Yin-Yang Exchange Disease refers to a condition where Yin and Yang energies mutually affect each other, causing pathogenic toxic factors to adhere to the body, resembling a swapping of bodies. If a man who has recently recovered from an illness engages in sexual intercourse with a woman, and the woman subsequently falls ill, it is called "Yang Exchange"; if a woman who has recently recovered engages in sexual intercourse with a man, and the man subsequently falls ill, it is called "Yin Exchange". However, no such exchange occurs between two men or two women. Nevertheless, when a woman transmits the disease to a man, death is rare; but when a man transmits the disease to a woman, if treatment is delayed even slightly, almost none of the ten will survive. If a woman transmits the disease to a man, but the man suffers a relapse due to overexertion (Lao Fu), the woman will not fall ill; conversely, if a man transmits the disease to a woman, but the woman suffers a relapse due to overexertion, the man's illness will be milder. Wealthy families may know of this phenomenon, yet young heirs often act recklessly and indulge themselves, leading to many untreatable cases; rural people, ignorant and confused, only know that Shanghan (Cold Damage) can cause death, unaware of this specific disease, resulting in three or four out of ten deaths attributed to it. They do not understand the cause of their affliction, which is deeply lamentable.

The symptoms of Yin-Yang Exchange Disease in both men and women include body pain, sensation of heat rushing up to the chest, heaviness of the head making it difficult to lift, discharge in the eyes, stiffness and cramping of the four limbs, severe colic in the lower abdomen, curling of hands and feet, and even sudden death, though some do not die immediately. If there is urgency and tightness in the lower abdomen, heat rushing up to the chest, heaviness of the head making one reluctant to lift it, a sensation of joints separating, slack and weak meridians, deficiency of blood and Qi, exhaustion of bone marrow, shortness of breath with diminished strength, inability to move while lying in bed, requiring others to pull them up when getting up or down, and eventual death after months or years, this formula is suitable: Foot Nail Ash Powder.

Take twenty nails from the hands and feet of the woman with whom sexual contact occurred, along with hair from within one chi near the genital area, and burn them together into ash. Mix with rice water and take two qian per dose, three times daily. Recovery is indicated by slight swelling of the glans penis and free urination; if not recovered, moxibustion on the glans penis for one hundred Zhu will cure it. The acupoint is located at the pubic margin; lift the genitals upward, and the point directly facing is the acupoint.

For women suffering from Yang Exchange, take the nails from the hands and feet of the man, along with hair near the genital area, and process as described above. Moxibustion can be applied to the Qugu acupoint, located centrally above the horizontal crease of the pubic hair, one hundred Zhu per point. For men suffering from Yin Exchange, apply moxibustion using the previous method. If the testicles are retracted and have not descended, moxibustion should be applied to the Xuannong area on the dorsal side of the big toe, seven small moxa cones, which corresponds to the Dadun acupoints. For both men and women newly afflicted with Yin-Yang Exchange Disease, administering Xi Gen Shu Shi Tang (Scallion Root and Rat Feces Decoction) initially, inducing sweating, has proven effective.

Formula for treating dry mouth and excessive salivation following Shanghan:
Jujubae Fructus (Big Dates) (40 pieces, boiled, skin and pits removed)
Mume Fructus (Smoked Plum) (10 plump ones, pits removed, ground into powder)
Mix the above ingredients with jujube pulp to form pills. Hold in the mouth to dissolve slowly, allowing the natural juice to flow and swallow.