Small doses (3 gr.) taken several times daily, in water, cause dryness of mouth and throat, thirst, and diminished secretion in the alimentary canal, the stools being rendered harder and less colored than normal (Wibmer). Doses of 10 gr. disorder the digestion by lessening the gastric secretion, and from 15 to 60 gr. cause cramping pain and nausea (Barthez): 2 to 3 dr. induce vomiting without much straining, and larger continued doses may cause colic and diarrhoea with considerable increase of secretion from the intestinal mucous membrane.

In rabbits, which do not vomit, 2 dr. proved fatal, with evidence of inflammation and erosion of the stomach (Mitscherlich). To dogs, Orfila gave 1 to 2 oz. without other marked effect than vomiting, though if a ligature were passed round the oesophagus, 1 oz. would cause death in a few hours (Devergie). In these cases the gastric membrane was found to be either white and wrinkled, almost tanned, or was distinctly inflamed in patches.

Devergie concluded from his experiments that the human was more sensitive than the canine stomach, and certainly large doses of 1 to 2 oz. cause in man much burning pain, frothing at mouth, vomiting, purging and depression: the symptoms of gastro-enteritis may develop themselves, but usually the emetic action gets rid of the drug before serious injury is produced. The results vary somewhat with the condition of the stomach at the time, for at a trial in Paris it was proved that a lady, the subject of chronic dyspepsia, took about 20 gr. of burnt alum (by mistake for gum arabic), and suffered from enteritis in consequence. Orfila gave evidence that such a result was due to exceptional causes, and that 4 to 6 dr. were often given without inconvenience. More recently, death has been reported in a man aged fifty-seven from taking 13 dr. of burnt alum: he suffered from a sensation of burning and constriction, general malaise and anguish, hurried respiration, and nausea with sanguineous vomiting: intelligence remained good (Union Medicale, No. 64, 1873).

Alum was at one time largely, and even now is to some extent used in the adulteration of bread, for it gives a whiter color to the flour. Injurious effects, such as dyspepsia and constipation, have been attributed to it, and though Christison failed to notice bad results from any amount that came under his notice, I have myself often traced indigestion to alum in the bread: it would certainly follow the use of any large quantity. (It may be noted that ordinary natural wheat flour would give about 4 gr. of silicate of alumina to the 4-lb. loaf, and the determination of the amount of added alum has been a frequent puzzle to analysts. - Medical Times, ii., 1875.)

Theory Of Action

We are not yet able to explain exactly the manner in which alum produces its effects, though doubtless its affinity for water, and its power of coagulating albumen, are important factors. M. Mialhe supposed the astringent action to depend upon a chemical decomposition, viz., the precipitation of alumina by the alkaline elements of secretions, or of blood; and he further supposed that the secondary effect of increased discharge - which we have mentioned - was due to an absorption of the recently-formed alumina rendering the blood more fluid (v. Stille, vol. i.). This chemical explanation is not, however, satisfactory, for taking only the latter point, astringent effects persist, as a rule, after the absorption of any ordinary doses, and it is only under the continuance of large doses (1 to 2 oz.), irritative by their mere mechanical effects, that discharge is increased; such increase, therefore, is better explained as a consequence of direct local irritation than of fluidity of blood. It is not uncommon for astringents - nitrate of silver, for example - in dilute solution to lessen discharge, and when more concentrated to increase it.

Synergists

Tannin, sulphuric acid, and astringents generally, favor the action of alum, and are often combined with it; but as tannin decomposes alum, it seems probable that if given in the same mixture or compound, the substances may really prove less astringent than when given separately.

Antagonists - Incompatibles

If an over-dose of alum be taken, mucilaginous and albuminous liquids, such as milk with white of egg, or gum arabic, or fluid glue, should be freely given. Magnesia should be added, according to v. Hasselt, or carbonate of ammonia in small quantities (Taylor). Alkalies and their carbonates, and acetate of lead, are chemically incompatible with alum.

Therapeutical Action (External)

Alum is one of the oldest known remedies, and was often prescribed by Hippocrates and Celsus: its properties, as already described, render it unsuitable for the acute stages of any active inflammation, but most useful in many chronic catarrhal conditions, and relaxed states of mucous membrane.