Li Shi-zhen was a  famous  pharmacologist during the Ming Dynasty. 
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While practising medicine and collecting the specimens of medicinal herbs,
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Li soon came to feel the need for a better understanding of  the  principles
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in treating disease. So he  devoted  himself  to the task of compiling a new
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edition of  the pharmacopoeia  known under  the generic name of Ben-cao
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Gang-mu (Compendium of Materia Medica). In order to complete this masterpiece,  Li proceeded on his own,  consulting many books, 
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reviewing a vast quantity of literature and, wherever he happened to be, collecting necessary pharmacognostic specimens. The result 
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was the Ben-cao Gang-mu,  a voluminous work which took him thirty years to accomplish.  The book contains  1,892 descriptions and 
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11,000 prescriptions. It is generally considered as an encyclopaedia of pharmacology in ancient China.