Dead animal structure, submitted to the action of astringent substances, especially to those of vegetable origin, has long been known to undergo condensation, in consequence of chemical combination between constituents of the tissue and the astringent substance. In relation to the vegetable astringents, their tannic acid unites with the albumen and gelatin of the animal product, to form insoluble tannates, as in the preparation of leather from hides; in relation to the mineral, the metallic salt or its oxide also combines with albumen, producing compounds insoluble in water. The chemical therapeutists suppose that this same reaction takes place between the astringent and the living tissue, and ascribe the effects of the medicine to this agency. But there is no proof whatever that such a combination takes place in life. It could not do so, to any considerable extent, without destructively disorganizing the part affected. The force of life opposes these chemical reactions, and successfully so long as the medicine is moderately employed. If this be applied abundantly, it may first exhaust the vital forces by the excess vital reaction it excites; and the chemical affinities may then triumph, with the effect of destroying the life of the part. But, under such cir-cumstances, it ceases to be a medicine, and becomes a poison. The rapidity, moreover, and amount of local astringent effect are far greater than can be explained on the chemical principle. Every one knows how sudden and great is the contraction produced in all the tissues of the mouth by a very minute quantity of alum. It appears to me absurd to ascribe all this effect to chemical combination. Even were the whole of the alum which could possibly be absorbed in such a case to combine chemically with the tissues, it could not produce an amount of contraction in any degree approaching to that really experienced. Besides, the contraction, if chemical, would be much more permanent than it really is.

The following appears to me to be the true explanation of the phenomena, so far as they are at present susceptible of explanation. All the living tissues have a certain degree of vital cohesion essential to the due performance of their functions; and this cohesion probably depends on a property of organic contractility, which is called into action and sustained by the healthy stimulus of the blood and nervous influence. If these fail, the cohesion diminishes, and a condition of relaxation takes place. Now astringent substances have the peculiar property of stimulating this organic contractility; and it is this property by which they are characterized as a class of medicines. All that we know upon the subject is that, in consequence of the contact of these substances with the tissues, the contractility of the latter is called into action, and they shrink. The effect is in no degree more singular than that a similar shrinking should take place under the influence of cold.

It is a very singular mistake, which still prevails with some writers, that astringents act especially or peculiarly on the muscles. It is true that they do increase the vital cohesion of this structure, rendering the muscle firmer, but they also act equally on every other tissue capable of shrinking; as may be distinctly seen in their effects upon the skin, and felt in their effects on the mucous membrane of the mouth.