XI. (28) “But a fountain went up upon the earth, and watered all the face of the earth.” He here calls the mind the fountain of the earth, and the sensations he calls the face of the earth, because there is the most suitable place in the whole body for them, with reference to their appropriate energies, a place that nature which foreknows everything, has assigned to them. And the mind waters the sensations like a fountain, sending appropriate streams over each. See now how all the powers of a living animal depend upon one another like a chain. For as the mind, and sensations, and the object perceptible by the external sense are three different things, the middle term is sensation; and the mind, and the object perceptible by the external sense, are the two extremes. (29) But the mind is unable to work; that is to say, to energize according to sensation, unless God rains upon and irrigates the object perceptible by the external senses, nor is there any advantage from the object perceptible to the external sense when watered, unless the mind, like a fountain, extending itself as far as the sensation, puts it in motion when it is quiet, and leads it on to a comprehension of the subject. So that the mind, and the object perceptible by the external senses, are always endeavouring to reciprocate with one another, the one the being subject to the sensations as a kind of material would be, and the mind stirring up the sensations toward the external object, as a workman would do, in order to create an appetite. (30) For a living animal is superior to that which is not a living animal in two points, imagination and appetite. Accordingly, imagination consists in the approach of the external object striking the mind by means of the sensations. And appetite is the brother of imagination, according to the intensive power of the mind, which the mind keeps on the stretch, by means of the sensation, and so touches the subject matter, and comes over to it, being eager to arrive at and comprehend it.