Again, deposits may be caused by an excess of acid or of alkali in the blood, which excess is excreted by the kidneys, and causes a lithic or phosphatic gravel, without an excess of Lithates or of Phosphates in the urine. Whatever be the condition of Uric acid in urine, it is certain that it is held in solution by some matter of an alkaline nature.[36] When this alkaline matter is neutralized by an acid, the Uric acid precipitates. This may perhaps be caused in Rheumatic fever by an excess of Lactic acid. The Phosphates are held in solution by Phosphoric acid, or by that matter which gives to healthy urine its slight acid reaction.[37] An excess of alkali in the blood, which may probably occur in Typhoid and low fevers, will cause their precipitation. Or the alkali may be formed in the bladder by the decomposition of the urine. This may occur in inflammation of the bladder; or in retention of urine caused by paraplegic paralysis.
In such cases there is no absolute excess of the deposited matter; but it is in relative excess, for the substance which should properly dissolve it is neutralized by a reagent of an opposite nature. Acids and alkalies have already been mentioned as efficacious in these instances; the former in phosphatic, the latter in lithic deposits. They directly neutralize the disturbing cause; the alkali, or the acid. They are not in such cases truly solvents; they do not themselves hold in solution the insoluble material, but they set free something else that shall be capable of doing so. (Vide Acids; Alkalies.)
A suppression of the secretion of the skin causes a lithic deposit in some cases, as in a common "cold." For the perspiration contains a free acid, probably lactic or butyric; and when it is suppressed, the secretion of this acid is thrown upon the kidneys, and the urine is rendered more acid than naturally. The obvious indication in the treatment is to restore the function of the skin, as by warm baths, diaphoretics, etc.
It is in the case of urinary deposits produced in the fourth way that true solvents are appropriate.
From some morbid condition of the system, it happens that these insoluble constituents of the urine are secreted in absolute excess,—in a larger quantity than in health. Now the system labours to excrete them in solution, even when in excess; and often succeeds in doing so. But frequently this cannot be done, it being impossible for a sufficient quantity of the solvent material to be formed out of the blood. There is then a deposit in the urine.
We have seen that when such matters are deposited because in relative excess, the only fit mode of treatment consists in the administration of an acid or an alkali, which shall neutralize the morbid reaction of the blood. Such a case is rare; but these cases of absolute excess are much more common. There are two ways in which we may treat them; we may adopt either curative or palliative remedies. We may aim at the cause of the disease, which is generally in the blood. An absolute excess of Lithates may be caused by dyspepsia, or by a gouty disorder. This is most surely controlled by a Catalytic medicine. (Vide Antiarthritics.) An absolute excess of Phosphates may be caused by an organic derangement of the nervous centres, when it is very difficult to cure; or it may simply be due to great nervous excitement, hard study, or melancholia. Such cases should be distinguished from a mere alkaline condition of the urine, without absolute excess of Phosphates, and may often be cured by attention to the disturbed nervous functions.
Such a curative course of treatment aims at the primary cause of the deposit; but when we are unsuccessful in our attempt to control this, or when the excess of solid matter is so great as to be positively dangerous, we are then driven to have recourse to palliative remedies. These are Solvents; medicines which pass into the blood, combine there with the peccant matters, pass out with them into the urinary secretion, and hold them there securely in solution. Such an agent may often be advantageously combined with the Catalytic remedy, which tends to cure the systemic disorder. It is a blood-medicine. Its action is so far permanent, that it effects its object definitely, dissolving and carrying away a certain portion of insoluble matter. But as it also passes out itself, it requires to be frequently repeated, because the deposit continues to be formed, and requires each time a fresh portion of solvent. It obviously acts on the Restorative principle. The deposit should be excreted in a dissolved state, but is not. The remedy therefore supplies a want.
Water is the simplest and most efficacious of all solvents, and should in all cases of gravel be very freely administered. Bouchardat has remarked that great water-drinkers are never afflicted with stone. All the urinary deposits are, to some extent, soluble in water, although comparatively insoluble. Whenever the urine is of higher specific gravity than it should be in health, more water should be drunk. The average specific gravity of healthy urine is about 1.018.[38]
Acids and Alkalies are most important as solvents. They do not now act indirectly, as in the case before mentioned, but directly dissolve the insoluble matter. Acids dissolve a phosphatic, and Alkalies or their carbonates a lithic deposit, in the body, as well as out of it. Although the natural solvent may be neither an acid nor an alkali, but something else different in nature from these, yet any thing that will rightly dissolve the deposit will be fit to supply its place. Any of the free Acids may serve to dissolve a precipitated phosphate. Hydrochloric is perhaps the best of the mineral acids, although Phosphoric has been recommended on theoretical grounds. Sulphuric is the least efficacious because it does not always pass out in the urine. (Vide Chap. IV.) Sour fruits, as Currants or green Gooseberries, may be useful in phosphatic cases; but ripe fruits have an opposite tendency. Acidulous drinks may be recommended, as Cider, Perry, and Rhenish wines. Of the free alkalies used to dissolve a lithic sediment, Potash is preferable to Soda, because it forms a more soluble compound with Uric acid. The Bicarbonates of the fixed alkalies are best, because least irritant. Bicarbonate of Soda is contained in Vichy water. The soluble Bicarbonate of Magnesia may be given with advantage. The Carbonate of Lithia has been recommended by Mr. A. Ure; but it is comparatively insoluble. The neutral vegetable salts of the alkalies, and sweet fruits which contain them, are equivalent to the Carbonates, because converted into them in the system, as has already been shown. They may be pleasantly administered in the form of effervescing draughts, in the formation of which the Carbonic acid of an alkaline carbonate is displaced by Citric or Tartaric acid.