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112 The olfactory organ in man appears to differ from that in other animals as his eyes differ from those of creatures in which they are hard; for man's eyes are furnished with a rampart, and a kind of sheath in lids, without the elevation and drawing asunder of which he cannot see, while hard eyes, having no such provision, are instantly sensible of whatever may be present in the diaphanous medium. In accordance with this, the olfactory organ is, in such creatures, like the eye, uncovered; but, in such as breathe, it is furnished with a cover, which during inspiration is lifted up, as the veins and pores are then dilated. On which account, creatures which breathe cannot smell while in the water, as in order to smell they must inspire, and while in the water they cannot possibly inspire.

In fine, odour is derived from what is dry, as savour is from what is moist; and the olfactory organ, when in potentiality, is analogous to that from which odour is derived.