First Physical Dissertation on the Bond Connecting Soul and Body

Thus, in Minerals no less, the aether performs the role of a soul, while those various juices from which ores arise are digested, changed, and combined in various ways within the bosom of the earth by subterranean heat, partly and partly by solar heat, and thus metals are generated and augmented.

But it is not to be thought that a Vegetative spirit belongs only to plants and minerals. Indeed, animals also, brutes no less than humans, claim it for themselves: since we see these too nourished, grown, and multiplied. And indeed, animals are equipped with far more passages and tubules, and those more perfect, which the aether permeates, to which this duty is given, to temper the heat ignited from the Saline-Sulphureous particles of food and inherent in all humors, and to blow them like bellows. To this I refer the saying of VARRO, when he defines this vegetative soul thus: that it is air received by the mouth, heated in the lungs, warmed in the heart, diffused into the body; in LACTANTIUS, On the Workmanship of God, Chapter XVII, page 719 (Lyon Edition, 1587).

And this vegetative soul of man is the source and origin of the word "soul," when it is drawn out to signify the immaterial spirit of man. The foundation of this application lies in the analogy conceived between those substances with respect to our eyes. For just as the rational soul is truly and properly superior to all external senses, so the Vegetative is improperly, at least, called invisible due to the weak condition of our lights and the nearly incredible subtlety of the aether.