Purpuric Acid. Dr. Prout has discovered that if into a strong solution of the above crystals in water, whilst boiling hot, we carefully drop some pure ammonia, the solution acquires a beautiful purple[[195]] colour, and crystals of purpurate of ammonia speedily begin to form and subside. If these crystals are treated by means of potass and sulphuric acid, pure Purpuric acid is obtained in the form of a yellowish, or cream-coloured powder.
3. The Phosphates. As the Phosphoric acid and its compounds perform an important part in the generation of calculi, their origin[[196]] and history demand particular attention from the chemist. The Phosphoric acid frequently exists in the urine in a free state, when it would appear to act, like any other acid, as a precipitant of the Lithic acid; this however is not the circumstance that renders its presence formidable; it is to the abundance of its compounds that we are to look for mischief. In healthy urine the phosphoric acid appears to exist in union with soda and ammonia, and partly with lime and magnesia; the latter salts being retained in solution by an excess of acid; but the proportion of these bodies is liable to considerable variation.[[197]]
Having thus briefly noticed those particular points in the chemistry of the subject with which the therapeutic principles are more immediately connected, we shall be better prepared to examine and appreciate the several plans of treatment which have been proposed for the prevention, cure, or palliation of calculous disorders; and here the subject naturally divides itself into two parts; the one comprehending the modus operandi of Antilithics, or those remedies which prevent or correct the calculous diathesis; the other, explaining the solvent action of Lithonthryptics over concretions already formed.
The line of demarcation by which healthy and morbid urine are separated, is so slight that it is difficult to define its limits; nor would the circumstance appear to be materially important, for the boundary is daily exceeded, not only with impunity, but even without our consciousness of the event; and Dr. Prout has accordingly denominated such occasional deviations, the “Sediments of Health.”
The same enlightened author considers that mechanical deposites from the urine, although composed of the same general ingredients, may, in a pathological point of view, be conveniently divided into three classes, viz. Pulverulent or Amorphous Sediments; 2. Crystalline Sediments, usually denominated gravel; and 3. Solid Concretions, or calculi formed by the aggregation of these latter sediments. The first of these may be passed over, as unconnected with the present subject; the latter however constitutes an essential object of research; for a complete acquaintance with the chemical history of calculi can alone furnish the true indications of cure.
Scheele,[[198]] with whom the inquiry originated, conceived that every calculus consisted of a peculiar concrete acid, soluble in alkaline lixivia, and which Morveau denominated the Lithic Acid; but the subsequent researches of Fourcroy, Vauquelin, Wollaston, Pearson, Henry, Brande, Marcet, and Prout, have demonstrated the existence of several bodies in the composition of urinary calculi, viz. Lithic Acid; Phosphate of Lime; Ammoniaco-magnesian Phosphate; Oxalate of Lime; Cystic Oxide;[[199]] and Xanthic Oxide;[[200]] to which may be added an animal cementing ingredient. The varieties of calculi produced by the combination or intermixture of these ingredients, are represented in the following Tabular Arrangement.
| A TABULAR VIEW OF THE DIFFERENT SPECIES OF URINARY CALCULI. | |||
|---|---|---|---|
| Species of Calculi. | EXTERNAL CHARACTERS. | CHEMICAL COMPOSITION. | REMARKS. |
| 1. Lithic or Uric. | Form, a flattened oval; Specific gravity, generally exceeds 1·500; Colour, brownish or fawn-like; surface smooth, texture laminated. | It consists principally of Lithic Acid; when treated with nitric acid, a beautiful pink substance results. This calculus is slightly soluble in water, abundantly in the pure alkalies. | It is the prevailing species; but the surface sometimes occurs finely tuberculated. It frequently constitutes the Nuclei of the other species. |
| 2. Mulberry. | Colour, dark-brown; texture, harder than that of the other species; Sp. grav. from 1·428 to 1·976. Surface, studded with tubercles. | It is Oxalate of Lime, and is decomposed in the flame of a spirit lamp, swelling out into a white efflorescence, which is Quick-lime. | This species includes some varieties which are remarkably smooth and pale coloured, resembling a hemp seed. |
| 3. Bone Earth. | Colour, pale brown or gray; surface smooth and polished; structure, regularly laminated; the laminæ easily separating into concrete crusts. | Principally Phosphate of Lime. It is soluble in muriatic acid. | |
| 4. Triple. | Colour, generally brilliant white; surface uneven, studded with shining crystals; less compact than the preceding species; between its laminæ, small cells occur, filled with sparkling particles. | It is an Ammoniaco-magnesian phosphate, generally mixed with phosphate of lime; pure alkalies decompose it, extricating its ammonia. | This species attains a larger size than any of the others. |
| 5. Fusible. | Colour, greyish-white. | A compound of the two foregoing species. | It is very fusible, melting into a vitreous globule. |
| 6. Cystic. | Very like the Triple Calculus, but it is unstratified and more compact, and homogeneous. | It consists of Cystic Oxide; under the blow-pipe it yields a peculiarly fetid odour. It is soluble in acids, and in alkalies even if they are fully saturated with carbonic acid. | It is a rare species. |
| 7. Alternating. | Its section exhibits different concentric laminæ. | Compound of several species, alternating with each other. | |
| 8. Compound. | No characteristic form. | The ingredients are separable only by chemical analysis. | |
Let us now inquire into the circumstances under which the several substances enumerated in the foregoing table, are found to be deposited; and first of the Lithic acid Diathesis. It has been already stated, that the lithic acid exists in the urine in combination with ammonia, so as to be held in solution under ordinary circumstances; if however any free acid be generated, the lithic acid is immediately precipitated, giving rise to the appearance so well known under the name of red gravel; from this view of the subject the lithic acid deposite must be considered as arising, not from the excess of that substance in the urine, but from a decomposition of the compounds into which it enters by the agency of a free acid. M. Majendie is therefore incorrect in attributing its appearance to the quantity of azote in the ingesta; an opinion which has been very ably controverted by Dr. Philip, in a paper published in the sixth volume of the Medical Transactions. It appears, moreover, that whatever tends to disturb the process of digestion, by favouring the production of acid, may be considered as the exciting cause of the lithic deposites; especially where the cutaneous functions are imperfectly performed; for Dr. Philip is of opinion, that the precipitating acid, in a healthy state of the system, is thrown off by the skin; and he supposes that even when generated in excess, it may be diverted to the surface of the body by merely increasing the insensible perspiration. The medical treatment of the lithic diathesis is thus rendered simple and satisfactory; and if the opinion of Dr. Prout be true, that at least two-thirds of the whole number of calculi originate from lithic acid, the extreme importance of the subject is too apparent to require comment. Remedies, medicinal and dietetic, that are capable of correcting dyspeptic symptoms, such as slight bitters,[[201]] will doubtless prove valuable resources; while all those agents which have a tendency to correct and regulate the insensible perspiration, will necessarily fall under the head of anti-lithic remedies. Mr. Copland Hutchison, in a paper which has been published in the Transactions of the Medico-Chirurgical Society, has shewn a comparative rarity of calculous disorders in British seamen. Can the quantity of muriate of soda taken with their food, from its stimulating influence upon the cutaneous functions, be considered as affording a plausible explanation of this fact? The Phosphatic Diathesis seems to be accompanied with considerable derangement of the chylo-poietic viscera, and Dr. Prout very justly remarks, what I have frequently observed, that the stools are extremely unnatural; as the phosphates are retained in solution by an excess of acid, it would appear as if an alkaline principle was occasionally developed, and it is not unreasonable to suppose that this may be sometimes derived from bilious regurgitations;[[202]] in some cases, the alkali is derived from the spontaneous decomposition of urine itself, especially where the bladder has lost its governing power,[[203]] as from some injury[[204]] of the spine; or from some local affection of the bladder or prostate gland; wherever the urine undergoes an incipient process of decomposition, ammonia will be generated, and an ammoniaco-magnesian phosphate[[205]] be immediately precipitated: hence in cases where the bladder is unable to discharge its contents, this deposite is very apt to take place, as in diseases in the prostate; and this explains the reason why the triple phosphates are so frequently formed in elderly people, who cannot wholly evacuate their bladder.
It will appear evident from these cursory observations, that some varieties of Calculi will be influenced by acids, and others by alkalies, and that the exhibition of such remedies will be liable to palliate, or to aggravate the symptoms, according to the character and composition of the offending calculus, and according to the prevailing diathesis of the patient; as a general rule to direct us in the chemico-medical treatment of these cases, Dr. Marcet states, that “Whenever the lithic acid predominates, the alkalies[[206]] are the appropriate remedies, but that when the calcareous or magnesian salts prevail, the acids are to be resorted to.” But if it be asked how we are to discover the nature of the calculous affection, so as to direct the suitable remedy? the reply is obvious—by an examination of the sediment deposited by the recent urine, or by an analysis of the small fragments which are frequently voided with it; the Phosphates subside from the urine as a white, lithic acid, generally, as a red deposit; and since the phosphates are held in solution in the urine by an excess of acid, it is evident that whenever such acidity is diminished by the hand of Nature or art, a white sabulous deposit will ensue; hence, says Mr. Brande, it occurs in the urine of persons who drink soda water, or take magnesia; the remedy of such a deposit, when it takes place habitually, is a course of acidulous medicines; on the contrary, since lithic acid is precipitated by the acids, alkalies are naturally suggested for the prevention of that deposit. In the compound calculi, acids and alkalies may be equally injurious or beneficial, for since these bodies are composed of a variety of ingredients, the action of any one solvent must be partial, and may convert the smooth calculus into a rough and highly irritating body, or vice versa. In the alternating calculi it may be judicious to exhibit these remedies alternately, as the symptoms of the case and the deposit of the urine may indicate. After all, however, the solvent powers of Lithonthryptic remedies must be very limited, and in advanced cases we can never expect to procure more than palliation. With respect to the agency of these different remedies, as Antilithics, I would observe, that while experience bears us out in confiding in the production of certain chemical effects from their use, we must not forget that much is to be effected by their judicious administration as vital agents: and it will be hereafter my duty to point out the many advantages that may be obtained, by combining in one formula, medicines which individually belong to each class.
Independent of any chemical effect, alkaline substances are found by daily experience to allay the morbid irritability of the urinary organs in a manner not yet explained; alkalies may also prove generally serviceable in these disorders, by acting immediately upon the digestive organs, for the disposition of forming calculi is always, more or less, accompanied with the indications of deranged digestion; and it is probable that the first link of the series of actions, which cause this disposition, has its origin in the stomach.