Observing the complexion and feeling the pulse to first differentiate between Yin and Yang
Yin and Yang can not only summarize the entire condition of an illness but also be used to analyze individual symptoms. In the "Suwen · Great Treatise on Yin-Yang Correspondence to Images," it states: "When observing the complexion and feeling the pulse, first differentiate Yin and Yang." It also says, "For a Yang disease, treat the Yin; for a Yin disease, treat the Yang." Zhang Zhongjing classified cold damage diseases into Yin and Yang syndromes, using the Three Yin and Three Yang as the main principles. The Ming dynasty physician Zhang Jingyue also emphasized, "In all cases of pulse diagnosis and treatment, one must first examine Yin and Yang, for this is the fundamental principle of medical art." This Yin and Yang is the master principle of the Eight-principle syndrome differentiation. It can govern the other three pairs of principles: exterior-interior, cold-heat, and deficiency-excess. Therefore, some people refer to the Eight-principle as the "Two Principles and Six Essentials." This shows the important position of Yin-Yang differentiation in disease diagnosis.
Yin Syndrome and Yang Syndrome
All diseases that are interior, in the blood, of cold nature, with insufficient vital qi, and where the body's reactions show signs of decline are classified as Yin syndromes. Its symptoms include listlessness, pale complexion, aversion to cold and cold limbs, shortness of breath and a weak voice, no thirst, loose stools, clear urine, pale tongue with a white coating, and a deep, slow, and weak pulse. Its etiology and pathogenesis are due to old age and weakness, or internal injury from a chronic illness, or external pathogens transmitting into the internal organs, leading to a decline of vital qi, a deficiency of Yang, and an excess of Yin.
All diseases that are exterior, in the qi, of an excess or heat nature, with vital qi not yet damaged, and where the body's reactions show signs of hyperactivity are classified as Yang syndromes. Its symptoms include irritability, red face and body heat, strong voice and high volume, thirst with a preference for cold drinks, coarse breathing, abdominal pain that resists pressure, constipation, short and dark urine, a red tongue with a yellow coating, and a floating, surging, slippery, and rapid pulse. Its etiology and pathogenesis are caused by the invasion of pathogenic factors, where the pathogen is strong and the vital qi is also strong, leading to a struggle between the vital qi and the pathogen.
Yin Deficiency and Yang Deficiency
Yin deficiency and Yang deficiency are syndromes resulting from the impairment of the Yin and Yang of the body's organs. In a normal physiological state, the body's Yin and Yang must maintain a relative balance, that is, "When Yin is peaceful and Yang is secure, the spirit is harmonious" ("Suwen · Sheng Qi Tong Tian Lun"). Once this relative balance is lost, changes in excess and deficiency of Yin and Yang will occur, leading to disease.
The symptoms of Yin deficiency syndrome include tidal fever, night sweats, heat in the palms and soles, emaciation, dry mouth and throat, short and dark urine, a red tongue with little coating, and a thready, rapid, and weak pulse. Its etiology and pathogenesis are due to chronic illness, or overexertion from sexual activity, leading to a deficiency of essence, blood, and body fluids, so that Yin can no longer control Yang.
The symptoms of Yang deficiency syndrome include fatigue and listlessness, pale complexion, shortness of breath and reluctance to speak, aversion to cold and cold limbs, spontaneous sweating, a bland taste in the mouth with no thirst, loose stools, clear and copious urine, a pale tongue with a white and moist coating, and a weak pulse. Its etiology and pathogenesis are due to chronic illness, or strain, or excessive sweating, vomiting, or diarrhea, leading to a severe decline of Yang qi, so that Yang can no longer control Yin.
Collapse of Yin and Collapse of Yang
Collapse of Yin and Collapse of Yang are often critical conditions that develop during the progression of a disease. Collapse of Yin often occurs in situations where Yin fluid is rapidly lost, such as high fever with heavy sweating, severe vomiting and diarrhea, or excessive bleeding. It is commonly seen with sticky sweat, shortness of breath, warm limbs, restlessness, a preference for cold drinks, a flushed face, a dry red tongue, and a rapid but weak pulse. Collapse of Yang is often caused by the raging virulence of pathogenic factors, or severe damage to the body's Yang qi from internal organ diseases. It can also be caused by excessive sweating, vomiting, diarrhea, or massive bleeding. It is commonly seen with cold sweat like beads, a sallow and pale face, shallow breathing, aversion to cold and cold limbs, listlessness, a pale tongue with a moist coating, and a faint and nearly imperceptible pulse.