URINE, the secretion of the kidneys, the chief fluid excretion of man and of the higher animals. Healthy human urine is a transparent light amber colored liquid, having a saline taste, a peculiar aromatic odor, an acid reaction, and a density varying from 1.010 to 1.025. Its chief constituents are urea, uric, lactic, and hippuric acids, and crea tine, together with calcium and magne sium sulphates, chlorides and phosphates, alkaline salts, certain imperfectly known principles, and a coloring substance. The urine contains the liquid portion of use less and noxious residuum left after the assimilation of whatever is useful to the structure.
Morbid states of the urine occur—the aqueous, the subaqueous, the lithic, the phosphatic, the purpuric, the albuminous, and the saccharine. Aqueous urine, with a diminution in its solid contents, is passed in large quantity by nervous and hysteric persons, especially when they approach old age. Subaqueous urine, in
some respects the opposite of the first, carries off an unduly large proportion of solid matters, and exists chiefly in de cline of the bodily powers, which it tends to accelerate. Lithic urine deposits a pink or purple sand or "gravel," con sisting of lithia ; its ultimate tendency is to produce lithic calculi. Phosphatic urine contains an excess of phosphatic salts, and deposits a white earthy or chalky powder. Purpuric urine deposits a lateritious sediment. Albuminous urine deposits albumen; sometimes it is an un important, but at other a very formidable disease. Saccharine urine is an attendant on diabetes. The mechanism by which the urine is secreted is apparently of a double kind: (1) uriniferous tubules, which seem to be actively secreting struc tures, and (2) the Melpighian capsules, which appear to act rather as a filtering apparatus.