Shen Nong Ben Cao Jing or Shen Nong's Herbal, the earlist material medica extant in China, is believed to be the product of the Eastern Han Dynasty (25-220).  Most medicinal substances listed in the book have been in use ever since; the efficacy of which are tested and proven in clinical practice and modern research.  It has had significant influence on the development of material medica and it still serves as an important reference book for the study of Chinese medicine. 365 kinds of medicinal substances are listed in the book for about 170 diseasess covering subjects from internal medicine, external medicine, gynecology to pediatrics.  Based on its action and toxicity, the medicinal substances are divided into three classes: superior, common and inferior.  120 superior medicinal substances are intoxic and tonic, indicated for long-term administration to treat diseases, tonify body and prolong life.  120 common medicinals are intoxic or low toxic.  Most of them have the dual action of tonifying the body and dispelling pathogens, but cannot be administrated on a long-term basis.  125 inferior medicinal substances are mainly indicated for expelling pathogens, and many of them are toxic or fierce in effect.  They tend to damage healthy qi, so overdosage and prolonged administration are forbidden. In addition, Shen Nong Ben Cao Jing (Shen Nong's Herbal) also elaborates on the property and formulating principles.  Four qi (cold, hot, warm and cool) and five flavors (sour, bitter, sweet, acrid and salty) are the mature of medicinal substances.  Medicinals of different properties are chosen based on different types (cold, heat, dampness and dryness) of disease nature: medicinals hot in property for diseases of cold nature; medicinals cold in property for diseases of heat nature; medicinals warm and dry for diseases of damp nature; medicinals cool and moistening for diseases of dryness nature.   They are usually put in a compound formula to treat various diseases.     Shen Nong Ben Cao Jing (Shen Nong's Herbal)