GREEK BIOLOGY AND MEDICINE He drew, nay he drained, his teleology from Aristotle, and, like the Master, applied it to every part of the organic structure: Nature makes nothing without a purpose, and nothing in vain. When Galen is considering the nature and action of an organ, or of the body gen- erally, his mind passes quickly from the sheer description of the thing, and even from the consideration of its efficient cause, and springs forward to grasp its final cause or purpose: therein lies the explanation of the thing, and the explanation, nay the true description, of the function which it is its nature to fulfill. Galen's passionate preoccupation with the purpose of a living organ, colors and even fashions his description both of the organ itself and of the process through which it performs its function. The function of the body generally is to afford a setting for the soul or life. The bearer of life, or of the vital forces vivifying the body and directing it to the performance of its functions, is the pneuma. Entering with the breath, it becomes threefold: the psychic pneuma (or, in English, the animal spirits), working in the brain and through the nervous system; the Wie-pneuma (or vital spirits) of
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