There are few more valuable medicines for external use than sulphate of zinc. Being at once excitant and decidedly astringent, it serves to stimulate enfeebled surfaces, and, by contracting their blood-vessels, to obviate inflammation in them. But there is something, also, in its mode of operation, which we do not exactly understand, by which it changes the condition of parts even specifically diseased, and disposes them to take on a healthy action, to which otherwise they would have no tendency. In other words, it is alterative, as well as tonic and astringent, in its local influence.

It has been used as a simple styptic to bleeding surfaces, though probably inferior in this respect to some other astringents, such as alum and acetate of lead.

As a collyrium in the very commencement of inflammation of the conjunctiva, in slight affections of the kind at any stage, in chronic cases or the declining stages of the acute, and whenever the blood-vessels appear to be merely passively dilated, it is among the safest and most efficient remedies. For this purpose, it may be dissolved in rose-water, or in pure distilled water, in the proportion of one grain to the fluid-ounce, or even less when the eye is very sensitive. The solution may be applied twice a day, and gradually strengthened, if requisite. In very slight cases, which, however, are sometimes troublesome by interfering with the use of the eyes, a single application often proves sufficient.

In gonorrhoea, in any stage, unless when the inflammation is very high, and involves more than the mucous membrane, it is a very efficient remedy, if properly used. At the very commencement of an attack, it will sometimes almost immediately arrest the affection. The strength of the solution should not at first exceed two grains to the fluidounce of water, and it may he even weaker in very sensitive conditions of the urethra. To be successful, the injection must be very frequently repeated, so as not to allow the impression to subside before it is renewed; every three or four hours for example, or six or eight times in the twenty-four hours.

In leucorrhoea the same injection will often prove highly useful, employed two. three, or four times in the twenty-four hours; but little good can be expected from it when the discharge is sustained, as it too frequently is, by organic disease.

In chronic inflammation of the rectum, with mucous discharges, it is an invaluable remedy; whether this condition be original, or a mere accompaniment or consequence of dysentery. The method of administration has been mentioned in the remarks made on the use of the remedy in that affection.

Chronic purulent discharges from the ears, and the same affection of the nostrils known under the name of ozaena, are other complaints in which sulphate of zinc is often extremely useful. In these cases, the strength of the solution, at first only two or three grains to the fluid-ounce, should be increased, as the parts will bear it, to five or even ten grains. Whenever the immediate seat of the discharge can be seen, as sometimes when an ulcer exists, even a stronger solution than the strongest mentioned, may be directly applied to the diseased surface by means of a camel's-hair pencil, leaving the sound parts untouched.

But perhaps the local affections most amenable to the remedy, are ulcers and pseudomembranous patches in the mouth and fauces. Whenever the surface of the ulcers, in these positions, is covered with a whitish exudation, whatever may be their duration or size, from the small superficial aphthous ulceration to the obstinate and destructive cancrum oris, the solution of sulphate of zinc will, according to my observation, effect a cure. I do not include in this category the gan-graena oris, which I believe to be a different affection, and which is more effectively treated by more active escharotics, as nitrate of silver or sulphate of copper, nor syphilitic ulcers, in which corrosive chloride of mercury is more effectual. The solution should have the strength of fifteen or twenty grains to the fluidounce of water, and should be applied daily or twice a day, by means of a brush or hair-pencil, exclusively to the diseased surface, and continued until the whitish exudation, before alluded to, gives way to a red surface, after which it should be omitted. As soon as this change takes place, the ulcer speedily heals.

A much weaker solution, say of two or three grains to the fluidounce, may sometimes be used in obstinate cases of the infantile thrush or muguet of the French, with great benefit.

The same remedy is applicable to all ulcers, wherever seated, which, in consequence of a loose, flabby, debilitated state of the old tissue, or of the new granulations, refuse to take on the healing process; and especially when the ulcers are attended with a copious purulent discharge. The strength of the solution must, in these cases, vary so much that no precise rule can be given. It may contain from two to twenty grains to the fluidounce.

Dr. F. L. Keyes, of Jerseyville, W. Canada, strongly recommends a solution containing three grains of the sulphate to a fluidounce of water, as a dressing for burns and scalds, of all kinds, except those produced by gunpowder, and containing grains of the powder in the wound. (pharm. Journ. and Trans., Dec. 1865, p. 338).

Certain cutaneous eruptions yield to the local use of this solution. I have found it specially beneficial in that brownish superficial discoloration, which sometimes spreads over large portions of the surface, to the great anxiety of the patient, and which is now, under the name of pityriasis versicolor, recognized as a parasitic affection. Made in the proportion of from two to five grains to the fluidounce, and thoroughly applied morning and evening, the solution has, I believe, invariably within my recollection, effected cures.

Sometimes a mixture of acetate of lead and sulphate of zinc in solution, has been employed as a collyrium, and as an injection in gonorrhoea, preferably to the sulphate alone In this case, a double decomposition takes place, with the production of sulphate of lead, which is precipitated, and of acetate of zinc, which remains dissolved. If the liquid, therefore, be employed clear, it is the latter salt which is the real agent; if it be agitated, the insoluble sulphate of lead is applied at the same time. It is possible that this salt may add something to the curative effect by affording a sort of protective covering to the mucous surface. When it is the effect of the acetate of zinc alone that is wanted, recourse should be had preferably to a solution of the pure salt. The proportion of the two salts employed is usually three grains of the acetate of lead to two of sulphate of zinc, in a fluidounce of water.