男女大不同。古典醫學如《黃帝內經》便以生理週期的不同體液做為男女性別的最主要差異。女性成長是以月經做為指標，相對來說，男性以精液做為獨特的生理特質。中國早期醫學文獻也清楚地討論男、女的性器官，涉及女性子宮的功能；同時也注意到宦官、陰器受傷之人、男性生殖器發育不全者等的身體構造的相應解說。凡此，無不顯示古典醫學極其鮮明的性別意識。這篇論文旨在探討以督脈所形成的男性身體觀。督脈位於人體的中軸線，是所謂「奇經八脈」的主脈。督脈的起點分別經過男、女的陰器，沿著脊骨，與人體最重要的兩個臟器──腎與腦──連結。腦由髓液所組成。人飲食所產生的精微汁液，滲進骨骼，使關節屈伸自如，同時滋補腦髓。腦是人身髓液匯聚之地。值得注意的是，腦髓、脊髓與腎精之間形成流動的關係。根據醫經的記載，男性流湎房事不僅導致精液外流，而且腦部髓液隨之遞減。腦髓與腎精之間的流體可以相互轉換，而以循行脊柱的督脈是其流通的管道。督脈是人體中心的象徵，也是歷代養生實踐的核心經脈。男性的精液下漏，使腦髓虛空；而房中養生之術則倒行逆施，設法固守精液，並且使腎精上聚於腦以補填髓液。中國早期醫學文獻有「腎藏精」的論述，這裡的精包含男性生殖精液之意。到了《難經》成立也就是東漢中期，腎與呼吸的功能建立起明確的關係。將腎視為呼吸的門戶，與房中養生觀念的變化有關。所謂「還精補腦」的房中術，即出現在東漢末年道教經典《老子想爾注》之中。其技法大致是主張男女交合不瀉精、甚至採補女性在行房中所產生的精氣，最終目的是補益人體可能流失的腦髓。男女都有相同的經脈、臟腑等身體構造，但個別的經脈及其相關的器官卻有性別的意涵。與督脈相關的腦、髓、骨等人體構造，是古典醫學中邊緣化的一組概念「奇恒之府」。透過「奇經」這一系統經脈的研究，我們深覺目前醫學史成果對古典醫學體液了解的缺乏。「津液論」的探討應該是緊接「氣論」的研究，成為下一個研究階段的重心所在。同時，我們在爬梳古典醫學的身體觀之外，應發掘養生論述的身體想像及身心經驗。最後，我們特別注目「房中」這一系統醫學的生命觀念之研究，不僅有助奇經八脈全面性的理解，也將促使性別史、身體史的探討邁進一個新的里程碑。

Classical medical texts, such as the Inner Classic of the Yellow Emperor, stress that the most significant difference between men and women is evident in the excretion of fluids linked to biological cycles. A woman’s growth is marked by changes in menstruation, while the most significant physical characteristic of the male is his semen. Early Chinese medical literature discusses the male and female sexual organs with great clarity, describing the normal womb and penis, and contrasting them with injured or incomplete sexual organs, such as those of eunuchs. Throughout, classical medical texts are preoccupied with the physical differences between the sexes.In this paper, I examine the role of the idea of dumai (the “central vessel”) in the formation of the conception of the male body. The dumai is located on the central axis of the body; it is, literally, the “central vessel” of the “extraordinary eight vessels” 奇經八脈. The dumai originates in the male or female sexual organ, runs along the spine and connects to the kidneys and the brain, the two most important organs of the human body. The brain is made up of marrow-like fluid. When a person eats and drinks, he or she produces refined fluids that enter the bones, lubricating the joints while nourishing the brain’s marrow. These marrow-like fluids thus collect in the brain. Of particular note is that the marrow of the brain and spine interact with the essence (jing) of the kidneys. According to medical texts, excessive sexual activity not only saps the male body of semen, but also depletes the fluids of the brain. Fluids in the brain and kidneys may supplement one another, but only via the dumai that runs along the spine.The dumai is a symbol for the center of the body and was for centuries thought to be the main vessel for techniques used to nourish the body. When the male loses semen, thus depleting his brain fluids, it was thought sexual techniques could be used to reverse the process, solidify the semen, and channel renal fluids to supplement the brain. Early Chinese medical literature contains one discourse over the “essence of the kidneys.” Here, the use of the term “essence” also includes semen. By the composition of the Nanjing in the middle of the Eastern Han, a close relationship had been established between the kidneys and the respiratory function. The kidneys were seen as the “gateway to breathing,” a notion tied to changing conceptions of sexual techniques that were used to nourish the body. The sexual practice of “returning the semen to nourish the brain” appears in the Daoist Xiang’er Commentary to the Laozi, written during the final years of the Eastern Han. The main tenet of the practice was that men were not to release semen during sexual intercourse. In fact, the man was to absorb the “essence and breath” (jingqi) created by the woman during intercourse in order to supplement the fluids of the brain that he may have depleted. Men and women were thought to have the same courses and vessels, and their organs shared same basic structure, but among the functions of the vessels and related organs were discernable differences between the sexes.The system composed of the brain, marrow and bones, all of which are related to the dumai, was subsumed into the concept of the “abnormal fu organ” 奇恒之府, a relatively marginal concept in classical medical writings. Investigation into the system of “abnormal vessels” has revealed how little we understand the place of fluids in classical medical literature. Research into fluids, following closely on research into qi, ought to become a more central concern to historians of Chinese medicine. Furthermore, in addition to exploring the conception of the body in classical medical texts, we also ought to explore the conception of the body and sensory experience as expressed in discourse on “nourishing the body.” Finally, we should pay especial attention to conceptions of health in the medical literature related to sexual yoga. This material is not only helpful in understanding the eight extraordinary vessels more fully, it also provides us with an opportunity to advance dramatically the fields of the history of gender and the body in China.