Pure uric acid is solid, of a pale yellow colour, heavier than water, without taste or smell; it is not decomposed by the action of air or water; boiling water only dissolves 1-1150th of its weight, and, consequently, the urine at 60°, which is its temperature in a state of health, will hold in solution only about 1-1500th of its weight of uric acid.

To ascertain the Causes of Red Gravel, the circumstances which determine the separation of uric acid from the urine in which, in health, it is in a state of solution, must be investigated. Three evident causes can diminish the power the urine possesses of dissolving uric acid; these may not be the only causes, but they are the chief. 1. Augmentation in the quantity of uric acid, the quantity of urine remaining in the same, or not augmenting in proportion to the acid. 2. Diminution in the quantity of the urine, that of uric acid remain ing the same, or not diminishing in the same proportion as the urine. 3. Diminution in the temperature of the urine, its quantity either remaining the same, or undergoing the changes above-mentioned.

1. Causes tending to augment the Proportion of Uric Acid, and to produce in consequence Red Gravel. Amongst the most evident is high living; thus, lovers of good eating, who indulge in large quantities of meat, fish, game, and highly azotized dishes, and who have passed the age for muscular exertion, are the frequent subjects of gravel. The following case illustrates this proposition. A merchant in one of the provincial towns of France possessed, in 1824, a considerable fortune; he was fond of the luxuries of the table, and was tormented with gravel and gout; owing to political misfortunes he lost his property, and fled into England, where he spent a year subject to extreme privations, but his gravel and gout disappeared; gradually his affairs became more prosperous, he resumed his good living, and with it the concomitant disease; by a second misfortune he lost all that he possessed, and returned to France without resources, his diet was as scanty as his means, and the gravel disappeared; by his industry he again raised himself to affluence, he returned to the pleasures of the table, and with them re-appeared the gravel and the gout, for which he consulted M. Majendie. Another proof of the influence of diet on the proportion of uric acid may be taken from individuals habitually moderate, who make an unusually large meal; the next morning, or even the same evening, their urine is s'ronglycoloured, and deposits a considerable quantity of uric acid. If sedentary and elderly men, who use but little their muscular system, take very substantial food, they are more likely to be affected with gravel than those who exercise their muscles vigorously, for the mus cular system, when fully exercised, is that in which nutrition is most active, and which requires the most azotized nutriment; if the same diet is taken, and in considerable quantity, without exercise, the muscles do not require the azotized nutritive matter, it is in excess in the economy, and is directed to the principal emunctories of nitrogen, the kidneys, where it is converted into uric acid, and forms gravel. As long as the quantity of urine is sufficient to dissolve the uric acid, it produces no inconvenience, and this is the case with many persons who indulge in this luxurious diet; but if the proportion of urine diminishes, uric acid is immediately deposited.

2. Causes which augment or diminish the Quantity of Urine, and which are favourable or unfavourable to the Deposition of Red Gravel. Putting aside the chemical nature of the fluid, it is true that the more is drunk, the more abundant is the urine. This is correct as far as relates to those liquids which contain a large proportion of water, as beer, cider, or diluted wine; but it does not apply to strong wines or spirituous liquors, which contain much more alcohol than water, nor wholly to warm drinks, as tea, coffee, punch, &c. which produce cutaneous perspiration. If, then, a man who eats much animal food, drinks much water, or weak and effervescing wines, the quantity of his urine will be more than sufficient to dissolve the uric acid formed by the kidneys, and he will be less exposed to be attacked by

gravel. If, on the other hand, he drinks but little, or not in proportion to the food he takes, or if he drinks freely of heating wines, brandy, strong liqueurs, or any fluids highly charged with alcohol, his urine will be less abundant, and, consequently, will dissolve less uric acid; his urine will, therefore, be so much the more disposed to deposit gravel. If it was merely sufficient to drink much to avoid the gravel, those who are most subject to it (les grands mangeurs et les gastronomes) would suffer from it rarely. But a particular and imperfectly known cause acts upon them in an inverse ratio; this is, the diminution of the action of the kidneys by the use of animal food. In experiments which M. Majendie has made on animals to ascertain the effects of azotized and non-azotized food, he has found that the use of the latter augments sensibly the quantity of urine; thus, a dog fed with sugar, and a given quantity of water, makes, in 24 hours, a much greater quantity of urine than another dog, drinking the same proportion of water, and fed with meat. M. Majendie has often observed the same thing in man. Individuals who feed on meat alone, for the cure of any disease, are remarkable for the small quantity of urine they secrete. The contrary is the case with persons who are on a strictly vegetable diet. M. Clouet, wishing to make an estimate of the nutritive properties of the potatoe, eat that root alone for some time; at the end of 12 or 15 days he was seized with a diuresis, which had some analogy with diabetes. A further proof is deduced from the comparison of the quantity of urine secreted by carnivorous and by herbivorous animals, in the former it is much more considerable thus, contrast a cat and a rabbit of the same size, although the latter never drinks, it secretes urine much more abundantly than the former. The fact which M. Majendie has endeavoured to establish, that meat and other analogous food tend to diminish the quantity of urine, at the same time that they augment the quantity of uric acid, will be found to form the basis of his treatment. It is almost unnecessary to add, that all causes diminishing the quantity of urine, such as abundant perspiration, sweats, liquid evacuations, &c. will be favourable to the formation of gravel, by preventing the solution of uric acid. In the same manner, prolonged confinement to bed, either by exciting cutaneous perspiration, or by retarding the passage of the urine into the bladder, favours the formation of gravel. Van Swieten relates the case of a man who had never had any symptom of gravel, but was attacked with a calculus nephritic colic a few weeks after the cure of a fracture in the thigh, for which he had remained in bed and in one position for ten weeks. After great pain he expelled a small rough calculus, and became subject to gravel. Similar effects may be caused by habitually retaining the urine a long time in the bladder.

3. Influence of the Temperature of the Urine on the Deposition of Red Gravel. The tendency which old people especially have to deposit gravel is owing to the diminution of animal beat. M. Majendie has found, from thermometrical experiments, that after 60 years of age, the temperature of the body is reduced many degrees; it rarely exceeds 96 (Fahr.) even in the arm-pits or groin, which are the hottest parts of the surface of the body, and which follow almost always the temperature of the internal cavities. The urine is proportionally cool, Majendie has rarely found it above 86°, that is 140 or 180 below its ordinary temperature. From this circumstance alone, cæteris paribus, the old man is more exposed to gravel, as his urine is less able to dissolve uric acid. Perhaps the long continued action of cold in the adult may produce a similar effect..

2. White Gravel. This is found next in frequency to the red. It is deposited in 2 forms.. 1. As a white powder. 2. As small angular and irregular gravel, of various consistence. This is almost entirely composed of phosphate of lime, with a little phosphate of magnesia. It dissolves readily in weak muriatic acid, and the phosphate of lime is precipitated without effervescence by ammonia. Prout prescribes white and friable concretions, formed almost wholly of carbonate of lime; these of course would be distinguished by their effervescing

with acids. Majendie has never found them in the urine of man, but in that of animals, particularly of the horse, they are common. If the experiment on the dog, fed on nonazotized substances, be referred to, it will be found that the presence of phosphate of lime in healthy urine is evidently connected with animal diet, for on depriving the animal of it for 20 or 25 days, no traces of the phosphates could be discovered in his urine. In fact, all the remarks of the causes which favour the deposition of the red gravel, are applicable to the white, formed of phosphate of lime. The presence of carbonate of lime, a principle which does not exist in healthy human urine, seems to depend on an exclusively vegetable diet, as this salt is found in the urine of herbivorous animals.

3. Hairy Gravel. This exists either in the form of a whitish powder, mixed with hairs, or as gravel of various sizes, hairy on the surface, and sometimes connected together as a bunch of grapes. In the powdery state, the small hairs which are mixed with the white powder vary in length, from a line to an inch, or more; they differ little from ordinary hairs, being only a little finer, and of a cindery-grey colour. The saline matter forms a layer at the bottom of the vessels; if it is left for some time it cakes, and can only be detached in layers of some lines in thickness; on breaking these, the hairs are seen on the edges of the fracture. M. Pelletier analysed this, and found it to consist of phosphate of lime, with a little phosphate of magnesia and traces of uric acid. The first case in which M. Majendie observed this peculiar disease was of a professor of the university; the deposition was so great that he filled, in some days, a vessel which held more than a pint; the quantity which this man had passed in several years was truly extraordinary. The second case was that of a sailor, who evacuated gravel connected by hairs. In neither of these cases, nor in a third, which will be detailed when the treatment is discussed, could excess in animal food account for the production of the phosphates; they were very sober men. M. Majendie offers no explanation of the source from whence these hairs were derived. He does not appear to have been aware that Hippocrates had observed a similar deposition in the urine, σκόσοισι δε εν τω ουρηματι παχει εοντι, σαρκια μικρα τριχοειδέα συνέρχεται, ταυτα δε από των νεφρών ειδέναι χρη εοντα και των αρθριτικων.—(Hipp. Sec. 3, p. 230. Tom. I. folio. Geneva, 1657.) Hippocrates does not assert that they are actual hairs, but that they are small fleshy bodies like hairs, in thick urine-that they come from the kidneys, and from those persons affected with gouty disease of the joints.

4. Grey Gravel. Majendie has never seen this deposited as sand; in some cases, the concretions were smooth and similar in form, and nearly the size of an olive or pistachio nut, in others spherical and rough; they are formed of concentric layers, indicating the slowness of the deposition; they are true urinary calculi, but their size is not voluminous enough to prevent their expulsion through the urethra. They are composed of the ammoniaco-magnesian phosphate, united to a small quantity of animal matter, and some traces of uric acid. From the presence of ammonia, it is probable that a highly azotized diet is the chief source of this gravel; M. Majendie has never observed it, except among "veritables gastronomes."

4. Yellow Gravel. This, which is composed of oxalate of lime, is rare. M. Majendie has seen but one instance of it; the gravel stone which was expelled was about six or seven lines in length, and from 1 to 2 lines in breadth, elongated, flattened on two sides. hard, of an orange-yellow colour, and uneven surface; M. Desprex, an excellent chemist who examined it, found that it consisted of oxalate of lime, nearly pure. M. Majendie was surprised to find such a product in an individual whose corpulence, age, habits of life, &c. were favourable conditions for the secretion of uric acid, and, therefore carefully investigated his diet. His patient, who had always indulged in the pleasures of the table,

had been on a political mission to a neighbouring country, where "le goût de la bonne chère est fort répandu," and had received and given numerous official dinners, where he had shewn himself "à la fois diplomate habile et gastronome éclairé." On his return he gave up his official station, and on entering into private life, he resolved to reform his habits and to adopt a cooling regimen. For this purpose he took every morning a large plate of sorrel, and continued this nearly a twelvemonth; at the end of this period he was attacked with a fit of gravel, and expelled the oxalate of lime calculus. Its origin was thus readily traced to the immoderate use of sorrel.

6. Transparent Gravel. These concretions are composed of cystic oxyde, and are very rare. They are of a yellow, citrine colour, and of the transparency of topaz; on breaking them they appear to be composed of an aggregation of crystals, mingled together without order. On burning, they exhale a fetid odour; they are soluble in acids and alkalies. Cystic oxide was discovered by Wollaston. M. Lassaigne analysed a specimen found in a dog's bladder, and the following was its composition :

The chemical nature of this gravel connects it evidently with uric acid, both as to its origin and relation with animal nutriment.

Of some of the particular Causes of Gravel. M. Majendie allows that there are many causes of gravel which he cannot explain by the physiological or chemical laws; he admits that we see individuals daily, who, from their age, diet, and habits, present the most favourable conditions for the formation of these concretions, but who are not subject to them; and that, on the other hand, there are examples of persons attacked with gravel, whose diet and modes of life are very different from those who are generally the subjects of it. Thus, according to Scudamore, gravel is frequent among the poor between Tunbridge Wells and Lewes in Sussex, although their food is almost exclusively vegetable, with hard beer, and yet it spares the better fed inhabitants. Gravel is not unfrequently expelled after making a violent exertion, also, by individuals sober and otherwise healthy, if they nave indigestion, accompanied by bitter or acid eructations, pyrosis, &c. M. Majendis met with an instance of a boy, who expels two drachms of red gravel the day after he has eaten a salad, and Béclard informed him of an individual who discharged one or to small calculi invariably after eating unripe fruit. He believes that dyspepsia and gravel, which exist simultaneously in the same subject, are effects of the same cause, and do not reciprocally produce each other. It has been for a long time observed, that the inhabitants of temperate and of moist climates were most subject to calculous affections, and that in cold and equatorial countries it is rare, and authors have attributed this to the difference in temperature. M. Majendie has been led to believe that this absence of calculous disease depends on the vegetable diet, from the following fact, related to him by M. Orfila. The inhabitants of the Island of Minorca live principally on fish and other animal food, they season these substances highly with pepper and other spices; their drink is a generous wine, which they rarely dilute, they also use freely brandy, rum, and punch. During Orfila's residence there, in 1816, he remarked that calculous diseases were very common, and that the urine of the inhabitants was highly charged with uric acid, which produced small calculi, that were expelled with the usual symptoms. Gravel has been believed to have been caused by the stony concretions of some fruits, particularly of

pears, but Maquart and Vauquelin have studied their chemical composition, and find that they are neither composed of phosphate nor of carbonate of lime, nor of uric acid, as had been suspected, but of a woody matter like that of the tree which produced the fruit, confusedly crystallized, and mixed with a kind of starch. Thus they could not be a cause; and, besides, Majendie has frequently found that they have passed through the intestines without undergoing any change. Hales has stated that gravel often was produced by drinking waters containing carbonate of lime; but it appears from the reports of Chopart and Dessault, who practised surgery in the largest hospitals of Paris, that stone or gravel was very rare in the village of Arcueil, although its water is impregnated with carbonate of lime. Besides, the composition of calculi is not similar to this salt. The same argument applies to common salt, which many authors have stated to be one cause. To recapitu late, the causes of gravel, either direct or indirect, are, 1. Mature or old age. 2. Too nutri. tious diet, principally composed of substances containing much nitrogen, or of substances capable of forming deposits in the urinary passages. 3. Want of exercise, literary studies, confinement to bed, &c. 4. A small quantity of drink. 5. Generous wines and strong liquors. 6. Perspiration, abundant sweats, and all serous evacuations in those disposed to gravel. 7. The habit of keeping the urine a long time in the bladder. 8. Some parti cular causes, whose effects are obvious, but whose modus operandi is unknown.

Symptoms of Gravel. Most frequently, some months before the expulsion of gravel, a sense of numbness and uneasiness is felt in the region of the kidneys, the urine is deeper in colour, and deposits a reddish sediment on cooling. These symptoms attract but little attention, but they increase; there is greater pain and weakness in the loins, and the day after this pain has been most severe, a certain quantity of sand is evacuated with the urine; this is frequently attended with heat and burning pain in the course of the urinary passages, sometimes the pain is acute and is attended with fever. The symptoms generally become more severe, the pains in the kidneys increase in violence at each attack, and at times are intolerable, the patient tracing the torturing descent of the stone through the ureter; this is almost always accompanied with frequent desire to make water, retraction of the testicle, cramps, nausea, and vomiting; the patient cannot remain in the same posture, he cannot stand or walk; this remains 36 or 48 hours, and suddenly ceases. During the day the patient expels, with some difficulty, one or more calculi. From these general symptoms the important deduction may be drawn, that the solidification of gravel takes place as soon as the urine is formed, that is, in the pelvis of the kidneys, and perhaps, as the numbness and uneasiness in the loins seem to indicate, in the tubular structure of the kidneys themselves. M. Majendie found, in the tubular structure of the kidneys of an old woman, who was subject during her life to gravel, small concretions of uric acid, varying in size, from fine sand to elongated calculi, an inch in length. Chopart (Maladies des Voies Urinaires) says that he has found gravel stones in the tubular structure of the kidneys. It is probable that the solidification, in some instances, takes place either in the ureter or bladder. If, from its size or shape, a portion of gravel is arrested in its descent, it impedes more or less other particles; this is generally the origin of renal and vesical calculi. Stones in the kidneys, ureters, and bladder are most frequently the sequelae of gravel, or its third degree, the expulsion of sand being the first, and of gravel the second.

Treatment of Red Gravel. There are four principal indications.-1. To diminish the quantity of uric acid which the kidneys form. 2. To augment the secretion of urine. 3. To prevent the solidification of uric acid by saturating it. 4. The gravel being formed, to Savour its evacuation and to attempt its solution.