Aristotle's biology two we may regard pretty much as one and the same); thirdly, the material; and fourthly, the moving principle or efficient cause." ^® " Now that with which the ancient writers, who first philosophized about nature, busied themselves, was the material principle and the material cause. They inquired what this is, and what its character; how the universe is generated out of it, and by what motor in- fluence, whether, for instance, by antagonism or friendship, whether by intelligence or spon- taneous action,'^ — the substratum of matter being assumed to have certain inseparable properties; fire, for instance, to have a hot nature, earth, a cold one; the former to be light, the latter heavy. For even the genesis of the universe is thus explained by them. After a like fashion they deal with the develop- ment of plants and of animals. They say, for instance, that the water contained in the body causes by its currents the formation of the stomach and the other receptacles of food or of excretion; and that the breath by its passage breaks open the outlets of the nostrils; air and water being the materials of which bodies are made; for all represent nature as composed of such or similar substances.
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