Ntia, Astricto Ria. Astringents, (from astringo, to bind). Adstringentia; called also anastaltica; constringentia.

The solid parts of the human machine, from various causes, are often so relaxed that they are unfit to perform properly their different functions. It seems necessary, therefore, that there should be such remedies as can correct debility, and bring back our solids to their former, healthy state. Remedies of this sort among physicians are called astringents. That many substances have the power of condensing and strengthening the solid parts of animal bodies, is proved from that well known art of tanning and preparing leather by oak bark, and other similar bodies, until it acquires a remarkable hardness and firmness; chemistry has lately taught us that this change is produced by a principle called from its effects tannin, whose immediate action is to precipitate the gelatine. The application, however, of this principle to the human machine is not

Ee easy. Tannin cannot be introduced between every minute fibre of which the human body consists, nor could it precipitate the gelatine without its consequences being obvious, perhaps dangerous. We see no gelatine in the mass of blood; and the albumen, which does not greatly differ, forms that portion of the blood which is connected with the strength of the system; for in proportion to the density of the crassamentum, which is formed from the albumen, the strength is estimated. As the beneficial effects of astringents are first felt in the stomach, it is probable that the tannin acts on its fibres, with which those of the whole nervous and muscular systems seem to sympathize, unless we suppose that it produces such a chemical change on the chyle as to obtain a more dense and nutritious blood. In either way the change may perhaps be explained, and though not clearly and satisfactorily, yet as perfectly as many of the medical effects produced in our systems. The former of these ideas is not very different from the opinion of Dr. Cullen, who says,"that by the corrugation and constriction of the whole mouth and fauces, from a small portion of astringents being applied to a small part of the tongue, astringents act upon the sentient nerves; and that, taken into the stomach, they show their effects in other parts of the body so quickly, that they can hardly be supposed to have passed the stomach itself: therefore, their sudden effects in distant parts must be ascribed to an astringent power communicated from the stomach to those distant parts."the discovery of tannin is, however, of a later date, and its chemical effects seem to change the state of the question.

These considerations, however, assist us but little in explaining all the effects of astringents. While they render the simple solids more dense, they add also to the tone of the system, and give energy and activity to the vital. Muscular action is, at least, attended with increased density, and a stronger cohesion of the muscular fibres; and we can therefore perceive how astringents can increase their energy. But the tone of the nervous system is apparently connected with a fluid confined to the nervous fibrils; and the little we know of its nature shows no very striking connexion between increased density and increased nervous power. To avoid this difficulty, it has been supposed that astringents unite a tonic power; and, as we certainly possess tonics that are not astringent, so, on the contrary, some astringents may not be tonics, or the latter power may be combined without altering the sensible qualities of the former. The flowers of zinc and arsenic are certainly tonics without astringency; and catechu, the most powerful astringent, is not a tonic. It is not, therefore, improbable, that the two qualities may be combined; yet they are so often united in a body, that we are anxious to find a closer connexion. We may reflect, then, that though the astringents can have no effect on any fluid in the nerves, yet it seems probable that the state of this fluid, or power, differs according to the state of the simple solid, and to that of the nerves as such. In a warm climate, and from warm confined air, which relaxes the simple solid, the nervous energy is more mobile, but less strong. From cold, and in cold climates, the contrary takes place; and, in general, astringency and relaxation seem respectively to attend tone and irritability. Thus it happens that astringents lessen irritability; and it is not improbable that the whole of their apparent tonic power is merely the diminution of irritability, by the condensation of the simple solid and the nervous system, so far as it is such.

Astringents are of very different kinds; or rather medicines of different powers produce their effects. Those which strictly deserve that title, make the impression of astringency or acerbity on the tongue, for the latter is the effect of astringency joined with acidity. To these only the explanations we have already entered into apply. The principle on which their power depends, we have said, is the tannin, in itself bitter, but probably uniting in the vegetable something which adds to its power. The property of striking a black with chalybeates, supposed to be the distinguishing quality of astringents, is now found to be characteristic of the gallic acid, which sometimes accompanies the tannin. The catechu, which we have styled the strongest astringent, produces no change of colour with vitriolatcd iron.

The natural orders, stellatae,senticosa, and -aaginales oleracea, afford astringents of moderate power; and among the cryptogamiae we may mention the filix florida, trichomanes, equisetum, and muscus pyxida-tus. The ash, the haematoxylum campechianum (logwood), the pomegranate, and the oak, are more powerful: and the contortae, including the bark and the mahogany tree, perhaps equally so. The acerb fruits, particularly the sloes, are active astringents; but the inspissated juices, the acacia and catechu, from two species of mimosa, and the kino, are the most certain astringents of the vegetable kingdom. The dragon's blood has obtained its credit, from having been an ingredient in an active formula with other medicines of this class.

The mineral kingdom affords powerful astringents; but we do not certainly know on what principle this depends. Yet, as we find among minerals combinations not very different from those of the vegetable kingdom, we may conclude that a similar principle exists in them. This idea is strengthened, by finding that alum may, in many instances, be substituted with effect for some of the substances already enumerated. Vinegar and vitriolic acid possess an astringent power, and it is of course found in their salts: thus, the acetites of lead, and copper, and the sulphats of clay and copper, are employed with singularly good effects.

External astringents are styled styptics, and we can more readily understand their action; but some of these act mechanically, as meal, lint, puff ball, and spider's webs. By inviscating the blood and assisting its coagulation, they form a thrombus, which fills the wound of the artery. The other external astringents are some of the substances already mentioned, particularly the earthy and metallic salts; but there is a third kind which act by coagulating the blood more directly: these are ardent spirits.

Astringents are employed externally, in haemorrhages, in bruises, strains, and inflammations. In the three last the vessels are distended and weakened, and their effects are sufficiently obvious, but will be fully explained under the article Inflammation, q. v.

Internally, they are used also for checking haemorrhages, and immoderate evacuations of every kind; but the haemorrhages to which they are adapted are the passive, for when the action of the vessels is strong, and blood abounds, by lessening the area of the canals, they increase the disease. Their effect is probably produced by their action on the stomach, with which the extreme vessels sympathise; and as these are more irritable than the larger arteries, the astringent power is more conspicuous in them. In general, we have said that they lessen irritability; and they seem in many instances to correct acidity. From each effect they appear to be useful in calculous and nephritic cases. General debility is obviated rather by tonics than by astringents.

There is no great choice in the astringents employed. In moderate complaints it may not be necessary to use at once the strongest; and, in general, if we want a rapid change, sedatives and inirritants, particularly cold, nitre, and opium, are preferable to astringents, which always operate slowly. The acetite of lead is of an equivocal nature; but we have been unreasonably terrified on this subject, and if we interpose oily laxatives, it may be given with some continuance very safely.

Astringent vegetables yield their virtue to water, less perfectly to spirit. The astringency does not rise in distillation, nor is it dissolved by oils.

Medicines which imitate astringents in their effects have been arranged in this class. We have already alluded to sedatives and inirritants. The solanaceae and the rhaeades, including the fox glove and the poppies, have been for this reason accounted astringents. Abstinence and evacuations have been considered of the same kind.

Demulcents and antacids appear more decidedly astringent, by checking discharges from the bowels. The various boles, for ages commended and employed, may derive some virtue from the iron they contain, if iron be in reality an astringent. The argillaceous earth, of which they chiefly consist, acts as a demulcent in sheathing the abraded bowels. The gum arabic, as its parent plant, the mimosa nilotica, affords the acacia, may perhaps be supposed to possess a real astringency: it is, however, only a demulcent, and the calcined hartshorn is no more.

Chalk, oyster shells, and lime water, seem to act by absorbing redundant acids, which may prove a source of irritation; and, it is said, the earthly salts thus produced are astringent. Of this quality there is indeed no proof; and their combinations with the acetous acid are not found to be so, though of this kind is the acid which abounds in the stomach. If calcareous earth be so useful in leucorrhoea as some have supposed, it will show a degree of astringency at least in the combinations formed within the body. Strontian earth is an active absorbent, and has been, on this account, also recommended as an astringent. But of the virtues, or indeed the safety of this medicine, we know nothing.

See Fordyce. Gregory Conspectus Med. Wallison Health and Disease. Cullen's Materia Medica.