[190] [cap.46] Some one will say, We at once comprehend colours. How so? Do we not do so by means of the external things, air and light, and also by the moisture which exists in our eyes themselves? And in what way are sweet and bitter comprehended? Is it apart from the moisture in our mouths? And as to all the flavours which are in accordance with, or at variance with nature, are not they in the same case? What, again, are we to say of the smells arising from perfumes which are burnt? Do they exhibit plain unmixed simple natures, or rather qualities compounded of themselves and of the air, and sometimes also of the fire which consumes their bodies, and also of the faculty existing in our own nostrils?