌讳密集。所谓“疏”，不仅仅是指数量稀少，如果痘疹排列磊落、大小均匀洁净，也可以称为疏；所谓“密”，也不一定是数量众多，如果痘疹攒聚粘连、层层重叠，即使只有几处，也可以称为密。
出现稀疏却预后凶险的情况也有几种：比如刚出痘时只见到红点两三处，热度随即消退，看似稀疏，但如果大热不退，嘴唇口舌干燥破裂，大小便闭塞不通，烦躁不安，或者身体没有发热，只是烦渴加重，这是由于毒邪深重郁结在体内，不能迅速透发出来，日复一日逐渐发出，且逐渐变得稠密，这是一类情况。又如刚出一两点，痘顶焦黑，或三四粒聚集在一起，仅在几处出现，其他地方没有发出，患儿喜欢睡觉且不进食，烦躁口渴，大小便涩滞，这是由于毒邪伏藏在体内，如果出现胡言乱语等神志症状，甚至不需要等到痘疹起发就会死亡；如果能起发，后来必然会发生痈毒，这是第二类情况。也有痘疹出现确实稀疏，但家长因此产生轻视疏忽之心，不遵守禁忌，不躲避风寒，饮食不当受伤，或随意尝试汤药丸剂，导致病情发生不可预测的变化，这是第三类情况。
假设有痘疹密集但预后吉祥的情况，是因为治疗及时，护理严密，体内没有病变，而痘疮都能顺利成熟。
我常看到早晨开花的草，傍晚就凋零零落，而松柏的坚韧，经历寒冬也不衰败。草木的坚脆不同，坚韧的难以损坏，脆弱的容易受伤，何况人的体质有浓薄之分，元气有强弱之别呢？那些疮痘的毒邪，喜欢“老”而厌恶“嫩”。“苍蜡”与“娇红”，是颜色的老嫩；“紧实”与“虚浮”，是形态的老嫩；“浓浊”与“清淡”，是脓浆的老嫩；“坚浓”与“软薄”，是结痂的老嫩。老嫩的原因，由卫气主宰。经书说：“卫气，是用来温养肌肉，充实皮肤，肥厚腠理，主管汗孔开阖的。”所以卫气强盛，则肌肉坚实，皮肤厚实，腠理致密，开阖功能正常，从而能够收敛约束，制约毒邪使其不能放肆妄为，因此颜色呈苍蜡色，形态紧实，脓浆浓浊，结痂浓厚坚硬，自然容易壮盛（发育良好）且容易结痂愈合，即使有邪风秽毒侵袭，也不能伤害它。如果卫气虚弱，则肌肉脆弱，皮肤薄，腠理疏松，开阖功能失常，因而无法承受毒邪，毒邪得以肆意猖狂，所以颜色娇嫩鲜红，形态虚浮，脓浆清稀淡白，结痂软薄，容易破损且难愈合，不需要等待邪风秽气，就已经先败坏了。观察疮痘的老嫩，就知道元气不可不养护了。
The eruption of smallpox (or chickenpox) should be sparse; if sparse, the toxin is less severe. It should not be dense; if dense, the toxin is profound. This is a confirmed theory from ancient and modern times. The distinction between sparse and dense has its respective preferences and taboos. For instance, the head and face should be sparse, as the head is the "chief" and must not be invaded; the neck should be sparse, as the "pipe and lock" (throat/airway) must not be blocked; the chest and back should be sparse, as they are where the Shu (Back-Shu points) and Mu (Front-Mu points) of the Zang-Fu organs are attached. As for the hands and feet, density is not taboo.
To call it "sparse" does not merely mean few in number; if arranged distinctly and evenly in size and cleanliness, it can also be called sparse. To call it "dense" does not necessarily mean numerous; if clustered and adhering, layer upon layer, even if only in a few places, it can still be called dense.
There are several types of sparse eruptions that indicate a ominous prognosis. First, when the eruption first appears, only two or three red spots are seen, and the fever subsides immediately, which seems sparse. However, if high fever persists, lips and mouth become dry and cracked, urination and defecation are obstructed, and there is restlessness and irritability, or if there is no body heat but increased thirst and irritability, this is because the toxin is deep and repressed internally, unable to emerge quickly. Day by day, more emerge, becoming increasingly dense. This is the first type. Second, if one or two spots appear initially with blackened, necrotic tips, or three or four grains cluster together, appearing only in a few places while others do not erupt, accompanied by lethargy, anorexia, irritability, thirst, and difficult urination/defecation, this indicates toxin hidden internally. If delirium occurs, death may ensue before the eruption rises; if it does rise, abscesses and toxins will likely develop later. This is the second type. Third, although the eruption is truly sparse, negligence arises due to laxity in observing taboos, failure to avoid wind-cold, dietary injury, or inappropriate use of decoctions and pills, leading to unpredictable changes. This is the third type.
Conversely, there are cases of dense eruptions with a auspicious prognosis. This occurs when treatment is early, care is strict, there is no internal disease, and all lesions mature successfully.
I often observe that morning-blooming grass withers by evening, while pine and cypress remain resilient through winter. Plants differ in hardness and brittleness; hard ones are difficult to damage, while brittle ones are easily injured. How much more so for humans, whose constitution varies in thickness/thinness and Qi in strength/weakness? The toxin of sores and pox prefers "mature/old" (Lao) and dislikes "tender/young" (Nen). "Cangla" (dark waxy) versus "Jiaohong" (delicate red) refers to color maturity. "Jinshi" (tight/solid) versus "Xufu" (empty/fluctuant) refers to form maturity. "Nongzhuo" (thick/turbid) versus "Qingdan" (clear/light) refers to pus maturity. "Jianong" (hard/thick) versus "Ruanbo" (soft/thin) refers to scab maturity.
The reason for maturity lies in Wei Qi (Defensive Qi). The Classics state: "Wei Qi warms the muscles, fills the skin, thickens the interstices, and controls the opening and closing." Therefore, strong Wei Qi results in firm muscles, thick skin, dense interstices, and proper regulation of opening/closing. It thus restrains and binds the toxin, preventing it from running rampant. Consequently, the color is dark-waxy, the form is tight-solid, the pus is thick-turbid, and the scab is hard-thick. Naturally, it becomes robust and heals easily. Even if attacked by evil winds and foul toxins, it cannot be harmed.
If Wei Qi is weak, muscles are brittle, skin is thin, interstices are loose, and opening/closing is disordered. It cannot withstand the toxin, allowing the toxin to act wildly. Thus, the color is delicate-red, the form is empty-fluctuant, the pus is clear-light, and the scab is soft-thin. It breaks easily and fails to heal. Without waiting for evil winds or foul air, it deteriorates prematurely. Observing the maturity of sores reveals that Qi must be nourished.