The cause and intimate nature of tastes are no better understood than those of odours. It is by volatilization that the intangible particles of the odoriferous principles reach us; it is by a solution more or less complete that substances impart their flavour, that inherent property which taste alone reveals to us. We recognize in this way their acidity or saltness, whether they are sweet or bitter, &c; but nothing in the nature of bodies, in their texture, or in their constituent elements, has ever yet explained their sapidity. Flavours elude analysis and defy classification, even that which divides them into agreeable and disagreeable, for the taste of individuals and of nations singularly differs in this respect. The Laplander and the Esquimaux drink great quantities of train-oil, which for them is a greatly esteemed article of food, and is most admirably adapted to the exigencies of a Polar climate; the Abyssinians eat raw flesh, and find its flavour excellent, while the inhabitant of the West partakes of it with the greatest repugnance, and only as a medicine. Oysters, which are so generally esteemed in our country, are to some persons disagreeable and nauseous; and truffles, the delight of the gourmand, are rejected by the uninitiated on account of their flavour and their perfume. It is the same with almost all alimentary substances; they are eagerly sought after by some, and despised or abhorred by others. Let us remember the proverb, and not dispute in regard to tastes; each is suited to its own country, and goodly numbers acclimatize themselves, to the great advantage of peoples, among whom at first they seem exceedingly strange. Man should control his taste, and habituate it to all wholesome aliment; this neither excludes choice, nor blunts the delicacy of the sense; and while we resist its seductions, we should give timely heed to its instincts and its counsels, for they are often invaluable.
Among the substances which we taste, there are few which address themselves solely to that sense, and not at the same time to the sense of smell. This mingling together in the same substance of flavours and odours, and the simultaneous action of the senses which perceive them, has induced some authors to consider them as forming but one. They are, notwithstanding, quite distinct in their seat and in their function; the mixed sensation resulting from the union of their impressions differs entirely from that which they cause singly; we may say that the sense of smell is the necessary complement of taste, for the latter is reduced to very trifling importance when it acts alone.
However much flavours may vary, they are all referable to a very few types, to the mixtures and shades of which we are quite indifferent when they do not offend us. The taste solely judges whether a substance is salt or sweet, acid or astringent, and so forth; but when our food does not awaken any other sensations, we are tempted, in spite of its flavour, to pronounce it insipid; vanilla cream and coffee cream, or ices with rum or with maraschino, do not differ in taste when the nostrils are closed. If, instead of olive-oil and wine-vinegar, bleached oil and acetic acid diluted with water be used to season a salad, we shall have the sensation of taste without that of smell. We must not then confound with natural taste that which smell adds to it, and it is to supply the lack in this respect of what is wanting in our food and in our blunted senses that we make use of condiments.
We must also distinguish the bodies the action of which is confined to the sense of touch exercised by the tongue, and many impressions reputed to be those of taste ought rather to be considered as purely tactile, such as astringency, tartness, the irritating or caustic action of certain substances, etc.
On this principle M. Chevreul has divided substances into four classes according to the impression which they produce in the mouth: 1st, bodies acting on the sense of touch in the tongue, such as rock-crystal, ice, and so forth; 2d, bodies acting on the sense of touch and of smell, such as aromatic metals, tin and copper for example; 3d, bodies acting upon feeling and taste, as sugar-candy, common salt, &c; 4th, bodies acting on the touch, taste, and smell, as mint-lozenges, chocolate, or volatile oils.
All alimentary substances figure necessarily in the latter class.
Authors do not agree upon the seat of taste; several believe it extends over nearly the whole surface of the tongue, to the pillars of the fauces, and to the upper surface of the soft palate, to the tonsils, and to the pharynx. It is now generally believed to be located at the tip, at the base, and on the edges of the tongue, and at a certain limited space on the anterior surface of the soft palate. According to M. Longet, the back of the tongue and the pillars of the fauces are not entirely destitute of gustatory sensibility.
Savoury substances do not produce the same impression upon all parts of the tongue, many salts on the tip of the tongue have an acid, salt, sharp, or styptic, at the base a bitter or metallic taste; others, on the contrary, have the same flavour on every part. In general, acidity is best perceived at the tip, and on the edges of the tongue, saline or metallic flavours are developed at the posterior portion.
In order to perceive the flavour, the savoury molecules must be bathed in saliva, and partially dissolved, so as to be placed in more immediate contact with the surface of the tongue. To further insure this contact, the tongue applies itself to the palatine arch, and presses the food against its surface. It is then that the gustatory impression is produced in its full force, and from this it has been inferred that the palate is the principal seat of taste. The action of the palate, however, is purely mechanical, and is limited, as we have stated, to securing immediate contact between the savoury bodies and the tongue. This is demonstrated by covering the palatine arch with a thin pellicle which is itself insipid and impermeable; the taste is just as acute under these conditions, but if the tongue is covered with this same pellicle, and the palate uncovered, no taste is perceived. The cheeks and lips also contribute to taste by carrying the particles of food which may have fallen outside the dental arch during mastication back to the tongue. Taste acts not less delicately in deglutition, when the contents of the mouth descend between the base of the tongue and the soft palate on its way through the throat Food and drink must remain for a certain time in the mouth in order that their full flavour may be perceived; thus the gourmand takes care to retain them, and exhaust, as it were, their aromas, before sending them to the stomach. For this reason, also, wine-tasters hold the wine in their mouth when they wish to judge of its quality, but they avoid swallowing this mouthful of wine after it is thus robbed of its bouquet; they reject it after thoroughly moistening the surface of the tongue, and they can then decide as to the vineyard and the year of the vintage. If they drank the wine which they taste, the smell, which here plays the principal part, would very soon become dulled.