ZINC, Medical Properties of—In the purely metallic state, zinc pro duces no effect On the human system, but its combination with oxygen, forming oxide or flowers of zinc, is sufficient to invest it with consider able power over various organs, both those with which it comes into direct contact and some remote ones, ewecially the nervous centres. Its local action is that of an irritant, astrineent, and desiccative, while its remote action is that of a tonic and antispasmodic. The emetic pro perties of the oxide are less than those of the sulphate or acetate, unless it meets with acids in the stomach. In this way it is rarely employed. It is for its remote effects that oxide of zinc is valued. While it has the properties common to all the metallic antispasmodics, it is dis tinguished by its power of restraining inordinate action of the nervous system ; being calming and soothing. The brain and the function of sensation appear to feel less of its influence than the spinal cord. Hence the nerves of motion, and the functions of the circulation and respiration, are chiefly acted upon ; it produces its effects speedily, bet they quickly disappear when given in such doses as can be safely administered. The long-coutinued use of it seems to produce a dryness and induration of the frame, which, if carried to excess, is clangorous, but the lesser degree of which is in all probability the source of the utility of this medicine, by diminishing the mobility of the system; irregularities in the circulation, and sudden congestions of blood, being the immediate causes of attacks of epilepsy and hysteria, the diseases which are most benefited by oxide of zinc. This desiccating property renders it the most potent means yet discovered of checking the col liquative perspirations of consumptive persons. (See ' Clinical Lectures on Pulmonary Consumption,' by Theophilus Thompson, M.D., p. 194.) For use in this way, and even for use as an ointment, it requires to be prepared in a state of far greater purity than it is met with when pre pared for use in the arts. Above all, it must be free from admixture with sulphate of zinc.
In spasmodic affections of the chest, such as asthma, angina pectoris, and palpitation of the chest, when these do not proceed from organic derangements, oxide of zinc is often serviceable, especially when bined with conium. In the cramps of the stomach to which habitual drynkards are subject, it is very useful.
Impure oxide of zinc is called tutty. It is sometimes used exter nally as a dusting powder, as a mild absorbent, on excoriations, and to heal chaps and cracks in 'the skin. It is also used as an ointment. Pure oxide of zinc forms an ointment of much value where a mild astringent is needed, especially in the chronic inflammation of the eyelids.
Carbonate of zinc when impure is termed calamine. This, after
being subjected to divers processes, is called prepared calamine. The only use made of it is to form an ointment, which is most useful as an application to burns, excoriations, and superficial ulcers.
Sulphate of zinc is in small doses a very valuable astringent, tonic, and antispasmodic ; in larger doses it is a very certain and speedily acting emetic ; and in very large doses it is poisonous. It is the most useful emetic in cases of narcotic poisoning, as it is not so apt to inflame the stomach as tartarised antimony : but the stomach-pump is preferable to either.
The tonic effects are best seen in affections of the mucous mem branes. In the suffocative catarrh of aged persons, and the extreme defluxions on the chest after influenza, sulphate of zinc affords a valuable remedy : it must be given in small doses, as the sudden suppression of the secretion may cause inflammation. Its utility is increased by combining it with the compound rhubarb pill, or with myrrh only. The use of the solution as an injection requires the same caution.
Acetate of zinc is possessed of nearly similar properties, but in a weaker degree ; and as an injection, seems in some cases entitled to a preference.
Chloride of zinc, called also butter of zinc, is a powerful escharotic or caustic ; this action results from its strong affinity for albumen and gelatine, which principles it abstracts from the living tissues, and so forms an eschar. Its powers in this way have been taken advantage of to destroy parts affected with malignant diseases, such as cancer and lupus, and to remove na:vi materni, or mother-marks. In none of these is it to be resorted to unless they are very superficial. Deep seated cancer of glands can scarcely be removed by it, but other forms are often successfully treated by it. (Waishe, ' On Cancer,' p. 219.) Properly diluted, chloride of zinc is most beneficially used to correct the fcetor from suppurating ears of children.
Cyanide or c7anuret of zinc is a powerful antispasmodic and tonic. No medicine is so potent in allaying irritability of the stomach, attended with great debility. The dose must be small and often repeated. Velerianate of zinc has lately been much recommended as a remedy against tic-douloureux and other nervous affections. Where the patients can tolerate the repulsive odour and persevere in its use, It often proves very serviceable.
Zinc pans have been much recommended for use in dairies, as the milk speedily coagulates in them, and the quantity of cream is great : but if the milk becomes sour while in them, the acid acts upon the zinc, and forms unpleasant, though perhaps not poisonous compounds. Upon the whole, white porcelain vessels, kept thoroughly clean, are the best material for milk-vessels.