The bitter taste is confined to the oily and resinous juices of vegetables, and to the inflammable oxides. It is communicated to all vegetable substances by what is styled by the French chemists their combustion, in consequence of their union with nitric acid. Many of the vitriolated neutrals are also bitter; but in detailing their properties we must confine ourselves to the bitter vegetables; for there is no reason to suppose that our artificial bitters agree with the natural. We find the pure bitter chiefly in the roots of the gentian, the male fern, and the white dittany; in the bark of the simarouba, the orange and the lemon peel; in the leaves and flowers of the carduus benedictus and the camomile; in the wood of the quassia; in the tops of the centaury and hop; in the seeds of the carduus benedictus and mariae; in the juice of the wild cucumber; in the aloes, the myrrh, and the bile of animals. It is seldom pure, and even in some we have mentioned it is joined with a little acrimony; in others with astringency, or acidity. The affinity of the acid with the bitter principle is very striking, since many plants which in some parts are bitter, in others are acid. We need not add any thing to what we have already said in the article Amara, q. v. except to observe, that some of these mentioned are actively purgative, a quality which certainly does not belong to the pure bitter.

The viscid taste is exemplified in the mallows, lint-seed, and almost all the pure gums, the cartilages and tendons of animals, particularly young animals. All these substances are demulcent and relaxant; consequently by sheathing abraded membranes, particularly of the urinary system and bowels, they relieve pain, and often appear to check immoderate discharges. They sometimes appear, when taken in excess, to destroy the appetite; and we have suspected them, when swallowed in large quantities, of lessening the urinary-discharge.

The salt taste is most pure in the muriated soda and the common culinary salt, for all others appear to join different flavours with it. In the vegetable kingdom, we find it, though less pure, in the crithmum, the ha-limus and salicornia. In the shell fish and the fuci, the taste appears to be derived exclusively from the sea water. See Marinus sal.

The watery taste chiefly arises from the excess of the aqueous fluid, diluting every peculiar flavour. The most striking instances are the oleracae, and some of the etiolated plants; and among the roots, the turnip. These substances are slightly nutritious, diluent, and demulcent. They were supposed to be of considerable and extensive use when diseases were attributed to lentor or viscidity of the fluids.

The sensation of dryness in the mouth arises very generally from stypticity; but by a dry taste is generally meant that which is produced for instance, by chalk. All the earths in a carbonated state are dry. The insipid woods and barks, the leaves of the ivy, and the dust of of the polypodium, are examples, in the vegetable kingdom. In the animal, the hart's horn, the crab's claws, the mother of pearl, and coral, are distinguished by a dry taste. These substances, however, unless capable of absorbing acids, are of little utility in medicine, but are by no means so injurious as have been supposed.

In general, we may remark that tastes have a much more pointed and clear connection with the medicinal properties of bodies than smells, and will, in many instances, explain, a priori, their virtues. Yet tastes are so infinitely varied by nature, that their composition cannot often be ascertained; and though the expressive language of Bergius conveys ideas peculiarly discriminated and exact, even this, in many instances, fails.

A very important distinction of tastes relates to their fugacity or permanence, their immediate impression, or their perception after some interval, their affecting the tip, the middle or back part of the tongue, or the throat. On these subjects our chief assistance is from Grew and Bergius; but we have not been able to connect these different sensations with the properties of the bodies. In general, the stimulants are immediately perceived to increase the heat chiefly on the fore part of the tongue; the narcotics only act after some time, and on the throat. The impressions of salt substances are generally diffused; of styptics confined to the checks and anterior fauces.

When the operations of chemistry attracted the attention of physicians, it was at once supposed that they would unravel every secret of nature, and among the rest, the constituent parts of medicines, so as to explain their operation. The members of the French academy laboured very earnestly in this department of the materia medica: Mr. Boyle and some others of the English and German chemists were equally assiduous; but they soon found, that aliments and medicines, the most salutary foods and the rankest poisons, were equally re-ijolvable into acids, oils, and salts, scarcely differing in their properties. In fact, in resolving the compounds of nature, they formed new ones of art, and were not nearer the destined goal. Neumann and Cartheuser did not wholly forsake the former path, but they interrogated nature by milder methods, and extracting different component parts by the peculiar affinities of water and alcohol, or by their volatility in a gentle heat, taught us what portions of gum, resin, and oil each vegetable contained. But even at a much later period, so rash was the analysis, and so powerful the means employed, that we have only of late discovered what is now styled the extractive matter, or that portion of the gum and resin combined with the peculiar oil and mucilage of the plant, which renders it equivalent to the vegetable itself, deprived only of its air, some portion probably of its water, and the woody fibres. When, therefore, in the vegetable analysis, the proportion of gum and resin with that of the extractive matter is mentioned, the quantity of the two former, or rather of the resin, shows the degree of decomposition which in general has taken place; we say in general, for in many plants, particularly in the roots, the resin exists in a separate state. Rhubarb is a striking instance of this kind.