The smell is perceptive through a medium, such as air or water, for aquatic animals seem to be sensible of odour; and so, likewise, are sanguineous and insanguineous creatures, as well as those which wing the air. Thus, some of these are to be seen proceeding from a distance towards food, of which they have been made sensible by the odour emanating from it. And hence the difficulty of determining why, if other creatures are sensible of odours in a like manner, man alone can smell neither when expiring nor when holding his breath but, only when inspiring; and this whether the odorous object be at a distance from or close to him, or placed immediately within the nostrils. It is common, it is true, to all the sentient organs to be insensible to impressions when objects are placed immediately upon them; but it is peculiar to man (as may be proved experimentally), to be unable to perceive odours without inspiring. So that as insanguineous creatures do not breathe, they ought to have some other sense besides those spoken of, but yet this cannot be, since they do perceive odour; for the perception of odour, whether agreeable or disagreeable, is smell; and as these appear to be destroyed by the same powerful odours as those which destroy man (odours, for instance, from pitch, sulphur, and other like substances), we must conclude that they have smell, although they do not breathe.
