The book of SHANG HAN LUN is the original text of internal medicine of Chinese medicine.
The author, Zhang Zhong Jing lived AD150-200, he was the genius, created the concepts of diagnosis and usages of herbs to treat patients.
He divides the levels of diseases in the six levels. For example, disease of Taiyang, Yangming, Shaoyang, Taiyin, Shaoyin, Jueyin. Every levels of diseases have its own unique characteristics of symptoms. For example, abdomen is stuffed, vomit, food doesn't descend, diarreia, sometimes have pains in the abdomen are unique characteristics of disease of level, Taiyin. And usually the kinds of Si Ni Tang that warms the spleen-pancreas system of body. Si Ni Tang is a formula that includes 3 types of herbs like Gancao, Ganjiang and Fuzi.
In the year of 1144, the chinese doctor, ChengWuYi explained the book of SHANG HAN LUN in his own ideas and opinions. He connected the names of six levels of diseases with the meridians because each meridians also have the same names like Taiyang, Yangming etc. And he explained the six levels of diseases in the point of view of meridians. But it was his own ideas and not the idea of ZHANG ZHONG JING, the original author of SHANG HAN LUN.