The senses of smell and taste require a passing notice. We conjoin these senses together, because the latter depends much for its discrimination on the functional perfection of the former; in fact, much of that which in the enjoyment of food is commonly attributed to the sense of taste, depends on the odour carried from the mouth to the nose. If, for example, we masticate any spice, or aromatic substance, as cinnamon, while at the same time the nostrils are strongly compressed, and breathing through those channels obstructed, we perceive no definite flavour from the spice, although the essential oil expressed may sting the tongue and palate. Stoppage of the nasal passages, from catarrh, influenza, or other affections, and preternatural dryness or thickening of the schneiderian membrane, impair or destroy both the sense of smell and taste. We may here observe, that irritation of the schneiderian membrane by ammonia, by snuff, and other things of the like nature, has nothing to do with the sense of smell residing in the nerves of that membrane: smell is the appreciation of odours; any delicate membrane may be irritated, as, for example, the conjunctiva of the eye. With irritants, scents may be combined; in such admixtures for the stimulation of the olfactory nerves many persons eagerly indulge, and under certain circumstances they are medicinally useful; but it is the perception of scent or odour, irrespective of irritation, which is the proper function of the olfactory nerves. With respect to taste, this sense resides in a branch of the fifth cerebral nerve, called, from its function, gustatory. For the sensation of taste, moisture must be present; an utterly insoluble body, as crystal, is tasteless; we reduce to a pulp, by means of the teeth and the saliva, the food which we eat, excepting, indeed, such articles as come under the denomination of drink, or, in other words, viands in a fluid state, such as wine, ale, coffee, etc. Perfectly pure water is tasteless. The contact of two metals in the mouth, producing a galvanic discharge, excites a sensation or flavour which cannot be well described; but the moisture of the saliva is requisite for the effect. It is said, that the superior flavour of porter drunk out of a pewter vessel results from a slight galvanic action going on. Mr. Mayo says, "various substances, after exciting the sense of touch on the fauces, and that of taste on the tongue, are capable of producing a third impression, which is popularly referred to the palate, but which is really felt upon the sentient membrane of the nostrils." In the case of metals taken into the mouth, this mode of the reception of flavour would appear to take place.