extractive principles of plants. I quote a few examples from the list given in GREGORY'S Organic Chemistry, p. 457.

Gentianine, from Gentiana lutea, forms yellow needles, very bitter. Absinthine, from Artemisia absintheum, or wormwood, is a semi-crystalline mass, very bitter, soluble in alcohol. Tanacetine, from tanacetum vulgare, is very similar to it. Syringine is the bitter principle of the lilac, syringa vulgaris. Colocinthine, the active principle of colocynth, is amorphous, intensely bitter and purgative.

Quassine is a yellow, crystalline, and very bitter substance, from the wood of quassia amara. Lupuline is the bitter principle of hops. Liminine, or Limine, is a bitter crystalline matter, found in the seeds of oranges, lemons, &c.

With regard to vegetable and animal substances in general, I quote the following paragraph from Gmelin. 'Some organic compounds, as gum, starch, woody fibre, white of egg, &c. have no Taste; others have a sour taste (most acids); or a rough taste (tannin); or sweet (sugar, glycerin, glycocol); or bitter (bitter principles, narcotic substances, and many acrid substances, also many resins); or acrid (acrid oils and camphors, acrid resins, acrid alkaloids); or fiery (alcoholic liquids, volatile oils, camphors).'

Not only are the different classes of vegetable and animal products distinguished by their taste, as apples from apricots, wine from cider, flesh from fat, but in every such class there are many distinguishable varieties. The class of wines based on the common ingredient, alcohol, spreads out into innumerable kinds from the presence of sapid substances in quantity so small as to elude the search of the chemist. It is shown by this and many other facts, that an extremely minute portion of a sapid substance may make itself acutely felt to the taste. The bitter principle of soot, for example, can be distinguished in cookery to a very high degree of dilution.

2. The organ of Taste is the tongue, and the seat of sensibility is the mucous membrane covering its surface.

*GMELIN'S Chemistry, vol. vii. p. 66.

The upper surface of the tongue is covered all over with numerous projections, or eminences, named papilla. They are found also upon the tip and free borders, where however they gradually become smaller, and disappear towards its under surface.' These papillæ are distinguished into three orders, varying both in size and form.

'The large papillæ, eight to fifteen in number, are found on the back part of the tongue, arranged in two rows, which run obliquely backwards and inwards, and meet towards the foramen cæcum, like the arms of the letter V.' The middlesized papillæ, more numerous than the last, are little rounded eminences scattered over the middle and fore part of the dorsum of the tongue; but they are found in greater numbers and closer together, near and upon the apex.' 'The smallest papillæ are the most numerous of all. They are minute, conical, tapering, or cylindrical processes, which are densely packed over the greater part of the dorsum of the tongue, towards the base of which they gradually disappear. They are arranged in lines, which correspond at first with the oblique direction of the two ridges of the large papillæ, but gradually become transverse towards the tip of the tongue.'

'These different kinds of papillæ are highly vascular and sensitive prolongations of the mucous membrane of the tongue. When injected, they seem to consist almost entirely of capillary vessels; the large papillæ, containing many vascular loops, whilst the smallest papillæ are penetrated by only a single loop. Nerves proceed in abundance to those parts of the tongue which are covered with papillæ, into which the nerve-tubes penetrate.' The papillæ are undoubtedly the parts chiefly concerned in the special sense of taste; but they also possess, in a very acute degree, common tactile sensibility.'-QUAIN, p. 999-1001.

3. With regard to the precise localities of the tongue where the sensibility resides, there has been some difference of opinion. We conclude generally,' say Messrs. Todd and Bowman, 'with regard to the tongue, that the whole dorsal, or upper, surface possesses taste, but especially the circumferential parts-viz., the base, sides, and apex. These latter

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regions are most favourably situated for testing the sapid qualities of the food; while they are much less exposed than the central part to the pressure and friction occasioned by the muscles of the tongue during mastication. The central region, as a whole, is more strongly protected by its dense epithelium, and is rougher, to aid in the comminution and dispersion of the food.' But in addition to the tongue, 'the soft palate and its arches, with the surface of the tonsils, appear to be endowed with taste in various degrees in different individuals.'—I., 443.

The increasing sensibility of the tongue, from tip to back, serves as an inducement to move the food gradually onward in the direction of the pharynx, in order to be finely swallowed. The same sensibility, acting according to the general law of feeling-guided action, or volition, keeps up the mastication, whereby the sapid action of the food is increased by solution and comminution of parts. Thus it is that mastication is purely a voluntary act, while deglutition or swallowing is purely reflex and involuntary.

Among the conditions of taste, in addition to solubility, it is noticed that 'taste, like touch, is much influenced by the extent of surface acted on; and is also heightened by the motion and moderate pressure of the substance on the gustatory membrane.' In order to taste, also, the tongue must not be in a dry or a parched condition. The impression of cold air deadens the sense of taste.'

4. The precise mode of action, whereby the nerves of the tongue are stimulated, has not been as yet explained. Taste may be produced by mechanical irritation of the surface, as by a smart tap with the fingers on the tip of the tongue, and by galvanism. Looking at the substances that cause tastes, it appears probable, that their chemical constitution is the determining circumstance, whence it would seem that the action is a chemical one. A certain secretion from the blood vessels that line the papillæ of the tongue combines with the dissolved food, and the act of combination constitutes the stimulus of the nerve fibres. We know that a chemical action on any surface or tissue will suffice to stimulate a

nerve and produce sensation; and it is difficult to assign any other mode of stimulus either in taste or in smell.

5. Having thus considered the external objects of the sense, and the structure of the organ, it remains for us to proceed to the mental phenomena, that is the Sensations themselves. At the outset we are met with a complexity, which hardly belongs to any other sense. From what has been already said, the reader will gather if he has not otherwise remarked it, that the tongue is the seat of a twofold sensibility, taste and touch. I am disposed to go still further, and to ascribe to it a threefold sensibility, viz.-touch, taste properly and strictly so called, and relish, or a participation in the alimentary sensations; my reasons are such as the following. First, there is an obvious continuity of structure in the tongue and alimentary canal, a common character of surface, as regards mucous membrane, glands, and papillæ, which would imply some community of action and feeling, in the midst of diversity. We may here allude to a certain gradation that is apparent from the papillæ of touch, through those of taste, to the absorbing viili of the small intestines. Touch shades into taste, and at a lower point sensibility is lost.'-(Todd and Bowman, I. 441.) Second, the tongue, besides its power of discriminating niceties of taste that have very little reference to digestibility, has the power of telling at once whether a substance will agree or disagree with the stomach, and this it can do only by being as it were a part of the stomach, affected like it by wholesome or unwholesome contacts. Third, the peculiarity we call relish is not the same as a mere taste. For the type of taste, I may take such substances as common salt, quinine, soot, Epsom salts; for relishes, I would select butter, animal flesh; the savoury in cookery being made up much more of relishes than of tastes. The condition of the stomach governs the one but not the other. After an attack of sea-sickness, a person is still in a condition to discriminate sour, bitter, alkaline, or acrid, when the choicest food has no feeling in the mouth. Fresh, disgusting, nauseous, are terms applying to the stomachic sensibility and to that portion of the tongue in sympathy

with the stomach, and not to tastes as I understand them. With this explanation I shall now proceed to examine in detail the sensations of the tongue.

6. Deferring for the present the consideration of the tactile sensibility, shared by the tongue in common with the skin and the inner surface of the mouth, we shall have to classify and describe the several kinds of sensations coming under both taste and relish. Following out our general plan of taking the least intellectual sensations first, we should commence with the relishes and disgusts of taste, which constitute its relation with the alimentary sensations already treated of. But these feelings need not be again gone into in the detail; all that appears necessary is to quote a few instances with the view of illustrating still farther the distinctions we have drawn between the alimentary sensations of the stomach and those of the mouth, and between both and the proper sensations of taste.

7. The classification will therefore commence with relishes. These are the agreeable feelings arising from the stimulus of food on the organs of mastication and deglutition; they are of an intense and massive kind. The substances that produce them in greatest degree are reckoned savoury by pre-eminence. Animal food has the greatest power of exciting a vigorous relish, or that keen sensation so powerful as a stimulus to mastication and the taking of food, rendering the individual for the time being voracious. A healthy digestion and the state of hunger are the necessary conditions of a strong relish, whether in the stomach or in the mouth, from which fact, as already said, we can discern the difference there is between a mere taste and a relish. Butter and oils and fatty substances are relishes, used for that purpose along with the more tasteless kinds of food, such as bread. Sugar I take to be both a taste and a relish. Being one of the necessaries of animal life, as is proved by the function of the saliva in producing it from starchy substances, there is a direct craving for it throughout the system, and everything craved for in this way is likely to produce a far deeper impression than a mere sensation of taste.