A more concrete summary of the causes of dis-eases was displated in Chen Yan's Prescriptions Assigned to Three Categories of Pathogenic Factors of Diseases. It focused on internal factors of disease: The imparirment caused by the seven emotions, as well as external factors: the impairment induced by the six climatic evils in excess, or of untimely occupance. It also focused on the non-endo-ex-0genous : impairment due to improper diet, epidemics, bites by insects and beasts, poison-ing, trauma, etc.. This type of classification corresponds more with clinical reality and be-came a new development of TCM etiology.

Each generation of doctors continue to study the past medical experiences found
within books such as the above. And each generation builds upon past information creat-ing richer and more developed theoretical ideas while gradually forming various types of schools of TCM. For example, influenced by the theory of the five elements and six kinds of climatic factors, the eminent physician Liu Hejian, during the Jin and Yuan Dynasties, emphasized the theory that the diseases caused by the six kinds of climatic factors could become the heat-fire evil in the body. He also pelieved that the heat and fire of the six kinds of climatic factors were the most important pathogenic factors thus explaining the pathological mechanism of the heat-fire evil.

Zhang Congzheng advocated that the diseases were cauded by exogenous evils which should be expelled using the methods of diaphoresis, emesis, and purgation. Li Dongyuan held that diseases were mainly brought about through the internal injury of the spleen and stomach, thus explaining the theory of the ascending and descending of the spleen and stomach, and creating the theory of relieving high fever with drugs consisting of sweet fla-vor and warm nature. Zhu Zhenheng advocated the theory that yang is ever in excess while yin is ever deficient. This further developed the theory of of ministerial fire and en-riched the theoretical system of TCM. In addition, there were Zhang Yuansu's theory of pathological mechanism of viscera, and Zhang Jing yue's explanation of Yin-Yang, the kidney and vital gate etc.. All of the above theories enriched and developed the theoretical system of TCM.

The theory of febrile diseases deals with the pathology, diagnosis and therapy of febrile diseases. In the period of the Ming and Qing Dynasties, the school of febrile dis-eases was developed. This symbolized the understanding and study of febrile diseases reached a new level. Wu Youke, a physician in the Ming Dynasty wrote the Treatise on Pestilence and offered the theory of pestilence-evil ,which was the first systematic explo-ration of the etiology and therapeutics of febrile diseases. This laid the foundation for the development of the theory of febrile diseases. During the Qing Dynasty, many books re-garding febrile diseases were compiled, some of which are the Treatise on Tropic Febrile Diseases written by Ye Tianshi , The Treatise on Differentiation and Treatment of Febrile Diseases written by Wu Jutong, The Treatise on Damp-Heat Diseases authored by Xue Shengbai ,and A Compendium on Febrile Diseases completed by Wang Mengying.

Within the above books, the authors systematically summarized the pathogenetic law of exogenous febrile diseases during the Ming and Qing Dynasties, making a breakthrough in traditional understanding that "all febrile diseases belong to cold-attack" ,thereby creat-ing the principles of differential diagnosis and treatment of febrile diseases on the basis of the theories of wei-qi-ying-xue as well as triple-jiao. This completed the theoretical sys-tem in such aspects as pathogenesis, pathology, pulse diagnosis and treatment etc.. Great contribution to the enrichment and development of the theoretical system of TCM was made. It is necessary to point out that the theories of both the cold-attack and febrile dis- eases are two major schools which supplement each other and play an important guiding role in the clinical practice and studies of TCM.

Great progress has been made in the development of TCM within the last 40 years. There has been an enhancement in the systematization , and research of the basic theories of TCM. The application of modern science and technology towards the understanding of the essence of Chinese medical theories have displayed remarkable achievements in such areas as the nature of yin deficiency and yang deficiency, the essence of cold and heat, the essence of kiney and spleen, meridians, etc.. Great interest has been aroused in medical circles both at home and abroad. The continuing development of the basic theories of TCM will facilitate the development of entire TCM and continue to modernize its theoret-ical system.