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188 sense for food and food is a tangible body; but sound, colour and odour neither nourish nor contribute to growth or decay. Thus, taste must of necessity be a kind of Touch from its being the sense which is perceptive both of what is tangible and nutritive; and, as these two senses are necessary to animals, it is manifest that there can be no animal without Touch.

The other senses, being for the higher good of animals, are allotted, not to all but, only to particular genera, as they are necessary to none but such as have the power of progression. If, indeed, such a creature is to preserve its existence, it must not only be sensible of objects when touching them, but be able also to perceive them when at a distance; and this can be effected if it be sensible through a medium, which, having been impressed and set in motion by the objects of perception reacts upon the percipient. And it is thus that the locomotive impulse acts until it cease in rest—that which impels something else communicates along with impulsion impelling power, and the motion is in a midspace; and as the first motor impels without having been impelled, so the last is impelled without impelling, and the intermediate links, of which there are several, both impel and are impelled. So is it too with respect to changes wrought in bodies, excepting that they are effected without change of locality—as if any one were to tinge a portion of wax, it would be in motion until