人以水谷为本，故绝水谷则死。仲景曰∶水入于经，其血乃成，谷入于胃，脉道
乃行。水谷之悍气为卫，精气为荣，水去则荣散，谷消则卫亡，故痘疮能食者，虽重亦
吉，不能食者，虽轻亦凶。然有能食而死，不能食而生者，何也？盖不能饮食者，是或
脏腑内实，大便不行，有旧谷气为养，而至疮成之后，自能消谷思食矣。其能饮食者，
是邪热杀谷也。叔和所谓∶口干欲饮水，多食亦饥虚是也。将不久而变生焉，惟疹家多
不能食者，以口中不和而不思食，疹退而自能食也。且病日无多，又无灌浆大伤气血，
故无害耳。
夫痘疹热微，气平神宁意适，此系佳兆也。如疼痛哓哓，烦躁不已，总属凶征，然
又有部位之分，时日之则焉。如痛在头额，而在初热时者，是火欲升也，治宜微表，在
行浆时者，此虚肿痘胖，是系正候，在收靥时者，是风寒不谨，或血气虚惫，浮火上逼
耳。宜加详治。如痛在咽喉而初热时者，其属火也，何疑？在起胀时痛极而嗽者，则喉
中痘必繁密，在收靥者，则是火毒相聚，须防喘急而为恶候。如痛在皮肤而初起时者，
是毒火欲泄而肌肤闭密也。在肿灌时者，则是毒化为脓，亦是正候在痂落后者，则是血
枯不能荣养皮肤，兼之火灼于外耳。如痛在胸腹而初热时者，是或饮食倍伤，或痘毒有
伏，或旧有是疾，宜细剖治。如痛在腰膝，而初热时者，虽曰肾经难治，然若视其唇不
肿，口不秽、斑不见，热不剧者，此是肾虚不能逐毒也。便宜升提达表，不可妄叶，用
药不可过凉，以致沉匿难出也。如在四肢作痛者，是或儿顽闪摄，气不顺舒，或经扑
跌，血瘀凝滞，或脾阴不足，不能灌溉四肢，是皆验痛之要略也。
人以水谷（饮食）为根本，所以断绝水谷就会死亡。张仲景说：水进入经脉，血液才能生成；谷物进入胃中，脉道才能通畅运行。水谷中剽悍滑疾的部分化为卫气（行于脉外，具有防御、温煦作用的阳气），精微柔和的部分化为营气（行于脉中，具有营养作用的阴气）。水液代谢失常则营气散乱，谷物消化殆尽则卫气消亡。因此，痘疮患者若能进食，即使病情严重也是吉兆；若不能进食，即使病情轻微也是凶兆。然而，也有能进食却死亡，不能进食反而存活的情况，为什么呢？大概是因为不能饮食的人，可能是脏腑内部实邪壅滞，大便不通，依靠体内原有的谷气来滋养，等到痘疮成熟之后，自然能够消化食物并产生食欲了。那些能进食的人，是邪热加速了谷物的消化（即“杀谷”）。这就是王叔和所说的：“口干想喝水，吃得多也感到饥饿虚弱。”这样的人不久后就会发生变证，只有患疹病的人大多不能进食，是因为口中不适而不思饮食，等疹子消退后自然就能进食了。而且病程不长，又没有灌浆期大量耗伤气血，所以没有危害。
痘疹发热轻微，气息平稳，神志安宁，心情舒适，这是佳兆。如果疼痛嘈杂，烦躁不安，总属凶险的征象，但这又有部位和时间的区别。比如疼痛在头额部，如果在初热阶段，是火气想要升发的表现，治疗宜用轻微的解表法；如果在行浆阶段，这是虚肿的痘疱，属于正常候象；如果在收靥阶段，这是因风寒护理不当，或血气极度虚弱，导致浮火上冲所致。应当详细辨证治疗。如果疼痛在咽喉部，在初热阶段，这属于火邪，有何可疑？在起胀阶段疼痛剧烈且咳嗽的，说明喉中的痘疹必然繁密；在收靥阶段疼痛的，这是火毒聚集，必须防止出现气喘急促等恶候。如果疼痛在皮肤表面，在初起阶段，是毒火想要宣泄但肌肤腠理闭塞所致；在肿胀灌浆阶段，是毒邪化为脓液，这也是正常候象；在痂皮脱落阶段，是血枯不能荣养皮肤，兼有火邪灼烧于外所致。如果疼痛在胸腹部，在初热阶段，可能是饮食过度损伤，或痘毒潜伏，或原有旧疾，应仔细剖析治疗。如果疼痛在腰膝部，在初热阶段，虽然常说肾经病症难治，但如果观察其嘴唇不肿，口无秽臭，斑疹未现，热势不剧烈的，这是肾虚不能驱逐毒邪的表现。此时适宜用升提透达的方法使毒邪外出，不可妄加用药，用药不可过于寒凉，以免导致毒邪沉伏隐匿难以透出。如果疼痛在四肢，可能是小儿顽皮闪挫，气机不畅，或因跌扑导致血瘀凝滞，或是脾阴不足，不能灌溉四肢，这些都是诊察疼痛的大略要点。
Human beings rely on water and grain (diet) as their foundation; therefore, if water and grain are cut off, death ensues. Zhang Zhongjing stated: "When water enters the meridians, blood is formed; when grain enters the stomach, the vessel pathways begin to circulate." The fierce and rapid qi derived from water and grain becomes Wei Qi (defensive qi that circulates outside the vessels), while the refined and gentle essence becomes Ying Qi (nutritive qi that circulates inside the vessels). If water metabolism fails, Ying Qi scatters; if grain digestion ceases, Wei Qi perishes. Therefore, in variola (smallpox), if a patient can eat, even severe cases are auspicious; if they cannot eat, even mild cases are ominous. However, there are cases where those who can eat die, and those who cannot eat survive. Why? Generally, those unable to eat may have internal excess in the zang-fu organs with constipation, relying on residual food qi for nourishment; after the pustules mature, they will naturally be able to digest food and desire eating. Those who can eat are suffering from pathogenic heat accelerating digestion ("killing grain"). This corresponds to Wang Shuhe's statement: "Dry mouth desiring water intake, eating much yet feeling hungry and weak." Such individuals will soon develop complications. Only patients with exanthems (rash diseases) often cannot eat because of oral discomfort and lack of appetite; once the rash subsides, appetite returns. Moreover, since the disease course is short and there is no significant depletion of qi and blood during the pustule-filling stage, it causes no harm.
If the fever from smallpox or measles is mild, with calm breathing, peaceful spirit, and comfortable mind, this is a favorable sign. Conversely, if there is painful restlessness and incessant irritability, these are generally ominous signs, though they vary by location and timing. For instance, pain in the forehead and head: during the initial fever stage, it indicates fire attempting to ascend, and treatment should employ mild releasing-the-exterior methods; during the pustule-filling stage, swollen and puffy pustules are considered normal manifestations; during the crusting stage, it results from careless exposure to wind-cold or extreme deficiency of qi and blood causing floating fire to rush upward. Detailed differentiation and treatment are required. Pain in the throat: during the initial fever stage, it clearly belongs to fire. During the swelling stage, severe pain accompanied by coughing indicates dense pustules in the throat; during the crusting stage, it signifies aggregation of fire-toxin, requiring vigilance against asthma-like urgency as an adverse outcome. Pain in the skin: during the initial onset, it means toxin-fire desires to vent but the muscle layer is closed and tight; during the swelling and filling stage, it means toxin transforms into pus, which is also a normal manifestation; after scabs fall off, it indicates blood dryness failing to nourish the skin, compounded by external fire burning. Pain in the chest and abdomen: during the initial fever stage, it may result from dietary injury, latent smallpox toxin, or pre-existing conditions, requiring careful analysis and treatment. Pain in the waist and knees: during the initial fever stage, although kidney meridian disorders are difficult to treat, if the lips are not swollen, the mouth has no foul odor, macules are absent, and fever is not intense, this indicates kidney deficiency failing to expel toxins. In such cases, lifting and venting methods should be used to guide toxins outward; one must not prescribe recklessly, nor use overly cold medicines, lest the toxins become sunken and hidden, making them difficult to emerge. Pain in the four limbs may result from pediatric sprains or strains causing stagnant qi, trauma leading to blood stasis, or insufficient spleen yin failing to irrigate the limbs. These are the essential principles for diagnosing pain.