Urine. Healthy urine is a transparent straw-coloured fluid of slightly acid reaction, of a specific gravity of about 1.020. The quantity of the constituents is subject to variations in accordance with season and the amount of drink and exercise. The average composition in 1,000 parts by weight may be given, however, as 967 parts of water, about 15 parts of urea, and about 10 parts of other nitrogenous crystalline bodies, what remains consisting chiefly of mineral salts. About 52 fluid ounces of urine are passed by a healthy male adult in the course of 24 hours, containing some 512 grains of urea, about eight grains of uric acid, 10 to 15 grains of hippuric acid, and about 150 grains of nitrogenous extractives, while of the mineral salts the large bulk is composed of chlorides, and there are small quantities of phosphates and sulfates, the bases with which the several acids are combined being the fixed alkaline bases, with a little lime and magnesia. It should be mentioned that the urine contains certain pigments derived from the pigment of the blood, and there is always a small amount of mucus shed from the mucous surfaces of the urinary passages. When urine is allowed to stand it throws down deposit, which contains mucus and under some circumstances phosphates, while under other circumstances it may contain urates and uric acid. Certain abnormal constituents are found in the urine in disease. The most important of these are albumen, sugar, the pigments of the blood, and bile, and in some instances materials which can be detected on microscopic examination, and which may afford an important clue to the nature of the malady from which the patient is suffering. The presence of albumen is commonly tested for by ascertaining whether coagulation is produced by the action of heat or on the addition of nitric acid, while a number of tests may be employed to ascertain whether sugar is present, the most important being that known as Fehling's test.