In the 3rd century CE, the Shang Han Lun (Treatise on Injury by Cold) by Zhang Zhong Jing classified fevers according to their progression through the six channels (taiyang, yangming,
shaoyang, taiyin, shaoyin and jueyin). This theory, according
to which pathogenic cold attacked and penetrated the body via the skin, dominated Chinese medicine until the early 17th century when the ‘wen bing’ (warm disease) theory was developed (predominantly by Wu You He, Ye Tian Shi and Wu Ju Tong).
The warm disease school placed the emphasis on febrile diseases due to injury by heat which penetrates the body via the nose and mouth, and classified fevers according to four levels of depth: the defensive level (wei fen), the qi level (qi fen), the nutritive level (ying fen) and the blood level (xue fen).
The defensive and qi levels correspond broadly to the taiyang and
yangming stages respectively of the Shang Han Lun.
When pathogenic heat penetrates further to the deeper levels of the body, it first enters the nutritive level, scorching the body fluids and the yin and disturbing the Pericardium and spirit, and then enters the blood level, giving rise to reckless bleeding.
Ling Shu (Spiritual Pivot) “Taiyang is the opening, yangming is the closing and shaoyang is the pivot”.