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Urinary Analysis

urine, quantity, passed, specific, time, specimen, sample, constituents and gravity

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URINARY ANALYSIS, that branch of chemical and microscopical analysis which has to do with the detection or quantitative estima tion of the constituents of urine. In practice, it is mostly concerned with the examination of the urine for such constituents as may have a known clinical significance. The average quan tity of urine passed by an adult is probably about 50 fluid ounces (1,500 cubic centimeters) per day, though this may vary widely within the limits of health. The quantity is increased by drinking large amounts of water, and, tem porarily, by the administration of diuretics; and it is decreased by unusual activity of the skin, as well as by several other causes. In general, the quantity of water taken into the system through the mouth must be equal, in the long run, to that which is eliminated through the kidneys, skin, bowels, lungs and nose. The specific gravity of the urine also varies to a considerable extent, the normal specific gravity, when the quantity passed is 50 ounces per day, being about 1.020. Any cause which tends to increase the quantity of urine secreted in general, decrease the specific gravity, and vice versa ; the total quantity of solid matter that the urine contains in solution being normally, much less variable than the quantity of the urine it self. The specific gravity has a marked significance only when it is high without the urine being scanty, or low without the urine being copious. The ideal way to obtain a sam ple for analysis is to save what is passed throughout the 24 hours, mix it, and take the sample from the result. Urine thus obtained is technically called "mixed urine.' It is often inconvenient to go to this trouble, especially in hot weather, when special care must be taken to prevent the mixed product from spoiling before the sample can be prepared and transmitted to the analyst; and it is, therefore, customary to take the sample from what is passed in the morning, experience indicating that a specimen taken at this time will correspond fairly well with mixed urine. Mixed urine should always show a slightly acid reaction, and the same is true of samples taken at any time during the day, except after a meal, when the reaction may be neutral, or even alkaline. Urine often con tains slight clouds of mucus or other substances, which become visible after the specimen has been allowed to stand for a short time. These are usually of no clinical importance, merely indicating some slight irritation along the uri nary passages, or some recent indiscretion in diet. After urine has been passed (and more quickly in hot weather than in cold) the urea that it contains decomposes and passes into the form of ammonium carbonate; and when the quantity of ammonium carbonate present is sufficient to make the reaction distinctly alka line, the urine becomes semi-opaque from the deposition of a white cloud of phosphates, orates and other substances.

In the examination of a specimen of urine, the analyst cannot undertake to test it for every constituent that might conceivably be present as a pathological symptom. He will he guided by the general nature of the patient's illness, and will seek for those elements which may be of special significance. In the examina tion of presumably healthy candidates for life insurance it is customary to look for nothing but albumin and sugar, unless the specific grav ity, when considered in connection with the quantity of urine passed, is high enough to indi cate the presence of an abnormal amount of some other constituent. In general practice, however, it is often necessary to examine, not only for sugar and albumin, but also for pus, biliary coloring matters, blood-corpuscles and °casts° from the little uriniferous tubes of the kidneys. It is frequently important, too, to make a more or less accurate quantitative de termination of the urea that is passed and some times of the chlorides also.

A "cast' may be 'formed in the kidney in any one of several ways, the simplest being by the direct exudation, into a little tubule of the kidney, of some coagulable constituent of the blood. After this becomes solidified, it may eventually become discharged from the tubule with the urine and pass into the bladder in the form of a microscopic plug of approximately cylindrical shape. To detect the presence of casts and of blood-corpucles and other undis solved constituents, the urine may be allowed to stand for some time in a conical glass ves sel, whose sides slope down• to an acute point at the bottom. After a couple of hours, or when it is judged that the solid constituents that may be present have settled to the bottom or risen to the top or taken such other positions as may correspond to their specific gravities, a few drops are drawn off by means of a pipette from the surface and from the very apex of the glass at the bottom and also from such other levels as may appear to contain floating matters; and every sample so taken away is separately and carefully examined under the microscope. The correct identification of the different objects that such an examination reveals calls for a con siderable amount of practical experience with the microscope. Much assistance may be de rived, however, from Beale's Hundred Urinary Depostts,> which gives engravings of all the ordinary deposits that the analyst will be likely to meet, including such extraneous things as fibres of wool and cotton and bits of feather, which often find their way into the specimen to be examined. In well-equipped offices and laboratories in which urine is analyzed, centri fugal machines (actuated by small electric motors) are used to separate the solid particles from the urine. This expedites the work greatly.

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