Acids are obtained from vegetable and mineral substances, either by fermentation or distillation.

The vegetable acids, however, such as the juice of limes and lemons, are frequently procured without the aid of art. They are of a saponaceous consistence, and therefore. in a variety of affections, emi-nently adapted to the human constitution. With respect to their general effects, it may be said that they attenuate the fluids, remove obstructions, stimulate the appetite, promote digestion, quench thirst, and, in hot seasons, counteract the putrid tendency of the animal humours : they afford an excellent remedy in pectoral, bilious, and inflammatory diseases, but particularly in the true, scurvy, as likewise in all maladies of the kidneys; and are the most effectual antidotes, against the narcotic vegetable poisons. Thus, a most powerful dose of opium may be cheeked in its soporific effects, if a proper quantity of the acid of lemons be taken with, or immediately after it. For in-star:' . grains of opium, or one hundred drops of laudanum, form a large, and sometimes fatal, dose; but if one ounce of pure lemon-juice, or twice that quantity of good vinegar, be added to every grain of opium, or to twenty-five drops of laudanum, we can declare from experience, that such a compound will produce a very different effect. Instead of stupifying the head, and producing troublesome costiveness, it will not only relieve the bowels, but also occasion a degree of chear-fulness never attainable by the use of opium alone, or strong liquors, and afterwards induce a composed and refreshing sleep. Hence the use of acids, to persons who are habitually obliged to take considerable doses of opiates, cannot be too strongly recommended. In the form of clysters, the mild vegetable acids, such as vinegar diluted with an equal quantity of cold water, are a . safe and effectual remedy for costive habits: and few persons will be inclined to doubt their good ef-s, when sprinkled about the floors and walls of rooms inhabited by patients labouring under putrid disorders, especially in the heat of summer. As a proper substitute for the acid of lemons, we refer to the article Barberries.

The mineral acids, however, are productive of very different effects:: when applied in a diluted state to the human body, whether externally or internally, they generally contract, and gently stimulate, the animal fibre; but, in a concentrated form, violently stimulate, corrode, and destroy its texture. With respect to their comparative activity, the nitric acid, or aqua fortis, is the most volatile; the vitriolic acid, the most diffusible; and the marine acid, or spirit of salt, perhaps the most active and permanent in its effects on the human system. Hence the last has lately been used byDr. R e i c h, of Erlang, in Germany, with unexampled success, in the cure of the. true typhus, or putrid nervous fever, after all other remedies had proved ineffectual. This bold practitioner did not hesitate to give the muriatic acid, diluted with the. smallest possible quantity of water, to an extent almost exceeding belief ; though his cures appear to be sufficiently attested by the Royal College of Physicians at Berlin. The particulars of these extraordinary . we propose to lay before the public under the head of Fever.