Iron in the intestine causes an astringent or constipating effect.
In cases where diarrhoea is very obstinate and lasts for weeks, sulphuric acid is sometimes more efficacious than alkalis; and in chronic colics it may be necessary to treat the mucous membrane by local application of astringent solutions.
As alum and green vitriol were applied to a variety of substances in common, and as both are distinguished by a sweetish and astringent taste, writers, even after the discovery of alum, do not seem to have discriminated the two salts accurately from each other.
The witch hazel is quite a distinct plant, Hamamelis virginica, of the natural order Hamamalideae, the astringent bark of which is used in medicine.
The astringent salts are therefore useful occasionally to check diarrhoea and dysentery.
The chief use of the preparations of lead, however, is as an astringent in acute diarrhoea, particularly if ulceration be present, when it is usefully given in combination with opium in the form of the Pilula Plumbi cum Opio.
The physical properties of the powder also give it a mild astringent action.
In China it was an old internal remedy for leprosy and struma, and is accredited with stimulant, tonic, sedative, astringent and vulnerary properties.
Internally lead has an astringent action on the mucous membranes, causing a sensation of dryness; the dilute solution of the subacetate forms an effective gargle in tonsillitis.
Soluble salts of manganese, aluminium, zinc, copper, gold, platinum and bismuth have, when given by the mouth, little action beyond their local astringent or irritating effects; but when injected into a blood vessel they all exert much the same depressing effect upon the heart and nervous system.