问婴儿三岁以下。看虎口三关纹色。其义云何。答曰。婴儿气血未盛。经脉未充。无以辨其脉象。故以食
指络脉形色之彰于外者察之。其络即三部之所发。其色以紫为风热。红为伤寒。青为惊恐。白为疳积。惟黄色
隐隐。或淡红隐隐为常候。至见黑色危矣。若虎口三关多乱纹为内钓。腹痛气不和。脉乱身热不食。食即吐而上唇
有珠状者。为变蒸也。其间纹色。在风关为轻。气关为重。命关尤重也。此言次指上三关近虎口一节为风关。
中节为气关。爪甲上节为命关。然纹直而细者。为虚寒少气。多难愈。粗而色显者。为邪干正气。多易治。纹
中有断续如流珠形者。为有宿食。其纹自外向里者为风寒。自内向外者为食积也。岐伯曰。阴络之色应其经。
阳络之色变无常。随四时而
行也。寒多则凝泣。凝泣则青黑。势多则淖泽。淖泽则黄赤。此皆常也。至三岁以上。乃以一指按三关。此言寸
关尺三部也。其脉常以六至为则。添则为热。减则为寒。浮弦为乳痫。弦紧为风痫。虚涩为慢惊。沉弦为腹痛。
弦实为气不和。牢实为便秘。沉细为冷乳不消。沉滑为宿食不化。或小或涩。或沉或细。皆为宿食停滞。浮大
为伤风。伏结为物聚。弦细为疳劳。沉数为骨蒸有热也。婴儿病赤瓣飧泄。脉小手足寒。难已。脉小手足温。泄
易已。小儿见其腮赤目赤。呵欠烦闷。乍凉乍热。或四末独冷。鼓栗恶寒。面赤气涌。涕泪交至。及耳后有红
丝纹缕。脉来数盛者。皆是痘疹之候。汤药之所当忌者最多。慎勿漫投以贻其咎也。
问：对于三岁以下的婴儿，观察其虎口三关的络脉纹色，其中的道理是什么？
答：婴儿的气血尚未旺盛，经脉尚未充盈，无法通过切脉来辨别脉象，因此通过观察食指络脉形色显露于外部的情况来进行诊断。这条络脉即是寸、关、尺三部脉气的发源处。络脉的颜色中，紫色主风热，红色主伤寒，青色主惊恐，白色主疳积（营养不良）。只有隐隐可见的黄色，或隐隐的淡红色，属于正常的征候。如果见到黑色，则病情危重。如果虎口三关处出现杂乱纹路，提示为内钓（一种以腹痛为主要表现的儿科病证），伴有腹痛、气机不和、脉象紊乱、身体发热、食欲不振，进食后即呕吐且上唇出现珠状颗粒的，是变蒸（婴儿生长发育过程中的生理现象）的表现。其中，纹路在风关（靠近虎口的第一节）表示病情轻浅，在气关（中间一节）表示病情较重，在命关（指甲上一节）则表示尤为严重。这里所说的次指（食指）上三关，近虎口的一节为风关，中间一节为气关，爪甲上方一节为命关。然而，纹路直而细的，属于虚寒少气，多难治愈；纹路粗而颜色明显的，属于邪气干扰正气，多易治疗。纹路中有断续如流珠形状的，说明有宿食停滞。纹路从外向里延伸的，属于风寒；从内向外延伸的，属于食积。岐伯说：“阴络的颜色与经脉相应，阳络的颜色变化无常，随四季气候而变化。”寒气多则血液凝滞，凝滞则呈现青黑色；热气多则血液润泽，润泽则呈现黄赤色。这些都是正常现象。到了三岁以上，才用一根手指按压寸、关、尺三部脉。婴儿的脉象通常以每呼吸一次跳动六次为标准，次数增多则为热证，次数减少则为寒证。脉浮弦主乳痫（婴儿癫痫的一种），脉弦紧主风痫，脉虚涩主慢惊风，脉沉弦主腹痛，脉弦实主气机不和，脉牢实主便秘，脉沉细主冷乳不消化，脉沉滑主宿食不化。或者脉小或涩，或者脉沉或细，都是宿食停滞的表现。脉浮大主伤风，脉伏结主有形之物积聚，脉弦细主疳劳（疳积日久形成的虚劳），脉沉数主骨蒸潮热。婴儿患赤瓣飧泄（大便带血且完谷不化的泄泻），若脉小且手足寒冷，难以治愈；若脉小但手足温暖，泄泻容易痊愈。小儿如果出现面颊红、眼睛红、打哈欠、烦躁闷乱、忽冷忽热，或者四肢末端单独发冷、颤抖恶寒、面部发红、气息上涌、鼻涕眼泪俱下，以及耳后有红色丝状纹路，脉搏来势急促有力的，都是痘疹（天花或麻疹等出疹性疾病）的征兆。此时应当禁忌使用的汤药非常多，千万不要随意投药以免留下后患。
Question: For infants under three years of age, what is the rationale behind observing the color and pattern of the collateral vessels at the "Three Passes" on the tiger's mouth (base of the thumb)?
Answer: The Qi and Blood of infants are not yet robust, and their meridians are not yet fully developed, making it impossible to distinguish pulse images through palpation. Therefore, diagnosis is made by observing the visible color and shape of the collateral vessels on the index finger. These collaterals are the origin points for the Cun, Guan, and Chi positions. Regarding color: purple indicates Wind-Heat; red indicates Cold Damage (Shanghan); green/blue indicates Fright or Alarm; white indicates Gan Accumulation (malnutrition). A faint yellow or a faint light red is considered a normal sign. The appearance of black is critical and indicates danger. If there are chaotic patterns across the Three Passes on the tiger's mouth, it suggests Neidiao (a pediatric condition characterized by abdominal pain and qi disharmony), accompanied by abdominal pain, qi disharmony, chaotic pulse, fever, anorexia, vomiting after eating, and bead-like formations on the upper lip, which indicates Bianzheng (physiological changes during infant growth). Among these, patterns in the Fengguan (Wind Gate, the first segment near the tiger's mouth) indicate mild conditions; patterns in the Qiguan (Qi Gate, the middle segment) indicate severe conditions; and patterns in the Mingguan (Life Gate, the segment near the nail) indicate particularly severe conditions. Specifically, the first segment of the index finger near the tiger's mouth is the Fengguan, the middle segment is the Qiguan, and the segment above the nail is the Mingguan. However, straight and thin patterns indicate Deficiency-Cold and insufficient Qi, which are difficult to cure; thick and distinct patterns indicate Pathogenic factors interfering with Healthy Qi, which are easier to treat. Patterns that are discontinuous like flowing pearls indicate retained food. Patterns extending from outside to inside indicate Wind-Cold; patterns extending from inside to outside indicate Food Retention. Qibo stated: "The color of Yin collaterals corresponds to the meridian; the color of Yang collaterals varies without constant rule, changing with the four seasons." Excess cold causes coagulation and stagnation, resulting in blue-black colors; excess heat causes moisture and luster, resulting in yellow-red colors. These are all normal phenomena. For children over three years old, one finger is used to palpate the Cun, Guan, and Chi positions. The infant's pulse should normally beat six times per breath cycle; an increase indicates Heat, and a decrease indicates Cold. A floating and wiry pulse indicates Ru Xian (infant epilepsy); a wiry and tight pulse indicates Feng Xian (wind epilepsy); a deficient and choppy pulse indicates Man Jing (slow convulsion); a deep and wiry pulse indicates abdominal pain; a wiry and excess pulse indicates qi disharmony; a firm and excess pulse indicates constipation; a deep and fine pulse indicates indigestion of cold milk; a deep and slippery pulse indicates undigested retained food. Whether small or choppy, or deep or fine, these all indicate retained food stagnation. A floating and large pulse indicates injury by Wind; a hidden and knotted pulse indicates accumulation of masses; a wiry and fine pulse indicates Gan Lao (chronic malnutrition leading to deficiency); a deep and rapid pulse indicates bone-steaming fever. In infants suffering from Chi Ban Sun Xie (dysentery with blood and undigested food), if the pulse is small and hands/feet are cold, recovery is difficult; if the pulse is small but hands/feet are warm, the diarrhea will easily resolve. If a child exhibits red cheeks, red eyes, yawning, restlessness, alternating chills and fever, coldness isolated to the extremities, trembling and aversion to cold, facial redness, surging Qi, copious tears and nasal discharge, red thread-like patterns behind the ears, and a rapid and abundant pulse, these are all signs of Dou Zhen (smallpox or measles). Many decoctions are contraindicated in this stage; do not administer medications recklessly to avoid causing harm.