Ord. 1. Astringentia Mineralia.
Ord. 2. Astringentia Vegetabilia.
The lists of these orders are given below. With regard to the first minor proposition, it has already been proved that most of these medicines pass into the blood. The minerals included in the first order have already been noticed as Hæmatic medicines. They are all soluble in water. They are absorbed in the stomach and intestines, and pass into the blood. Many of them pass on into the secretions. The astringent parts of the vegetables of the second order are also soluble. Tannic acid is the chief of them; it is simply an Astringent; it has been found in the blood, where it changes into Gallic acid, and in that form it passes into the secretion of urine.
What then are the active properties of these medicines? They have all a certain chemical power; and a certain dynamical power. All the mineral Astringents have the power of precipitating an albuminous solution. So also do Tannic acid, Turpentine, and Creosote, coagulate albumen. Tannic acid precipitates Gelatine too. The dynamical property, which is common to all of these substances, is a power of causing the contraction of muscular fibre. It seems to depend somehow on the chemical power just mentioned; for Astringents appear to constringe fibrinous as well as albuminous tissues by a chemical action. They also coagulate fluids and discharges which contain albumen.
When the solution of any Astringent is applied to a fresh fibre of dead muscle placed under the microscope, it is seen to contract. The power which they possess in causing the contraction of living blood-vessels may be witnessed in a similar way. The astringent solution may be applied to the web of a frog's foot, confined in an extended position. This web is traversed in all directions by minute ramifying capillaries; and these are found gradually to diminish in caliber. In the same way as the mechanical irritation of a small artery will act upon the unstriped muscular fibre contained in its coat, and thus cause the vessel to contract at one point; so it seems that an Astringent, by a chemical action on the same muscular tissue, is able to cause the capillary vessels seen under the microscope to contract and diminish in size. At all events we may conclude, both from actual experiment and from a comparison of their several operations, that Astringents are able to cause the contraction of muscular fibre.
In the third minor proposition the chief results of their operation are stated. These have already been briefly described.
They check secretion. They are thus prescribed when any secretion is excessive. The Tannic vegetables are given in diarrhœa; Nitrate of Bismuth is administered in Pyrosis; Sulphuric acid in profuse perspirations; Uvæ Ursi in mucous flux from the bladder.
They repress hæmorrhage. Thus Acetate of lead is employed in hæmoptysis; Creosote and Uvæ Ursi are used in hæmorrhage from the stomach or bladder; and the vegetable Astringents are prescribed in Dysentery.
They give tone to the system. They do this when there exists an over-relaxation of the solid fibres on account of any depressing cause, by exciting the muscles to a more or less permanent contraction, and by constringing the capillary vessels generally.
In the fourth place, it is maintained that their action in all these instances may be explained by a reference to their power in causing the contraction of muscular fibre; inasmuch as they are found to diminish the caliber of certain tubes and cavities, and these owe the contractility which they possess to the muscular fibre which is contained in their coats. It follows then from the rule of local access, that before they can influence these tissues they must pass directly to them from the blood.
Such appears to be the simplest and the most rational explanation of the action of Astringent medicines.