Renal colic is the appellation of a group of symptoms caused, in by far the greater proportion of cases, by the passage of a renal calculus through the ureter, or sometimes merely its engagement in the upper extremity and impaction or subsequent falling back. Other foreign bodies large enough to cause distension and obstruction, such as clots of fibrin or portions of hydatid cysts, may give rise to the same phenomena. Most physicians, however, have seen cases where the same set of symptoms have not been followed either by the discharge of the stone per urethram or by evidence of its continued sojourn anywhere in the urinary organs. They may occur in persons of a neuralgic tendency in connection with the uric or oxalic diathesis. The conclusiveness of such cases, as proving the possibility of a purely neuralgic or spasmodic attack, must of course depend upon the carefulness and intelligence of the patient and the opportunities of the physician for observation extending over years. As it is admitted, however, that these symptoms may occur without the demonstrated presence of a calculus, it would be perhaps better nomenclature to apply the term renal colic to painful and spasmodic affections of the kidney and ureter, however caused, and to describe the passage of a calculus or other obstruction under its own name. Calculi of various kinds, sizes, and shapes may be found in the pelvis of the kidney. They are most frequently composed of uric acid, which may exist alone or with layers of phosphates superimposed. They are usually in concentric layers, more or less irregular in shape, and of a reddish-brown color of various shades. Soft concretions of urates are occasionally noted. Oxalate of lime is the material of many small calculi, and may be the nucleus of a larger one or occur in alternate layers with uric acid. These stones are of a dark grayish-brown and are exceedingly rough and irritating. Among the most frequent constituents of renal calculi are to be found phosphates, either of lime or the triple salt of ammonia and magnesia. They may form layers with other material, or constitute alone the largest and most curiously shaped of all the renal calculi. Their surface may be smooth and almost polished, or roughened, eroded, and almost crystalline in texture. Cystine rarely forms a renal calculus, and xanthic oxide still more rarely. Masses of fibrin resulting from renal hemorrhage are described. They are said to be of the consistency of wax, tough and elastic. Coagula of the ordinary form may also give rise to the same set of symptoms. {43} On one occasion the writer saw the dilated pelvis of the kidney filled with hundreds of spherical brownish soft masses from the size of a mustard-seed to that of a pea, easily crushed in the fingers, burning with the smell of albumen, and leaving but a small amount of ash.