Active Ingredients. - Galls contain about thirty-five to forty per cent. of tannic acid, and about six per cent. of gallic acid; also a substance called ellagic acid, discovered by Chevreul and Braconnot, with some sugar, starch, gum, extractive, saline matter, and other subordinate ingredients. The soluble principles are taken up by forty times their weight of boiling water; the residue is tasteless. The light brown color of the infusion is deepened by ammonia, and changed to orange by nitric acid. Bichloride of mercury renders it milky, but with not one of these reagents is there any precipitate, nor yet with litmus, which the infusion reddens.

Tannic acid, C27H12O17, is well described in the British Pharmacopoeia, 1867, as occurring, when separated, in "pale yellow vesicular masses, or thin and glistening scales, with a strongly astringent taste, and an acid reaction; readily soluble in water and rectified spirit, very sparingly soluble in ether. The aqueous solution precipitates solution of gelatine yellowish white, and the persalts of iron of a bluish-black color. When burned with free access of air it leaves no residue."

Gallic acid, H1C7H3O5H1O, presents itself, when prepared, in the shape of crystalline, acicular prisms, or silky needles, sometimes nearly white, but generally of a pale fawn color. It requires about one hundred parts of cold water for solution, but dissolves in three parts of boiling water. It is soluble also in rectified spirit. The aqueous solution gives no precipitate with solution of isinglass, but with a persalt of iron it gives a black one. When dried at 212° the crystalline acid loses 9.5 per cent. of its weight. Burned with free access of air, it leaves no residue.1

Ellagic acid, C14H6O8, appears in the separated state as a white crystalline powder, and differs from tannin and gallic acid in being almost insoluble alike in alcohol, ether, and water. According to M. Pelouze,2 it does not exist ready formed in galls, but originates in the action of atmospheric oxygen upon their tannin; and the same, this author informs us, is the origin also of gallic acid. The quantity of ellagic acid contained in galls is only trifling, but the intestinal concretions called bezoars are said to be composed of it almost exclusively.

Physiological Action. - 1. Of Tannic Acid. Tannic acid, taken into the mouth, acts as a powerful astringent upon the mucous membrane of all the parts it comes in contact with, acting also upon the fauces.

Tannin scarcely deserves the name of a poison; its effects, even when given in the largest doses, being entirely local and not severe. Upon the mucous membrane of the stomach and intestinal canal these very large doses are capable of producing a peculiar effect by virtue of its power to combine with albuminoid matters in a manner similar to that which constitutes the essence of the tanning process in the curing of skins for leather. The consequences of this, in cases where large quantities have been taken, have been obstinate constipation and vomiting, thirst, and, in a few cases, cutting pains in the abdomen.

It is by virtue of its tendency to combine with protein tissues that tannic acid possesses a decidedly superior power as a local astringent over gallic acid.

Tannic acid, when absorbed into the blood, appears to suffer decomposition, the products of which are gallic acid, pyrogallic acid, and a humin-like substance. The principal fact in confirmation of this belief is that ordinary tannic acid is not found in the urine,3 but only the decomposition products already named, or some of them. Gallic acid is nearly always present, and can be recognized by its characteristic effect on persalts of iron; but Bartels has shown that occasionally only the humin-like body passes over, and sometimes even this trace of the tannin is lacking. Neither liver, pancreas, skin, nor pulmonary mucous membrane appears to excrete tannin unchanged; but the sputa, like the urine, have often been observed to be colored almost black.

1 Brit. Pharm., 1867.

2 United States Dispensatory, 12th Ed., p. 404.

3 Catechu-tannin and several other varieties do pass off in the urine unchanged.

The intensely powerful coagulating action of tannin upon blood, when mixed with it out of the body, might give rise to a belief that similar changes occur within the blood-vessels. But there is no proof of this, and there is much reason to think that very little tannin as such is absorbed into the blood. Tannin, in the form of albuminate, has been found in plenty in the faeces; but it is not likely that much passes through the gastro-intestinal mucous membrane without previous decomposition. The remote effects of tannin are therefore with great probability to be ascribed to its secondary products.

2. Of Gallic Acid the local action, as already said, is far less powerful than that of tannin, but the former passes rapidly through the body, appearing unchanged in the urine, and affecting various organs and functions in a manner which becomes important from a therapeutic point of view.

Therapeutic Action. - 1. Of Tannic Acid. This is now understood to be mainly local; but even with this limited range, the drug is highly useful in a variety of cases.

As a local Astringent, tannic acid fulfils many functions. Thrown (in the form of a fine powder, or in the shape of gargle, or of spray for inhalation) upon the mucous membrane of the fauces and air-passages, it checks congestion and inflammatory swelling, reduces excessive secretion, and arrests the tendency to capillary haemorrhage. Hence it is useful in quinsy, catarrhal affections, chronic bronchitis, laryngeal phthisis, and haemoptysis. Applied to a bleeding surface anywhere, if no large vessel be engaged, tannic acid is prompt in its styptic action, and among other uses may be applied to modify the fungating and easily bleeding surfaces of ulcers. But perhaps the most decided instances of its local utility are to be found in its application in the shape of the glycerine of tannin to eczematous skin (Ringer); blenorrhoeal and leucorrhceal states of the urethra and vagina; sore throat (painted on with a brush); intertrigo, rectal fissures, and prolapsus ani.

As an Antidote to alkaloid Poisons, tannin holds a high place. The observation was first made in regard to emetin-poisoning (or rather ipecacuanha-poisoning), sufficient to produce excessive vomiting; but the observation has been extended to opium and its salts, digitaline, nicotine, and other alkaloids. In metallic poisoning, particularly that with antimony, tannin has gained some repute; but it is not as effective as albuminous matter (white of eggs).

2. Of Gallic Acid, while the local effects are not particularly worth mentioning, since those of tannin are so superior, the remote effects are so remarkable as to render it in every way one of our best remedies. As a remote astringent, gallic acid enjoys a reputation which is doubtless somewhat exaggerated, but is in large part deserved. There are two principal forms in which this action can be brought into play.

In Haemorrhage of the most various kinds, but especially in haemoptysis, and in haematuria which depends upon morbid conditions of the mucous membrane of the bladder, gallic acid is often exceedingly effective.

Other remedies, and particularly ergot of rye, may perhaps supersede it to a considerable extent, but gallic acid remains one of the most useful agents of this class. "Ruspini's styptic " was mainly composed of it.

In Dropsy and Albuminuria, however, the astringent power of gallic acid is probably even more useful than in haemorrhagic conditions. There is a very general agreement among those who have practically tried it, that gallic acid can often do great service in checking the waste of valuable albuminoid matters which the system would otherwise have to support. It is remarkable that while albuminuria is strikingly diminished, there is usually an increase in the flow of urine. The action of gallic acid upon the tracts, pulmonary and urinary, through which it is eliminated, is used as a strong argument by the school of therapeutists which teaches that for one of the most promising modes of therapeutic influence we ought to look to the curative effects of drugs on organs by which they are cast out of the body.

Preparations and Dose. - Tinct. Gallae, 3j. - ij. (4.- 8.);

Ungt. Gallae; Acidum Gallicum, gr. v. - xx. (.30 - 1.20); Glyceritum Acidi Gallic, m xx. - 3 j. (1.20 - 4.); Acidum Tannicum, gr. v. - xx. (.30 - 1.20); Glycerit. Acid. Tannic, m xx. - 3 j. (1.20 - 4.); Suppositoria Acid. Tannic.; Ungt. Acid. Tannic.