It has been already stated that fresh healthy human urine presents an acid reaction. This reaction mainly depends upon the presence of acid phosphates of thc alkalies and earths, although the presence of free acids, such as free hippuric, or possibly lactic acid (which, however, is not a normal ingredient), may occasionally contribute to increase the acidity. To determine•the acidity of the collective 24 hours' urine, we take a solu tion of oxalic acid of known strength, and ascertain the relative quantities of IL solution. (of definite strength) of caustic soda which are required to perfectly neutralize equal vol umes of the urine and of the oxalic acid solution. In this way it is found that the total quantity of free acid in the daily urine of a healthy man corresponds in neutralizing power to about 36 grains of oxalic acid. The degree of acidity varies in different parts of the day. Dr. Bence Jones mooted the idea (in 1849), that the respective acidities of the secretions of the kidneys and stomach stood in an inverse relation to one another, and may even become alkaline during stomachal digestion. Dr. Roberts of Manchester. who has subsequently investigated this point, finds that the effect of a meal on the acidity of the urine begins to show itself in the second hour afterward, is most marked during the next three hours, and disappears by the end of the sixth hour, the fluid being ahnost always positively alkaline during the third and fourth liont-s. Independently of Ibis periodic alkalinity, the urine may be made alkaline at will by the administration of cam-tie alkalies, their carbonates or their salts, with organic acids (citrates, tartrates, etc. ; such as occur in many fruits); while after the administration of acids the acidity is much increased.
• In disease, the urine may either contain only its ordinary ingredients in abnormal proportions, or it may contain ingredients not occurring in the healthy fluid. Thus there
may be an excess or diminution of urea, an. excess of uric acid, a diminution of chloride of sodium, which, in cases of inflammation of the lungs, may fall from 266 grains to a mere trace, and, by its daily diminution or augmentation, tells with certainty whether the disease is gaining or losing ground; an excess of coloring matter or of mucus, etc.; or, on the other hand, the urine may contain albumen, sugar, oxalic acid (in combination with lime), fat, leucine and tyrosine, bile-pigment, biliary acids, etc. The subject of " the urine in disease," is, however, so wide a one that we must refer our readers for details to Lehmann's Physiological Chemistry, 3 vols. (translated for the Cavendish society), to Dr. Parkes's excellent work on The Urine, and to the various works of Dr. Beale.
We conclude with a few remarks ou the urine of mammals generally. The urine of the carnivore is clear, of a light-yellow color, a disagreeable odor, a nauseous taste, and an acid reaction. It contains much urea, little pigment, and little or no uric acid. The urine of the herbivore is turbid, yellow, of a less unpleasant odor, and alkaline. In addi tion to urea, it contains hippuric (but no uric) acid, alkaline lactates, carbonates of pot -ash and of the earths, oxalate of lime, and a small quantity of phosphates. By reversiug the natural food of these classes, we reverse the characters of the urine.
The urine in many forms of disease becomes turbid on cooling, and soon deposits a sediment; and even healthy urine, after a few days's exposure to the air, loses its clear ness, and throws down a deposit of mucus and various kinds of crystals. The investi gation of the nature of the deposits thrown down by comparatively fresh urine in dis ease, is a subject of the highest importance in medicine, and is noticed in the article URE.:'ARY SEDIMENTS.