(From calx, a lime stone). The gravel and stone. The Greeks call this disorder lithia-sis and adamitum; the Latins name it calculus; and in English we understand by gravel, small stones that pass from the kidneys through the ureters in a few days; and by the stone, a calculus concretion in the kidneys, or in the urinary bladder, which is too large to pass, or at least without great difficulty. Nephritis, in modern practice, is confined to an inflammation of the kidneys. See Nephritis.

When a disposition to form minute calculi exists, we often find nephritic paroxysms, as they are styled, which consist of pain in the back, shooting down through the pelvis to the thighs; sometimes a numbness in one leg, or a retraction of either testicle; symptoms arising from the irritation of a stone passing through the ureters as these cross the spermatic cord, or the nerves passing to the lower extremities. These pains, often violent, are terminated by the painful discharge of small stones through the urethra; and the patient is for a time easy. What, however, is meant by the stone, is a more serious and violent disease. It is singular that these discharges of small gravel do not usually terminate in stone. Many have experienced them during a long life, without any more serious inconvenience: while the latter is a disease chiefly of the young, and seemingly depending on a seminium, not easily explained. If the stone attacks persons more advanced in age, it is often the consecmence of paroxysms of gout, long protracted, and terminating imperfectly. Of nephritic paroxysms we must again speak, and shall now confine ourselves to calculus. It is not, like nephritis, usually attended with sickness of the stomach, unless the stone is confined in the cavity of the kidney, called its pelvis; for it is with affections of this part that the stomach seems to sympathise. Its commencement is marked only by frequent inclination to make water, pain during the discharge, and the stream often suddenly interrupted. It is a remark of Le Dran, that if there is pain while the first portion of the urine is discharged, the stone is small; if when the last, it is large: if, during the whole time, it does not proceed from a calculus. It is singular, also, that the pain is not in proportion to the size of a stone, for a small calculus-will produce violent fits of pain; a large one often very inconsiderable inconvenience. The pain from calculus is by no means constant: it conies on in violent paroxysms, which induced Hoffman to suppose it owing to spasm. All the parts adjoining are forced down, particularly the rectum, giving the sensation of an urgent necessity of having a motion. In many instances the patient can lie most easily on one side, and on turning feels a weight rolling to the opposite side. In the intervals of the paroxysm he is often perfectly easy. These symptoms will generally ascertain the existence of a calculus; but we have often better evidence by the introduction of a catheter. With this instrument we can search through the bladder, and feel a stone. Yet it is sometimes so small as to escape it; and, by some unaccountable accidents, after many trials it is not felt. It is then in a moment caught, again escapes, and can be discovered no more. It is equally singular that an inexperienced surgeon will sometimes discover it, •when the most able operator has been foiled. The stone is sometimes covered with a membranous coat, and then the catheter does not convey the proper sensation to the operator's hand: and it has happened, that when the stone has been once felt, at the moment of the operation it could not be again discovered. This may have been owing to its having forced its way through the fibres of the bladder, carrying with it the internal coat, which thus formed a covering for it on the outside of its cavity: and this, we were informed by the late Dr. \V. Hunter, was the case with one of the persons on whom Mrs. Steevens' medicine was tried, previous to her receiving the parliamentary reward. The stone, after taking the medicine, was not to be found; and, on the death of the patient, it appeared not to have been dissolved, but to have escaped detection in this way.

The nature and source of the calculus have been long unknown; nor, at this moment, is either indisputably ascertained. Calculi differ in all their external properties; they differ also in the facility with which they yield to different solvents, but their component parts are singularly uniform. The calculus, when single, is usually oval; when there are more, the shape is more irregular, and still more so in proportion to the number in the bladder. They are usually laminated; the laminae of different thickness, and irregular in their direction. The colour is occasionally white or brown, or resembling that of a mulberry in this respect, as well as in irregular points. The white laminae are usually on the outside, the brown in the middle, but the colours never alternate.

The calculus was always concluded to be sand or stone; nor was a hint beyond this idea started till the time of Van Helmont, who, catching a ray from the meteoric visions of Paracelsus, concluded it to be a coagulation of the urine by means of a volatile spirit. Hales undoubtedly threw a considerable light on its nature; but the first regular analysis was made by Scheele; and, about the same time, Bergman exerted his penetrating genius in the same pursuit. They were followed by Morveau, Fourcroy, Woolaston, and Pearson. To pursue the history, which, on the whole, would be neither unentertaining nor uninteresting, would, however, fill a disproportioned space in this work. We shall, therefore, give the analysis of Fourcroy as contained in the latest publication on the subject, the first volume of the Annales du Museum National, p. 93, etc. and add the experiments of Dr. Pearson, which differ from Fourcroy's in some essential respects.

M. Fourcroy found, on analysis, twelve different substances in the various calculi found in the body: - the lithic acid, first discovered by Scheele; urats of ammonia and soda; phosphat of lime; acid phosphat of lime; ammoniaco magnesian phosphat; oxalate of lime; carbonate of lime; flint; spermaceti; bezoardic animal resin; and gelatine. The uric acid is of a yellowish colour, from the light straw to the reddish yellow colour of bark. It is in fine laminae, but brittle, though susceptible of a beautiful polish. It is pure only in human urine, and forms the red sediment deposited after fevers, paroxysms of gout, etc. It is insoluble in cold, scarcely soluble in hot, water: softened, and in part dissolved, by alkalis, at least with the assistance of a little water; but unaffected by acids, except that the oxygenated muriatic acid changes it into the malic acid.