Woodblock illustration from an edition of 1738 (3rd year of the Qianlong reign period of the Qing dynasty). It shows the transmission process of Yang diseases from the exterior to the interior of the body. The so-called Yang diseases are those of the bodily surface (biao) and the fu viscera. The bodily surface includes the three sectors of the skin, the muscles, and the sinews and bones. The six fu viscera are the gall bladder, the stomach, the large intestine, the small intestine, the bladder and the sanjiao (Triple Burner). The first stratum of the bodily surface is the skin, the 'surface of the surface' (biao zhong zhi biao), which lies outside the bodily integument (quke). It governs nutrient and defensive factors and is internally related to the bladder and small intestine. It is known as the first Yang sector (yi yang bu). The second stratum consists of the muscles, which form the bodily integument. It is internally related to the stomach and large intestine. It belongs to the second stage of transmission of external Yang diseases, and is known as the second Yang sector (er yang bu). The third stratum consists of the sinews and bones, which lie within the bodily integument. It is internally related to the gall bladder and sanjiao. It belongs to the final stage of transmission of external Yang diseases, and is known as the third Yang sector (san yang bu). When the body is affected by malign Qi (xieqi), this is transmitted in sequence from the skin to the musculature to the sinews and bones; or alternatively diseases affecting the skin are internalised to the bladder and small intestine, diseases affecting the muscles are internalised to the stomach and large intestine, and diseases affecting the sinews and bones are internalised to the gall bladder, and sanjiao. This is what is meant by the sequence of transmission of Yang diseases of the surface from exterior to interior.
