ANTACIDS are medicines which correct abnormal acidity of the stomach and intes tinal canal by directly combining with the free acid that may be present. Their action is obviously merely temporary, as, unless combined with other medicines, they do not correct the morbid condition which causes the undue acidity; and their too prolonged use must be carefully avoided, since, at all events, some of these medicines, as the alkalies and their carbonates, are liable to induce a state of general antemia, morbid deposits in the urine, and a series of symptoms not unlike those of scurvy. Antacids are best given in association with vegetable tonics; and for the reasons already stated, their administration must be carefully watched, and should be occasionally omitted. Dr.. Neligan makes the following excellent remarks on the particular remedy to be employed for special forms of acidity: " When the acid exists in the stomach in the gaseous state, ammonia or its carbonates should be preferred, as, in consequence of their volatility, a gaseous acid which would elude the action of the fixed alkalies, may be neutralized by them. If the acidity be present in the lower bowel, as in the exeunt or colon, magnesia or lime ought to be administered, as being less likely than the other antacids to be neutralized or absorbed before it reaches that portion of the intestinal canal. When the acid exists in the urinary organs, the alkalies will be found best
adapted, as they have a tendency to act more directly on the kidneys; and when it is Whir (or urie)aeld which preponderates in the urine, the preparations of lithia or potash should be preferred to those of soda, as the salts formed by the two former with the acid in question are much more soluble than those formed with the latter. In persons of a corpulent habit of body, potash is to be preferred to ammonia or soda when the use of an alkali is indicated. And, finally, ammonia and its preparations are best adapted for the old and debilitated, as also for those of enfeebled constitution." The antacids include solutions of ammonia, lime (commonly known as lime-water), potash, and soda, various carbonates of these substances, magnesia and its carbonates, and the carbonate and citrate of lithia.
Many of the medicines of this class possess other properties besides that of neutraliz ing free acids; but a notice of such properties does not fall within the scope of the present article.