Intestinal colic is usually referred to the middle of the abdomen, is accompanied by constipation, while the movements of the intestines and of flatus are often distinctly perceived by the sensation of the patient or the ears of the bystanders, and on the whole the attack is less severe and the pain less intense. As has already been stated, it is probable that symptoms closely resembling if not identical with those of the passage of a calculus may occur when the substantial cause of them does not make its appearance; and although many of these may perhaps be accounted for by the ill-success of the search or by the calculus having ceased to pursue its downward course and having become quiescent in the kidney, yet it is well for the practitioner to be prepared for an occasional disappointment in obtaining tangible proof of the nature of the attack. Time may be required to decide whether an attack is due to calculus, or is simply one of the spasmodic or neuralgic paroxysms mentioned above. If after careful watching no stone makes its appearance, and on the other hand the pain does not continue and no pus gives evidence of pyelitis, it is highly probable that no stone is or has been present. A true neuralgia of the kidney may undoubtedly exist. Lumbago and lumbar neuralgia may simulate renal colic, but are almost always much less severe, the pain less sharp and more dull and aching, aggravated by movement, while the sympathetic phenomena, especially those connected with the urinary apparatus, are wanting. The diagnosis of the character of the calculus can sometimes be made with a reasonable degree of probability. If crystals of uric acid or of oxalate of lime have been or are present in considerable quantity, it is highly probable that a possible stone may consist of those substances. These crystals, however, are of little value in proving the presence of a stone. The important diagnosis of the occlusion of a ureter by a calculus, and at the same time that of the soundness of the opposite kidney, may be made with great certainty if the urine, which has previously been purulent, bloody, or containing renal epithelium or casts, suddenly becomes {45} clear coincidently with the occurrence of symptoms of the impaction of a stone. It is not of course necessary that in every case of impaction the flow of urine from the affected side should be entirely stopped, since the calculus may be of such a shape as to permit the passage of urine past it. The PROGNOSIS in this affection is extremely favorable, so far as the recovery from the individual attack is concerned, since if the stone is small enough to enter the ureter it will probably be successful in forcing its way through sooner or later. It is of course possible that this pain, like any other of excessive severity, might cause death, but such an occurrence must be extremely rare.