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In the differentiation of syndromes in surgery (Waike), distinguishing Yin and Yang is of primary importance. However, the terms "Yin" and "Yang" encompass a broad range of meanings; they are not limited to defining heat syndromes as Yang and cold syndromes as Yin, nor are they restricted to identifying redness and swelling with elevation as Yang, and flatness with hardness as Yin. Wang Hongxu, in his *Waike Zhengzhi Quansheng Ji* (Complete Collection of Surgical Syndrome Treatment), rigidly used the terms "Yong" (carbuncle) and "Ju" (deep abscess) to distinguish between Yin and Yang, asserting that those with high elevation and redness are Yong, representing Yang syndromes; whereas those with hard masses without redness are Ju, representing Yin syndromes. Most practitioners of external medicine at the time followed this view. Although borrowing these terms for distinction might be acceptable, one must reflect on the meaning behind the name. The precise definition of a character must align with its etymological roots, thereby establishing legitimacy and providing a standard for future learners. Do they know the original meaning of the characters "Yong" and "Ju"? "Yong" means obstruction or congestion; "Ju" means hindrance or blockage. Both refer to the stagnation and cessation of Qi and Blood flow. Originally, these were general terms for external sores, carrying no implication of superiority or inferiority, nor any distinction between Yin and Yang. How can one arbitrarily analyze them based on personal interpretation, claiming that ancient character creation should conform to one's own understanding? This is the old trick of local bullies acting dictatorially in their villages, which is highly inadvisable. *Yizong Jinjian: Waike Xinfa* (Golden Mirror of Medicine: Essentials of Surgery), which generally refers to all such conditions simply as "Yong and Ju" without distinguishing Yin and Yang, offers the most comprehensive and logical approach. All external sore terminology in ancient texts, whether called a specific Yong or a specific Ju, should be regarded as general terms. One must absolutely not trust Wang's theory and arbitrarily differentiate based solely on the characters "Yong" and "Ju". Although Yin and Yang syndromes lack specific representative characters, boundaries do exist. Their definitions are multifaceted; one must integrate and comprehend them thoroughly, grasp the ultimate principles, and then perceive the significant from the subtle, making decisive judgments without doubt.

There are cases where Yin and Yang can be distinguished by the location along the meridians. For example, the head and face belong to Yang, while the back belongs to Yin; the lateral aspect of the thigh is Yang, while the medial aspect is Yin.
There are cases where Yin and Yang can be distinguished by the anterior-posterior orientation of the body. For instance, the front of the face and the abdomen/head area mostly present Yang syndromes, while the back of the head and the lumbar-back area mostly present Yin syndromes. In ancient times, sages faced south and governed towards the sun. Therefore, the front belongs to Yang and the back belongs to Yin, which is indeed profound truth.

There are cases where Yin and Yang can be distinguished by the etiology's nature of cold-heat and deficiency-excess. For example, heat diseases are all Yang syndromes, and cold diseases are all Yin syndromes; excess diseases are mostly Yang syndromes, and deficiency diseases are mostly Yin syndromes.
There are cases where Yin and Yang can be distinguished by the speed of disease progression. Rapid onset, where the condition becomes severe within three to five days, indicates a Yang syndrome; slow onset, where there is little change over ten days or a month, indicates a Yin syndrome.
There are cases where Yin and Yang can be distinguished by the depth of the lesion. Lesions appearing on the skin surface, not involving tendons and bones, with free movement of limbs, are Yang syndromes; lesions penetrating deep into muscle tissue, adhering to tendons and bones, with impaired bodily movement, are Yin syndromes.
There are cases where Yin and Yang can be distinguished by the firmness or softness of the swelling. Swelling that is hard and solid, feeling like stone upon pressure, is mostly a Yin syndrome; swelling that is large but soft and pliable upon pressure, is mostly a Yang syndrome.
There are cases where Yin and Yang can be distinguished by the intensity of pain. Sudden, violent, and tearing pain indicates a Yang syndrome; numbness and insensitivity, or pain that is mild, dull, aching, or merely stiff without sharp pain, indicates a Yin syndrome.

Some insist that bright redness and high swelling indicate Yang, while diffuse swelling without redness indicates Yin. Speaking superficially, this may seem correct. However, one must understand that when the skin of a sore is deeply red, the pathology is shallowest, confined only to the interstices of the skin (Couli). Thus, the skin surface changes color easily. Conditions such as summer heat boils, prickly heat, rashes, tinea, and scabies are not major external surgical diseases. Furthermore, in areas with soft muscle, such as the axilla, groin, and thigh inner side, where individuals have small bones, fragile flesh, and fair, tender skin, sores often appear red. Conversely, consider Nao Ju (abscess of the brain/nape) and Bei Ju (abscess of the back); these pathologies reside in the Taiyang Cold Water meridian. The pulse is typically fine and small, and the tongue coating is white and greasy—all definite signs of Yin syndromes—yet the exterior may also present with high elevation and redness. This is because, at the initial stage, a lesion resembling a millet grain appears, with a white head and firm root, located within the skin and muscle layers, causing discoloration. Therefore, redness and swelling alone are insufficient evidence to definitively classify a condition as Yang. If a sore develops deep within the muscle, far from the hair follicles, even if suppuration occurs internally, the skin surface will likely not change color. Similarly, in areas with dense skin on the shoulders and back, or in individuals with dark, thick, aged skin, even shallow sores may not change color. How can one categorically label such cases as Yin syndromes simply due to the absence of redness? In summary, when observing signs and differentiating Yin and Yang, one must carefully examine the patient's constitutional strength (Qi and Blood) and the depth of the pathological source before reaching a conclusion. By observing complexion, differentiating pulses, and examining the tongue coating, and by considering the big picture, distinguishing between Yin and Yang, or deficiency and excess, becomes quite easy. Relying solely on the location of the lesion is not the argument of a knowledgeable person. Being pedantic about colors and shapes in a small area reveals short-sightedness and contributes nothing to understanding the disease condition or pathology.