Low specific gravities are the rule in diabetes insipidus and with acute and chronic diffuse nephritis. In chronic diffuse nephritis the specific gravity remains low even if the quantity of urine passed is very small. When there is almost suppression of urine from occlusion of the ureters the urine that is passed is of low specific gravity. These changes in specific gravity correspond of course to the amount of solid matter in solution in the urine, and may depend upon a change in the relative proportion of the fluid and solid constituents of the urine, or upon an absolute increase or decrease of the solid portions. Any change in the absolute amount of solid matter excreted in the urine must depend upon changes in the composition of the blood, or in the circulation of the blood through the kidneys, or in the structure of the kidneys themselves. All these three conditions seem to exist in Bright's disease, and either together or separately may diminish the daily excretion of solid matter. It is not necessary here to enumerate the different solid constituents of {75} the urine. A change in the amount of many of them merely indicates disorders of the digestive process. Urea seems to be the most important of the excretory substances, and its quantity is regularly diminished both in acute and chronic Bright's disease. Blood is found in the urine in a considerable number of cases of Bright's disease. If it is present in large quantities, the urine will be of a reddish color; if in smaller quantities, of a smoky color; and if in still smaller quantities, the color will not be changed. Blood is found regularly with acute diffuse nephritis, with the more severe cases of acute parenchymatous nephritis, with the exacerbations of chronic diffuse nephritis, and with suppurative nephritis. The blood seems to be derived from the tufts of vessels in the Malpighian bodies. Albumen in the urine is a very common symptom of renal disease, but it is not confined to such cases. It is also found without any structural lesions of the kidneys. 1. There are some individuals whose urine, for many years, will contain small quantities of albumen, and yet their general health is good and they never develop any renal symptoms. In some of these cases the urine is always somewhat diminished in quantity, and in some there is also a little sugar in the urine. 2. In a large number of perfectly healthy persons small amounts of albumen will appear as a temporary condition after muscular exercise, sea-bathing, eating certain kinds of food, etc. 3. Albumen may be present in considerable amount for weeks or months in the urine of young persons, and then disappear altogether. The general health may continue good or be somewhat depreciated. After a time the albumen disappears and the patients have no further trouble. 4. General convulsions, concussion of the brain, and transfusion of blood often produce a temporary albuminuria.