イブン・シーナーの自然精気

抄録

It is often stated that physicians in medieval Islam followed Galen in assuming that there were three kinds of pneumata (psychic, vital and natural) in human beings. This article examines the concept of the third kind of pneuma, the natural pneuma (ruh tabi i), in the medical theory of Ibn Sina (d. 1037). The examination of his medical works reveals that while Ibn SinS had some clear ideas about the workings of the vital and psychic pneumata, he proposed no definite theory of the natural pneuma. He refers only very rarely to the natural pneuma in his Canon of Medicine, Poem of Medicine and On Cardiac Medicaments, and in those few instances the natural pneuma is explained simply as being parallel to the other two pneumata in that it has its seat in a specific organ, is distributed through a specific passage, and gives rise to a specific faculty, namely that it is located in the liver, travels through veins, and gives rise to the natural faculty, just as the vital pneuma, with its source in the heart, travels through the arteries to give rise to the vital faculty, and the psychic pneuma, with its source in the brain, travels through the nerves to give rise to the psychic faculty. In sum, in the medical thought of Ibn Sina, the natural pneuma exists merely as a parallel to the other two pneumata, so as to ensure the existence of a triadic system in the human body.