In an impure form this salt has long been used in medicine, under the names of sal volatile, salt of hartshorn, etc. It may often be very usefully employed. In consequence of the energy and, at the same time, brevity of its stimulant action, it is admirably adapted to all those cases of sudden depression or collapse, which, if the patient survive, must be followed by febrile reaction, if not acute inflammation. The want of any special influence on the brain adapts it peculiarly to those in which the reaction will be likely to be attended with inflammation or great vascular excitement of that organ. Instances of the kind are not unfrequently presented in the cold stage of febrile diseases, the collapse of concussion of the brain, and the prostration of any sudden shock. Under these circumstances, it is an admirable adjuvant of the hot bath.

In all fevers, assuming in their progress a low form, requiring stimulation, this is one of the first of the diffusible stimulants which may be had recourse to. In typhus and enteric fevers, in the various exanthemata assuming a typhoid condition, especially scarlatina, smallpox, and malignant erysipelas, and even in the phlegmasiae when attended with the same state of system, it may often be used very advantageously, associated with other stimulants, especially with wine-whey, and the preparations of Peruvian bark. Its tendency to produce softness or moisture of the skin, adds to its usefulness; and sometimes, when the breath and exhalations from the patients have a sour smell, as they are apt to have in low fevers, its property of neutralizing acid, may be considered a peculiar recommendation.

In the malignant pustule, carbuncle, glanders, metastatic abscess, and all cases of purulent infection of the blood, and other affections of a similar kind, accompanied with a depressed condition of the system, it may be used, conjointly with other stimulants, with hope of benefit.

There are few conditions in which it acts more happily than in the advanced stages of the different pectoral inflammations, when the occurrence of suppuration with a tendency to prostration calls for the use of stimulants. I have frequently seen it of the greatest possible service in pneumonia under these circumstances, when the severe oppression of breathing, the cool skin, the feeble pulse, and the sweats at night, have indicated the probable approach if not occurrence of the third stage of the disease, and the absolute necessity of supporting treatment. 1 do not think it is going too far to say that I have repeatedly, in this condition, known it to be the main agent of safety to the patient. It probably operates, under such circumstances, not only by a general stimulation of the circulatory and nervous systems, but also by a special excitation of the ultimate tissue of the lungs, concerned in the respiratory function. In a somewhat less degree, it often proves serviceable in protracted acute bronchitis, with a suppurative condition of the mucous membrane. In chronic bronchitis also, and in phthisis, when the lungs are loaded with pus, and too feeble to discharge it effectually, the carbonate of ammonia yields much relief by stimulating the expulsive power.

It has been recommended both in chronic and acute rheumatism. There is a condition of the latter affection in which it may be very appropriately employed. This condition consists in an asthenic state of system, probably dependent on impoverished blood, in which, though there may be considerable inflammation, it is apt to be movable, changing its seat from place to place, and a good deal of nervous irritation mingles with it, along with a frequent but feeble pulse, a tendency to paleness, and, perhaps, coolness of the surface, and sweats during sleep. This is altogether different from the typhoid state of the system, with depraved blood, and yields more happily and speedily to a well-directed stimulation. Perhaps the use of the medicine may be ascribed in part to its alkalinity, which is indicated sometimes in these cases by an excess of acid in the system. In chronic rheumatism the medicine is usually given in connection with guaiacum, in the form of the ammoniated tincture of that resin; and probably acts by stimulating, in a manner similar to that of oil of turpentine, the ultimate structure of the inflamed tissue into a new action, which may supersede the old.

The medicine has been recommended in scrofula; but it exercises no special influence over the diathesis, and only proves beneficial sometimes in states of depression attendant on this disease, as in a similar state in any other.

As an antispasmodic in the nervous affections it has received high commendation. Hysteria and epilepsy are the particular complaints in which it has been most praised. In the former affection it will no doubt often prove beneficial, partly, in all probability, by a direct stimulation of the nervous centres, but much more, I believe, by obviating the flatulence, spasmodic pains, and other disordered sensations in the stomach and bowels which so often attend and aggravate the disorder. In epilepsy, when entirely functional, it may sometimes prove beneficial. Dr. Pereira thought he had derived much advantage from it both in epilepsy and hysteria, given in doses of fifteen or twenty grains three times a day, and continued steadily for two or three weeks.

Dr. Barlow recommends carbonate of ammonia in diabetes, in conjunction with a diet of animal food and the cruciferae, exercise, the warm bath, and opiates; but experience has not proved it to possess any special influence over that complaint. (Brit and For Med. Rev., Oct. 1841).

Cazenave has found it useful in scaly affections of the skin; but a much more effectual remedy, in these complaints, is arsenic in some one of its medicinal forms; and it is scarcely advisable to postpone the cure by using substitutes which exercise a comparatively feeble, and at best uncertain influence over the disease.

Carbonate of ammonia has been much commended for the possession of certain antidotal virtues. In the depressed state of system resulting from sedative poisons, such as tobacco, digitalis, and hydrocyanic acid, it is obviously indicated as a rapid and active stimulant; but, in regard to hydrocyanic acid, it has been supposed to have special powers as an antidote. Whether it can be of any service chemically by neutralizing the poison, is a matter of some doubt; but it should at least be employed as one of the most efficient agents, if not the most efficient, in counteracting its effects.

Either in this form, or that of solution or spirit of ammonia, the volatile alkali has obtained great credit, as an antidote to the bites of poisonous animals. Numerous cases are on record in which, applied locally and taken internally, it has been supposed to prevent the poisonous effects of the bites of serpents. But as these bites often produce no fatal effects if left alone, it is extremely difficult to decide upon the amount of credit which the supposed antidote may really merit. The reputation of the medicine was mainly based on the apparent success of the eau de luce, a liquid containing ammonia as its chief ingredient, which was given by Bernard de Jussieu to a servant bitten by a viper. But Fontana proved that the bite of the viper rarely causes death, and that its effects are in no degree diminished by the use of ammonia; and the same observation was extended to the bites of venomous insects. Trousseau and Pidoux state that they have never seen the external or internal use of ammonia modify, in the least degree, the symptoms of poisoning by the bites of venomous animals. (Traite, de Therap., 4e ed., i. 336.) I have never had the opportunity of trying the remedy in any serious case of the kind.

Another antidotal application of ammonia has been to the relief of the intoxicating effects of alcoholic drinks. Over absolute drunkenness it has no control whatever; but, in slight disorder from this cause, either the carbonate of ammonia, or the alkali itself in aqueous or spirituous solution, occasionally gives relief.

The local effects of carbonate of ammonia on the stomach and bowels are often advantageous. In excess of acid with a languid slate of the stomach, such as not unfrequently exists in dyspepsia, in sick-headache with the same complication, and in the spasmodic pain or other uneasiness of flatulence and atonic gout, it may be prescribed alone, or in connection with tonics and purgatives; but the aromatic spirit is usually preferred, under these circumstances, to the carbonate in its ordinary form.

The main contraindication to the use of carbonate of ammonia, to cases which may seem to call for it, is the existence of inflammation of the stomach.