volatile. But, as Zwaardemaker has pointed out, this is by no means always the case. Many substances of low volatility are nevertheless highly odorous, and vice versâ.
We turn now for a moment to consider the behaviour of the odorous vapour in the nose.
As it passes through the nose the current of inspired air sweeps along the lower and middle regions only ; the upper or olfactory region is not directly traversed. But almost certainly some of the air is diverted up into the olfactory region in light eddies, and the act of sniffing, which is a short inspiration abruptly begun and ended, and which we instinctively resort to when trying to detect a faint odour, is obviously of a nature to propel side-streams or eddies up into the olfactory zone. One is reminded of the production of smoke rings from a box.
We smell not only during inspiration, however, but also during expiration, the latter conveying to the olfactory region the flavours of food and drink.
Flavours, that is to say the olfactory elements of so-called “taste,” are not appreciated to the full until after deglutition. To most of us, although experts and connoisseurs can determine it by smelling the wine in the glass, the bouquet of port has really no meaning until after it is drunk, simply because the expiratory current of air as it
