Marked diminution in the amount of urine occurring in the course of acute and chronic Bright's disease is usually associated with the development of cerebral symptoms--headache, restlessness, delirium, muscular twitchings, convulsions, stupor, and coma. Such a change in the amount of the urine usually lasts only a few days and may terminate fatally, or the quantity of urine will increase and the patient get better. There are, however, cases in which the suppression of urine lasts for several days without the development of uræmic symptoms. Whitelaw[1] relates a {74} case of suppression of urine lasting for twenty-five days in a boy eight years old. The suppression began twelve weeks after an attack of scarlatina. There were no uræmic symptoms, and the child recovered completely. [Footnote 1: _Lancet_, September, 1877.] The suppression of urine due to injuries of the urethra gives rise to symptoms of great prostration--rigors, vomiting, and collapse--rather than to uræmic symptoms. Suppression of urine is also produced by occlusion of the ureters by calculi, new growths, etc. It is a curious fact that in these cases the patients continue to live for a number of days (9 to 11, Roberts), and no uræmic symptoms are developed until a few hours before death. The most marked examples of persistent increase in the quantity of urine are afforded by cases of diabetes mellitus and diabetes insipidus. But a daily excretion of from 70 to 100 ounces is common enough with atrophied kidneys, with large white kidneys, and with waxy kidneys. It is exceedingly difficult to form any rational idea of the causes of the variations in the amount of urine in the course of the same case, and in different cases with similar kidney lesions. Various explanations have been attempted, ascribing these changes to the hypertrophy of the left ventricle of the heart, to changes in blood-pressure, to lesions of the arteries, to changes in the composition of the blood, to lesions in particular portions of the kidneys. But any one who tries to apply these explanations to any number of actual cases will find many difficulties. The most evident causes of diminution in the amount of urine seem to be an abnormal condition of the circulation of the blood and either congestion or structural changes of the kidneys. The specific gravity of the urine varies from day to day and from hour to hour in the same person, having a regular relation to the quantity of urine passed. But a long-continued deviation from the normal specific gravity is usually an evidence of disease. The highest specific gravities obtain with saccharine diabetes. Abnormally high specific gravities also often occur in the urine of patients with a high temperature, with chronic congestion of the kidneys, and in some cases of acute and chronic parenchymatous nephritis.